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internet service providerYour profile is an important factor to consider when buying a broadband package, below is a description and explanation of the various categories.
Despite the Internet being an essential part of all of our lives, there are different types of broadband user. This means that each of us falls into a different category of how much we use the Internet.
Some people will argue that it is impossible to define how much a person uses the Internet as we all use it for different things and for different lengths of time. However, after much study and observation, it has been found that people meet an average amount of hours based on the various activities they conduct using their broadband connections. Continue reading
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| 0.996107 |
Aleosan - Cotabato Province Destinations
Aleosan is a fourth-class municipality in Cotabato Province.
It is a major producer of various crops such as rice, corn, mangoes, jackfruit, banana, rubber, and coffee.
According to the 2000 national census, Aleosan has a population of 26,164 people in 4,950 households. Some 57 of the total population belong to the Ilonggo group while the remaining 43 is a combination of other tribes such as Cebuanos, Ilocanos, Maguindanaos, and Manobos.
Attractions at Aleosan
Liguasan Marsh
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| 0.997894 |
Early Adulthood Development
Some cultures and religions have formal rites of passage that mark when an adolescent becomes an adult. Discuss what “rites of passage” are common to adolescents in the United States. Are there any that are nearly universal?
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Tag Archives: keycap
Apple Keyboard (Aluminum) keycap removal
I decided to switch around my new Apple Keyboard to use the Dvorak layout. I didn’t find any resources when I searched, so here are photos and directions. It worked for me but I can’t guarantee your success. Research the cost and availability of replacement parts before attempting.
All of the keys that must be moved to convert the new aluminum keyboard to the Dvorak layout have their scissors arranged this way. The two clips along the top of the keycap hold onto the bars near the top of the scissors. These must be pulled free. Then the lower tabs are released by moving the key toward the upper edge of the keyboard; turning the keyboard face down helps.
I found these easier to remove than the keycaps on the MacBook Pro—I didn’t break any of the scissors this time! Also, the scissors appear to be harder to replace as a result of their stronger design. If you break one, leave a note to help others avoid the same outcome.
Keycap Removal
1. Slide a thin, non-marring tool such as a fingernail under the top edge of the keycap.
2. Depress the bottom edge of the keycap.
3. Rotate the keycap up with increasing pressure until the two top clips are released from the scissor.
4. Invert the keyboard and jiggle the key to release the lower hinges.
Keycap Replacement
1. Drop the keycap into place.
2. Jiggle the key to seat the lower pivots.
3. Press down with increasing pressure until the top clips click into place.
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| 0.881697 |
{ "resourceType": "ValueSet", "id": "v3-ActRelationshipHasSubject", "language": "en", "text": { "status": "generated", "div": "
" }, "url": "http://terminology.hl7.org/ValueSet/v3-ActRelationshipHasSubject", "identifier": [ { "system": "urn:ietf:rfc:3986", "value": "urn:oid:2.16.840.1.113883.1.11.20014" } ], "version": "2.0.0", "name": "ActRelationshipHasSubject", "title": "ActRelationshipHasSubject", "status": "active", "date": "2014-03-26", "description": "Relates an Act to its subject Act that the first Act is primarily concerned with.\r\n\r\nExamples\r\n\r\n1. The first Act may be a ControlAct manipulating the subject Act\r\n2. The first act is a region of interest (ROI) that defines a region within the subject Act.\r\n3. The first act is a reporting or notification Act, that echos the subject Act for a specific new purpose.\r\n\r\nConstraints\r\n\r\nAn Act may have multiple subject acts.\r\n\r\nRationale\r\n\r\nThe ActRelationshipType \"has subject\" is similar to the ParticipationType \"subject\", Acts that primarily operate on physical subjects use the Participation, those Acts that primarily operate on other Acts (other information) use the ActRelationship.", "immutable": true, "compose": { "include": [ { "system": "http://terminology.hl7.org/CodeSystem/v3-ActRelationshipType", "filter": [ { "property": "concept", "op": "is-a", "value": "SUBJ" } ] } ] } }
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| 0.998797 |
Look for Frequent Updates!
Intervention was an honorable tool originally designed for State Boards of Education to assist children and their educators in erradicating the chance that a seriously impaired child would develop poorly due to lack of proper diagnosis and treatment. This would help ensure that all children had an equal chance at a good life. The Indiana State Board of Education, Title 511, Article 7, Rules 3-16 for Special Education still allows and suggests interventions be carried forth. Specifically, refer to pages 31-78. Also, see page 39 under the heading of 511, IAC 7-11-5, Emotional Handicap, Section 5a, number 5. "Inappropriate behaviors or feelings under normal circumstances". This is very vague and allows for very subjective analyses to take place. This description allows the corrupt educators to continue abusing the system. This is one of their main windows of opportunity or vehicle to target your child unfairly. This means, if a teacher or school official's opinion of your child is not favorable for any reason, they have a wide open door to target your child for their "intervention" and potentially have your child misdiagnosed. They cannot force you to comply as per the December 3, 2004 Federal Law, but they can make your child's life miserable, if you decline. All of which is under the guise of good intentions for your child. The incentives for corrupt educators to do this vary, but typically it points to a corrupt educator manipulating the system in order to obtain thousands, sometimes tens of thousands of dollars from State and Federal grants. The various State Boards of Education have what would be considered a relative 'honor system' in place. They must trust, for the most part, that the requests for special education funds are legitimate. They do not have neither the time, nor resources to extensively audit each request for its authenticity beyond a doctor's signature. This is a potential source for fraudulent interventions. The Indiana State Board of Education Title 511, Article 7 may be obtained by accessing http://baby.indstate.edu/iseas/art71.html.
I have my personal experience and the experiences of others as examples of how these things are and can be carried out. Click on Our Personal Experience for more information.
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| 0.897065 |
Is it cold at a hockey game
What do you wear to a hockey game?
10 Stylish Items To Wear To A Hockey Game Classic Pashmina. Bundle up at the rink with a chic oatmeal-colored scarf like this one ($12.90) with tassel accents. Tech Friendly Gloves. Cozy Beanie. Stylish Hoodie. Sporty Socks. Boho Sweater. Warm Boots. Long-Sleeve Henley.
How cold does it get at a hockey game?
sixteen degrees Fahrenheit
Is it cold at the ice hockey?
Ice temperature also sees a steady and significant increase during games. “The ice temperature before warm-up is about 18 degrees Fahrenheit, but that will climb as high as 24 degrees during the game,” says King. “The NHL’s standard for maximum temperature at the conclusion of a game is 24 degrees.”
How cold is an indoor ice rink?
In ice rinks , the refrigerant cools brine water, an anti-freezing agent, which goes through pipes underneath the ice . These steel pipes are typically embedded into a concrete slab and kept at 32 F / 0 C, so that any water placed on top of the slab freezes and becomes the skating surface that we see.
What should you eat before a hockey game?
Top off your fuel stores by eating a high-quality carbohydrate -rich meal the night before your first game . Pasta with red sauce and chicken breast and a side salad. Burrito or burrito bowl with grilled chicken/steak, brown rice, grilled vegetables and avocado (Athletes can even order this when eating out!)
How long does a game of ice hockey last?
A regular game consists of three 20-minute periods, with a 15-minute intermission after the first and second periods. Teams change ends for each period. If a tie occurs in a medal-round game , a five-minute sudden-victory overtime period is played.
You might be interested: Boston bruins hockey score
How thick is NHL ice rink?
approximately 3/4″
What is the hockey puck made out of?
vulcanized rubber
How cold is the Tampa Bay Lightning arena?
TAMPA — The ice temperature beneath the Tampa Bay Lightning players’ skates hovers between 22 and 23 degrees. The summer sear outside Amalie Arena punches past 90.
Why is ice slippery?
The ” slippery ” nature of ice is generally attributed to the formation of a thin layer of liquid water generated by friction, which for instance allows an ice skater to “surf” on top of this liquid film. The mystery of sliding on ice can therefore be found in the “viscous” nature of this film of water.
How do ice rinks work?
At the beginning of the hockey season, the arena uses an advanced refrigeration system that pumps freezing “brinewater” (salt water) through a system of pipes that run through a large piece of concrete known as the ” ice slab.” When the ” ice slab” gets cold enough, layers of water are applied to it.
How would you calculate the volume of ice in a hockey rink?
The formula for the volume of a rectangular solid is length-times-width-times-height. Since the ice sheet is very close to that of a rectangular solid, and since we know all these variables, it’s easy to calculate the volume of the ice sheet: 43.6 cubic meters.
What is under the ice in a hockey rink?
Underneath the insulation, a heated concrete layer keeps the area below the ice from freezing, which could damage the rink structure. Below that, there is a base layer of gravel and sand, which has a drain at the bottom.
You might be interested: Hockey skates vs figure skates
How much electricity does an ice rink use?
It takes a lot of electrical energy to run an ice skating facility. A typical community arena can consume between 600,000 and 2,000,000 kWh per year depending on the location and facility operating profile.
How cold is it in a curling rink?
Keep the humidity down and if needed supply some heat. The standard for curling ice is to measure the air temperature and humidity at a height of 1.5m and aim to achieve 8ºC and 40% relative humidity (dew-point temperature of – 4.3ºC at 1.5m), with the ice – surface temperature at – 4.5ºC.
Leave a Reply
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| 0.9841 |
Chapter 153 Measure
Every gaze in the area was raised towards sky where a dark golden pillar of Genesis Qi was rising into the heavens.
This scene was not unfamiliar to everyone present. The same thing had also happened to them when they reached the Heaven Gate stage.
It was known as Qi dashing through the Heaven Gate, and was measured in feet.
Simply put, the higher one’s Qi rose, the more abundant one’s Genesis Qi was. Of course, there were also various other factors such as the grade of the Genesis Qi, the grade of the Qi Dwelling...
It was not always the case that the higher one’s Genesis Qi rose, the stronger one would be in the future. But at the very least, for a certain period in one’s cultivation, the higher one’s Genesis Qi soared, the bigger the lead one would have over others.
In a certain sense, this achievement represented one’s foundations....
This chapter requires karma or a VIP subscription to access.
Previous Chapter Next Chapter
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| 0.997523 |
SQL portability
Writing portable SQL is mandatory, to support different kind of database servers.
This section provides hints to solve SQL incompatibility problems in your programs.
In addition to this SQL portability guide, read carefully the database-specific guides which contain database specific information about SQL compatibility issues.
To easily detect SQL statements with specific syntax, you can use the -W stdsql option of fglcomp:
$ fglcomp -W stdsql orders.4gl
module.4gl:15: SQL Statement or language instruction with specific SQL syntax.
This compiler option can only detect non-portable SQL syntax in static SQL statements.
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| 0.97919 |
Internet Security (cagatay parlak)
Presentation Description
No description available.
Presentation Transcript
Internet Security :
Internet Security Millions of internet users in risky. Prepaired by Çagatay Parlak
What is the internet security? :
What is the internet security? When a computer connects to a network and begins communicating with others, it is taking a risk. Internet security involves the protection of a computer's internet account and files from intrusion of an unknown user. Basic security measures involve protection by well selected passwords, change of file permissions and back up of computer's data.
What are the risks? :
What are the risks? Vulnerabilities Trojan horses Worms Viruses Keyloggers Sniffers Phishing
Trojan Horses :
Phishing :
Viruses :
Viruses A computer virus is a computer program that can copy itself and infect a computer without the permission or knowledge of the owner. Computer viruses can damage your computer software system even cause collapse your system. Its can delete your files.
Keyloggers :
Keyloggers Keyloggers are provide logging which you press on the keyboard buttons. Hackers can steal your passwords or your personal informations.
Computer Worms :
Computer Worms A computer worm differs from a computer virus in that a computer worm can run itself. A computer worm can spread without a host program, although some modern computer worms also use files to hide inside. It can damage your files and operation systems. It can spread rapidly on your system or lan to other computers.
Sniffers :
Sniffers is computer software or computer hardware that can intercept and log traffic passing over a digital network or part of a network. Hackers can sniff your packets with some softwares or hardwares and they can steal your creadit card numbers, paswords or e-mails.
How can we protect treats? :
How can we protect treats? We must use antiviurs softwares. We must use firewall for hacker attacks We shouldn’t open every files. When we receive an email, we should be carefully We shouldn’t share our personel information on the internet. We shouldn’t accept every file, when we talk our friends such as msn messenger.
Slide 14:
If we don’t obey protection rules, we can see some message on our websites by hackers. We can lose our esteem like on picture.
References :
Thank you for your attention :
Thank you for your attention If you wish more information about this topic, you can visit my personal web page or gemoodle blog.
authorStream Live Help
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| 0.898328 |
Product Import
The import process described here is obsolete and provided only for those still running an older version of AcctVantage. For a more current discussion of Product importing, please refer to Import Wizard.
1. Prepare the Product Import Template.
Prepare the Product Import Template.
2. Open the Product window.
Open the Product window.
3. Import the template.
Import the template.
4. Select the import template.
Select the import template.
5. Importing is complete.
Once Products have been created or imported, you can proceed to the next step of importing Product Aliases (optional).
Importing is complete.
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| 0.873615 |
Honoring Your Hunger – 003
Listen now
In episode three we're talking about honoring our hunger. What that means, what it can look like, and how it builds body trust. We also spend sometime talking about different types of hunger, and how to give yourself permission to honor all of them. Lastly, we talk about some decisions and actions that do not help us honor our hunger. Resources: The Nuance of Hunger (How to tell if you're hungry, and how to respond) https://encouragingdietitian.com/hunger-nuance Mindful Eating for Newbs (How to figure out what you crave and enjoy eating) https://encouragingdietitian.com/mindful-eating-newbs Find me on: Instagram: encouragingdietitian Twitter: encouragingRD web: encouragingdietitian.com
More Episodes
In this episode, Christyna breaks down why applying moral value to food doesn't work, why it's important to dismantle unhelpful associations you have with food, and why habituation works. connect with me IG: encouragingdietitian Twitter: encouragingRD web: encouragingdietitian.com
Published 02/22/21
In this episode, Christyna reminds us that intuitive eating and health at every size are very much a political stance. She reminds us that if we're feeling disconnected from our bodies based on current events we can still take of ourselves. Fighting for justice is a marathon, take care of...
Published 06/01/20
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Pneumocystis carinii
MeSH information
The prototype species of PNEUMOCYSTIS infecting the laboratory rat. It was formerly called Pneumocystis carinii f. sp. carinii. Strains that infect humans and cause PNEUMOCYSTIS PNEUMONIA were originally classified as Pneumocystis jirovecii or Pneumocystis carinii f. sp. hominis.
Bar chart showing 588 publications over 19 distinct years, with a maximum of 61 publications in 2011
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Divya Cherian
Dec 2010
I took this course with only slight pause due to old CULPA reviews, and I don't regret it at all. Professor Bakhle is a fantastic lecturer with a thorough insight into her subject. Moreover, she did an excellent job of contextualizing an extremely broad overview of South Asian history. While we covered a lot of material, I found that it was generally manageable to grasp what was going on and understand the narrative as it was presented. Professor Bakhle also made a tremendous effort to expand the course beyond Gandhi. We read numerous different opinions, and were presented with a class that put Gandhi in conversation with his contemporaries-- and allowed us to understand him within that context. Given that we had such a short amount of time in class and a large amount of material to cover, we actually read about a remarkable variety of the movements and disagreements that dotted Indian history from pre-colonial and briefly, post-colonial times. Class had two TA's. I had Divya, who was great at dissecting and making sometimes dense readings understandable.
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Sie sind auf Seite 1von 255
Ariacutty Jayendran
Mechanical Engineering
Grundlagen des Maschinenbaus in englischer Sprache
Ariacutty Jayendran
Mechanical Engineering
Grundlagen des Maschinenbaus
in englischer Sprache
Mit 168 Abbildungen sowie einer englisch-deutschen
und deutsch-englischen Vokabelübersicht
Bibliografische Information Der Deutschen Bibliothek
Die Deutsche Bibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie;
detaillierte bibliografische Daten sind im Internet über <> abrufbar.
Prof. Dr. AriacuttyJayendran, M. Sc. Ph. D. London, Chartered Engineer/MIEE London. Jetzteme-
ritiert, zuvor Prof. der Physik an den Universitäten Khartoum, Sudan und Colombo, Sri Lanka.
1. Auflage September 2006
Alle Rechte vorbehalten
© B.G. Teubner Verlag / GWV Fachverlage GmbH, Wiesbaden 2006
Der B.G. Teubner Verlag ist ein Unternehmen von Springer Science+Business Media.
Das Werk einschließlich aller seiner Teile ist urheberrechtlich geschützt. Jede Ver-
wertung außerhalb der engen Grenzen des Urheberrechtsgesetzes ist ohne
Zustimmung desVerlags unzulässig und strafbar. Das gilt insbesondere für Verviel-
fältigungen, Übersetzungen, Mikroverfilmungen und die Einspeicherung und
Verarbeitung in elektronischen Systemen.
DieWiedergabevon Gebrauchsnamen, Handelsnamen, Warenbezeichnungen usw. in diesem Werk
Sinne der Waren- und Markenschutz-Gesetzgebung als frei zu betrachten wären und daher von
jedermann benutzt werden dürften.
Umschlaggestaltung: Ulrike Weigel,
Druck und buchbinderische Verarbeitung: Strauss Offsetdruck, Mörlenbach
Gedruckt auf säurefreiem und chlorfrei gebleichtem Papier.
Printed in Germany
ISBN-10 3-8351 -0134-X
ISBN-13 978-3-8351-0134-0
Dieses Buch richtet sich an Studierende der Ingenieurwissenschaften und
praktisch tatige Ingenieure, die sich im Verstehen englischsprachiger
Lehrbucher und Fachtexte profilieren und ihr sprachliches Verstandnis
verbessern wollen. Es enthalt das Grundwissen wichtiger Fachgebiete des
Maschinenbaus und mochte eine Briicke schlagen zum Einstieg in englische
Das Buch ist als kompaktes Handbuch konzipiert und verbindet theoretische und
praktische Lehrinhalte. Die inhaltliche Gliederung und Kapitelabfolge entspricht
anderer deutscher oder englischer Handbiicher dieses Themenkreises.
Mit diesem Handbuch wird den Studierenden die Moglichkeit gegeben, ein
sprachliches Grundwissen in technischem Englisch zu erwerben und gleichzeitig
inhaltliche Grundkenntnisse der einzelnen Fachgebiete des Handbuchs kompakt
vorzufinden. Es ist in gut verstandlichem Englisch verfaBt. An zahlreichen
Stellen finden sich nach englischen Schliisselbegriffen die deutschen
Entsprechungen in Klammern beigeftigt. So ist dem Text sprachlich sehr gut zu
folgen, das englische Vokabular wird zunehmend verstandlich und der Einstieg
in andere englische Texte auf diese Weise sehr erleichtert.
Das Buch ist so kompakt wie moglich verfaBt worden und enthalt die
Grundkenntnisse einzelner Bereiche wie Mechanik, Maschinenelemente,
Thermodynamik oder auch Fertigungstechnik in der didaktisch ublichen
Reihenfolge. Der Schwerpunkt liegt nicht auf dem Unterricht der englischen
Sprache, sondern auf der Vermittlung von Grundkenntnissen einzelner Bereiche
des Maschinenbaus und Ingenieurwesens auf der Basis der englischen Sprache.
Es kann von Studierenden und Ingenieuren als Referenzbuch genutzt werden.
Die Zeichnungen sind nach der "British Standard Specification" erstellt,
Symbole entsprechen denen in englischer Fach- und Lehrbuchliteratur. Die
Leser erhalten so einen Einblick in die Unterschiede der Normung und
Formelnotation zwischen deutscher und englischer Literatur. Ein
Formelverzeichnis, eine englisch-deutsche und deutsch-englische Vokabelliste
und ein sowohl deutsches als auch englisches Stichwortverzeichnis unterstutzen
Zum weiterfuhrenden Verstehen englischer Texte des Maschineningenieur-
wesens empfehle ich elektronische Medien wie das "Cambridge Advanced
Learner's Dictionary on CD-ROM" (Cambridge University Press) zu nutzen.
Hier finden sich englisches und amerikanisches Fachvokabular mit
Aud iounterstiltzung.
Ausgezeichnete Hilfe bieten auch Worterbiicher im Internet, wobei besonders
die Worterbuchsammlung unter zu empfehlen ist.
Mein besonderer Dank gilt meiner Frau Christel, ohne deren Hilfe ich dieses
Buch nicht hatte schreiben konnen.
Wetter, im Juli 2006 Ariacutty Jayendran
Contents Inhaltsverzeichnis
I Mechanics I Mechanik 9
1 Statics 1 Statik 9
2 Dynamics 2 Dynamik 20
3 Hydrostatics 3 Hydrostatik 35
4 Fluid Dynamics 4 Dynamik der Fltissigkeiten 39
II Strength of materials II Festigkeitslehre 47
1 Basic concepts 1 Grundkonzepte 47
2 Bending loads 2 Biegebeanspruchung 54
3 The buckling of columns 3 Knickung 63
4 Torsion 4 Verdrehung 67
III Engineering materials III Werkstoffe 70
1 Properties of materials 1 Werkstoffeigenschaften 70
2 Iron and steel 2 Eisen und Stahl 72
3 Nonferrous metals 3 Nichteisenmetalle 83
4 Nonmetallic materials 4 Nichtmetallische Werkstoffe 89
5 The testing of materials 5 Werkstoffpriifung 95
IV Thermodynamics IV Thermodynamik 98
1 Basic concepts and temperature 1 Grundkonzepte und 98
2 Thermodynamic systems 2 Thermodynamische Systeme 102
3 The first law of thermodynamics 3 Erster Hauptsatz 105
4 The second law of thermodynamics 4 Zweiter Hauptsatz 107
5 Ideal gases 5 Ideale Gase 112
6 The transfer of heat 6 Warmeiibertragung 119
V Machine elements V Maschinenelemente 121
1 Limits and fits 1 Grenzmassen und Passungen 121
2 Rivets and riveted joints 2 Niete und Nietverbindungen 125
3 Screw joints 3 Schraubenverbindungen 126
4 Pins 4 Stifte 131
5 Axles and shafts 5 Axen und Wellen 132
6 Couplings 6 Kupplungen 135
7 Belt and chain drives 7 Riemen und Kettengetriebe 136
8 Bearings 8 Lager 138
9 Gears 9 Zahnrader 141
VI Joining processes VI Verbindungsarten 145
1 Adhesive bonding 1 Klebverbindung 145
2 Soldering 2 Loten 146
3 Brazing 3 Hartloten 147
4 Weldine 4 SchweiBen 147
VII Metal removal Processes VII Zerspanvorgange 154
1 Basics 1 Grundbegriffe 154
2 The use of hand tools 2 Formgebung von Hand 156
3 Drilling, sinking and reaming 3 Bohren, Senken und Reiben 162
4 The lathe and single point cutting 4 Drehmaschine und 167
tools DrehmeiBel
5 Milling machines 5 Frasmaschine 170
6 Broaching 6Raumen 173
7 Surface finishing processes 7 Oberflachenfeinbearbeitung 174
VIII CNC maschines VIII CNC Maschinen 177
1. Introduction 1 EinfUhrung 177
2 Geometrical basis for programming 2 Geometrische Grundlagen 180
3 Drives for CNC machines 3 CNC Maschinen Antriebe 183
4 Tool and work changing systems 4 Werkzeug und Werkstuck 184
5 Adaptive control for CNC machines 5 Erhohung des Nutzungs- 186
6 Programming 6 Programmieren 187
IX Other manufacturing IX Weitere Fertigungs- 193
processes verfahren
1 Bulk deformation processes 1 Massivumformprozesse 193
2 Forging 2 Schmieden 196
3 The casting of metals 3 Gielten 199
4 Shearing and blanking 4 Scheren und Stanzen 203
5 Thermal cutting of metals 5 Thermisches Trennen 206
6 Bending and forming processes 6 Umformverfahren 208
7 The coating of surfaces 7 Beschichten 211
8 The manufacture of plastic goods 8 Kunstoffproduktherstellung 214
10 Other topics
1 List of symbols 218
2 Vocabulary 1 Englisch / Deutsch 220
3 Vocabulary 2 Deutsch / Englisch 232
4 Index in English 244
5 Stichwortverzeichnis 249
6 Bibiliography 253
7 Appendix 1 : Alternate word forms in English 254
I Mechanics
1 Statics (Statik)
1.1 Forces (Krafte)
A force is a physical quantity which causes a change in the motion of a body or
in its form. A force has both magnitude and direction, and is therefore classified
as a vector quantity. When specifying a force, it is not enough to specify the
magnitude and direction of the force. It is also necessary to specify where a
force acts, and this is done by specifying its line of action. An external force
may be applied at any point along its line of action without changing its effect
on the body.
A force is usually represented in a diagram by an arrow as shown in Fig 1.1.
The length of the arrow is proportional to the magnitude of the force, while the
direction of the arrow is the same as the direction of the force.
A number of forces F]t F2, ,Fn can be added together to form a single re-
sultant force Fr which has the same effect on the body as all the individual
forces acting together. The SI unit of force is called the Newton.
The subject of statics is mainly concerned with the action of external forces
which are necessary and sufficient to keep rigid bodies in a state of equilibrium.
Changes inform do not come within the scope of statics.
Fig 1.1 Diagram of a force Fig 1.2 Diagram of a couple
1.2 Couples and moments (Kraftepaare und Momente)
1.2.1 Couples. (Kraftepaare)
A couple consists of two equal and opposite parallel forces F separated from
each other by a distance I. A couple tends to rotate a body and its effect cannot
be reduced to that of a single force. The moment of a couple M is a measure of
its ability to cause rotation and is given by the expression
Moment M = Force F X distance of separation /
The sense of rotation of a couple can be clockwise or counterclockwise.
10 I Mechanics
1.2.2 Displacement of a couple (Verschiebung eines Kraftepaares)
The moment of a couple remains
the same even if the forces forming 3N
the couple are displaced and their
magnitude and direction changed 2N 2m
(Fig 1.3), provided the forces re-
main parallel to each other, have 3m _L
the same moment, and remain in M.,= 2 x 3
their original plane (or in a parallel
Fig .3 Two equivalent couples with forces which
plane). The sense of rotation must are different in magnitude and direction
also remain the same.
1.2.3 Vector representation of a couple
(Vektor Darstellung eines Kraftepaares)
The magnitude, direction and sense of rotation of a couple can be completely
represented by a single moment vector M as shown in Fig 1.2. This is a line
drawn perpendicular to the plane in which the couple acts and whose length is
proportional to the moment of the couple.
1.2.4 The moment of a force about a point
(Moment einer Kraft beziiglich eines Punktes)
The moment of a force about a point P is the
product of the magnitude of the force and the
perpendicular distance of the line of action of
the force from this point.
Fig 1.4 Moment of a force about a
M=Fl point
1.2.5 The moment of a force with respect to a straight line
(Moment einer Kraft beziiglich einer Linie)
In this case, the force has to be resolved into two components parallel and per-
pendicular to the line. The moment of the force with respect to the line, is the
product of the perpendicular component of the force and the distance between
the line of action of the force and the given straight line.
1.2.6 Moving a force to act through any arbitrary point
(Verschiebung einer Kraft)
If we have a force F acting through any point A in a body (Fig 1.5(a)), we can
show that this is equivalent to the same force F acting through an arbitrarily
chosen point B and a couple (as shown in Fig 1.5(c)).
To show this, we place two equal and opposite forces F at point B (Fig 1.5 (b)).
This should have no effect on the body. It can be seen that the original force F at
A and the force —F at B form a couple having a moment M = Fd.
Thus as shown in Fig 1.5 (c), we have replaced the original force F at A by the
same force acting through an arbitrary point B plus a couple of moment M = Fd.
1 Statics 11
It is easy to see (by reversing the procedure) that the reverse is also true. This
means that a force F and a couple M acting on a body are equivalent to a single
force F acting through another point in the body.
Fig 1.5 (a) Fig 1.5 (b) Figl.5(c)
Fig 1.5 Moving a force to act through any arbitrary point
1.3 Composition and resolution of forces
(Zusammensetzen und Zerlegen von Kraften)
1.3.1 Parallelogram and triangle of forces
(Krafteparallelogramm und Kraftedreieck)
Fig 1.6 (a) Parallelogram of forces Fig 1.6 (b) Triangle of forces
If we have two forces F\ and F2 acting at a point as shown in Fig 1.6(a), these
two can be added vectorially to give a single resultant force Fr which is the di-
agonal ofthe parallelogram formed by the forces. It is often more convenient to
use a triangle which is half the parallelogram (Fig 1.6(b)) to find the resultant
graphically. Adding forces vectorially in this way is called the composition of
Here the resultant is Ff = JF2 + F22 +2FlF2cosa and /? = a r c s i n - ~ —
Conversely, a single force Fr can be resolved (or split) into two forces F and
F in any two directions, where
Fr sin
and F =F cos p-F cos a
sin a
12 I Mechanics
1.3.2 Composition and resolution of forces acting on a rigid body at a point
(Zusammensetzen und Zerlegen von Kraften mit gemeinsamem Angriffspunkt)
If we have a number of forces F, F , ,F acting on a rigid body at the
same point, then these forces can be resolved into components along three rec-
tangular coordinate axes. If any one of the forces Fi makes angles cc,p,y with
the x,y,z axes, then we can add the components of all the forces along each axis
algebraically and obtain the expressions
Fy =
where Fx,FFyy, Fz are the x.y.z components of the resultant p •
Therefore Fr = +Fy2 +Fz2
The angles made by the resultant with the three axes are given by
F Fv F
Fr ^ - , y r = arccos—-
Fr Fr
1.3.3 Composition and resolution of a number of forces with different
points of application in three dimensions
(Zusammensetzen und Zerlegen von Kraften im Raum)
Fig 1.7 (a) Figl.7(b) Fig 1.7 (c)
Fig 1.7 (a) Three forces acting at different points in a body.
Fig 1.7 (b) An arrangement equivalent to (a) with the same three forces
acting at an arbitrary point O together with three couples.
Fig 1.7 (c) Equivalent arrangement with a single force and a single couple.
Consider a body acted on by three forces/^, F ,FJ each acting at a different
point as shown in Fig 1.7 (a). As shown in section 1.2.7 each of these forces
can be moved individually to act through an arbitrary point O provided we
also introduce a couple for each force transferred. The result of such a transfer
is shown in Fig 1.7 (b) which shows the same three forces acting at an arbi-
trary point O together with three vectors which represent the three couples
which have been added. This may be further simplified as shown in Fig 1.7 (c)
to a single force Ff and a single couple of moment Mr. The point O is arbi-
trary, but the magnitude and direction of the force Fr will always be the same.
1 Statics 13
The value of F, is obtained in the same way as has been shown in section
1.3.2. and is given by
F - x
The values of MvM2,M-i and Mr will however depend on the point chosen.
The magnitude of Mr may be found by a similar process to that for finding F,.
2 22 22
It is given by Mr = ^ +M + M
The moment vector Mr makes angles ar,pr,yr with the x,y,z axes where
ar = arccos = arccos-
1.3.4 Conditions for equilibrium (Gleichgewichstbedingungen)
(a) When a rigid body is acted on by a number of forces at different points and
in different directions, equilibrium exists only when Fr = 0 and Mr = 0 which
means that the following six conditions must be satisfied.
^ = 0 , 7 ^ = 0 , ^ . =0 a n d M x = 0 , M y = 0,Mz=0
(b) When all the forces are in the same plane, equilibrium exists when the fol-
lowing three conditions are
satisfied. Fx = 0,Fy = 0,Mz = 0
1.3.5 Graphical methods (Graphische Methoden)
Fig 1.8 (a) Shows four forces acting at a point Fig 1.8 (b) Polygon offerees
Consider four forces which are in the same plane and acting at a point as shown
in Fig 1.8 (a). The resultant of these forces can be found by repeated use of the
triangle of forces (Fig 1.8 (b)). If we omit the closing sides of the triangles, we
have a polygon of forces, which in this case is not closed (i.e. has an open side
EA). The sides representing the forces can be taken in any order, the arrows
(showing their direction) go round the periphery of the polygon in the same di-
rection. The magnitude and direction of the resultant is represented by the clos-
14 I Mechanics
ing side of the polygon EA. Its direction however is counter to that of the other
sides of the polygon. Equilibrium exists when the polygon closes and the resul-
tant is zero. If the forces are not in the same plane, the resultant may be found
by adding these forces in space, forming in effect a polygon in space.
1.4 Centre of gravity, centre of mass and the centroid
(Schwerpunkt, Massenmittelpunkt und Flaschenschwerpunkt)
Any body can be supposed to be composed of a small number of particles each
of mass dm. The gravitational force
acting on each of these is gdm. All
these small forces together will have a
resultant which is equal to the total
force of gravity mg acting on the body
whose total mass is m. The force will
act through a point G called the centre
of gravity (Fig 1.9). The total mass of
the body may be considered to be con-
centrated at the point G. The centre of
gravity is therefore also termed the Fig 1.9 Centre of gravity
centre of mass.
When the density of the body is uniform through the whole of the body, then
bodies having the same geometric shape will have the same centre of gravity,
although their densities may be different. In this case the term centroid is used
for the centre of gravity, because the position of the centre of gravity depends
only on the geometric shape of the body.
1.5 Types of equilibrium (Arten des Gleichgewichts)
Fig 1.10 (a) Stable equilibrium (b) Unstable equilibrium (c) Neutral equilibrium
Consider a body which has the freedom to move but which remains at rest. It is
said to be in a state of equilibrium. We distinguish between three different
types of equilibrium.
1 Statics 15
(a) Stable equilibrium - An example of this is a ball rolling on a concave sur-
face as shown in Fig 1.10 (a). A state of stable equilibrium exists when the
slightest movement of the body raises its centre of gravity. When it moves
even slightly away from the minimum position, the force F has a tangential
component FT which moves it back to its original minimum position.
(b) Unstable equilibrium - A state of unstable equilibrium exists, when the
movement of the body lowers its centre of gravity as in the case of a ball
rolling on a convex surface (Figl.10 (b)). In this case the tangential compo-
nent FT tends to move it away from the equilibrium position.
(c) Neutral equilibrium - Neutral equilibrium exists, when a ball rolls on a flat
surface as shown in Fig 1.10 (c). Here any movement away from the equi-
librium position does not create a force which tends to move it towards or
away from its original position.
1.6 Friction (Reibung)
1.6.1 Introduction (Einfiihrung)
The term friction refers to the force of resistance which arises, when two sur-
faces which are in contact with each other, slide or tend to slide against each
other. When the surfaces are dry and free of contamination by liquids, the resis-
tance is called dry friction. An example of this is the friction that exists between
surfaces of a brake shoe and a brake drum. This friction is absolutely necessary
for the functioning of the brake, and must be maintained at a high level. For
many other applications however, it is desirable to reduce the friction by lubri-
cation. The term lubrication refers to the maintenance of a thin film of fluid
or gas between the sliding surfaces.
1.6.2 Static friction (Haftreibung)
Consider a body with a flat lower
surface lying on a flat horizontal
surface. Normally the weight FG
acts vertically downwards, and
the body remains in equilibrium
because Fa is opposed by a verti-
cal force of reaction FK. If we
now apply a horizontal force FT
which tends to move the body,
the body does not move because
the force Ft is opposed by a/r/c-
tional force FR. If we gradually
increase FT, the body remains at Fig 1.11 Static friction
rest until the force FR reaches
a limiting value FRO .
If FT exceeds this value, then motion takes place. We can see that the total force
F acting on the body is the vector sum of FG and FT and is inclined to the verti-
cal. The force of reaction Fe is the vector sum of FN and FR and acts along the
same line of action as F but in the opposite direction. Under equilibrium
16 I Mechanics
FG =FN =Fcosa
FT = FR = F sin a
-=r- = tan a
If a = p0, when FR has its maximum value FR0, then
Coefficient of static friction Mo = ~jf~= tan Po
Angle of static friction p 0 = arctan // 0
1.6.3 Sliding friction (Gleitreibung)
When the body starts moving (or sliding) on the surface, the frictional force FR
opposing the motion is less than the static value FR0. We can write
Coefficient of sliding friction n = -^- and angle of friction p = arctan /i
The value of this coefficient depends on a number of factors such as the nature
of the two surfaces, the lubrication, the velocity of the motion, etc.
1.6.4 Rolling resistance (Rollreibung)
Rolling is used as a way of moving
bodies in preference to sliding.
Frictional resistance to rolling is
considerably smaller than that
due to sliding. When a cylindrical
or spherical object rests on a flat
surface, the pressure exerted by the
object causes a slight deformation
of both the object and the surface.
A driving force F is required to ... . ,, ,, ...
° , „. . , . Fig 1.12 Rolling resistance
overcome the frictional resistance
FR when the object is kept moving with constant velocity along the surface.
As shown in Fig 1.11, the resultant driving force F (which is the vector sum of
FT and the load FL) must be in equilibrium with the force of reaction Fe .
We can write
L ~ N
Also by equating moments FJr = FLd
By substituting we have FRr =F^d
F r
From this we see that the coefficient of rolling friction is
1 Statics 17
To ensure that only rolling occurs and that no sliding takes place, it is necessary
that nr < M0
1.6.5 Resistance to motion (Fahrwiderstand)
When considering the resistance to motion of a vehicle, it is necessary to take
into account the resistance of the bearings whose effect must be added to the
frictional resistance. The effect of both these resistances can be combined to
give a combined coefficient of friction / / , . In this case the following condition
has to be satisfied. //, < fiQ
1.6.6 Friction in screws (Reibung beim Schrauben)
(a) Screw with square threads
(Schraube mit Rechteckgewinde)
The tightening or loosening of a screw
corresponds to the up or down move-
ment of a load on an inclined plane. If
p = pitch of the screw (see page 118)
a = inclination of the thread to the
horizontal (see page 118)
r2 =mean radius of the screw
ju = tan p = coefficient of friction of the
Fig 1.13 Friction in screw threads
screw thread
tan a = -
A force /^acting at right angles to the axis of the screw is required to keep the
screw in uniform motion.
FH = Ftan(a + p)
The moment of the force required to tighten or loosen the screw is given by
M = FHr2=F tan(a ± p)r2
In the absence of friction (p = 0), the force would be
Fo =F tan a
From this we can state that the efficiency of the screw is
Ftana tana when the nut is raised
'•f t- p)
tanfa - p)
tan(a +
and ri = — J —— when the nut is lowered
When a < pn, the moment M is negative or zero. When a = , the efficiency
tana = 0.5
tan 2a
I Mechanics
(b) Screws with V and trapezoidal threads
(Schraube mit Spitz- und Trapezgewinde)
As seen from Fig 1.14 the force FN acting at right
angles to the surface of the thread is given by
F N =F/cos(/?/2)
The friction in the thread is greater than for a rec-
tangular thread and is given by
cos {PI2)
We can write = tan p = -
' COS(J3I2)
From this it is clear that that the relationships
given for square (or rectangular) threads hold also Fig 1.14 V and trapezoidal
for V and trapezoidal threads, provided we re- threads
place p by p' and /i by / / .
1.6.7 Friction due to ropes, belts, etc. (Seilreibung)
Consider a rope, belt, or band which is
stretched over a drum or pulley. The
tensional force Fx is greater than the
force 7*2 because of the frictional force
FR along the area of contact between
the belt and the drum. Let a be the an-
gle subtended by the arc of contact
between belt and drum in radians. Fig 1.15 Friction due to ropes and
The sliding coefficient of friction /i has to be used in the above relationship
when slip takes place, and the static coefficient // 0 when there is no slip.
1.6.8 Friction in pulleys (Reibung in Rollen)
(a) Fixed pulley (Feste Rolle)
The frictional resistance that exists between
the pulley and its bearing, together with the Pulley
resistance of the rope to flexing, necessitates a holder
pulling force (or effort) F which is larger than
the load Fx . If the load and the pulling force
both move through a distance s, then the effi-
ciency of the fixed pulley is
F,s _FL
11, =~FT ~ F Pulley
f Fs Fig 1.16 Fixed pulley
The efficiency is about 0.96 for plain bearings and 0.97- 0.98 for ball bearings.
1 Statics 19
(b) Single moving pulley (Lose Rolle)
The load is divided between two ropes. Movement
of pulling force 5^ = 2 x movement of load s . F
if /•—-v
( >
Fsf 2Fsx
F + Fr
Figl .17 Moving pulley
The pulling force F = —5—. If r\f = 0.95, then r\m = (l + 0.95)/2 = 0.975.
It follows that a moving pulley has a higher efficiency than a fixed pulley.
1.6.9 Friction in pulley systems
Pulley systems which consist of more than two pulleys have a mechanical ad-
vantage and enable a small force (or effort) F to lift a much bigger load F\.
Mechanical advantage = Load / Effort = F\/F
If the total number of pulleys (without counting the last direction changing pul-
ley) is n, then the number of sections of rope carrying the load is (n +1).
Therefore sf = \)s[
If there are no frictional losses F = ——. If the efficiency of the pulley system
is T| , then the lifting force is F = - —. when the direction changing pulley is
a moving pulley. If the turn-around pulley is a fixed pulley, then F = -
Direction Pulley blocks
n=3 n=4
Fig 1.18 Pulley systems
20 I Mechanics
2 Dynamics (Dynamik)
2.1 Kinematics (Kinematik)
Kinematics is the study of the motion of bodies without reference to their
masses or to the forces that cause their motion.
2.1.1 Basic quantities (BasisgroBen)
a) Displacement — The displacement of a point may be defined as the dis-
tance moved in a specified direction. It is a vector quantity and has the
symbol s. The unit of displacement is the metre (m). The term distance is
however a scalar quantity with the same unit i.e., metre .
b) Velocity — The velocity of a point is also a vector quantity, and is the
rate of change of displacement with time.
Velocity v = dt
The unit of velocity is the metre per second (m/s).
c) Speed — The speed of a point is a scalar quantity and refers to the rate
of change of distance with time. When a body moves with constant
speed, the magnitude is constant while the direction may be changing.
A body moving round a circle is moving with constant speed but not
with constant velocity. Speed has the same units as velocity (m/s).
d) Acceleration — The acceleration of a point is a vector quantity and is
defined as the rate of change of velocity.
Acceleration a = —-
A body can move with uniform or with nonuniform acceleration. When
a body moves with negative acceleration, meaning that its velocity is de-
creasing with time, it undergoes deceleration. Acceleration and decelera-
tion are expressed in units of metre per second per second (m/s2).
2.1.2 Uniform motion (Gleichformige Bewegung)
o t 0 t
Fig 1.19 Distance vs time diagram Fig 1.20 Velocity vs time diagram
2 Dynamics 21
A body is said to be in a state of uniform motion if its velocity is constant,
which implies that its acceleration is zero. The change in distance with time can
be shown in a s,t diagram as shown in Fig 1.19. The change in velocity with
time can be shown in a v,t diagram as shown in Fig 1.20. In the case of uniform
motion the velocity is constant and this is represented in the diagram as a hori-
zontal line. The shaded part under the velocity line represents the distance trav-
elled during a given time.
2.1.3 Nonuniform motion (acceleration or deceleration)
(Ungleichformige Bewegung - Beschleunigung oder Verzogerung))
When a body is in a state of nonuniform motion then its velocity is changing,
and it travels different distances during equal intervals of time. The change of
distance with time is shown in the s,t diagram of Fig 1.21. The slope of the
curve at any point gives the velocity at that instant of time.
Fig 1.21 Nonuniform motion Fig 1.22 Uniform acceleration
2.1.4 Uniform acceleration (Gleichmafiig beschleunigte Bewegung)
The v,t diagram in Fig 1.22 shows the change in velocity with time for a body
which has an initial velocity u and a uniform (or constant) acceleration a. If the
body moves for a time t, then
Increase in velocity = at
Final velocity v = initial velocity u + increase in velocity at
or v = u + at
2.1.5 Distance travelled when a body moves with uniform acceleration
(Weglange unter gleichmaBig beschleunigter Bewegung)
The distance travelled can be found as shown below.
Average velocity = - — -
Since v = u + at
. . . . u + u + at 1
Average velocity = = u + -at
Distance travelled = average velocity X time
22 I Mechanics
Distance travelled =(« +—at)t
1 9
or s = ut + -at
The distance travelled is easily shown to be equal to the area of the trapezoidal
space below the velocity line (shown shaded in Fig 1.22).
A useful third equation may be obtained which does not involve the time t.
If we square both sides of the equation
v = u + at
v2 =M 2 +2uat + a2
we obtain
= ul +2a(ut + -atl)
The term in the bracket is equal to s, and therefor
v 2 = M 2 +2 ay
2.1.6 A body falling freely under the action of gravity (Freier Fall)
When a body falls freely under the action of gravity, it has an acceleration of g
whose magnitude is very nearly equal to 10 m/s . If it is dropped from a height
of h metres above the ground, and the initial velocity u is zero, and the time /
taken to reach the ground may be found as follows.
v = u + gt
where v is the velocity of the body when it reaches the ground.
v = 0 + gt
Time taken to reach the ground is given by
Since v2=0 + 2gh t= ^
2.1.7 A body thrown vertically upwards (Senkrechter Wurf)
Let the initial vertical upward velocity be u. In this case the body will suffer a
deceleration g until its velocity becomes zero. After that it will move downwards
with an acceleration g. For the upward movement, we can use the equation
v 2 = M2 - 2gh
0 = w2 -2gh
To find the time taken to reach this height, we write
v = u-gt
0 = u-gt
2 Dynamics 23
2.1.8 A body projected with an initial horizontal velocity
(Horizontaler Wurf)
Consider a body initially projected with O
a horizontal velocityu^. The motion of
the body is a combination of the verti- V COS0
cal motion of the falling body and the y
horizontal motion due to the velocity
of projection. The horizontal velocity
remains constant. The path of the mo- v sind
tion is a parabola. If we resolve the ve-
Fig 1.23 A body projected horizontally
locity v at a point A along its path, then
v v =vcos6> = w, = const.
= vsinB = gt
Velocity after falling through a distance h is
v = Ju2, +2gh
2.1.9 A body projected upwards at an oblique angle(Wurf schrag nach oben)
Consider a body projected with an ini-
tial velocity u at an angle 6 to the
horizontal. We can resolve u into two
components and as was stated in the VCOS0
last section, the horizontal component
ucosd remains constant right through
the motion. The vertical component x
Msin<9 undergoes a deceleration g until I— w »-l
the body rises to a maximum height h. Fig 1.24 Body projected at an oblique angle
It then moves downwards with an
acceleration g.
1. Time taken to reach the maximum height h is t=
2. Time required for the body to reach the ground is 2t = lusinQ
2 2
3. Maximum height reached by the body is u sin 6
4. Horizontal distance travelled by body is given by w = wcos 9 x It
w = ucos 9 x -
24 I Mechanics
The path of the body is a parabola and the horizontal distance travelled by the
body reaches a maximum when 6 = 45°.
2.1.10 Angular motion (Drehbewegung)
Consider a particle P moving round the a p
circumference of a circle with constant '" ' '
angular velocity. This means that equal
angles A<j> are covered by the point in
equal intervals of time At. It follows
that equal distances As will also be
traced in equal intervals of time A?. An- j ~*
gular velocity a> = — and A<j> = —
_\ As _v
~~ 7^A/ ~ 7 (v = linear velocity of P)
v = rco Fig 1.25 Particle moving round a circle
The particle P moves with constant angular velocity and constant speed. How-
ever its direction and velocity are changing and it is therefore undergoing accel-
eration. A force has to be applied constantly, to deviate it towards the centre.
Such a force is called a centripetal force. An equal and opposite inertial force is
generated by the resistance of the body to the change in the direction of the ve-
locity and this is called a centrifugal force. The acceleration required to keep a
particle moving round in a circle is aN = v2lr. Therefore the force required is
Fn — ma = mv2 Ir
2.1.11 Harmonic motion (Harmonische Bewegung)
Consider a point moving round the cir-
cumference of a circle with uniform
angular velocity a in an anticlockwise
direction. As the point P moves round
the circumference, the projection of P
on any diameter XX' (which is the
point A) moves in a straight line. If the
point starts at X' and moves along the
circumference to P in time t, then the
angle 9 = a t. If CP = r, then F i g , 26 H a r m o n i c m o t i o n
1. Distance moved by A in time t is s =X'A =r- rcoscot
2. Velocity of A along the x-axis is = cors'mcot
2 Dynamics 25
3. Acceleration of A along the x-axis is — = a>2 cos cot
4. The period T=—
The period T is the time taken by the point P to complete one cycle of motion
(or go round the circle once). This is also the time taken for the point A to com-
plete a full cycle on the x-axis by moving from X' to X and back to X'. The
point X goes through a reciprocating motion. The displacement, velocity and
acceleration of the point A can be seen to be sinusoidal functions of time.
The reciprocating motion of the point A is called harmonic motion.
2.2 Kinetics of translational motion
(Kinetik des translatorisch bewegten Korpers)
The term kinetics refers to the study of the motion of bodies as a consequence of
the forces and moments which act on them.
2.2.1 Work (Mechanische Arbeit)
Work (or mechanical work) is said to be
done when the point of application of
the force moves. The amount of work
done is measured by the product of the F i g , 2i Work done by a force
force and the distance moved in the di-
rection of the force.
Work done = Force x distance moved in the direction of the force.
Work is a scalar quantity.
If we consider the body shown in Fig 1.27 to be moved through a horizontal dis-
tance ds, the work done by the force is given by
= Fcos6ds
W=\2 Fcos0ds
The work done by a couple of moment M when it causes a body to rotate
through an angle d6 is given by
dW = MdO
W= [2Md0
The SI unit of work is the Joule (J) and is the work done when the point of appl-
ication of a force of one Newton (N) moves through a distance of one metre (m)
in the direction of the force.
Joule = Newton x metre
U = INm = Ikgm 2 /s 2
26 I Mechanics
2.2.2 Work done in lifting a weight (Arbeit der Gewichtskraft)
The weight or gravitational force acting on a mass m is equal to mg. This can be
assumed to be a constant. If a body is raised through a vertical distance h, the
work done is
W = mgh
2.2.3 Work done in stretching a spring (Formanderungsarbeit einer Feder)
When a spring is stretched, the restoring force is proportional to the elongation
of the spring when it is stretched.
Restoring force = constant x elongation
F =cs
s c 2 _ 2i
Work done = f 2 csds = —- —
i, 2
2.2.4 Work done in overcoming friction (Reibungsarbeit)
When a body has to be moved against frictional forces, work has to be done and
this work is converted into heat. If we have a body of weight mg resting on a
horizontal plane, then the force of friction is given by fimg where n is the
coefficient of friction. If we now apply a horizontal force which moves the body
through a distance s, then
Work done = fimgs
If the body rests on an inclined plane of slope a and if we apply a force parallel
to the slope to move it through a distance s,
Work done = /umgs cos a
2.2.5 Power (Leistung)
Power may be defined as the rate of doing work.
and W=\P(t)dt
The SI unit of power is the watt (W) and corresponds to work being done at the
rate of one joule per second.
1W = U/s
Larger units are the kilowatt (kW) and the megawatt (MW).
2.2.6 Efficiency (Wirkungsgrad)
The efficiency of a machine (or a process) is the ratio of the useful work done
by the machine (or process), to the total work put into the machine (or process).
This ratio is usually expressed as a percentage and we may write
2 Dynamics 27
Efficiency^ ° r k 0 U t p U t x 100%
Work input
The efficiency is always less than 100%.
2.2.7 Newton's laws of motion (Newtonsche Grundgesetze)
When a single force or a number of forces act on a body, the body moves. The
relationships between the forces which cause the motion and the motion itself,
are clearly stated in Newton's laws of motion.
1) The first law states that a body continues in its state of rest or of uniform
motion in a straight line unless it is compelled by some external force to act
otherwise. The tendency of a body to remain in a state of rest or continue to
move in a straight line is described as inertia.
2) The second law states that the rate of change of momentum of a body is
force acts. The momentum p of a body is defined as the product of its mass
and its velocity. Momentum is a vector quantity and has the units kg m/s.
Momentum = mass x velocity
p = mv
According to Newton's second law
T7 dv
3) Newton's third law of motion states that when & force acts on a body, an
equal and opposite force acts on another body. This has been sometimes
stated in the form, for every action there is an equal and opposite reaction.
An example of this is a bullet fired from a gun. When the bullet is fired,
equal and opposite forces act on the bullet and the gun during the time that
the bullet is passing through the gun.
2.2.8 Energy and the law of conservation of energy
(Energie und Energie Erhaltungssatz)
The term energy is used to denote the ability of a body or a system to do work.
Anything that can do work is said to possess energy. Energy like work is a sca-
lar quantity. There are many types of energy like mechanical energy, heat en-
ergy, electrical energy, chemical energy, etc.
There are also many types of mechanical energy. Among these are kinetic en-
ergy, potential energy and the deformation energy of an elastic body. One form
of energy can be converted into the other.
28 I Mechanics
A swinging pendulum is an example of a body whose energy can be kinetic or
potential or a mixture of both. It is completely potential at the beginning of the
swing and completely kinetic when passing through its rest position.
This is an example of the law of conservation of energy which states that energy
cannot be destroyed. It can only converted to another form of energy.
2.2.9 Conversion of work into translational kinetic energy
(Umwandlung von Beschleunigungsarbeit in kinetische Energie)
A moving body has the energy of motion or kinetic energy. When a force acts
on a body and the body moves, work is done by the force. This work is con-
verted into kinetic energy. The kinetic energy of a body of mass m moving with
a velocity v has been defined by the expression
Kinetic energy =-mv2
Work done = f Fds = L m-^-ds = J f mvdv
•S] *, dt Vj
1 2 1 2 c. c
= — mv~ mv, = Er,-E,
2 2
2 2 ' '
Work done = Change in kinetic energy
2.2.10 Impulse and momentum (KraftstoB und Impuls)
The product of force and time has been termed impulse. This is a vector quan-
tity with units of Newton second (Ns). Impulse is useful in calculating the effect
of a force on a body for a short time, and also when the force is not constant.
F = ma = m—
Impulse = f 2 Fdt = f mdv = m(v - u)
where u is the initial velocity and v the final velocity
The momentum of a body mv is defined as the product of its mass and its veloc-
ity. It has units of kg m/s.
It follows that Impulse = Change in momentum
2.2.11 Law of conservation of linear momentum (Impulserhaltungssatz)
The law of conservation of momentum states that the linear momentum of a
system of bodies is unchanged if there is no external force acting on the sys-
tem. If X j2
then V
2 Dynamics 29
It follows that momentum is conserved when no external force acts on the sys-
tem. A simple example is a system consisting of two bodies which collide with
each other. We can write mlul + m2u2 = mlvl +m2v2
where uv u2 are the initial and vp v2 the final velocities. It follows that
Momentum before collision = Momentum after collision
2.3 Kinetics of rotational motion (Kinetik der Rotation des starren Korpers)
2.3.1 Rotation of a rigid body about a fixed axis
(Rotation eines starren Korpers um eine feste Achse)
Consider the motion of a small particle
of mass dm which is part of a rigid
body rotating about an axis passing
through O (Fig 1.28). If the distance of
the particle from the axis is r and the o
tangential force acting on it is dFT,
dFT = aTdm
where aT is the tangential acceleration
Fig 1.28 Rotation about an axis
of the particle. The moment of this
force is
dM = rdFT = ra^dm
The sum of the moments of all the elementary forces dFT acting on the total
mass m is given by
M = jraTdm
We know that aT =r— where a is the angular velocity. Substituting for aT'm
the previous equation, we have
M = J \raTdm=J \rr—dm
' dt
The angular acceleration a> is the same for all the particles dm and so we can
write M = —r- J\r dm
^ where J = fr2
We can write M = J-^- is known as the moment of iner-
2.3.2 Moment of inertia J(Tragheitsmoment)
The moment of inertia depends both on the mass of the body and the distribu-
tion of mass in the body. It also depends on the axis of rotation . This is a scalar
quantity and its units are kg m2. The equation M = J— in rotational motion is
similar to F-ma in linear motion.
30 I Mechanics
We can consider force and moment to be similar quantities in the sense that
force causes linear motion while moment causes rotational motion. Also mo-
ment of inertia in rotational motion is similar to mass in linear motion.
2.3.3 The parallel axes theorem (Satz von Steiner)
The moment of inertia of a body about
any given axis is equal to the moment
of inertia about a parallel axis through
the centre of gravity, plus the product
of the square of the distance between
the two axes and the mass. Consider a
body which has a moment of inertia J
about an axis CC passing through its
centre of gravity. Fig 1.29 Parallel axis theorem
We wish to find the moment of inertia J'about another axis OO' which is paral-
lel to CC and at a distance / from it. If r is the perpendicular distance of an ele-
ment of mass dm from the axis OO', and p its distance from the axis CC
through the centre of gravity, then
J' = \r2dm = \{l + p) dm
J' = \l2dm+ Vllpdm+\p2dm
J'=l2\dm + 2 l\p dm + \p2dm
The integral \dm = m. The integral \p dm = 0 because this is the sum of the
moments of all the elements of mass about the axis CC'( see p58). Since this
passes through the centre of gravity, it follows that the integral must be zero.
The integral jp dm = J .Therefore we can write
J' = l2m + 0 + J
or J' = J + ml2
If a body is composed of a number of parts, the moment of inertia of the body J
about any axis is equal to the sum of the moments of inertia of the parts J\,
J2, , Jn about the same axis. Therefore
J = J. + J~ + + l/ti
2.3.4 The radius of gyration (Tragheitsradius)
The mass of a body is usually distributed over a large volume. We can however
imagine the entire mass to be concentrated at a point. The distance k (from the
axis of rotation) at which the point mass has to be placed so that the moment of
inertia remains the same is called the radius of gyration.
2 Dynamics 31
J = k2m
2.3.5 Rotational kinetic energy (Rotationsenergie)
The definition of kinetic energy as given by E = —mv2 also holds for each par-
ticle of mass dm in a rigid rotating body. If we use the relation
v = rco
Rotational energy Erot = j-dmv2 =- ja2r2dm
Since a> is a constant for all the particles in the body
rot = 2a
Here again it can be seen that J has a similar position in rotational energy to that
which m has in translational energy.
2.3.6 Work done in increasing the rotational energy of a body
(Umwandlung von Beschleunigungsarbeit in Rotationsenergie)
When a couple acts on a body that can be rotated, the angular velocity of the
body is increased. When the angular velocity is increased, the rotational kinetic
energy is also increased.
Consider a tangential force FT acting on a body and rotating it through a small
angle dd.
Linear distance moved ds = rdd
Work done dW = FTds = FTrdd
Since FTr = M
Therefore dW = MdG
W = \Mdd
Since M = J-^-
w= u^
= E2-E}
Work done = Change in rotational energy
A moving body can have both translational and rotational kinetic energy.
32 I Mechanics
Total kinetic energy = Translational kinetic energy + Rotational kinetic energy
n 1 2 1 r 2
E = ~mv +-Jco
2 2
2.3.7 Angular Impulse (Drehimpuls)
Analagous to the quantity linear impulse in linear motion, we can also define
the quantity
Angular impulse = Mdt = J-j-dt = Jdco
If the angular velocity of a body changes from a>l to a>2 in time t\ to t2 then
2.3.8 Conservation of angular momentum (Drehimpuls Erhaltungssatz)
It can be shown that similar to the case of the conservation of linear momentum,
the angular momentum of a system of bodies is unchanged if there are no ex-
ternal forces (or couples) acting on the system.
2.4 Impact (StoB)
2.4.1 Forces acting during an impact (Krafte beim StoB)
The term impact applies to the collision between two bodies in which relatively
large forces act between them over a comparatively short period of time. The
motion of the bodies is changed by the impact. No external forces act on the
bodies during an impact and therefore the forces exerted by the bodies on each
other must be equal and opposite as would be expected from Newton's third
law of motion. It follows that the law of conservation of momentum holds and
that the total momentum after the collision is equal to the total momentum be-
fore the collision. Therefore
WJMJ + m2u2 = OTJVJ +m2v2
where uv u2 are the velocities of mx, m2 before the impact
and Vj,v2 are the velocities of mv m2 after the impact.
2.4.2 Collinear or direct central impact (Gerader zentrischer StoB)
When two bodies collide with each other, a tangential plane drawn through the
point of contact of the two bodies is called the plane of contact. A line drawn
normal to the plane of contact through the point of contact, is called the line of
If the line of impact passes through the centres of gravity of both bodies, then
the impact is called a central impact. Any other impact is called an eccentric
If the linear momentum vectors of the bodies are also directed along the line of
impact at the beginning of the impact, then the impact is called a collinear im-
pact or a direct central impact. Any other impact is called an oblique impact.
2 Dynamics 33
2.4.3 Elastic and inelastic impacts (Elastischer und unelastischer StoB)
During a collision the bodies undergo deformation. If the bodies are restored to
their original state without suffering any permanent deformation, the impact is
elastic and there is no loss of energy during the impact. This is the case when
two billiard balls or two rubber balls strike each other. On the other hand, if
there is permanent deformation and the restoration of energy is incomplete, the
impact is inelastic.
2.4.4 Elastic collinear impact (Elastischer gerader zentrischer StoB)
Fig 1.30 (a) Approaching spheres before impact
Fig 1.30 (b) Spheres during contact
1 2
Fig 1.30 (c) Spheres moving apart after impact
Consider two spheres of mass mv m2 moving along the same line with velocities
Wj, u2 where ux > u2 (Fig 1.30 (a)). The impact can be divided into two stages.
First (or compression) stage
This stage begins with the moment of contact, and ends when the distance be-
tween the centres of gravity is a minimum (Fig 1.30(b)). At the end of this stage
they have a common velocity v.
Applying the law of conservation of momentum, we have
+ m2u2 = ^v + m2v
34 I Mechanics
m U
_ \ \
Second (or restoration) stage
This stage begins when the separation between the bodies is a minimum and
ends with the complete end of contact between them. The velocity of the first
body is changed from v to vv and that of the second from v to v 2 . In the second
or restoration stage, the same force acts on both spheres as in the first compres-
sion stage. Consequently each sphere undergoes equal changes in velocity in the
two stages.
Mj - v = v - Vj and v - u2 = v2 - v
VJ=2V-MJ and v 2 = 2v-w 2
Substituting for v from the previous (first stage) equation we have
(m, -m,)K,+2M, . (ntr. -m,)u~+ 2m,u,
v,1 =
= —-! ^ - J *-*- and v, = -—* — —
{mx+m2) (mx+m2)
If the spheres have the same mass, then ml=m2, we can show by substituting in
the equation for Vj that Vj = u2 and v2=u{.
This means that after the collision, each sphere has the same velocity that the
other had before the collision.
2.4.5 Coefficient of restitution (StoBzahl)
Real bodies are neither fully elastic nor fully inelastic. In the case of real bodies,
the ratio of the velocity of separation to the velocity of approach is a constant
called the coefficient of restitution.
Coefficient of restitution k = — -
The law of conservation of momentum applies in this case also. Using this fact
and the above equation for k, we can show that
WJMJ + m2u2 -m (ux-u2)k
v, =
ntyUl +m2u2 +171^71-1 ~u2)k
v2 =
The energy loss AE during the collision can be shown to be
AE = —
2 mx+m2
3 Hydrostatics 35
3 Hydrostatics (Hydrostatik)
3.1 Properties of fluids and gases
(Eigenschaften der Fliissigkeiten und Gase)
An ideal fluid (as compared to a solid) is only able to transmit normal forces
and is unable to resist shear forces. In practice all real fluids show some
internal friction and shear resistance. Fluids can be divided into two types,
liquids (which are virtually incompressible) (and gases which are compressible).
3.1.1 Density (Dichte)
The density of a. fluid is defined as its mass per unit volume. The density of a
liquid changes with temperature, but shows negligible change with pressure.
The density of a gas is however a function of both temperature and pressure.
3.2 Hydrostatic pressure (Hydrostatischer Druck)
The force exerted by a liquid on a surface is always normal to the surface. The
pressure exerted on a surface is the force per unit area and the unit of pressure is
Newton per square metre (N/m ). This unit has a special name, the Pascal (Pa).
Pressure P = FN/A
where FN is the force acting normal to the surface and A the area of the surface.
1 Pa = lN/m2
l b a r = 1 0 5 P a = 0.1MPa
3.3 The transmission of pressure (Druck Ausbreitungsgesetz)
When the pressure due to the force of gravity is neglected, the hydrostatic
pressure is transmitted through a liquid in accordance with Pascal's principle.
According to this principle, the pressure exerted by a fluid (which is in
equilibrium) on a surface is always at right angles to the surface. Moreover, the
pressure at any point in the fluid has the same magnitude in all directions.
If an external pressure is exerted on a closed volume of a liquid (for example by
a piston), this pressure is transmitted unchanged to all parts of the fluid and in
all directions.
3.4 Applications of the law of pressure transmission
(Anwendungen des Druck Ausbreitungsgesetzes)
3.4.1 Force exerted on the
wall of a vessel
If we consider the pressure
exerted on the hemispherical
surface BCD shown in Fig
1.31, then the total force exerted
on the hemispherical surface is
the product of the pressure P
and the projection of the
hemispherical surface on a
plane at right angles to the Fig 1.31 Force on a curved surface
36 I Mechanics
direction of the force. Here the
force is
3.4.2 Cylindrical tube (Rohr)
If we have a cylindrical tube of
diameter d and length /, the
projection of half the cylinder-
ical surface on the diametral Fig 1.32 Force on one half of a cylinder
plane is
A = dl
Then the force exerted on each half of the tube surface is given by
The forces tend to tear the tube apart.
3.5 Pressure due to the weight of a fluid
(Druckverteilung durch Gewichtskraft der Flussigkeit)
Consider the forces acting on a
cylindrical part of a fluid which is in
equilibrium. If the surface area of each
flat surface of the cylinder is A, then the
volume of the cylinder is
V = hA
and the weight of the cylinder of liquid
is given by
If the forces acting on the flat surfaces
are F, and F2 as shown in the figure, Fig 1.33 Pressure at a depth h
then for equilibrium
If the upper flat surface of the cylinder lies on the top surface of the liquid, then
P - 0 and we can write
= pgh
The hydrostatic pressure caused by gravity is therefore proportional to the
depth h below the surface. If an additional pressure Pa is exerted on the surface,
then the total pressure at a depth h is given by
P = Pa+pgh
3 Hydrostatics 37
This total pressure is everywhere the same at this depth and also on the wall of
the container.
3.6 Hydrostatic forces exerted on the walls of open containers
(Hydrostatische Krafte gegen ebene Wande offener GefaBe)
3.6.1 Force exerted on the base of a
vessel (Bodenkraft)
The force exerted on the plane base of
an open vessel (as shown in Fig 1.34)
and is independent of the shape of the
Fig 1.34 Force on the base of a vessel
3.6.2 Force exerted on the sidewalls (Seitenkraft)
Consider a vessel whose sidewall is
inclined at an angle a to the
horizontal. The force F which acts on
an area A of the sidewall is Area
proportional to
1. the depth hc of the centre of
gravity of the area A
2. the density of the liquid p
3. the area A of the sidewall which Centre of
is being considered gravity
F = pgh A Fig 1-35 Force exerted on a sidewall
The location of the force can be shown to be at a depth of
hf =hQ+ IG (sina) /hcA
where Io is the areal moment of inertia taken round its centre of gravity.
3.7 Buoyancy and the principle of Archimedes
(Auftrieb und das Prinzip von Archimedes)
Archimedes principle states that when a body is partially or completely
immersed in a fluid, an upthrust or buoyant vertical force Fu equal to the
weight of liquid displaced acts on the body (through the centre of buoyancy B).
Upthrust Fv =pgVD = weight of liquid displaced
Where V is the volume of fluid displaced. If the body is made of material of
density p' then, the weight of the body FQ = p'gVD
The apparent weight of the cylinder F is equal to the difference between the
real weight and the upthrust.
Apparent weight = Real weight - Upthrust
= (P'-P)gVD
38 I Mechanics
3.8 Floating bodies (Schwimmende Korper)
When a body is placed in a liquid, there
are two forces acting on it, the weight
Fa, and the upthrust (or buoyant
vertical force) Fv. The weight acts ( Q]
vertically downwards through the
centre of gravity G and the upthrust ^^ I
through the centre of buoyancy B.
Three things can happen depending on
the relative magnitudes of the two
forces. The body can sink, float or _. , „ , _ ^. , ,
. . : .. , Fig 1.36 A floating body
remain in a random position anywhere
in the fluid.
1. A body sinks when its weight is greater than the upthrust.
2. If a floating body is still partially immersed in the liquid, then the weight
of liquid displaced is exactly equal to the weight of the body. The centre
of buoyancy is below the centre of gravity on the same vertical line.
3. If the body remains completely immersed in any random position in the
liquid, then the weight of liquid displaced is equal to the weight of the
3.9 Stability of floating bodies
(Gleichgewichtslagen schwimmender Korper)
Fig 1.37(a) Body in a stable position Fig 1.37 (b) Body in a displaced position
When a floating body is in a stable position as shown in Fig 1.37(a), then the
centre of gravity and the centre of buoyancy lie on the same vertical line.
The body is in stable equilibrium if the centre of buoyancy B is below the
centre of gravity G. If the body is displaced from the stable position as in Fig
1.37(b), a restoring couple is created, and this tends to return the body back to
its original position. The point M where the line of action of the buoyant force
intersects the centre line of the body is called the metacentre.
It can be easily shown that if the centre of buoyancy B is above the centre of
gravity G, a couple is created which tends to overturn the body. In this case, the
body is in a state of unstable equilibrium.
4 Fluid dynamics 39
4 Fluid dynamics (Hydrodynamics)
(Dynamik der Fliissigkeiten, Hydrodynamik)
4.1 Basic concepts (Grundlagen)
4.1.1 Ideal and real fluids (Ideale und nichtideale Flussigkeiten)
Substances which are initially at rest respond to the application of a shear stress
in different ways. Consider two very large plates of equal size (as shown in Fig
1.38) separated by a small distance;/. The upper plate is moved while the lower
plate is kept stationary. The space between the plates is filled with a substance
which may be a solid or a fluid.
The surfaces of the substance adhere to the plates in such a manner, that the
upper surface of the substance moves at the same velocity as the upper plate
while the lower surface remains stationary. If a constant force Fs is applied, the
moving plate attains a constant velocity u. The shear stress that arises is defined
by T = —— where As is the surface area of the plate. The applied stress causes
the substance to be deformed and the rate of deformation is given by du/dy.
Deformation characteristics for various substances are shown in Fig 1.39.
Moving plate
7 I
7 dy
I ~V \
| 7ciu
Stationary plate Rate of deformation du/dy
Fig 1.38 Flow of a substance between Fig 1.39 Deformation characteristics of
parallel plates different substances
An ideal (or elastic) solid resists shear stress and its rate of deformation will be
zero. If a substance cannot resist even the slightest shear stress without
flowing, then it is a fluid. An ideal fluid does not have internal friction and
hence its deformation rate lies along the x-axis as shown in Fig 1.39. Real fluids
have internal friction and their rate of deformation depends on the applied
stress. If the deformation is directly proportional to the stress, it is called a
Newtonian fluid. If the deformation is not directly proportional it is called a
non-Newtonian fluid.
Fluids can be of two types, compressible and incompressible. A liquid can be
considered to be incompressible, while gases and vapours are compressible.
40 I Mechanics
4.1.2 Steady and unsteady flow (Stationare und nichtstationare Stromung)
The flow of a liquid is said to be steady if the fluid properties like pressure and
density are only dependent on the space coordinates and not on the time. The
flow is unsteady if the properties at a point vary with time.
4.1.3 Streamlines, stream tubes and filaments
(Stromlinien, Stromrohre und Stromfaden)
If we follow the movement of a fluid particle through a fluid, then a streamline
is a line which gives the direction of the velocity of the particle at each point in
the stream. If there is steady flow, then the streamlines are identical to the flow
lines of the liquid. They axe fixed in space and do not change with time. If there
is unsteady flow, the streamlines change their position with time.
If a number of streamlines (in steady flow) are connected by a closed curve,
we have a stream tube. They form a
boundary through which the fluid
particles do not pass. Parts of a stream
tube over which the pressure and the
velocity remain constant are called
stream filaments. When an ideal fluid
flows through a tube, the values of
pressure and velocity are constant
across the entire cross-section of the
tube, and the whole contents of the tube
can be considered to form a single
stream filament. This enables the flow
of the fluid to be considered to be a Fig 1.40 Stream tubes and filaments
single dimensional flow.
4.1.4 Viscosity (Viskositat)
Viscosity is the term used to specify the internal friction of a fluid, which
means its resistance to shear motion. The two terms dynamic viscosity and
kinematic viscosity are defined as follows:
Shear stress
Dynamic viscosity t| = -j-—
\au Rate of deformation
Kinematic viscosity v = — Dynamic vis cos ity
P Density
Units: Dynamic viscosity Units: Kinematic viscosity
10 Poise = INs/m 10 Stokes (St)=lm 2 /s
1 P = 0.1Ns/m2 1 St=10" 4 m 2 /s
4 Fluid dynamics 41
4.1.5 Reynolds number (Reynoldssche Zahl)
The amount of influence that frictional forces have on the flow of a fluid is
indicated by the Reynolds number which has the symbol Re (or R (American)).
wdp wd
Ke = —
T] V
where w is the average velocity, d the diameter of the tube, p the density, n the
dynamic viscosity and v the kinematic viscosity.
In streamline or laminar flow the particles of a fluid move in parallel layers,
while in turbulent flow the particles have additional velocity components in the
x,y,z directions.
Small values of the Reynolds number correspond to laminar flow while large
numbers correspond to turbulent flow. The change from laminar to turbulent
flow takes place when the critical value of 2300 is exceeded.
4.1.6 The Mach number (Machsche Zahl)
The Mach number is the ratio of the average fluid velocity w to the speed of
sound c. The symbols used are Ma or M (American).
If w is small compared to c, the compressibility of the fluid does not play a role.
The flow of gases can be considered to be incompressible when Ma < 0.3
corresponding to w = 100 m/s in the case of air.
4.2 The basic equations of fluid flow (Grundgleichungen der Stromung)
4.2.1 The continuity equation (Kontinuitatsgleichung)
The continuity equation is a special
case of the law of conservation of
mass. When a fluid flows through a
tube, the mass of fluid flowing through
any cross-section must be the same. If
the cross-sections at two points in a
tube are A\ and Ai and the correspond-,
ing average velocities are w\ and w>2,
then the mass of fluid qm flowing F i g M1 The continuity equation
through any cross-section per second is
If the fluid is incompressible, the volume q flowing through must also be
constant. Therefore
42 I Mechanics
4.2.2 Energy equation for fluid flow (Bernoulli equation)
(Energieerhaltungssatz der Stromung, Bemoullische Druckgleiehung)
Application of the principle of
conservation of energy to fluid p ^
flow results in the following 2' *•
equation which is known as the
Bernoulli equation. Consider a
tube containing a fluid as shown
in Fig 1.42. The fluid is made to
r, r- •. • 1 * -i u 4 F'g 1.42 Energy equation for fluid flow
flow from positions 1 to 2 bet-
ween heights h\ and hi.
An amount of work P\ V\ is done on the fluid at 1 and an amount of work
is done by the fluid at 2. Although the work may be supposed to be done by the
movement of the pistons, their presence is not really necessary.
The fluid possesses at positions 1 and 2 potential energies oimgh\ and mgh2 and
1 2 1 2
kinetic energies — mw^ and — mw where m is the mass and w the average
If friction losses are neglected, we can write
Energy at the end of = Energy at the beginning ± Amount of work
the process of the process delivered to the fluid
Since m = pV,
=P2V2 +PVgh2+jpVw^ = constant
Dividing by V we have for an incompressible fluid
1 2 1 2
P + pgh, + - pw, = P + pgh + - pWj = constant
i 2 2
This is known as the Bernoulli equation. If this equation is divided by pg, we
P, w? P7 w?
have —— + h-\—— = —— + l«, + ~^-
Pg 2g pg 2g
The individual terms correspond to heights (with units in metres (m)). For this
reason, the height corresponding to each type of energy can be termed a head.
— = static pressure head of the fluid
h= potential head of the fluid
— = velocity head of the fluid
4 Fluid dynamics 43
4.2.3 Individual pressure terms (Einzelne Druckglieder)
In cases where the fluid flow is horizontal, the gravitational term may be
omitted in the Bernoulli equation and we can write
The pressure P is called P stat , and this is the static pressure which causes the
flow. The term pw /2 is a measure of the kinetic energy per unit volume of the
fluid flowing with an average velocity w. This is called the dynamic pressure
Pdyn- The sum of these terms is equal to the total pressure Ptot.
Aot = Pstat + Pdyn
4.3 Applications of the Bernoulli equation
(Anwendungen der Bernoulligleichung)
4.3.1 Fluid flow past an obstacle
(Auftreffen einer Stromung auf ein festes Hindernis)
When an obstacle is in the path of flow (Fig 1.43), the flow can be studied by
looking at two representative points 1 and 2. At point 1 the flow is normal,
while at point 2 stagnation occurs and there is no flow. If we write the Bernoulli
equation corresponding to the points 1 and 2, it has the form
At point 2, w~ = 0, and therefore
1*2 ~ iyn
P is equal to the sum of the two
pressures while Pi = P sta t
Fig 1.43 Fluid flow past an obstacle
4.3.2 Measurement of the static and total pressure
(Messung des statischen und des Gesamtdruckes)
Fig 1.44(a) Static pressure measurement (b) Total pressure measurement
44 I Mechanics
The measurement of the static pressure Pstat may be carried out by using the
device shown in Fig 1.44(a). This consists of a closed tube with small holes on
the side walls connected to a U-tube manometer.
where /?, is the density of the liquid in the manometer.
The measurement of the total pressure can be carried out by using an open tube
connected to a U-tube manometer as shown in Fig 1.44 (b). Here the flow path
is blocked by the liquid in the U-tube and we have
The dynamic pressure P&yn can be measured by combining the two tubes to give
a difference measurement.
4.3.3 Venturi tube
A venturi tube can be used to
calculate the flow velocity in
a flow tube by measuring the
pressures at different points.
Writing the Bernoulli eqn for
the points 1 and 2, we have
and from the equation of
continuity we have
The pressure difference is
given by Fig 1.45 A venturi tube
From the above two equations, we obtain
4.3.4 Outflow of liquids from openings in containers and tanks
(AusfluB aus einem GefaB)
The outflow of liquids from openings in containers and tanks is usually less than
the value that is theoretically expected, because the average velocity is less than
the theoretical value of w = -Jlgh . The reduction in velocity is a consequence of
the internal friction present in the liquid and the friction of the walls of the
4 Fluid dynamics 45
tank. The ratio of the actual velocity to the theoretical velocity is the coefficient
of velocity <p.
Another reason for a reduction in the outflowing quantity of liquid is the
contraction of the flow stream due to the sudden change in the direction of the
flow. If the actual area of the opening is A, then the effective area of the opening
is a A where a is the coefficient of contraction.
The product of the coefficient of velocity #> and the coefficient of contraction a
is termed the coefficient of discharge ju.
Coefficient of discharge n = a<p
4.3.5 Open container with constant pressure head
(Offenes GefaB mit konstanter Druckhohe)
If the head of liquid is maintained
constant at a value h, then we can
wi = 0 and Pl =P2 = PQ
where PQ is the atmospheric pressure.
Using the Bernoulli equation we have
Fig 1.46 Open container with a constant
Using the continuity equation and pressure head
taking into consideration the coefficient
of discharge JX, we obtain the express-
ion for the out flowing volume
4.3.6 Container closed at the top with constant pressure head
(Geschlossenes GefaB mit konstanter Druckhohe)
In this case, the pressure at 1 is no longer the atmospheric pressure PQ , but some
other value of pressure P\. The pressure at the outflow opening is however Po.
If we write the excess pressure Pe= P\- PQ, then we obtain using the Bernoulli
equation an expression for the velocity of outflow
and for the volume flow
46 I Mechanics
f P )
The quantity g/j + — can be found by using a manometer which is placed at
the height of the output point.
4.4 Resistance to fluid flow in horizontal tubes
(Widerstande in Rohrleitungen)
4.4.1 Drop in pressure and the resistance coefficient
(Druckabfall und Widerstandszahl)
The flow of a fluid through a straight horizontal pipe is only possible when a
pressure gradient exists along the length of the tube. This is almost linear and
the pressure at the outlet is equal to the atmospheric pressure. In the case of
streamline or laminar flow in a tube with smooth walls, the fall in pressure AP
depends on the average velocity w. For a pipe of diameter d and length / we
AP = X-^w2
where A is a resistance coefficient that depends on the Reynolds number and the
roughness of the walls.
4.4.2 Cylindrical tubes with smooth walls (Glattes Kreisrohr)
The flow of a fluid in a straight tube with smooth walls remains laminar up to a
Reynolds number Re = 2300. In the laminar region the resistance coefficient X
• . , . 64 AP2d
lsgivenby X = — = —j—
Combining this with the relation Re = —
we have AP = 32^-
4.4.3 Cylindrical tubes with rough walls (Rauhes Kreisrohr)
For higher values of the Reynolds number, the resistance coefficient X depends
only on the relative wall roughness factor kid. For granular roughness (in
contrast to wavy roughness) the expression for X is
>•- 2
where d is the diameter in mm, and k a number corresponding to the roughness
of the walls. The boundary region between laminar and turbulent flow presents
serious difficulties but specific expressions are available in this region as well.
4.4.4 Valves and bends (Ventile und KrUmmer)
In the case of valves and bends, the loss in pressure is dependent on the average
value of the flow velocity and is given by
The resistance number £ depends on the dimensions involved.
II Strength of materials
1 Basic concepts (Grundkonzepte)
1.1 Scope of the strength of materials
(Bereich Festigkeitslehre)
The strength of materials is a subject which deals with the effect of external
forces on elastic bodies (and structures) which are basically in a state of
equilibrium. It can be considered to be a part of mechanics and is partly based
on the principles of statics. In addition, it uses experimentally obtained data
about the changes in the dimensions of elastic bodies when external forces act
on them.
When a solid body is subjected to the action of external forces, it becomes
deformed. If the forces are relatively small, the body regains its original form
when the forces are removed. This type of deformation is called elastic
deformation. If the forces exceed a critical value called the elastic limit, there is
a permanent change in the dimensions of the body called plastic deformation.
Further increases in the forces can result in the body becoming fractured.
The external forces create stresses in the body, which lead to dimensional
changes which are called strains. The data which is available from previous
experimental studies in the strength of materials can be used to specify the
dimensions that a component needs to have, to remain within the elastic range
and consequently avoid becoming fractured.
• The strength of materials is an indispensable tool in the hands of design
engineers, who use the extensive information acquired about materials
over the years, to design structures which are both safe and economical.
• A safety margin has to be allowed when a component is designed. It is
necessary to ensure that factors like variations in the properties of
materials used, defects in manufacture or slight overloading, will not lead
to the component becoming damaged. A component can be designed in
many ways. It is however desirable that it is designed in such a way that it
can be produced at the lowest possible cost. The component has to be safe
to use and economical to produce.
• Tests under actual working conditions are important once the component
has been manufactured. The load that a component can be subjected to, is
fixed by the design. However, it is desirable that the correctness of the
design should be tested after manufacture. Modifications can then be
carried out to correct any deficiencies that the component may have.
1.2 The method of sections and the free body (Schnittverfahren)
When external forces act on a body, internal forces are created inside the body
in order that equilibrium may be maintained. These are a direct consequence of
48 II Strength of materials
the action of the external forces themselves. A convenient way of studying the
internal forces in a body is by the method of sections.
Consider the rod AB which is in equilibrium under the action of two equal and
opposite forces Fas shown in Fig 2.1 (a). If we make a section at right angles to
the axis through any point C in the rod, we obtain two parts AC and CB which
can be called free bodies.
•F F-
Fig 2.1 (a) Rod before sectioning (b) Two parts resulting from section at C
It is necessary to apply two forces F at C, in order to fulfil the requirement that
both parts should be in equilibrium. From this we can see that internal forces of
magnitude F are produced in rod AB, when external forces F act on it. In a free
body the internal forces can be considered to have been replaced by external
forces. This facilitates the study of the problems involved in bodies which
although in equilibrium, are in a state of stress under the action of external
1.3 Stress (Spannung)
1.3.1 Normal stress (Normalspannung)
The type of loading experienced by the rod in Fig 2.1 is called axial loading,
because the external forces acting on the rod are directed along the axis of the
rod. Let the area of cross-section of the rod be A. The force per unit area of the
cross-section is called the normal stress, and is denoted by the greek letter a.
Normal stress aav = —
The stress that exists under the conditions of axial (or longitudinal loading) is
called the normal stress because it acts in a direction normal to the cross-section.
Normal stress can be of two types (a) tensile or tensional stress and (b)
compression or compressional stress (Fig 2.2).
Fig 2.2 (a) Tensile stress Fig 2.2 (b) Compressional stress
The stress taken over the whole cross-section is the average value aav. The
stress may vary over the cross-section and to find the stress at any point we
should consider the magnitude of the force dF acting over a small area dA
surrounding the point. The internal force F acting over the cross-section is given
by F= \dF = \adA
1 Basic concepts 49
1.3.2 Shear or shearing stress (Abscherspannung)
The type of stress which occurs when transverse forces are applied to a rod as
shown in Fig 2.3 is called shear or shearing stress.
Fig 2.3(a) Transverse forces acting on a bar (b) Free body with section at C
If we make a section at a point C between the points of application of the two
forces, we have the free body AC as shown in Fig 2.3(b). For equilibrium to be
maintained, it is necessary for an internal force F to exist which is tangential to
the plane of the section. Such a force is called a shear (or a shearing) force.
Dividing the shear force by the area of cross-section A, we obtain the average
shear stress. This is denoted by the greek letter r and we can write
*m- A
As stated in the case of the normal stress, the shear stress can also vary over the
1.4 Strain (Verformung)
1.4.1 Longitudinal strain (Dehnung)
When a body is subjected to the action of external forces, it can change its form.
The longitudinal strain which is denoted by the greek letter e is equal to the
ratio of the increase in length to the original length of the rod.
Longitudinal strain e =
1.4.2 Hooke's Law (Hookesches Gesetz)
When a body is subjected to the action of external forces and the changes in
form are elastic, then the longitudinal strain produced is proportional to the
longitudinal stress. This relationship is called Hooke's Law.
Stress a = constant E x strain e
a =
E is a constant for a given material and is called the modulus of elasticity or the
Young's modulus.
50 II Strength of materials
The strain is a quantity which is dimensionless and therefore the modulus E has
the same units as the stress. The stress and the Young's modulus are usually
expressed in units of N/mm2.
1.4.3 Shear strain (Schubverformung)
Consider a cubic element of material as shown in
Fig 2.4(a). Let us apply two parallel external forces
F in a direction tangential to the top and bottom
faces of the cube. These are shear forces which
form a couple which tends to deform the cube.
As a consequence of this, two internal forces F are
created, and these form an internal couple which
opposes the shearing action of the external couple.
The cube is in equilibrium under the action of the
Fig 2.4 (a) Shear forces external and internal couples, and changes its
in a cube shape to that of an oblique parallelepiped, the
cross-section of which is shown in Fig 2.4 (b). The
shear strain is equal to the angle y.
For values of stress which are within the elastic
limit, the shear strain y is proportional to the stress.
We can therefore write for a homogeneous
isotropic material
Shear stress T = constant G x shear strain y
or T = Gy
where G is a constant called the modulus of rigidity
or the shear modulus. The angle y is in radians and
F is dimensionless. The modulus G has therefore the
Fig 2.4 (b) Shear Strain same units as the stress t, namely N/mm2.
1.4.4 Poisson's ratio (Poisson's Zahl)
If a homogeneous slender bar is axially loaded, the Hooke's law is valid
provided the elastic limit of the material is not exceeded. We can write using
Hooke's law
where E is the modulus of elasticity (Young's modulus) of the material.
The normal stresses along the y and z-axes are zero.
a =(J =0
y z -
However the strains sy and sz are not zero.
In all engineering materials, an elongation produced in the axial (or
longitudinal) direction, is accompanied by a contraction in the transverse
1 Basic concepts 51
direction provided that the material is homogeneous and isotropic. In this case
the strain is the same for any transverse direction.
Therefore sy = sz
This is called the lateral strain, and the ratio of the lateral strain to the
longitudinal strain is called Poisson 's ratio (indicated by the greek letter v).
v = Lateral strain / Longitudinal strain
y e,
or v = —£- = ——
e £
x x
From this we can write expressions for the three strains as follows:
a a
x x
£ £
* = -E> y=£z=-v-i
1.5 Types of Load (Beanspruchungsarten)
1.5.1 Tensional and compressional loads
(Zugbeanspruchung und Druckbeanspruchung)
These types of axial load have already been discussed in section 1.3. Both
compressional and tensional loads are possible, and the stress which is called the
normal stress acts in a direction normal to the cross-section.
1.5.2 Loads which cause bending (Biegebeanspruchung)
In pure bending, a bar is acted on by two equal and opposite couples acting in
the same longitudinal plane. In many cases of bending however, shear forces
also exist and need to be considered.
1.5.3 Loads which cause buckling (Knickbeanspruchung)
When an axial compressional load is applied to a bar, the bar can suddenly
buckle when the load reaches a certain critical value. The shape of the
deformed bar may appear to be similar in the cases of bending and buckling, but
there is clearly a basic difference between the two cases. Bending is caused by
stress in the material, while buckling is caused by instability.
1.5.4 Shear loads (Abscherbeanspruchung)
In the case of shear loads, the external forces act in a direction which is
transverse to the axis and tend to push successive layers of material in a
transverse direction. Internal transverse forces are created which tend to resist
the change in shape. These internal forces are called shear forces.
1.5.5 Torsional loads (Verdrehbeanspruchung)
The external forces corresponding to torsional loads, are in the form of an
external couple which twists a rod about its axis. This results in an internal
couple being created which opposes the twisting moment of the external couple.
1.6 Strength (Festigkeit)
1.6.1 Concept of strength (Begriffder Festigkeit)
The meaning of the word strength in the context of the strength of materials,
refers to the ability of a material or a component to resist fracture under given
conditions of mechanical loading.
52 II Strength of materials
Tests to determine the strength of a material are carried out under standard
conditions. A numerical value is obtained, which gives a good indication of the
strength of a material and enables us to compare strengths of different materials.
1.6.2 Determination of strength under conditions of static loading
(Festigkeit bei statischer Belastung)
The specimen to be tested is carefully made to standard dimensions. It is then
placed in a test machine and subjected to a gradually increasing tensional load,
starting at zero and ending at a value for which the specimen breaks. The values
of stress and strain are found for various loads, and a graph between stress and
strain is plotted as shown in Fig 2.5(a) for annealed soft steel.
In the region OP, the strain is proportional to the stress and Hooke's law holds.
Just above this is the point E, which corresponds to the elastic limit. If the load
is removed at this stage, the specimen reverts to its original shape and size. The
behaviour of the material so far has been elastic, and the material is said to have
undergone elastic deformation.
If the load is further increased, a stage is reached at Y, where a sudden increase
in length takes place without any increase in load. The stress corresponding to
Y is called the yield strength. Beyond the point Y, the deformation is no longer
proportional and elastic. This deformation which is called a plastic deformation
is permanent. In the region YB, the specimen elongates permanently and its
cross-section becomes reduced uniformly along its length.
The material becomes stronger and is said to be strain hardened or work
hardened. Beyond point B which corresponds to the maximum possible load,
the cross-section decreases only at its weakest point. This is called necking. The
stress at B is called the ultimate tensile strength (UTS). The specimen finally
breaks (or fractures) at C and this stress is called the breaking strength.
t ; Plastic deformation i Necking,
O Strain —I I—
0.2% strain
Fig 2.5 (a) Stress vs strain curve for (b) Stress vs strain curve for (c) necking
annealed steel hardened steel
Basic concepts 53
A curve of the type shown in Fig 3.3 (a) which shows a clear change at the yield
stress is only observed in some materials like soft steel. In the case of materials
like hardened steel, the curve is as shown in Fig 3.3 (b).This curve is a smooth
one, which has neither a definite elastic limit nor a yield stress. In such cases, a
different method has to be adopted to find the yield strength. The method that
has been universally adopted, has been to specify the stress corresponding to a
permanent extension of 0.2% as the yield strength. This can be found by
drawing a straight line through the point corresponding to 0.2% strain. The
straight line is drawn parallel to the initial part of the curve which is the
proportional region. This meets the curve at the point Y which corresponds to
the yield stress. The modulus of elasticity (or the Young's modulus) can be
found from the slope of the curve in the proportional region.
| Young's modulus E = Stress/Strain (N/mm2) |
1.6.3 Strength under dynamic loading conditions
(Festigkeit bei dynamischer Belastung)
The test values obtained for the strength of materials obtained under conditions
of static loading may not be useable in many types of applications. A good
example is the case of materials used in the construction of machines which are
subjected to repeated stress.
In these cases it is necessary to carry out a dynamic test where a polished sample
of the material is subjected to a dynamically varying load. This gives a value for
the fatigue strength which is usually less than the static value. It may also be
both desirable and necessary to test not only a standard specimen of the
material, but also the actual component under dynamic loading conditions.
1.6.4 Effects of irregularities in the cross-section (Kerbwirkung)
The cross-section of a component is rarely uniform like the cross-section of a
test sample. Components often have notches, channels, splines and other
irregularities which cause the stress to be nonuniform across the cross-section.
This means that the component has to withstand higher stresses and has
therefore to be made of stronger material or of larger cross-section.
1.7 Allowable stress and the safety factor
(Zulassige Spannung und Sicherheitsfaktor)
When a component is designed, the load that it is allowed to carry under
operating conditions is called the allowable load. For reasons of safety, this
allowable load must be well below the ultimate load which is the load under
which the component will break.
A safety factor v has been defined in terms of the ratio given below, but can
also be defined in terms of other similar ratios.
ultimate stress
Safety factor v =
allowable stress
54 II Strength of materials
The determination of a safety factor which is useful and relevant under a certain
set of conditions is a very important engineering task. In addition to the above
considerations, material variations, fatigue and the effect of other components in
the structure must be considered.
If the safety factor is too small, the chances of failure may become
unacceptably large. If the safety factor is too large, the component would
become too uneconomical to make. High safety factors may not be acceptable
in aircraft design where weight is an important factor.
The safety factor for steel is of the order of 1.5. Materials like grey cast iron are
extremely brittle. Here the value for the breaking stress can be used instead of
the value for the ultimate stress. A safety factor of 2 is appropriate for cast iron.
2 Bending loads (Biegebeanspruchung)
2.1 Pure bending (Reine Biegung)
2.1.1 Beams of uniform cross-section
(Trager mit gleich bleibendem Querschnitt)
Fig 2.6 (a) Pure bending of a uniform beam (b) Free body after sectioning at C
Consider a beam of uniform cross-section being subjected to the action of two
equal and opposite couples M as shown in Fig 2.6 (a). The couples act in the
same longitudinal plane and the beam is symmetric with respect to the plane of
the couples. When a beam bends under these conditions, it is said to undergo
pure bending.
If we make a section in the beam at C, it is clear that the forces exerted on AC
by the portion CB must be equivalent to a couple as shown in Fig 2.6(b). Thus
the internal forces acting at any cross-section when pure bending occurs are
equivalent to a couple. The moment M of the couple is known as the bending
moment at this cross-section. Since the point C chosen by us is an arbitrary
point, it follows that when a beam undergoes pure bending, the bending
moment is the same at all cross-sections and has the value M.
Example 20kN 20kN
An example of a beam being subjected 2m
to pure bending is shown in Fig 2.7.
Making a section at any arbitrary point
E, we can verify that the internal forces A
acting at any cross-section at any point •10m
E between D and C are equivalent to a Fig 2.7 Pure bending of a transversely
couple of moment 40kNm. loaded beam
2 Bending loads 55
2.1.2 Deformations produced in a beam undergoing pure bending
(Verformungen in einem Trager)
Consider a uniform beam having a plane of symmetry which is subjected at its
ends to equal and opposite couples M acting in the plane of symmetry (Fig 2.8).
The beam will bend under the action of the couples, but will remain symmetric
with respect to the longitudinal plane in which the couples act. Since the
bending moment is the same at any cross-section, the beam will bend uniformly
(Fig 2.8). Thus the lines AB and A'B'(not shown) which were originally
straight lines, will now become arcs of circles with centre C.
We can see that while AB has c
decreased in length, the length of A'B' A
has increased (not shown).Therefore
there must be a surface which is
parallel to the upper and lower
Plane of
surfaces where the change in length is symmetry
zero. This is called the neutral
surface. The neutral surface intersects
the plane of symmetry along an arc of
a circle, and intersects the transverse
section along a straight line called the
neutral axis. Two sections, a longitud- Neutral surface
inal section (the plane of symmetry)
and a transverse section are shown in Fig 2.8 Beam undergoing pure bending
Fig 2.9. The neutral surface intersects the plane of symmetry along the arc of
the circle DE as shown in Fig 2.9(a) and the transverse section along a straight
line called the neutral axis (Fig 2.9 (b)).
Fig 2.9 (a) Longitudinal vertical section Fig 2.9 (b) Transverse section
(plane of symmetry)
56 II Strength of materials
If the radius of the arc DE is p and the angle subtended at the centre 9, then
l = P9
where / is the length of DE. This is also the original length of the undeformed
bar. If we consider an arc LM at a distance y above the neutral surface and
denote its length as /', then /'= (p-y)9
the change in length 8 is 8 = l'-l = (p-y)9-p8 or S = -y9
The longitudinal strain is x and therefore
/ p9 p
If the distance from the neutral surface to the top of the beam is c, then the
largest value of the strain em is sm = —
2.1.3 Stresses and strains in the elastic range
(Spannungen und Verformungen im elastischen Bereich)
If we limit the bending moment M to y
values within the elastic range, then
x = Esx
eX ~- -
Therefore a
x =~— t
The normal stress is proportional to the Fig 2.10 Distribution of normal stress
distance from the neutral surface as in a bent beam
shown in Fig 2.10. In the case of pure
bending there can be no net force in the longitudinal direction which means that
\oxdA = 0 for any cross-section.
ax dA = (-2-om)dA = -^- \ydA = 0
which gives \ydA = 0
The first moment of the area taken about the neutral axis is zero. From this it
follows that the neutral axis passes through the centroid (pl4, p58) of the cross-
The elementary force dFx acting on an area dA is given by
dFx = ax dA
The moment of this elementary force at a distance y above the neutral axis is
dM = -ax ydA
If we write / = \y2dA
2 Bending loads 57
The integral / is the second moment of an area (p58) for the cross-section with
respect to the neutral axis.
The ratio - is dependent only on the geometry of the cross-section. This ratio is
termed the elastic section modulus S.
Elastic section modulus S = —
Therefore am = —
The maximum stress am can be seen to be inversely proportional to the section
modulus S. From this it is clear that it is an advantage to design beams with as
large a value ofS as is practical so that the maximum stress is kept low.
For a beam with a rectangular cross-section having a width b and a depth h.
--Ah (A= area of cross-section)
c h/2 6
If two beams have the same area of
cross-section as in Fig 2.11 (a) and (b),
the beam of larger depth (b) is able to
resist bending better than (a). Also
wide flanged beams with cross-section
as shown in Fig 2.1 l(c) are able to
resist bending better than other shapes.
(a) (b) (c)
For a given area of cross-section and a Fig 2.11 Beams with different cross-sections
given depth, these beams have a large
part of their cross-section located away
from the neutral axis. This shape provides large values of/ and S.
2.1.4 Radius of curvature and curvature (Krummungsradius und Krummung)
As seen in section 2.1.2 when a uniform beam is subjected to pure bending, the
beam bends to form the arc of a circle. The radius of curvature p was given by
e = —
m n
The term curvature is used for the reciprocal of the radius of curvature p.
Curvature = — = —
In the elastic range Sm=
Substituting we have
p Ec Ec
_ 1 M
Curvature = — = —
p El
58 II Strength of materials
2.2 First and second moments of an area
(Flachenmoment 1.Grades und Flachenmoment 2.Grades)
2.2.1 First moment of an area and the centroid
(Flachenmoment 1.Grades und Flachenschwerpunkt)
Consider an area A which is in the xy
plane. If the coordinates of a small
element of area dA are x and y, then the
first moment of the area A with respect
to the x axis is defined as the integral
Qx = \ydA
Similarly, the first moment of area can
be defined with respect to the y axis as
the integral
Fig 2.12 First moment of an area
Qy =
The centroid of the area is defined as the point C having coordinates x and y
which satisfy the relations
jxdA = Ax and \ydA=Ay
It follows that Qx = Ay and Qy = Ax
The first moment of an area with respect to an axis of symmetry is zero. From
this it follows that if an area has an axis of symmetry, the centroid must be on
this axis. If an area has two axes of symmetry, the centroid must lie on the point
of intersection of these axes. Therefore the centroids of a rectangle or a circle
must coincide with their geometric centres.
2.2.2 Second moment of an area (or areal moment of inertia)
(Flachenmoment 2. Grades)
The moment of inertia of a solid body is defined by the integral J = \y2dm.
A similar quantity can be defined with
respect to an area and is called the
second moment of an area (or the
areal moment of inertia). If we have an
area A in the xy plane as shown in Fig
2.13, the second moments of the area
with respect to the x and y axes are
defined by the integrals
Ix = \y2dA and ly = \x2dA
A ^
These integrals are called rectangular
moments of inertia. Fig 2.13 Second moment of an area
2 Bending loads 59
The polar second moment of an area A with respect to point O is defined by
I =\p2dA=Ux2+y2)dA
It follows that IO=IX+ Iy
where p is the distance of dA from the origin O.
The different radii of gyration for an area are defined by the following relations.
y ~^y
2.2.3 Parallel axis theorem (Steinersche Verschiebesatz)
The parallel axis theorem for moments
of inertia (proved on p22) also holds
for second moments of an area and will
only be stated here.
Let Ix be the second moment of an
area A with respect to an arbitrary x
axis and / , the second moment of the
same area with respect to a parallel
x' axis passing through the centroid C.
If the separation between the two axes
is /, then we can write
Fig 2.14 Parallel axis theorem
/ = / , + Al2
x x
A similar formula holds for the polar moment of inertia as given below.
Here IQ and /c are the second moments of the area A with respect to an
arbitrary point O and with respect to its centroid C. The distance OC = /.
2.3 Transverse loading and shearing stresses
(Querkraftbiegung und Schubspannung)
When uniform beams are in a horizontal
position and have vertical loads, then the
loading is transverse.
A cantilever beam is shown in Fig 2.15.
This has one fixed end B. A single force
F acts at the free end A. Let us make a
section at C at a distance x from A and
consider the free-body diagram of the
part AC. The internal forces acting on
AC must be equivalent to a shearing Fig 2.15 Stresses in a cantilever
60 II Strength of materials
force V of magnitude V = F and a couple
A/of bending moment M = Fx.
As seen previously, the stress normal to
the cross-section is required to form the dA
bending moment. Shearing stresses are
also present and we can write for the
y direction \xXy dA= — V and
for Fig 2.16 Stress components in a
the z direction \txz dA = 0 beam
An analysis of the shearing stresses in a beam are beyond the scope of this book.
However a summary of some of the the most important features is given below.
1. When the width and height are small compared to the length, the shearing
stress is much smaller than the normal stress, typically less than 10%.
2. The distribution of normal stresses in a cross-section is the same as when
it is subjected to a pure bending couple of moment M = Fx and is not
affected by the deformations caused by the shearing stresses.
3. If the width is small compared to the depth, the shearing stress varies
very little across its width and we may replace it by the average stress xav.
4. For a beam of rectangular cross-section as shown in Fig 2.18(a), the stress
varies along its depth according to the formula given below.
r ^
c = 0.5h
*- r
c = 0.5/7
— b—-I
Fig 2.17(a) Beam of rectangular cross-section Fig 2.17 (b) Distribution of shear stress
The distribution of shear stress in a transverse section of a rectangular beam is
shown in Fig 2.17(b). The curve is parabolic and the maximum stress is
2 Bending loads 61
2.4 The deflection of beams (Durchbiegung von Tragern)
2.4.1 Determination of the deflection by integration
(Integrationsmethode fur die Bestimmung von Durchbiegung)
It has been seen that if a beam of narrow cross-section is subjected to pure
bending, it is bent into an arc of a circle. The curvature of the neutral surface
(when the bending is within the elastic range) is given by the expression
Curvature — = —
p El
The curvature at a point P (x,y) on a plane curve is given by the expression
d2 y
Curvature — = dx2
P 3/2
In the case of bending in beams, the gradient dyldx is very small and the
square of this is much smaller than unity and can be neglected. Therefore
Curvature — = £
P dx2
El is known as the flexural rigidity and is constant for a uniform beam.
2.4.2 Example: Deflection of a cantilever by the method of integration
(Durchbiegung eines Freitragers mit Einzellast)
Consider the cantilever beam AB of
length / having a load F at its free end. / j
The bending moment and the curvature
of the beam vary from cross-section to
cross-section. For a section at a
distance x from A we can write
\ _d2y _ Fx '/
P dx2 El
The curvature of the neutral surface
varies linearly with x from zero at A to
-Fl/EI at B.
El = -Fx
Fig 2.18 A cantilever
Integrating with respect to x, we have
""at—I" "ci
To find C\ we use the boundary condition at the fixed end, where
x = I, — = 0. Substituting, we obtain c, = -Fl2
dx ' 2
62 II Strength of materials
Therefore El— = —Fx + — FI
dx 2 2
Integrating both sides of the equation with respect to x, we have
y - - x 2 c2
Using the boundary condition for the fixed end which is x = l,y = 0, we have
6 2
Therefore c
Substituting for c2 we have Fv-3 3 j l+-Fl
EIy= --Fx
, , - _ ! IT/2,x - -Fl3
6 2 3
or J = -^(-x3+3/2x-2/3
The deflection and slope at the free end can be found by substituting x = 0.
From this we find and
dx 2EI
2.4.3 The moment-area method for finding the deflection of beams
(Momentenflachen Methode fur die Bestimmung von Durchbiegung)
This method uses the geometric prop-
erties of the elastic curve (which is the
curve into which the axis of the beam is
bent when loaded). The elastic curve of a
cantilever with a single load is shown
Fig 2.19 (b). The two points 1 and 2 are
separated by a very small distance ds
and the angle between the tangents at 1
and 2 is dO. Therefore dd = —
The curvature is very small and
therefore ds can be replaced by dx.
Using the previously obtained result
— = ——, we have dd = —-M(x)dx
p hi El
where M(x) is the bending moment at x.
If we plot M(x) vs x as in Fig 2.19 (c),
M(x)dx is the shaded area and therefore
dAM=M{x)dx and d ^M
Fig 2.19 Cantilever with elastic curve
where AM = total area under the curve. and moment-area diagram
3 The buckling of columns 63
Deflection angle a = jdd = — jdA' M
4_i i
a = ET~E12J 2 £7
Vertical deflection
The element of area dAM =Mxdx is shown shaded in Fig 2.19 (b) and Mxxdx
is the moment of this about a vertical axis at the load end. The sum of all the
elementary moments is JMxxdx= AMxQ where AM is the total area under the
curve and xQ the distance from the vertical axis to the centroid S of the areaAM-
Total vertical deflection f =r==A,,xn
For a cantilever A,, -FI--
M o
and -h
2 3
f- 1 F1 2,F1
J and tance = -
El 2 3 El 2EI
which are the same as the values obtained by integration in section 2.4.2
3 The buckling of columns (Knickung)
When a bar or column is axially loaded and the load is gradually increased,
failure occurs in relatively short columns when the compressional stress
exceeds a certain value for a given material. However, when the length of the
column is large in comparison with its transverse dimensions, failure occurs by
buckling (or transverse bending) when the stress reaches a critical value acr
which is well below the allowable compressional stress aau. i.e., acr < aau.
3.1 Pin-ended columns (Beidseitig
gelenkig gelagerter Druckstab)
We wish to find the critical value acr for
which a column ceases to be stable. If the
applied stress a > acr, then the slightest
misalignment or disturbance causes the
column to buckle. A column AB of length
/ which supports an axial load F and is pin-
connected at both ends is shown in Fig
2.20. Consider a point Q on the elastic
curve of the beam at a distance x from the
end A. The lateral deflection of Q is
denoted by y and the bending moment at Q
• tr _ _p Fig 2.20 A column with pins on
*' both ends
64 II Strength of materials
Substituting in the equation derived in section 2.4.1
d2y _M
. d2y F
we have ^L = - y
This is a linear homogeneous differential equation with constant coefficients. If
? F d^"v 7
we write p = —, then —£• + p y = 0
^ dxl
The general solution of this differential equation is given by
y = Asinpx + Bcospx
We now apply the boundary conditions which have to be satisfied.
At end A of the column x = 0 a n d y = 0 which gives B = 0.
At end B of the column x = l and y = 0 which gives
A sin pl = 0
This condition is satisfied if A = 0 or sin pi = 0.
1. lfA = 0, then y = 0. JAe column remains straight and rfocs MO/ buckle.
i F
2. If sinp/ = 0, pl = nn. Substituting for/? in the expression p = — ,
we have F= =—
The smallest value of F obtainable from this expression corresponds to n = 1.
This is the critical value Fcr = —^~
This expression is known as Euler's formula. The value of p for this case is
given by p = n/l. Substituting this value in the equation for y and assuming that
5 = 0, we get y = Asm—
1. If F < Fcr , the condition sin pi = 0 is not satisfied and we assume that A
= 0. From this it follows that the column remains straight and does not
2. If F > Fcr, the column buckles (or undergoes a lateral deflection) and the
elastic curve has the form of a sine curve.
3 The buckling of columns 65
The magnitude of the stress that corresponds to the critical load is called the
critical stress acr. If we write / = Ar2 where r is the radius of gyration and A the
area of cross-section, we have
_ Fcr _ K2EAr2 _ n2E
cr ~ —T TTf
The quantity l/r is termed the
slenderness ratio of the column. A • (MPa)
graph of acr vs l/r is shown in Fig 2.21
for steel. It is assumed that E = 200 300
GPa and (the stress corresponding to)
the yield strength^ = 250 MPa. The
region for which acr>aY need not be
considered because this is outside the
elastic range. The Euler formula leads 100
us to the conclusion that the critical
load at which buckling occurs does not
depend on the strength of the material. 100 200 Vr
It depends only on the modulus of Fig 2.21 Graph of ocr vs l/r
elasticity and the slenderness ratio.
Two slender columns having the same dimensions one of high tensile strength
steel and the other ofmild steel will buckle under the same conditions of load. It
can also be seen that Fcr can be increased by increasing /. This can be achieved
without changing the cross-section by using tubular rather than solid columns.
3.2 Column with one fixed end and
one free end
(Einseitig eingespannter Druckstab)
Consider a column with one fixed end
B and one free end A which supports a
load F (Fig 2.22). The column behaves
like the upper half of a pin-ended L = 2l
column. The critical load in this case is
the same as for a pin-ended column
with length equal to twice the length /
of the given column. The effective
length / e = 2/ and substituting in Euler's
formula Fcr =
i, Fig 2.22 Column with one fixed end
e and one free end
and K E
arr =-
66 II Strength of materials
3.3 Column with two fixed ends (Beidseitig eingespannter Druckstab)
Fig 2.23 Column with two fixed ends
A column with two fixed ends supporting a load F is shown in Fig 2.23 (a). The
symmetry of the supports and the conditions of the load requires that the shear
force at C and the horizontal components of the reactions at A and B should be
zero (Fig 2.23(b)). If we consider the upper half AC, the forces exerted on AC
by the support at A and by the lower half CB must be identical. From this it
follows that AC is symmetrical about its midpoint D (Fig 2.23(c)). This is a
point of inflection where the bending moment is zero. Similarly the bending
moment for the lower half CB is also zero at its midpoint E. The portion DE has
zero bending moment at ends D and E and is similar to a pin-ended column with
zero bending moment at its ends. It follows that the effective length is le = 1/ 2.
3.4 Column with one fixed end one pin connected end
(Gelenkig-eingespannt gelagerter Druckstab)
This case is shown in Fig 2.24 and it can be
shown that the effective length is le = 0.7/.
3.5 Tests on columns ( Priifungsergebnisse)
Euler's formula can be used to find the
critical load for slender columns. Practical
tests have been carried out on steel columns
to verify the values predicted by this formula.
In each test a centrally placed axial load was
applied to the column and the load increased
until failure occurred. The results of a large
number of tests are shown in Fig 2.25. The Fig 2.24 Column with one fixed and
one pin connected end.
results show a lot or scatter, but definite
4 Torsion 67
conclusions can be drawn.
1. In the case of long columns, Euler's
formula closely predicts the correct (Tcr
value of acr at which failure occurs Euler's
corresponding to a given value of formula
slendemess ratio IJ r.
The value of acr depends on the
modulus of elasticity E, but not on
the yield stress ay •
2. Failure occurs in short columns at
Fig 2.25 Results of load tests
the yield stress and we can write
3. In columns of intermediate length, failure occurs at values of stress which
depend on both E and aY.
Empirical formulae which give the values of allowable stress or critical stress
corresponding to a given slendemess ratio have been used for a long time and
have been refined with the passage of time. As may be expected, a single
formula is not adequate for all applications. Several formulae each applicable to
a range of values of slendemess ratio have been developed for different metals.
4 Torsion (Verdrehung)
Shafts of circular cross-section are used in many engineering applications. When
such shafts are subjected to twisting couples or torques, they are said to be in
4.1 Torsion in a cylindrical shaft (Torsion in einem Kreiszylinder)
Consider a cylindrical shaft which is fixed
at one end B as shown in Fig 2.26 (a). If a
torque T is applied to the other end A
(called the free end), this end will rotate
through an angle f which is called the
angle of twist (Fig 2.26(b)). Experiment
shows that if we operate within the elastic
1. The angle of twist q> is proportional
to the torque T.
2. The angle is also proportional to the
length/of the shaft.
It is further observed that the shape of the
shaft does not change when it is in a
state of torsion. Different cross-sections of Fig 2.26 (a)&(b) Torsion in a cylindrical
the shaft rotate through different angles, shaft
but each retains its original shape.
68 II Strength of materials
4.2. Shear strains in a cylindrical
shaft (Schubgleitungen in einem
Kreiszylinder) Square
A cylindrical shaft of length / and
radius c is shown in Fig 2.27(a). Let us
consider a very small square element
formed between two adjacent circular
cross-sections and two adjacent straight
lines on a cylindrical surface of radius
p before the shaft is loaded (Fig
2.27(a)). If the shaft is now subjected
to a torsional load, the square is
deformed into a rhombus (Fig
2.27(b)). It has been stated in section
1.4.3 that the shear strain y in a given
element is equal to the change in the
angles which the sides of the element
Fig 2.27 Shear strain in a cylindrical shaft
undergo when subjected to a shear
The angle y in this case is the angle between the lines AB and A'B. Since the
angle is small, the length AA' = ly. But AA'is also equal to p(p
and therefore pm where y and <p are in radians.
This shows that
1. The shear strain y is proportional to the angle of twist (p.
2. The shear strain y is also proportional to the distance p of the point under
consideration from the axis of the shaft.
3. The shear strain is a maximum on the outer surface, and if the radius of
_ c(p
the shaft is c, then fmax ~ ~j~
4. Shear strain for any radius p is y = —ymax
4.3 Shear stresses in a cylindrical shaft
(Schubspannungen in einem Kreiszylinder)
If the applied torque is of such a magnitude that the shear stresses remain below
the yield strength of the shaft, then Hooke's law applies and we can write
Shear stress T = G x shear strain y
or r = Gy
where G is the shear modulus or the modulus of rigidity of the material.
Since y = — ymax it follows that T = — rmax and therefore r varies linearly with p.
c c
4 Torsion 69
The sum of the moments of the elementary shearing forces acting on any cross-
section of the shaft must be equal to the torque T exerted on the shaft.
dF = xdA and T = \p(zdA)
Substituting r = — rmax in the above equation, we have T= \p2dA
jp2dA is the polar moment of inertia I of the cross-section with respect to its
centre O. Therefore T= ° or
Substituting for T,maxi we express the shear stress at any distance p from the axis
of the shaft as
The above two equations in boxes are known as the elastic torsion formulae.
4.4 Shafts for the transmission of power (Stabe fur Leistungsiibertragung)
The polar moments of inertia for the area of cross-section of solid and hollow
cylindrical shafts are given by
/„ =—;rc4 for solid shafts and /„=—Tzfc, — c, ] for hollow shafts.
0 2 ° 2 V 2 ! )
The material and the cross-section has to be selected so that the maximum
shearing stress allowed will not be exceeded. The specific requirements to be
satisfied are the power transmitted and the speed of rotation. The power
associated with a body which is rotating under the action of a torque T is
P = Tw
Since co = 2irf, we can write P = liufT and T = —-
The value of rmax for the material which is selected is substituted in the formula
max - — • From this we obtain — =
1 C ^max
Since T and tmax are known, we can obtain a value for —.
In the case of solid shafts I = —xc4 and — = — ncJ
What we need to find is the minimum allowable value of c. This can be done by
substituting the value of - which had been found previously into the above
formula. If the shaft is hollow, the value — has to be used, where c2 is the
outer radius of the shaft.
Ill Engineering materials (Werkstoffe)
1 Properties of materials (Werkstoffeigenschaften)
1.1 Basic concepts (Grundlagen)
The choice of materials to be used for a particular application will depend on
many factors. The properties of the materials are usually the first things to be
considered, but other factors like availability and cost also play an important
part. Among the properties which need to be considered, are physical properties,
chemical properties and mechanical properties.
Physical properties include quantities like density, electrical resistance, linear
expansivity and the melting point. Chemical properties of interest are properties
like oxidation, combination with other elements and compounds, corrosion and
chemical reactions with other substances. Materials should also be recyclable,
and must not have an adverse effect on the environment.
Mechanical properties are the ones that are of the greatest importance in the
engineering industry. When a material is stressed, it undergoes either an elastic
deformation or a plastic deformation depending on the magnitude of the load.
In structural applications like columns and machine frames, it is important to
keep loads within the elastic range, so that no plastic deformation takes place.
In applications like the stretching, bending and deep drawing of metal, plastic
deformation has to take place, if the shape of the metal is to be changed. A brief
summary of the most important mechanical properties is given below.
1.2 Some mechanical properties (Einige mechanische Eigenschaften)
• Strength refers to the ability of a material to resist tensional or
compressional stresses without breaking. The yield strength, the ultimate
tensile strength and the breaking strength of a material are important
quantities in engineering design.
size after the load has been removed.
• Plasticity is the ability of a material to be permanently deformed without
• Ductility refers to the ability of a material to undergo deformation under
tension without rupture as in a wire or tube drawing operation.
• Malleability on the other hand refers to the ability of a material to with-
stand compression without rupture as for example in forging or rolling.
• Toughness refers to the ability of a metal to withstand the application of
shear stresses like bending without fracture. Copper is by this definition
extremely tough, while cast iron is not. Toughness is clearly different
from strength.
1 Properties of materials 71
• Brittleness refers to the ease which with a material breaks. Brittle
materials are said to be fragile can only be deformed elastically. They
break easily when subjected to plastic deformation. Brittleness is the
opposite of toughness. Cast iron is a brittle material which breaks easily
in comparison with steel, which has a much higher breaking strength.
• Impact properties - An impact test gives an indication of the toughness
of a material and its ability to resist shock. Brittleness resulting from
incorrect heat treatment or other causes may not be revealed by a tensile
test, but is usually shown in an impact test.
• Hardness refers to the ability of a material to resist abrasion or
indentation. The hardness of a material can be indicated by a hardness
test like a Brinell test. Hardness is often a surface property.
• Fatigue - When a material is subjected to constant loads well below the
yield strength of the material, permanent deformation does not normally
occur. However the application of repeated alternating stresses well
below the yield strength can cause cracks to appear. These cracks can
gradually become bigger, and finally lead to fatigue fracture.
• Creep - Tests such as the tensile test and the impact test give information
about the behaviour of a material over the short term. However, when a
metal is loaded over a long period of time, it may exhibit gradual
extension and ultimately fail even though the stress is well below the
ultimate tensile stress. This phenomenon usually occurs at high
temperatures and is called creep.
• Properties which facilitate manufacture like easy machinability, free
flow of the melting metal during casting, and good welding properties
also need to be considered when a material is being chosen.
A product can be manufactured in many ways, for example by casting, by
welding, by machining, etc. One has to decide not only on the most
appropriate type of material, but also on the process which is most
suitable and cost-effective for use with the chosen material.
1.3 The testing of materials (Werkstoffprufung)
Since properties like ductility, malleability and toughness cannot be expressed
in numerical terms, it has become necessary to use mechanical tests to obtain
numerical values which help us to compare different materials. Tests such as
the tensile test, and the impact test give values which form the basis of material
selection and engineering design. In addition to testing the materials, it is also
necessary to carry out tests on the finished component to see if it performs
satisfactorily under actual working conditions, and under possible conditions of
overloading. Long term testing may be required to avoid failure due to
phenomena such as creep and fatigue.
72 III Engineering materials
2 Iron and steel (Eisen und Stahl)
2.1 The production of iron (Herstellung von Eisen)
2.1.1 The production of pig iron (Herstellung von Roheisen)
The first step in the manufacture of iron and steel is the production of a very
impure form of iron called pig iron. This is done by reducing iron ore (which is
mainly composed of iron oxides) in a blast furnace. The addition of materials
like coke and limestone is necessary to carry out this process, and in the end the
pig iron together with the slag is run off through an outlet near the bottom of the
furnace. Pig iron is the raw material for all iron and steel products. In addition
to iron, pig iron contains up to 10% of other elements like carbon, silicon,
manganese, phosphorous and sulphur.
2.1.2 The production of wrought iron (Herstellung von Schmiedeeisen)
Wrought iron is formed by removing carbon and other impurities in a puddling
(open hearth) furnace. This is a highly refined form of iron which contains a
minute amount of slag. The slag is aligned along the length of the iron and gives
it a fibrous structure. Wrought iron is a tough material which can be welded
with ease and is highly resistant to shock. It can be bent and formed easily into
various shapes and also does not rust easily.
2.2 The manufacture of steel (Stahlerzeugung)
Steel is an alloy of iron and carbon. The carbon content should not exceed 2 %
if the carbon is to be remain alloyed with the iron. If it exceeds 2 % , the carbon
separates out as graphite and the material is called cast iron. Steel is
manufactured from pig iron and scrap by oxidizing the impurities in these
substances. This is done in various types of furnaces.
2.2.1 The oxygen furnace (Sauerstoff - Blasverfahren)
This is a barrel shaped furnace, which is open at the top and closed at the
bottom. Scrap which is sufficient to fill about 30 % of the furnace is put in first,
and then molten pig iron is poured in. Pure oxygen is blown in from above so
that it strikes the surface of the molten metal. Some of the iron in the melt is
converted into ferrous oxide. This rapidly reacts with the impurities to remove
them from the metal. Limestone is added as a flux. The process is a very rapid
one and is usually completed within half an hour.
2.2.2 Electric steel furnaces (Elektrostahlverfahren)
Electric arc, induction and resistance furnaces are used to produce high quality
steels. The most commonly used furnace is the arc furnace which uses a three
phase mains power supply. The furnace is charged with scrap steel, and
impurities are oxidized by the use of gaseous oxygen or iron oxide. The slag is
removed, and alloying elements are added until the desired composition is
obtained. Induction furnaces are used to make a particular type of alloy steel by
first starting with high grade scrap of known composition. During the melting
process more elements are added until steel of the right composition is obtained.
2 Iron and steel 73
2.3 The heat treatment of steels (Die Warmebehandlung der Stahle)
2.3.1 The basis of heat treatment (Warmebehandlungsbasis)
Steel is unique in its ability to exist both as a soft material which can be easily
machined, and after heat treatment as a hard material out of which metal
cutting tools can be made. Steel is an alloy of iron and carbon and it is the
presence of carbon as an alloying element which makes these changes in
hardness possible.
To understand why the changes in hardness occur, consider what happens to
iron when it is heated. When pure iron is heated to 910°C, its crystal structure
changes from a body-centred cubic structure to a face-centred cubic structure.
When cooled below 910°C, it changes back to the body-centred cubic structure.
This reversible transformation is very important because up to 1.7 % carbon
can dissolve in face-centred cubic iron, forming a solid solution, while no more
than 0.03 % carbon can dissolve in body-centred cubic iron.
The term alpha iron is used to denote the body-centred cubic structure of iron
existing below 910°C containing the weak solid solution called ferrite. The term
gamma iron denotes the face-centred cubic form of iron containing the stronger
solid solution called austenite. When the carbon is not in solution in iron, it
forms the compound iron carbide (Fe3C) which is called cementite.
Steel containing carbon at room temperature is not hard. The amount of carbon
in solution is less than 0.03 %. When steel is heated above the critical
temperature, the crystal structure changes and up to 1.7 % carbon can dissolve
in it. If the steel is now cooled suddenly, the carbon does not have sufficient
time to separate to form a carbide. The sudden cooling of the face-centred cubic
austenite leads to the formation of highly stressed needle-shaped crystals called
martensite. The steel becomes extremely hard and brittle due to the presence of
martensite, and is usually subjected to a tempering process which reduces both
the brittleness and hardness while increasing the toughness.
2.3.2 Stress relieving (Spannungsarmgluhen)
Metals become work (or strain) hardened when they undergo plastic
deformation by hammering, rolling, etc. Work hardening occurs because the
individual grains of steel become elongated, thereby changing the
microstructure of the steel. Metals in such a state are under stress and can
break easily. A stressed metal component to have its stress removed before it
can be used. This can be done by a stress relieving process in which the
components are heated to a temperature of about 600°C for about one or two
hours (Fig 2.1). Although the grain structure may not change, this process is
popular because it uses a relatively small amount of energy. A further
advantage is that the surface is not spoilt by oxidation or scaling.
Recrystallization and a change in grain structure can take place if the metal is
heated for a longer time at this temperature.
74 III Engineering materials
Upper critical temperature line
Lower critical temperature line
Stress relieving and recrystallizing
% Carbon -
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Fig 3.1 Temperatures for the normalizing, annealing and stress relieving of steel
Tempering temperatures
% Carbon
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Fig 3.2 Temperatures suitable for the hardening and tempering of steel
2 Iron and steel 75
2.3.3 Annealing (Weichgliihen)
Annealing is a process which makes steel (and also other metals) completely
soft, while at the same time increasing its ductility, toughness and
machinability. In the annealing process, steel is first maintained at a temperature
of about 700°C for several hours. When the heating is stopped, the furnace and
the steel components are allowed to cool down slowly together.
2.3.4 Normalizing (Normalgluhen)
Normalizing is a process which is used when the steel has a coarse grain
structure, or is nonhomogeneous and stressed. In this process, the steel is
heated above the upper critical temperature (Fig 3.1) for a short time, and
allowed to cool in air at room temperature. This gives the steel a finer grain
structure which makes it stronger, more homogeneous and stress free.
2.3.5 Hardening (Harten)
There are two reasons for hardening steel components.
• Steel components are hardened to make them more wear resistant.
• Metal cutting tools made of steel are hardened so that they will acquire
the ability to cut through steel and other metals which are in a softer
Steel is hardened by heating it to a temperature above the upper critical
temperature (Fig 3.2) and then quenching in water or oil. The steel is now glass
hard because it has acquired a needle like microstructure called martensite.
2.3.6 Tempering (Anlassen)
Steel that has been hardened and quenched is too brittle and can break easily.
It has to be tempered before it can be used. The tempering process reduces the
hardness and brittleness of the steel while increasing its toughness. In the
tempering process, the steel component is heated to a suitable temperature below
the lower critical temperature (Fig 3.2) and then allowed to cool slowly.
The temperature to which the component is heated will depend on the purpose
for which the component is to be used. The surface is often polished before
tempering. This makes it possible to observe the colour of the oxide film formed
on the surface, which gives an indication of the temperatures reached.
Razors, cutting tools, etc which have to a high degree of hardness but need not
be too tough, are tempered at 200 to 250°C. They acquire a pale yellow surface
colour. Screwdrivers, springs, etc which have to be tough but not so hard, are
tempered at a higher temperature of 300 to 350°C and acquire a deep blue
surface colour.
2.3.7 Surface hardening (Hartung von Oberflachenschichten)
It is quite often necessary to have a component with a hard outer surface and a
tough interior. If the whole component is hardened, it can become brittle and
break. Two of the methods used for surface or local hardening are given below.
These methods can only be used with steels having a carbon content of more
than 0.35 % . Mild steel is unsuitable for this purpose.
76 III Engineering materials
2.3.8 Flame hardening (Flammharten)
In this process the surface of the steel is heated by a flame to a temperature
above the upper critical temperature, so that a hardenable layer is formed on the
surface. The heated part is immediately quenched (usually by spraying water).
The depth of the hardened layer can vary from 1.5 mm to about 6.5 mm.
After quenching, tempering to a temperature of about 200°C is usually
sufficient. Flame hardening can be used for castings, forgings, etc. Applications
include the hardening of machine parts, gear teeth, cams, etc.
2.3.9 Induction hardening (Induktionsharten)
Local hardening can also be achieved by using electrical heating. Induction
heating is mainly used for the surface hardening of cylindrical parts. Coils
carrying a high frequency current are placed round the component. Due to the
skin effect, the high frequency currents which are induced in the steel
component to be hardened, penetrate only the surface layers. The surface layers
are heated above the upper critical temperature and become hardened, while the
interior remains at a lower temperature and does not become hard. The surface
is quenched by spraying with water.
2.3.10 Case hardening (Einsatzharten)
Components having a hard surface and a soft interior can also be produced by
case hardening. There are two stages in this process (a) carburizing, (b) heat
treatment, which includes hardening tempering and refining. Low carbon steel
with 0.1% to 0.2 % carbon is used at the start.
(a) Carburizing (Aufkohlen) - In the carburizing process carbon is made to
diffuse into the surface of low carbon steel at high temperatures so that the
carbon content of the outer layers exceed 0.35 % , while the carbon content
of the interior remains lower at about 0.2 %. The outer layers can be
hardened while the interior cannot be hardened. Carburizing methods can be
divided into three groups.
Solid carburizing is carried out by using a mixture of sodium, barium and
other carbonates and wood charcoal. The components and the carburizing
mixture are packed into boxes made of heat resistant alloy. The boxes are
slowly heated to about 925°C, and are kept at this temperature for several
hours. Case depths (or hardened layers) of 1 mm or more can be achieved.
Liquid carburizing is done in baths containing sodium cyanide together
with sodium or barium chloride. The baths are heated to about 900°C and
the components are immersed for periods of up to 2 hours depending on the
case depth required. Continuous operation and automatic quenching are
possible keeping operating costs low.
Gas carburizing is carried out in both batch type and continuous furnaces.
The components are heated for 3 to 4 hours to a temperature of 925°C in an
atmosphere of gases like methane, ethane or carbon monoxide. All these
gases break down, depositing carbon on the exposed surfaces. Here again
automatic quenching and low labour costs are possible.
2 Iron and steel 77
(b)Heat treatment after carburizing (Warmebehandlung der Einsatzstahle)
If the carburizing has been done correctly, the core will have a low carbon
content (0.1 to 0.2 % of carbon) while the case (outer layers) will have a
maximum content of 0.83 % . The prolonged heating produces a coarse grain
structure in the core, and the size of the grains are reduced by a process
called refining. This increases the toughness and the strength of the core.
Refining the core - This is done by heating the component to just above its
upper critical temperature (about 870°C for the core) when the coarse
ferrite/pearlite structure is replace by refined austenite crystals. The
component is next quenched in water so that a fine ferrite/martensite
structure is obtained.
Refining the case (or surface layers) - The component is heated to about
760°C at which temperature the coarse martensite of the case changes to fine
grained austenite. Quenching produces a fine grained martensite in the case.
Present day cost saving procedures - The above procedure is costly. At the
present time it has become possible to adopt the cheaper procedure of
quenching the component direct from the carburizing medium. This is
followed by tempering at about 200°C to remove the quenching strains. This
procedure works satisfactorily due to the availability of steels which
maintain a fine grain size at carburizing temperatures. Distortion of the
component is less than that experienced in other types of case hardening.
2.3.11 Nitriding (Nitrieren)
In the nitriding process, special alloy steels containing aluminium, chromium
and vanadium are heated to temperatures of about 500°C for 50 to 90 hours in a
chamber through which ammonia gas is passed. Hard nitrides of the alloying
metals as well as iron are formed on the surface. All machining and heat
treatment operations must be carried out before nitriding.
Advantages of nitriding are that the hardness is maintained at high temperatures
and that the fatigue resistance is also increased. Resistance to corrosion is good
if the component is left unpolished. The process is cheap if large numbers of
components are treated simultaneously.
2.4 Steel types (Stahlsorten)
A very large number of steel types are presently available being manufactured
on accordance with specifications set by various private and governmental
institutions. In the U.S.A. the relevant bodies are the American Society for
The American Society of Automotive Engineers (SAE). In Europe the EU
specifications are relevant, while in Germany the DIN specifications are used.
Steel is basically an alloy of iron and carbon, and steel that contains only these
two elements is called carbon steel. Low carbon steels with a carbon content of
up to 0.25 % (also known as mild steel), are used where moderate strength with
high plasticity is called for. These steels cannot be hardened or heat treated.
78 III Engineering materials
Medium carbon steels having up to 0.55 % carbon are called machinery steels
and can be heat treated to acquire strength. High carbon steels contain from
0.60 to 1.30 % carbon can be hardened and are used to make tools.
2.4.1 General purpose steels (Allgemeine Stahle)
These include carbon steels and steels with a low content of alloying metals.
These steels which are very widely used have varying compositions and heat
treatment requirements which are tailored to the application. They must have
good mechanical properties like strength, toughness, ductility, weldability, etc.
Applications include steel for buildings, containers, vehicles, machines, etc.
Rolled sheet and drawn wire are the starting points for numerous products (see
p 193) like cans, containers, vehicles, screws, bolts and nuts, etc.
2.4.2 Fine grained welding steels (SchweiBgeeignete Feinkornstahle)
These are special steels with a carbon content of less than 0.22 %. Alloying
metals like aluminium, niobium and vanadium are added to produce a steel that
has the properties of high strength and good weldability.
2.4.3 Quenching and tempering steels (Vergutungsstahle)
These are steels with a carbon content of 0.2 to 0.65 % and are available as plain
carbon steels or steels with a low alloy content. They need to be heat treated
(hardened and tempered) before use because heat treatment increases their
strength and toughness.
2.4.4 Case hardening steels (Einsatzstahle)
These are steels with a low carbon content (about 0.20 %) and are available as
plain carbon steels or steels with a low alloy content. They are used to
manufacture components with a hard surface and a tough interior. This is
achieved by case hardening.
2.4.5 Free-cutting steels (Automatenstahle)
These steels are used in automatic lathes for the mass production of small
components. They are plain carbon steels in which the sulphur and
phosphorous content have been increased. Lead is also frequently added to the
steel. The addition of these elements result in a steel in which chips produced
during the turning process are short and do not break easily. This results in an
improved surface finish.
2.4.6 Nitriding steels (Nitrierstahle)
These are special alloy steels which contain nitridable elements like chromium,
aluminium and titanium. Components which have been nitrided have a hard
surface and a tough interior.
2.4.7 Spring steels (Federstahle)
Spring steels which are used in machines and vehicles are usually plain carbon
steels of high purity. For other applications, alloy steels which can be hardened
and tempered are used. Spring steels must in general have a high elastic limit,
high tensile strength and good resistance to fatigue.
2 Iron and steel 79
2.4.8 Stainless steels (Nichtrostende Stahle)
These are steels that have the ability to resist rusting and corrosion. They have a
chromium content of at least 12% and in addition other metals like nickel,
vanadium and molybdenum.
They are used in the chemical industry for containers, pipes, machine parts,etc.
They are also used in the food industry and in domestic kitchens for cooking
utensils, sinks, dishes, etc.
2.4.9 Low temperature steels (Kaltzahe Stahle)
These are steels that do not become brittle and retain their toughness at
temperatures below -50°C. They are used for making containers, pipes and
other items which are required for the production and transport of liquid gas.
2.4.10 Heat resistant steels (Warmfeste Stahle)
These steels need to retain good mechanical properties at temperatures of up to
800°C. Plain carbon steels can be used up to a temperature of about 400°C and
steels with a low alloy content of metals like chromium, molybdenum and
vanadium can be used up to about 540°C. For higher temperatures, steels
containing up to 12 % chromium with other metals like nickel, molybdenum,
titanium and vanadium are needed. Heat resistant steels are used in the chemical
industry and in power plants.
2.4.11 Corrosion resistant steels (Korrosionsbestandige Stahle)
These are special steels that must have a resistance to the corrosive effect of
gases at temperatures of about 500°C. In these steels the chromium content is
increased by up to 30 %.
2.4.12 Steel for electrical machines (Stahle fur elektrische Maschinen)
Steels used for electrical work must have special magnetic properties. Two types
of steel are required.
a) Soft magnetic materials are steels which lose their induced magnetism
when the magnetizing field is removed. These materials are used in the
magnetic cores of transformers, motors, generators etc., where an
alternating magnetic field has to exist.
Soft magnetic materials used in AC machines are iron-silicon alloys with
practically no carbon. The metal is supplied as sheets from which
laminations are stamped. The use of laminations (thin sheets) in the core of
machines and transformers reduces eddy current losses.
Transformers and coils used in the communication and audio industry need
materials with a high permeability and low hysterisis loss. Alloys for this
purpose have a high nickel content and also other metals like cobalt.
b) Hard magnetic materials are steels which retain their magnetism when the
magnetizing field has been removed. Hard magnetic materials are used in
permanent magnets.
80 III Engineering materials
A permanent magnet should retain its magnetism for a long time (after the
magnetizing field has been removed). The flux in a permanent magnet
depends on its design and on the steel alloy from which it is made. The steels
used for permanent magnets nowadays are aluminium nickel alloy steels.
2.4.13 Tool steels (Werkzeugstahle)
Tool steels are used in tools for operations like shearing, cutting, forming,
extruding, rolling, etc. Cutting tools should be hard and resistant to wear. They
should have the ability to cut at high speeds and high temperatures. Forming
tools should be tough and shock resistant. Tools used for tasks like extruding or
hot rolling should be able to maintain their strength at high temperatures. Tool
steels may be divided into the following categories.
a) Cold working steels may be used in applications where the surface
temperature does not exceed 200°C. They are available as plain carbon
steels and also as alloy steels.
b) Hot working steels are able to work continuously at temperatures of up
to 500°C. They are used for making extrusion and casting dies as well as
in press applications like blanking and forming. They must possess good
mechanical properties at high temperatures like toughness, strength, wear
resistance and the ability to withstand deformation. These steels contain
alloying elements like tungsten, molybdenum, vanadium and chromium.
c) High speed tool steels - These steels are used to make metal cutting
tools which are able to work at high speeds and temperatures of up to
600°C without losing their hardness. They have a high carbon content of
above 0.75 % and contain alloying metals like tungsten, molybdenum,
chromium, vanadium and cobalt.
d) Special purpose steels - There are steels used for special purposes like
dies for die casting, dies for the hot pressing of nonmetals, plastic
forming, etc.
2.4.14 Steel castings (StahlguG)
Steel castings have the advantages that are usually associated with steel, like
good tensile strength, toughness, high rigidity, good welding properties and
excellent endurance properties. Steel castings with a high alloy content have
good heat and corrosion properties. Compared with cast iron, the higher melting
temperatures and poorer flow properties during casting are disadvantages. In
the manufacture of complex parts, cast steel parts have a considerable cost
advantage over forged parts. Small complex parts can be made by precision
casting methods like investment casting (lost wax casting). Most of the castings
are from plain carbon or low alloy steel. Steel castings are used for
mechanically stressed parts for turbines, valves, aircraft engine parts, machine
components, etc. Steel castings are also used in the construction of railroad cars,
trucks, trailers, tractors, etc. Large castings find use in ships, rolling mills, and in
the mining and logging industries.
2 Iron and steel 81
2.5 Cast iron (GuBeisen)
2.5.1 General properties (Allgemeine Eigenschaften)
The term cast iron has been used for iron with a carbon content of between 2
and 4.5 %. Cast iron usually contains varying amounts of impurities like silicon,
sulphur, manganese and phosphorous. Alloy cast irons contain alloying
elements like nickel, chromium, vanadium, etc. Cast iron is made in furnaces
from a charge of pig iron, steel scrap, coke, and scrap from castings. In general
there are two types of cast iron, white cast iron and grey cast iron.
1. White cast iron is produced by the rapid cooling of the melted charge.
The carbon is present as iron carbide (cementite). Cementite is a hard,
white, brittle compound, and cast irons containing this show a white
fractured surface when broken.
2. Grey cast iron is produced when the cast iron is cooled slowly. The
carbon exists in the form of graphite. A fractured surface appears grey
and such irons are called grey irons.
Silicon dissolves in the ferrite of a cast iron and has a controlling influence on
the relative amounts of graphite and cementite present. When the silicon content
is small, the carbon is in the form of cementite. Increasing the silicon content
causes decomposition of the cementite, producing graphite and grey cast iron.
Cast iron is a relatively cheap material compared to steel. It can be cast at a
lower temperature than steel and is a hard wearing material. However it is
brittle and lacks toughness. It has good corrosion resistance.
2.5.2 Grey or lamellar cast iron (GuBeisen mit Lammellengraphit)
Grey cast iron is the most frequently used of all cast irons. Carbon is present in
the form of graphite flakes. The tensile strength of the cast iron depends on the
size of the flakes, being higher when the flakes are finer in composition. The
compression strength is four times higher than the tensile strength. The
malleability and impact strength of this type of cast iron is poor. Grey cast iron
has good damping and sliding properties.
The presence of graphite makes the iron softer and gives it good machining
properties. It is used for making machine beds because of its good damping
properties. If small quantities of alloying elements like chromium, nickel,
molybdenum and copper are added the strength can be increased. Grey cast iron
is used to make engine blocks, cylinder heads, machine frames, etc.
Meehanite is a cast iron with particularly fine graphite flakes. It has good
strength and is free of stress. It is free of defects, holes, etc. and can be
hardened and improved by heat treatment.
2.5.3 Nodular (ductile) cast iron (GuBeisen mit Kugelgraphit)
The long thin flakes of graphite in grey cast iron have negligible tensile strength
and act as discontinuities in the structure. A great improvement can be achieved
if the graphite flakes are replaced by spherical particles of graphite. The
formation of spherical (or nodular) graphite is effected by adding small
quantities of cerium or magnesium (up to 0.5 %) to the molten iron.
82 III Engineering materials
Magnesium is added in the form of a nickel-magnesium alloy. Nodular cast iron
is stronger and tougher than grey cast iron. A further improvement in
mechanical properties is possible by alloying and heat treating. Nodular cast
iron is used for crankshafts, gear wheels, machine housings, pipes for the
chemical industry, etc.
2.5.4 Malleable cast iron (TemperguB)
Malleable cast iron is used to make components which have complicated shapes
and also need to be tough and impact resistant. The castings are brittle when
cast, but have their malleability increased considerably by subsequent heat
treatment. There are two types of malleable cast iron, whiteheart cast iron and
blackheart cast iron. The original castings used as starting points in both these
processes are made from brittle white cast iron.
Whiteheart process - In this process, the castings are heated for days at about
1050°C in an oxygen rich decarbonizing atmosphere. The carbon at the surface
is removed by oxidation and the outer layers are ferritic in character. When
fractured they present a white appearance and hence the name whiteheart. In
castings which have larger cross-sections, the interior can contain some graphite.
Blackheart process - In this process, the castings are heated in a neutral
atmosphere for about 30 hours at about 950°C. This results in the breakdown of
the cementite into ferrite and graphite in the form of small rosettes of temper
carbon. A fractured section appears black and hence the term blackheart.
2.5.5 Hard cast iron (HartguB)
This is a cast iron in which there is no graphite and the carbon exists entirely in
the form of cementite. Hard cast iron is able to withstand compressional stress,
but not tensional stress. It is extremely brittle. By adding alloying elements and
by subjecting the material to suitable cooling processes, it is possible to have
castings with a hard surface and a tough interior. This material is used for
castings which need to be hard and wear-resistant like rollers, camshafts and
deep drawing tools.
3 Nonferrous metals (Nichteisenmetalle)
3.1 Copper and its alloys (Kupfer und Kupferlegierungen)
Copper is a metal with a high electrical conductivity and is used in electrical
cables. The extremely pure copper required for this is refined electrically.
Copper is soft, ductile and very tough. Although copper is corrosion resistant, a
green layer of copper carbonate called verdigris forms on the surface when it is
exposed to the atmosphere. Copper can be cast, soldered or welded without any
difficulty. It is used as a conductor for power and other cables. It is also used in
applications where a high thermal conductivity is required. Large quantities of
copper are used in the making of alloys like brass and bronze.
3.1.1 Brass (Messing) - This is a Cu-Zn alloy and is the most used of the heavy
nonferrous metal alloys. The copper content must at least be 50 % , otherwise
the alloy becomes too brittle.
3 Nonferrous metals 83
The yellow colour, the high degree of polish, and the resistance to corrosion
make brass a suitable alloy for decorative purposes. It is used for watch parts,
electrical parts, pinions, hinges, brackets, etc.
High tensile strength brass (Messing mit hoher Zugfestigkeit) - This is a brass
with good hot working properties, high tensile strength and resistance to
abrasion. It is sometimes called manganese bronze due to an oxidized bronze
appearance on the surface of extruded parts.
Free-cutting brasses (Einfach zerspanbarer Messing) - These are of the 60-40
type and contain about 2 % of lead. They are easy to machine.
3.1.2 Bronze (Zinnbronze)
The bronzes are copper-tin alloys containing 83 to 98 % copper, and 2 to 15 %
tin. Some of them also contain other metals like zinc, nickel and lead.
Tin bronzes - These bronzes combine hardness and ductility with high resist-
ance to corrosion. Wrought alloys have a tin content of up to 10 %. Cast alloys
have a tin content of up to 20 %. Due to the good sliding properties and the
resistance to wear, they are used to make highly stressed shell bearings and
worm gears.
Phosphor bronzes — Phosphor bronzes contain between 0.1 and 1 % of
phosphorous. The phosphorous is supposed to increase the tensile strength and
the corrosion resistance. Phosphor bronzes are mainly used for plain bearings
and other components where a low friction coefficient combined with high
strength are required.
Bronzes containing zinc - These bronzes are available as wrought and cast
alloys. The wrought alloys were mainly used to make coins, while the cast
alloys were used where strong corrosion resistant castings were required.
Bronzes containing lead — These bronzes contain at least 60 % copper and a
lead content of up to 35 % . In addition they contain alloying metals like tin,
zinc and nickel. Since lead is not soluble in copper, it appears in the form of
spheres in the bronze. This results in good lubricational properties allowing
higher loading and higher speeds for bearings made from this type of bronze.
These are used for aero and automobile crankshaft bearings.
Aluminium bronzes - Aluminium bronzes are available as wrought and cast
alloys with an aluminium content of up to 11 % . These alloys are able to retain
their strength at elevated temperatures, have a high resistance to oxidation and
good corrosion resistance at ordinary temperatures. They have good wearing
properties and some alloys have a pleasing colour which makes them a
substitute for gold in imitation jewellery. Their high resistance to corrosion
which results from an exposure to salt water, make them useful for ship
propellers and turbine blades as also for parts in the chemical industry. These
alloys are difficult to solder or weld.
84 III Engineering materials
3.1.3 Copper-Nickel alloys (Kupfer-Nickel Legierungen)
These alloys contain 40 to 45 % of nickel. They are the most corrosion
resistant of all copper alloys. Alloys called nickel-silver contain 50-63 % of
copper, 10 to 23 % of nickel and the remainder zinc. They are white in colour
and have been used to make tableware and ornamental objects. They are also
used for making coins, for resistance wire in the electrical industry, and in the
chemical industry.
3.2 Nickel and nickel alloys (Nickel und Nickel Legierungen)
Nickel is a metal with a high tensile strength and a high degree of toughness.
The addition of manganese increases the strength without affecting the tough-
ness. It retains its strength at 500°C and remains tough at low temperatures.
Nickel can be cast, welded and soldered without difficulty.
Alloys like Monel (nickel 67 % , copper 30 %, the remainder iron and mangan-
ese) are used because of their good high temperature properties and their
resistance to corrosion, in the manufacture of valves, blades for turbines,
equipment for chemical plant, etc. Nickel alloy (Nichrome) wires are used in the
manufacture of precision electrical resistors.
3.3 Zinc and its alloys (Zink und Zink Legierungen)
Zinc is a cheap metal which is very much used as a protective coating for steel
which is exposed to the atmosphere. A coating of zinc carbonate is formed on
the surface which protects the metal from further erosion. The process known as
hot dip galvanizing is widely used to protect all kinds of steel objects and
structures. Zinc shows poor corrosion resistance against acids and salts.
Zinc alloys which contain aluminium and copper are used in die casting
processes. The low melting point of these alloys is an advantage. Objects made
by the die casting process have excellent dimensional accuracy and surface
finish eliminating the need for further finishing processes. However these
objects lack stability at high temperatures and have poor corrosion resistance.
3.4 Tin and its alloys (Zinn und Zinn Legierungen)
Very pure tin is used largely as a protective coating for steel to make tinplate,
which is used to make containers in the food industry. It is used in industry as an
alloy with lead to make solder. Pewter is an alloy used for ornamental objects
and consists 91 to 93 % tin, 6 to 7 % antimony and 1 to 2 % copper.
3.5 Lead and its alloys (Blei und Blei Legierungen)
Pure lead is used in the chemical industry because of its corrosion resistance
particularly against sulphuric acid. It is used as a screening metal i.e., to
protect people and objects from the harmful effects of X'rays and radiations
from radioactive substances. It can be easily cast, welded or pressed and is used
for making plates for accumulators. Telecommunication and other cables which
are laid underground usually have a protective coating of lead.
3 Nonferrous metals 85
3.6 Aluminium and its alloys (Aluminium und Aluminium Legierungen)
Aluminium is a silver white metal with a density of about one-third the density
of steel. When exposed to the atmosphere an oxide coating forms on the surface
and this coating prevents further oxidation. Pure aluminium is relatively soft and
weak and for engineering applications aluminium is mostly used in the form of
an alloy. Aluminium alloys containing small amounts of other elements are used
to make castings for the aero, automobile and constructional industries.
Alloying and heat treatment can produce aluminium components which are
weight for weight stronger than steel and this fact has lead to the extensive use
of aluminium alloys in air-frame construction.
Aluminium is a good conductor of both heat and electricity. It is ductile and is
particularly suitable for manufacturing objects by cold drawing and cold
pressing. The strength of aluminium is increased by work hardening processes
like rolling, drawing, pressing and hammering.
3.6.1 Aluminium alloys (Aluminium Legierungen)
The addition of alloying elements is carried out mainly to improve the
mechanical properties like tensile strength, rigidity, hardness and machinability.
Sometimes alloying improves casting properties like fluidity. The chief alloying
elements are copper, magnesium, manganese, zinc and nickel.
3.6.2 Wrought alloys of aluminium (Knetlegierungen)
Some wrought alloys are meant to be heat treated and some are not. The ones
that are meant to be heat treated contain magnesium and silicon and are resistant
to sea water corrosion.
Heat treatment improves the strength of the alloy without impairing its ductility
and cold formability. Heat treatment is carried out by first heating the alloy
components in an oven or salt bath to temperatures of about 500°C which is
close to their melting point. The objects are then quenched in water and then
allowed to remain at room temperature for a period of days. The strength is
increased in this way by a process termed age hardening. This process can be
shortened by keeping the quenched alloy at higher temperatures of 100 to
3.6.3 Cast aluminium alloys (Aluminium GuBlegierungen)
These alloys are used in sand castings and also in gravity and pressure die
castings. The most important alloys are those containing about 12 % silicon and
of approximate eutectic composition. These alloys have good fluidity. The
coarse eutectic structure can be changed to fine grained structure by adding
small amounts of sodium just before casting. Silicon alloys have high strength
while the addition of magnesium gives good corrosion resistance and heat
conductivity. The aluminium-copper-titanium alloy castings have the highest
strength and are used in components for aircraft and automobiles provided the
castings have a microstructure which is free of failures. Pressure die castings
have good dimensional accuracy and surface quality. However oxidation leads
to defects, bubbles, etc. in the castings, which reduce their strength.
86 III Engineering materials
3.6.4 Anodizing of aluminium (Anodisieren von Aluminium)
Anodizing is a way of improving the corrosion resistance of aluminium and its
alloys. It also produces a coloured finish on the surface which may be desirable
for ornamental purposes. In the anodizing process, the parts to be anodized are
made the anode in an electrolytic bath containing chromic, oxalic or sulphuric
acid. When a current is passed through the circuit, a tough coating of aluminium
oxide is formed on the surface of the parts. To obtain a coloured finish, the parts
are dyed by immersion in cold baths of dyestuff. The porous anodic coating can
be sealed by treating it with hot or boiling water.
3.6.5 Uses of aluminium (Verwendung von Aluminium)
Aluminium is second only to steel in its usefulness. It is used in transport
vehicles like aircraft, trains, ships etc. It is also used in packing (films, tubes,
boxes, cans, containers etc.), in electrical work (cables, capacitors, wiring,
switches, light housings, etc.), in household items (plates, vessels, containers,
etc., and in numerous other objects like instruments and machines.
3.7 Magnesium and its alloys (Magnesium und Magnesium Legierungen)
Magnesium is the lightest industrial metal available and is almost never used in
a pure form because it burns easily. It can however be used in alloyed form, and
its alloys are used where moderate strength and extreme lightness are required.
Magnesium alloys are considerably lighter than aluminium alloys and
magnesium alloy castings are used in the automobile and other industries for
housings, cylinder heads, machinery parts, etc.
Magnesium alloys are available both as wrought alloys and cast alloys. A large
variety of castings, forgings and extruded shapes are available for a wide variety
of applications. Articles made from magnesium alloys may be joined by welding
or riveting.
3.8 Titanium and its alloys (Titan und Titan Legierungen)
Titanium and its alloys have strengths that are close to alloy steels while their
weight is only about 60 % of the weight of steel. These materials have excellent
corrosion resistance properties comparable to or even better than those of
stainless steel. Titanium has good fatigue resistance and a high melting point.
Its ability to retain its strength at high temperatures is a property which favours
its use in jet engines. Titanium is mainly used in the aircraft industry where its
strength, toughness and corrosion resistance can be used to advantage. It is also
used in the chemical industry for the manufacture of pressure vessels, pumps,
cooling pipes, etc.
3.9 Soldering alloys (Werkstoffe fur Lotungen)
Solders are nonferrous metal alloys which are commonly used to join metals.
Solder melts at temperatures that are lower than the melting points of the metals
being soldered.
Soft solder is an alloy consisting typically of 50 % lead and 50 % tin. Brazing
or hard soldering is similar to soldering, but uses alloys which have a higher
melting point. It is used where a tougher, stronger joint is required. Brazing
3 Nonferrous metals 87
solder which is called spelt or silver solder contains typically 50 % copper and
50 % zinc.
3.10 Bearing metals (Lagerwerkstoffe)
A bearing metal has to be tough and ductile so that it can withstand mechanical
shock, but at the same time hard and abrasion resistant so that it can withstand
wear. It must also have have low friction losses.
3.10.1 Copper based bearing alloys (Lagerwerkstoffe auf Kupfer Basis)
Plain tin bronzes containing from 10 to 15 % tin and phosphor-bronzes
containing 0.3 to 1.0 % phosphorous are widely used where the loads are heavy.
For small bearings, sintered bronzes are often used, and are made by sintering
copper and tin powder together with graphite. These bearings are usually of the
self-lubricating type.
Leaded bearings are used in the manufacture of main bearings for aero-engines
as also for automobile and diesel crankshaft bearings. They are wear-resistant
and their good thermal conductivity keeps them cool while running.
3.10.2 White metal bearing alloys (Lagerwerkstoffe auf Blei oder Zinn-Basis)
These may be either lead base or tin base alloys. These are cast to form bearing
surfaces on bronze, steel or cast iron shells. These bearings work satisfactorily
against a soft steel shaft. At higher temperatures, they are subject to spreading,
fatigue and a lowering of strength.
3.11 Precious metals (Edelmetalle)
Gold is used for the manufacture of jewellery and other decorative objects, and
also in the electrical industry as a protective coating, which is deposited by
electrical means. Its use as a monetary standard has been declining in recent
Silver is used in the manufacture of jewellery as well as in the electrical industry
for the manufacture of heavy electrical contacts. It is also used in the manufact-
ure of tableware and in the making of photographic emulsions.
Platinum is a metal known for its chemical inertness, high melting point and
its usefulness in catalytic reactions. Its chemical inertness is used to advantage
in the manufacture of laboratory equipment. It can be used at high temperatures
without a protective atmosphere. It is used in high temperature thermocouples,
for making electrical contacts and in the manufacture of jewellery.
3.12 Sinter materials (Sinterwerkstoffe)
In sintering processes (also called powder metallurgy), very fine powders of
metals, alloys, refractory materials and compounds are compacted into the final
product. The following steps are involved.
1. The powder is produced by mechanical means and may be composed of
a single material or a mixture of materials.
2. The powder is pressed into the desired shape by using suitable moulds.
3. The pressed articles are subjected to a sintering process which is
essentially a heating operation.
88 III Engineering materials
Sintering processes have the following advantages:
a) Metals like tungsten which are difficult to melt, may be powdered and
sintered. A combination of dissimilar materials and refractory materials
may also be sintered.
b) It is a cost-effective method for producing parts in large numbers even
allowing for the high cost of dies.
c) No further finishing processes are required. The desired mechanical
properties may be obtained by using the right mix of powders.
Disadvantages are that high pressures and expensive dies are required. The size
of the components that can be made are limited, and it is not possible to make
certain forms like screw threads.
3.13 Cemented carbides (Sinterhartmetallkarbide)
Cemented carbides are used as tips of cutting tools for lathes and other
machines. They are second only to diamond in hardness. They are also used in
any other devices where wear-resistance is essential, like in wire drawing dies,
gauges, die linings, etc. These are produced by using powder metallurgy
Carbides of metal such as tungsten or titanium are produced by adding carbon to
the metal or oxide (or to a mixture of metals and oxides) and heating in a
reducing atmosphere to a temperature of about 1400°C.The carbide powder is
mixed with a powdered metal binder (usually cobalt), and then pressed and
sintered. The strength and hardness can be controlled by varying the quantity of
binder. Lathe cutting tools are made by brazing cemented carbide tips of the
right shape to the steel body of a normal lathe tool.
4 Nonmetallic materials (Nichtmetallische Werkstoffe)
4.1 Ceramic materials (Keramische Stoffe)
4.1.1 Bricks (Ziegelsteine)
Bricks are small blocks of material used primarily for building purposes. They
are machine made in moulds under pressure from mixes of clay. The wet bricks
from the mould are first dried in air and then baked in ovens at temperatures
between 900°C and 1300°C. Bricks are resistant to freezing and attacks from
chemicals. They are resistant to fire and provide good thermal insulation as
well as insulation against noise.
4.1.2 Fire-resistant materials (Feuerfeste Steine)
Fire-clay bricks are used to line kilns, ovens, furnaces, etc. They are made out
of a mixture of flint and clay and can withstand temperatures of over 1500°C.
High-alumina bricks are made from materials like bauxite and diaspore which
are rich in alumina. They are used where the temperature and load conditions
axe particularly severe.
Silica bricks are made from crushed rock which contains up to 98 % silica. As
material for bonding 2 % lime is used. The bricks are useful under conditions
where the strength at high temperatures has to be good.
4 Nonraetallic materials 89
4.1.3 Cement (Zement)
The normal cement used for building purposes is called portland cement. It is
made from a mixture containing 80 % calcium carbonate (chalk, limestone, etc.)
and about 20 % clay. The mixture is finely ground and calcined in kilns to a
clinker. After cooling, this clinker is ground to a fine powder. During the
grinding process, a small amount of gypsum is usually added. The gypsum
regulates the setting of the cement.
4.1.4 Concrete (Beton)
Concrete is made from a mixture of cement and a combination of inert
particles of various sizes like gravel, sand, broken stone etc. When mixed with a
suitable quantity of water and placed in moulds, it hardens into blocks having
the desired shape.
4.1.5 Reinforced concrete (Stahlbeton)
Ordinary concrete has a high compressive strength, but poor tensile strength.
Reinforced concrete is a composite material in which mild steel usually in the
forms of bars is imbedded in the concrete. The presence of steel increases the
tensile strength of the concrete and makes it possible to use it in beams, pillars,
etc. which can bend without breaking.
4.1.6 Prestressed concrete (Spannbeton)
This is a form of reinforced concrete where the reinforcing is done by
imbedding bars of high tensile strength steel. The bars are given initial stresses
opposite to those caused by the load. This is called pretensioning.
4.2 Glass (Glas)
Glass is a noncrystalline material which is made by melting a mixture of silica,
alkali and stabilizing substances like alumina, lime, lead and barium. Small
quantities of manganese and selenium oxide are added to obtain colourless glass.
Different types like window glass, laboratory glass, optical glass and also
coloured glasses can be made by adding different metallic oxides to the mixture.
Glass in molten form can be moulded or fabricated into different shapes. It is
rigid at room temperature, but may be remelted and remoulded repeatedly.
Glass has many uses. It is used for making containers like bottles and also as
window glass. Glass fibre is used as a thermal insulating material (fibre glass)
and also in glass fibre telecommunication cables. It is used in the building
industry in the form of glass bricks and for ornamental purposes.
4.3 Wood (Holz)
Wood is popular as a raw material because of its strength and the ease with
which it can be worked. Its attractive appearance makes it a much sought after
material in the manufacture of furniture, doors, door ways, ship interiors, etc.
Wood is a fibrous composite material composed of cellulose, lignin and resins.
Plywood is made by glueing together an odd number of layers of veneer with
alternate layers having their grain at right angles to each other. The alternation
of the direction of the grain tends to give the plywood equal strength in the two
face directions.
90 III Engineering materials
4.4 Plastics (Kunststoffe)
The term plastic refers to artificially made organic substances which do not
exist in nature. A feature that is common to all plastics is the fact that they are
composed of long chain-like macromolecules.
The oldest plastics like celluloid were made from natural materials. More
recently plastics have been made from coal, acetylene and mineral oil. Plastics
are very much used in the mass production of consumer products, because they
are light, cheap and easy to manufacture. Plastics can be classified into three
groups: thermoplastics, thermosetting plastics, and elastomers.
4.4.1 Thermoplastics (Thermoplaste)
Thermoplastics become soft when heated and can be moulded into different
shapes. They become hard on cooling, but can be reheated and remoulded
repeatedly. Larger quantities of mass produced goods are made from
thermoplastics as from any other type of plastic. This is due to the ease with
which they can be moulded and also due to the large range of plastics available.
Some of the most commonly used types are briefly mentioned below.
Polyamide (PA) (Polyamide) - This is milk white in appearance and has a
surface with good sliding properties. It has a high tensile strength and is also
wear-resistant, hard and tough. It is used to make gear wheels, cams, guide
pulleys, fuel tanks, protective helmets, etc.
Polyethylene (PE) (Polyethylen) - Also known as polythene, this plastic has a
colourless to milky appearance and a wax-like smooth surface. It is resistant to
acids and alkalies. There are two types as follows:
Hard polyethylene — poor flexibility, used to make containers and tubes.
Soft polyethylene — good flexibility, used for films, hoses, wire coatings.
Polymethylmethacrylate (PMMA) (Polymethylmethacrylat) - Known under
trade names like acrylglass or plexiglass. It is colourless, glass clear and has a
glossy surface. It is hard, tough and difficult to break. Resists the action of
acids and alkalies, but is soluble in certain solvents. It is used to make optical
lenses, safety glasses, transparent housings and roofings, sanitary articles, etc.
Polypropylene (PP) (Polypropylen) - Polypropylene is similar in appearance
and has similar properties to hard polyethylene. It is however harder, and retains
its shape better at temperatures of up to 130°C, and is therefore able to
withstand boiling water indefinitely. It is used for washing machine and
automobile parts.
Polystyrene (PS) (Polystyrol) - Polystyrene is colourless, has a glossy surface
and is glass clear. It is hard and brittle and breaks easily. It is able to withstand
acids and alkalies, but shows poor resistance to organic solvents. It can be made
less brittle by adding acrylnitrile. It is used to make show windows, containers,
glasses, etc.
Polyvinylchloride (PVC) (Polyvinylchlorid) - Polyvinylchloride is transparent
and resistant to both acids and alkalies. Two types are available, hard and soft.
4 Nonmetallic materials 91
The hard PVC is tough and difficult to break. By adding suitable softeners, the
material can be made to have properties similar to rubber, and leather. Hard
PVC is used to make objects like housings, tubes, valves, etc. Soft PVC is used
to make artificial leather, gloves, soles for shoes, boots, etc.
Polytetrafluoroethylene(PTFE) (Polytetrafluorethylen) - Also known as
teflon, this plastic has a milky white appearance and a wax like slippery low
friction surface. It is soft, flexible, tough and wear-resistant. It can be used
over a wide temperature range from -150°C to 280°C. It is used to make gaskets,
non-stick surfaces, electrical insulation, coatings, lubricants, etc.
4.4.2 Thermosetting plastics (Duroplaste)
Thermosetting plastics can be heated and moulded only once, and do not
become soft when reheated. They are known for their strength, dimensional and
thermal stability, resistance to chemicals, durability and good electrical prop-
erties. The polymer is mixed with fillers before moulding. Fillers include
powdered minerals, wood flour, clays, cellulose, glass and textile fibers.
Phenol resin (PF) (Phenolharz) - It is yellow-brown in colour, hard, brittle and
fractures easily. The resin is mixed with fillers before use.
Melamine resins (MF) (Melaminharz) - It is colourless to light yellow, hard,
and brittle. It fractures easily. In a pure form, it is used as a wood binding
material. Compounded with a filler, it is used to make housings and small parts.
Unsaturated polyesterresins (UP) (Ungesattigste Polyesterharze) - These
resins are colourless and glass clear, with a glossy surface. They can vary from
hard and brittle, to soft and elastic. They have good adhesive strength and good
moulding properties.
Epoxyresins (EP) (Epoxidharze) - These resins are colourless to honey yellow
in colour, tough and unbreakable. They have good adhesive, casting and
moulding properties. They are used as adhesive resins, resins for paints, casting
resins, and in glass-reinforced fabrics. They are also used in the manufacture of
composite materials like resins reinforced with glass or carbon fiber. These are
used to fabricate, boats, aircraft parts, sports equipment and corrugated sheets.
Polyurethane resins (PUR) (Polyurethanharze) - These are honey yellow in
colour, transparent and vary from hard and tough, to soft and elastic . They
have good adhesive properties and can be used to produce foam materials. They
are resistant to weak acids, alkalies, salt solutions and solvents. Pure resins are
used to make gear wheels, bearing boxes,etc. Medium hard resin is used to make
toothed belts, bumpers for cars, rollers, etc. Soft resins are used for gaskets and
packings. Polyurethane resins are also used for paints and adhesives.
Silicon resins (SI) (Silikonharze) - These are milk white in colour and vary
from stiff and solid, to soft and elastic. They repel water and adhesives, but
show poor resistance to acids, alkalies and solvents. They are used in insulating
paints, water repelling paints, gaskets, moulds for castings, etc.
92 III Engineering materials
4.4.3 Elastomers (Elastomere)
The most important characteristic of elastomers like natural rubber is their high
degree of elasticity, meaning their ability to return to their original form after
they have been subjected to large deforming forces. Elastomers need treatment
before use, because in the raw state they are soft and sticky when heated, and
hard and brittle when cooled.
Natural rubber (Naturkautschuk) — Natural rubber is produced by coagulating
the latex of the rubber tree. Freshly cut rubber has the property of self adhesion.
For most applications, the rubber is vulcanized. In this process, the rubber is
made to combine with sulphur or other chemical substances. This process
improves mechanical properties, reduces stickiness, makes it insoluble in
solvents, and enables it to be less affected by temperature changes. Carbon
black is added to increase tensile strength and resistance to abrasion. Various
other substances are added like colouring pigments, protective agents, and
vulcanizing accessories. Natural rubber is used in a multitude of products like
auto tyres, rubber springs, conveyor belts, rubber treads, etc.
Synthetic rubber (or Butadiene - Styrene copolymer (GR-S))
(Synthesekautschuk oder Butadienkautschuk)
GR-S is the most most used synthetic elastomer. The two materials butadiene
and styrene (which are petroleum products) are copolymerized to form GR-S. It
has better wear resistance and temperature properties than natural rubber. It is
used to produce auto tyres, gaskets, shoe soles, hoses, conveyor belts, etc.
Nitrile rubbers (Acrylnitryl- Butadien Kautschuk)
These are the elastomers that are most used to produce objects that are resistant
to oil, fat and fuel. These are not resistant to benzol, glycol based brake fluids,
etc. They are used to make benzene hoses, gaskets, membranes, etc.
Polyurethane rubbers (Polyurethankautschuk) - These have twice the tensile
strength of conventional rubber. Solid as well as foamed articles can be made
from these elastomers. Used to make guide wheels, shock absorber parts, foam
articles, etc.
Silicon rubbers (Silikonkautschuk) - These can be used over a wide range of
temperatures (-100°C to +200°C) and are flame-resistant. They are resistant to
oils and fats, but not to hydrocarbons, fuels, acids and alkalies, or to hot water
and steam.
Butyl rubber (Butylkautschuk) - This elastomer has good damping properties
and good ageing properties. It is resistant to acids, alkalies, acetone and
hydraulic fluids but not resistant to fats, fuels and is used to
make inner tubes for tyres, insulation, damping elements, hot water hoses, etc.
4.5 Composite materials (Verbundwerkstoffe)
Composite materials are used when a single material does not have the required
properties. Examples of commonly used composite materials are reinforced
concrete and wood, which is a natural composite material composed of
4 Nonmetallic materials 93
cellulose and lignin. Alloys are not classed as composite materials, but
laminated materials together with fibre or particle reinforced materials warrant
this description.
4.5.1 Fibre-reinforced materials (Faserverstarkte Werkstoffe)
The reinforcing fibre that is most used is glass fibre. It has great strength, low
density and is relatively cheap. The fibre can be in the form of strands, mats, or
in a woven form like cloth. For applications where even greater strength is
required as in aircraft construction, carbon, metal or ceramic fibres are used.
Glass fibre-reinforced materials consist of thermosetting plastics like polyester
or epoxy resins reinforced by glass fibre. They are used to make objects like
tennis racquets, gear wheels, automobile bodies, boats, aircraft components, etc.
4.5.2 Particle reinforced materials (Teilchenverstarkte Verbundwerkstoffe)
These are made by using a thermosetting plastic reinforced by suitable fine
particle materials. The thermosetting plastics include melamine, phenolic resins
or polyester resins. These are stronger than parts made of the pure plastic. They
are used for small parts, electrical components, housings, etc.
Polymer concrete (Polymerbeton) - This is a particle-reinforced material made
from epoxy resin and a filler composed of granite particles. Bodies of machine
tools made from this material have better damping properties than bodies made
from grey cast iron. This results in an improvement in the accuracy of the parts
produced by the machine tools.
Grinding wheels and honing tools (Schleifscheibe und Honwerkzeuge)
These are abrasive grinding stones in which the abrasive material is aluminium
oxide, silicon carbide or diamond, bonded in a plastic, ceramic, or metal body.
In the grinding stones, the cutting is done by the abrasive particles, while the
body acts as a bonding medium giving the tool strength and toughness.
4.5.3 Laminated materials (Schichtverbundwerkstoffe)
In materials like plywood, laminated plastics and paper, thin layers of material
are covered with an adhesive, placed one over another and then pressed together.
The grain in each layer (as for example the wood grain in plywood) is at right
angles to the adjoining layer, giving the final laminated product good strength
in all directions.
4.6 Lubricants (Schmierstoffe)
Most machines have surfaces and bearings in which two surfaces are in contact
and move relative to each other. It is necessary to reduce the friction between
the surfaces so that the wear, damage and heat generated can be minimized.
This is done by a process called lubrication in which a friction reducing
substance is introduced between the surfaces. The substance may be a solid,
liquid or a gas. Lubricants are manufactured to have specific physical and
chemical properties. An appropriate lubricant is chosen to suit the particular
application. Chemicals called additives are added to modify certain
94 III Engineering materials
characteristics of a lubricant. Viscosity is probably the most important property
of a lubricant and is a function of the temperature, pressure and flow of the
4.6.1 Liquid lubricants (Fliissige Schmierstoffe)
Many liquids including water are used as lubricants, but the ones most used are
of two types (a) lubricants obtained from refined petroleum
(b) synthetically produced lubricants.
4.6.2 Lubricants from petroleum (Mineralole aus Erdol)
These lubricants are oils obtained from petroleum. Additives are added to these
lubricants to improve their resistance to corrosion, resistance to the action of
high pressures, and to improve their ageing properties. Although the viscosity of
these oils change with temperature, satisfactory performance over a wide range
of temperatures is possible by using additives.
4.6.3 Synthetic oils (Synthetische Ole)
These oils are synthesized from hydrocarbons. Synthetic oils have a better
viscosity versus temperature relationship than petroleum lubricants, and better
ageing properties, but are relatively expensive.
4.6.4 Lubricating greases (Schmierfette)
Lubricating greases are made by adding a soap-like substance to mineral or
synthetic oil. This converts it into a paste-like substance called grease. Other
substances like clay, chemicals and polymers may also be added. Greases are
used to lubricate ball and roller bearings and heavily loaded guideways.
4.6.5 Solid lubricants (Festschmierstoffe)
Solid lubricants are used when the relative speed between two sliding surfaces is
too small for the building of an oil film, and also under severe conditions of
temperature and pressure.
The simplest are unbonded lubricants in powdered form. The most commonly
used substances are graphite, molybdenum disulphide, PTFE and also metal
oxides, talc and salts. The life of these lubricants may be limited and longer life
may be realized by using bonded solid lubricants. The solid lubricants are
mixed with binding materials (binders) and applied to the sliding surfaces.
4.6.6 Gases (Gase)
Gases have low viscosity coefficients. In order that the two sliding surfaces may
be separated, small holes are drilled in the bearings and the gas is fed into these
under pressure.
4.7 Additives and fillers (Zusatzstoffe und Fullstoffe)
It is often necessary to introduce additional substances (called additives) into
materials in order to modify and improve their properties. The added substances
fall into two groups. Substances which enter the molecular structure of the
materials are called additives, while those that remain separate are called fillers.
5 The testing of materials 95
4.7.1 Additives (Zusatzstoffe)
Additives are usually added in small quantities, but usually have a marked effect
on the properties of a material. There are many types of additives which can
perform different tasks. These can be added to plastics, paints, lubricants, fuels
and to a wide range of mixtures and compounds.
Some types of additives used are listed below.
1. Accelerator (Beschleuniger)
2. Antioxidants (Oxydierungsschutzmittel)
3. Dyes and pigments (Farbstoffe und Pigmente)
4. Lubricants and flow promoters (Schmiermittel und Stromforderungsmittel)
5. Plasticizers (Plastifizierungsmittel)
6. Solvents (Lo'sungsmittel)
4.7.2 Fillers (Fullstoffe)
Fillers are used to reduce material costs, to ease processing, reduce shrinkage,
and to increase the electrical or thermal conductivity. They are also used as
reinforcing materials. Some of the fillers used are listed below.
1. Alumina Tonerde 5. Talc Talk
2. Clay Lehm 6. Wood flour Holzmehl
3. Minerals Mineralien 7. Synthetic Synthetische
4. Quartz Quartz fibres Fasern
5 The testing of materials (Werkstoffpriifung)
5.1 Tensile tests (Zugversuch)
This test has already been described under II Strength of materials, section
1.6.2 (p 44). As mentioned there, quantities like yield strength, ultimate tensile
strength (UTS) and breaking strength of a material need to be known, before a
material can be selected for a particular task.
5.2 Notched bar (Izod) impact test (Kerbschlagbiegeversuch)
In this test, a metal test piece is subjected
to a violent blow given by a heavy
pendulum. If the pendulum makes an
angle $, with the vertical when released,
it would make almost the same angle Pendulum
when it swings to the other side if no test
piece was present. The test piece is
accurately made to the dimensions
specified in the test and usually has a
notch cut in it (Fig 3.4). If test piece is
now placed in the path of the pendulum, it Test piece
will either be bent or broken on impact.
The pendulum will lose energy and its
swing on the other side will be reduced Fig 3.3 Principle of the impact test
96 III Engineering materials
The value of the angles $, and <f> can be read off on a scale (not shown in the
figure). The energy loss of the pendulum corresponding to each specimen can be
calculated from the difference in the maximum heights of the pendulum before
and after the impact. The smaller the angle #, the tougher the material. One
possible pendulum arrangement is shown in Fig 3.4.
5.3 Hardness tests (Harteprufungen)
Hardness has been defined as the ability of a material to withstand abrasion or
indentation. In components and tools, quite often only the surface is hardened,
while the interior remains tough. Minerals are classified for hardness on the
Mohs scale for minerals. In this scale ten minerals are so arranged that a pointed
fragment of each mineral will scratch the next mineral lower down on the scale.
In industry, the resistance to indentation or penetration is widely used as a test
for the hardness of metals and other engineering materials. Some of the
indentation tests used are briefly described below.
5.3.1 Brinell hardness test (Harteprufung nach Brinell)
In this test a hardened steel sphere is forced under a known load into the surface
of a material and the diameter of the indentation created is measured. The
Brinell hardness number is obtained by dividing the load in kg by the surface
area of the indentation.
5.3.2 The Vickers hardness test (Harteprufung nach Vickers)
This test uses an indenter with a diamond tip having the form of a pyramid.
Since diamond is the hardest substance available, this test can be used to test
hardened cutting tools. Tables are usually provided with each instrument giving
the hardness number in terms of the length of the diagonals of the indentation.
5.3.3 The Rockwell hardness test (Harteprufung nach Rockwell)
This differs from the above tests in that the hardness is determined by the depth
of penetration of an indenter with a radiused diamond tip. Hardened steel
spheres are also sometimes used. The reading for hardness can be obtained
directly from a dial which measures the penetration. This type of instrument
allows rapid measurement of the hardness and is much used in production.
5.4 The chemical analysis of materials (Chemische Priifungen)
It is often necessary to know the composition of materials and this can be done
by chemical analysis. The amount of material needed for analysis will depend
on whether a macroanalysis or a microanalysis is planned.
5.5 Optical spectrum analysis (Optische Spektralanalyse)
In this method, the emission spectrum of the material is first produced and both
the wavelengths and intensities of the spectrum lines are measured. From the
results obtained, the types of elements in the sample and their relative quantities
can be found.
5 The testing of materials 97
5.6 Fatigue tests (Dauerfestigkeitspriifung)
Materials which are subjected to repeated loading at levels well below the yield
strength of the material, can gradually deteriorate and fracture. To avoid this
kind of failure, fatigue tests are often made on materials. In these tests, the
specimen is subjected to periodically varying stresses of constant amplitude. At
higher stress values, the material fails after a number of cycles. By lowering the
value of the applied stress, a value can be found which does not produce failure
regardless of the number of cycles.
5.7 X'ray fluorescence analysis (Rontgenfluoreszenzanalyse)
Here again as in the optical spectrum, the X'ray spectrum of the sample is
produced, and from a study of the spectrum, the components may be identified.
5.8 Electron beam microanalysis (Elektronenstrahlanalyse)
In this method, the composition of a tiny area of a material can be studied. A
very fine electron beam strikes the sample which emits X'rays which are
characteristic of the elements in the small area of the sample.
5.9 Metallographic analysis (Metallographische Untersuchungen)
Both macroscopic and microscopic metallographic studies are possible.
Macroscopic studies are able to reveal the existence of cracks, pores, fractures,
etc. Microscopic studies are carried out on etched and polished samples. The
microstructure of the crystal grains is visible under the microscope, and a
study of their composition, shape and orientation, gives much information about
the state of the specimen.
5.10 X'ray and y ray tests (Rontgen- und Gammastrahlenprufungen)
X'rays can be used to detect internal defects like cracks, porosity, inclusions,
corrosion, etc. in metallic, nonmetallic and composite materials. Gamma rays
may be used in cases where it is difficult to use X'ray equipment as for example
where electrical power is not available or where the source cannot be placed in a
particular position. The methods are similar to those for X'rays.
5.11 Magnetic particle tests (Magnetische RiBprttfungen)
This method can be used to detect surface defects in ferromagnetic materials.
The object to be tested is magnetized and then finely divided magnetic particles
are sprinkled on its surface. Any field discontinuity due to defects or cracks
attracts the particles and gives a visible indication of the discontinuity.
5.12 Eddy current tests (Wirbelstromprufungen)
Eddy currents are induced when a metal is placed in a varying magnetic field.
The eddy currents create a magnetic field which opposes the inducing magnetic
field. Imperfections and discontinuities in the metal cause a change in the
apparent impedance of the field producing coil or the detector coil. This
method can be used to investigate cracks, inhomogeneities, thickness, case
depth, composition, hardness, heat treatment, etc. Care has to be taken in
interpreting the results. The frequencies used lie between lHz and 5 MHz.
4 Thermodynamics (Thermodynamik)
1 Basic concepts and temperature(Grundkonzepte und Temperatur)
1.1 Macroscopic and the microscopic points of view
(Makroskopische und Mikroskopische Betrachtungsweise)
In any type of scientific study, attention is focused on a region of space or a
finite portion of matter which we can call a system. Anything which is outside
the system and which affects its behaviour can be called the surroundings.
The behaviour of a system can be studied from two separate points of view,
macroscopic and microscopic. In studying the behaviour of a system, we must
choose suitable quantities (or coordinates) which define the states of a system.
A macroscopic study of a system uses a few large scale properties which are
directly measurable. No assumptions concerning the structure of matter are
made. For example if we need to study the behaviour of a gas, useful
coordinates would be composition, volume, temperature and pressure.
A microscopic study of a system involves the small scale properties of a system.
Assumptions have to be made regarding the structure of matter in such a
system. For example a gas can be supposed to be composed of a large number
of molecules moving at high speeds in a container. In this case a large number
of quantities have to be specified, which are not directly measurable. Only by
using statistical methods is a satisfactory study of such a system possible.
Although these two points of view are different, both deal with the same system
and arrive at the same conclusions. Hence there must be a relationship between
them. This lies in the fact that the macroscopic description of the system uses as
coordinates a few directly measurable quantities, which are the time averages
of a large number of microscopic quantities.
1.2 Thermodynamic systems and the state of a system
(Thermodynamische Systeme und der Zustand eines Systems)
Thermodynamics uses the macroscopic point of view to study particular types
of systems and focuses on the interior of the systems. A system can be in one of different states, and each system requires a definite number of macros-
copic quantities or coordinates to define each of its states. For example each
state of an ideal gas can be defined by two coordinates P and V.
The type and number of coordinates required for the description of each state of
a given thermodynamic system are found by experiment. Such coordinates are
called thermodynamic coordinates.
1.3 Thermal equilibrium and temperature
(Thermisches Gleichgewicht und Temperatur)
It has been seen that the state of a system may be specified in terms of a few
macroscopic coordinates. A system is said to be in a state of equilibrium if its
coordinates do not change as long as the external conditions do not change.
1 Basic concepts and temperature 99
If we have two systems close to each other separated by a wall, the thermal
influence exerted by one system on the other, depends on the type of wall that
separates them. Walls can be of two types, adiabatic or diathermic. An
adiabatic wall is a wall that forms a thermal barrier between the systems. A
diathermal wall (like a thin metal sheet) allows a free thermal flow between the
systems until the two systems are in equilibrium with each other. The two
systems become part of a combined system which is in thermal equilibrium.
Zeroth law - If two systems are in thermal equilibrium with a third system, they
are in thermal equilibrium with each other. This statement is called the zeroth
law of thermodynamics.
1.3.1 The concept of temperature (Das Temperaturkonzept)
Temperature has been said to be a
measure of the degree of hotness in a
body. Consider two systems A and B,
each of which require only two
independent coordinates for the
specification of a state of the system.
System A which is in a state having
coordinates (Xi,Yi) is in thermal
equilibrium with a system B which is
in the state (X'i,Y'i). If the system A is Fig 4.1 An isotherm of system A
removed away from B and changed,
it is found that there are a number of states (Xh Y{), (X2, Y2), (X3, Y3),
each of which is in equilibrium with the same state (X'i, Y'i) of system B, and
all of which by the zeroth law of thermodynamics are in equilibrium with each
other. When all these points are plotted on a diagram (Fig 4.1), we have a curve
which can be called an isotherm. An isotherm can be stated to be the locus of all
points corresponding to the states of a system which are in thermal equilibrium
with one state of another system.
System A System B
Fig 4.2 Corresponding isotherms for two systems
Similarly with system B, we can find we can find different states (X'i, Y'i),
(X'2, Y' 2 ), (X'3, Y' 3 ), which are in equilibrium with one state (X1; YO of
100 IV Thermodynamics
system A, and therefore in thermal equilibrium with one another. If these states
are plotted on a diagram, we can obtain an isotherm I'. It follows that all states
on the isotherm I of system A are in equilibrium with all states on isotherm I'of
system B. The curves I and I' may be called corresponding isotherms. All states
belonging to corresponding isotherms of all systems have something in
common, this being that they are all in thermal equilibrium with each other.
This property which determines whether a system is in thermal equilibrium with
other systems can be called temperature. Temperature is a scalar quantity and
the temperature of all systems in thermal equilibrium with each other may be
represented by a number. A temperature scale is established by adopting a set
of rules to assign a number to a set of corresponding isotherms and a different
number to a different set of isotherms.
1.3.2 Measurement of temperature (Messung der Temperatur)
The practical measurement of temperature is accomplished by selecting a system
which has a property which varies with temperature and assigning a number to
the temperature associated with each of its isotherms.
If the thermometric property has the coordinate X, then we can assume the
temperature 6 to be proportional to Xand write,
0(X) = aX
Such a procedure will lead to a different temperature scale for each different
thermometric substance or system chosen. In the end only one temperature scale
will have to be selected as the most fundamental and used as a standard
temperature scale.
1.3.3 Fixed points on a temperature scale (Fixpunkte einer Temperaturskala)
To have a temperature scale, it is necessary to have one or more arbitrarily fixed
points on the scale. In the past, two fixed points had been used, the melting point
of ice and the boiling point of water. More recently only one point has been
used, the triple point of water which is the point at which pure water exists as
an equilibrium mixture of ice, liquid and vapour. The temperature of this point
is given the arbitrary value of 273.16 Kelvin or 273.16 K.
Thus for a constant volume gas thermometer
Temperature T= 273.16 K
as measured on the Kelvin scale, where P is the pressure at the triple point.
1.3.4 The Celsius scale (Die Celsius-Skala)
In the Celsius scale of temperature, the degree (interval) has the same
magnitude as the degree (interval) in the ideal gas scale. The zero point of the
Celsius scale is such that the temperature of the triple point of water is .01
degree Celsius (or 0.01°C). Thus if 9 is the temperature on the Celsius scale and
T the temperature on the Kelvin (or absolute) scale, then
6>°C = T(K) - 273.15
1 Basic concepts and temperature 101
1.3.5 The Kelvin (or absolute) scale and the ideal gas scale
(Die Kelvin-(oder absolute) Skala und die ideale Gas-Skala)
A practical scale of temperature like the ideal gas scale is dependent on the
properties of the thermometric substance used. It can however be shown that
there exists a scale of temperature which is independent of the properties of the
substance used. Such a scale of temperature is called an absolute scale of
temperature and the temperature on this scale is measured in degrees Kelvin.
An absolute scale of temperature would remain an abstraction unless a way of
realizing such a scale in practice can be found. It can be shown that the ideal
gas scale is numerically identical to the absolute or Kelvin scale of temperature,
and that the temperatures measured on the ideal gas scale are the same as those
on the absolute scale in degrees Kelvin. For this reason, the ideal gas scale is
used as the fundamental scale for the measurement of temperature.
1.4 Thermal expansion (Warmeausdehnung)
When a body is heated, its dimensions change.
The coefficient of linear expansion (or the linear expansivity) of a solid is
defined as the increase in length per degree rise in temperature divided by the
length at 0°C.
The coefficient ofareal expansion of a solid (or areal expansivity) is defined as
the increase in area per degree rise in temperature divided by the area at 0°C.
The coefficient of volume expansion of a body (or the volume expansivity) is
defined as the increase in volume per degree rise in temperature divided by the
volume at 0°C.
We can write
Coefficient of linear expansion Wo and h = i
Coefficient ofareal expansion and At AQ(l + at)
Ao t
Coefficient of volume expansion t~V0 and V (! + (
7= V
For a homogeneous isotropic solid, it can be shown that p = 2a and y = 3a
The coefficients of expansion for solids are small (much smaller than for liquids
and gases), However large lengths of a solid expand to such an extent, that gaps
have to be left to allow for expansion. A good example is the gap that is left
between two lengths of steel rails in a railway line, or in the supporting beams of
a bridge. Failure to allow for expansion can cause serious damage.
102 IV Thermodynamics
2 Thermodynamic systems and work
(Thermodynamische Systeme und Arbeit)
2.1 Thermodynamic equilibrium (Thermodynamisches Gleichgewicht)
The number of thermodynamic coordinates which are necessary and sufficient
to provide a macroscopic description of a particular system can be found by
experiment. The state of a thermodynamic system is determined by the values
of its thermodynamic coordinates.
(It is necessary to state here that that the expression change of state does not
refer to a transition from solid to liquid, or liquid to vapour. In thermodynamics
such changes are referred to as changes of phase)
For a system to be in a state of thermodynamic equilibrium, it must satisfy the
conditions for three other types of equilibrium, mechanical, thermal and
a) A system is in a state of mechanical equilibrium when there is no
unbalanced force in the interior of the system and also between the
system and its surroundings.
b) A system which is in mechanical equilibrium is also in chemical
equilibrium, when it does not experience a change in its internal
structure, such as a chemical reaction or a transfer of matter from one
part to another, by processes such as diffusion or solution.
c) If a system is in mechanical and chemical equilibrium, then it is also in
thermal equilibrium when it is separated from its surroundings by a
diathermic wall. In thermal equilibrium, all parts of a system are at the
same temperature, and the temperature is the same as that of its
surroundings. When this is not the case, a change of state will take
place until thermal equilibrium is achieved.
When all three conditions are satisfied, the system is in a state of
thermodynamic equilibrium. Under these conditions, there is no tendency for
any change of state by the system or its surroundings. States corresponding to
thermodynamic equilibrium can be described in terms of thermodynamic
coordinates. These are macroscopic coordinates which do not involve the time.
2.2 Equations of state (Zustandsgleichungen)
The concept of an equation of state can be conveniently illustrated by
considering the behaviour of a constant mass of an ideal gas whose pressure P,
volume V and temperature T can be measured. If the magnitudes of P and V are
fixed, then we know that Talso assumes a fixed value. This means that of the
three thermodynamic coordinates, only two are independent variables and that
there exists a relationship between the three coordinates which deprives one of
them of their independence.
An equation of state is a relationship between the thermodynamic coordinates
of a system which is in thermodynamic equilibrium. Different systems have
different equations of state, and an equation of state has to be determined
2 Thermodynamic systems and work 103
experimentally for each system. It cannot be determined by thermodynamics
alone. It is an experimental addition to thermodynamics.
2.3 Hydrostatic systems (Hydrostatische Systeme)
An isotropic system which has a constant mass and exerts a uniform
hydrostatic pressure on its surroundings is called a hydrostatic system. Pure
substances, homogeneous and heterogeneous mixtures of solids, liquids and
gases are examples of hydrostatic systems. Experiments have shown that the
states of equilibrium of a hydrostatic system can be described in terms of three
macroscopic coordinates. These are, the pressure P which the system exerts on
its surroundings, the volume Fand the absolute temperature T.
2.4 Work (Arbeit)
If a force acts on a system and the system undergoes a displacement under the
action of this force, then work is said to be done. The amount of work done is
equal to the product of the magnitude of the force and the component of the
displacement in the direction of the force.
When a system as a whole exerts a net force on its surroundings and a
displacement takes place, the work done is called external work. This external
work can be done by the system or on the system. The term internal work refers
to work done by one part of a system on another.
Only external work which involves an interaction between a system and its
surroundings is of significance in thermodynamics. Internal work is not
considered in this context, and the term work as used in thermodynamics means
external work.
2.5 Quasi-static processes (Quasi-statische Prozesse)
When a system is in a state of thermodynamic equilibrium, there is no tendency
for a change of state in the system or its surroundings. A change of state of the
system is only possible if a finite unbalanced force acts on the system. The
action of a finite unbalanced force however upsets the conditions for
mechanical and consequently thermodynamic equilibrium. A finite unbalanced
force causes turbulence, acceleration, etc. and makes the system to go through
nonequilibrium states.
When a system undergoes a change, it goes through a succession of states. If the
successive states of a system in a process of change are to be described by
thermodynamic coordinates, then it is clear that the change must not be caused
by & finite unbalanced force. We can however think of a situation, where the
change is caused by an unbalanced force which is infinitely small.
Such a process is called a quasi-static process and in such a process the system
is always infinitesimally close to a state of thermodynamic equilibrium. In such
an ideal process, all the states through which the system passes can be described
by thermodynamic coordinates. It follows that an equation of state holds for all
these states.
104 IV Thermodynamics
2.6 Work done by a gas (Arbeit die ein Gas verrichtet)
One way of effecting the transfer of energy between a system and its
surroundings is by doing work. Work done by a system on its surroundings is
considered to be negative, while work done on the system by the surroundings
is considered to be positive.
Consider a gas of volume V contained in a cylinder, at a pressure P and at a
temperature T. This system is in a state of thermodynamic equilibrium. The
pressure of the gas P is balanced by the pressure P exerted by the surroundings.
If the volume of the gas increases by a small amount dV and the process of
change is a quasi-static process, the work done by the gas is given by
dW = -PdV
If the volume of the gas is now
changed in a quasi-static process from
an initial volume V- to a final volume
Vf , the work done by the gas is
If we move along the same path in the Fig 4.3 Expansion and contraction
opposite direction, the work done on along the same path
the gas is
Wj. = — \PdV . Since the process is quasi-static, we can write
if ft
2.7. A cyclic process (or cycle) (Ein Kreisprozess)
A series of processes represented by a closed figure is called a cycle and the
enclosed area represents the net work done by a system. A cycle for a gas
consisting of two stages, an expansion and a compression is shown in Fig 4.4.
The changes inP and V during the expansion are shown in Fig 4.4 (a). The
work done is negative, and is given by the shaded area under the curve. Fig 4.4
(b) shows the work done during the compression. Here the work done is
positive. In Fig 4.3 (c) both curves are drawn together to show that after the two
processes, the gas is in its initial state. The enclosed shaded area represents the
net work done. Here the direction of traverse of the cycle is such that net work
is done by the gas, and this is negative. If the direction of traverse was reversed,
the net work is done on the gas and this would be positive.
It is clear that the work done depends on the path. This means that the work
done depends not only on the initial and final states, but also on the
intermediate states.
3 The first law of thermodynamics 105
Fig 4.4 (a) Expansion (b) Compression (c) Two stage cycle
3 The first law of thermodynamics (Erster Hauptsatz)
3.1 Heat and work (Warme und Arbeit)
Thermodynamics concentrates on the study of two quantities, heat and work.
We know that heat is a quantity that flows from a body at a higher temperature
to a body at a lower temperature. Heat can therefore be conveniently defined as
a quantity that can be transferred between a system and its surroundings. An
adiabatic wall is one that prevents the flow of heat, and is therefore a heat
insulator. A diathermic wall is one that allows a free flow of heat. An example
of a diathermic wall is a sheet of metal.
A system that is completely insulated from its surroundings by an adiabatic
envelope does not allow the transfer of heat between the system and its
surroundings. However it can be mechanically coupled to its surroundings so
that external work can be done. Such work is known as adiabatic work and the
state of a system can change from a given initial state to a final state by the
performance of adiabatic work only. Experiments show that the amount of
adiabatic work does not depend on the path (or on the intermediate states), but
only on the initial and final states of the system.
3.1.1 Internal energy function (Innere Energiefunktion)
From this it follows that for a thermodynamic system, there exists a function
whose final value minus its initial value is equal to the adiabatic work done in
moving from the initial state to the final state. This function is known as the
internal energy function and is denoted by U. We can therefore write
Adiabatic work wif = uf - u .
The difference U, - Ui represents the increase in the internal energy of the
system. We have seen that the equilibrium states of a hydrostatic system can be
described in terms of three coordinates P, V, T.
If an equation of state exists, then only two coordinates are required. We can
therefore represent the internal energy as a function of two thermodynamic
106 IV Thermodynamics
For example U = f(P,V) or U = f{V,T)
In a nonadiabatic system in addition to the transfer of energy by work, there can
also be a transfer of energy between the system and its surroundings due to a
difference of temperature. This type of energy transfer is what we have called
heat. Applying the principle of conservation of energy
or Uf- Ui = Q+W
The convention adopted here is that Q is positive when it enters a system and is
negative when it leaves the system.
The above relationship is known as the first law of thermodynamics.
We have seen that the work done on or by a system depends on the path by
which the system is moved from the initial to the final state. It follows that both
heat and work are not functions ofthermodynamic coordinates and are inexact
For an infinitesimal quasi-static process, we can write the first law in the form
dU = dQ + dW
For an infinitesimal quasi-static process of a hydrostatic system, this becomes
dU= dQ- PdV
or dQ = dU + PdV
3.2 Heat capacity (Warmekapazitat)
When a quantity of heat is absorbed by a system and this results in a change of
temperature from T- to T, , the average heat capacity of the system is defined
Average heat capacity = T T
Tf - r .
For an infinitesimal change of temperature dT this may be written as
The specific heat capacity of a substance c (usually abbreviated to specific heat)
is the amount of heat required to increase the temperature of 1 kg of the
substance by 1 K without any change in phase.
The units of c are J/kg K or J/kg °C.
4 The second law of thermodynamics 107
An important quantity is the molar heat capacity. This is the heat capacity
corresponding to the molar mass M of a substance. The molar heat capacity is
measured in J/mol. K or J/mol.°C. The specific heat (per kg) and the molar heat
capacity are designated by c, while the heat capacity for any arbitrary mass is
designated by C.
3.3 Specific heat capacities c and cv(Spezifische Warmekapazitatenc & cv)
Two important values for the specific heat are the specific heat at constant
pressure c and the specific heat at constant volume cy. They are given by the
cp and cv usually have different values.
For ideal gases it can
be shown that cp — cy=R-
and that cp /cv = K
4 The second law of thermodynamics (Zweiter Hauptsatz)
4.1 Conversion of heat into work and work into heat
(Umwandlung von Warme in Arbeit und Arbeit in Warme)
It is a matter of common experience that work can be completely transformed
into heat. For example when we rub two objects together, the work done against
frictional forces is transformed into internal energy causing a rise in
temperature. In the converse process where heat is converted into work, a 100 %
conversion is not possible. Only a partial conversion is possible and this is
usually done in a heat engine. The
principle involved in a heat engine is |_|0^ reservoir I
shown in Fig 4.5. A heat engine ~
works between two heat reservoirs. It '"''
absorbs heat from the hot reservoir, / \ y\j
converts some of this into work, and I I '
rejects the remainder into the cold N^_^/
reservoir. This contains the basic Q2 |
concept involved in the second law I Q Q ^ rese rvoir j
of thermodynamics. This law has
been stated in many ways. One F i g 4.5 Principle of the heat engine
statement is the following:
Second law of thermodynamics (first statement): No process has been
developed which converts the heat extracted from one reservoir into work
without rejecting some heat into a reservoir at a lower temperature.
108 IV Thermodynamics
4.2 The heat engine (Die Warmekraftmaschine)
In a heat engine an amount of heat Q^ is absorbed from a hot reservoir and an
amount of heat Q2 is rejected into a cold reservoir. The quantity Q] is larger
than Q2 and part of the difference Qx - Q2 is converted into work W.
_ work output
The thermal efficiency
heat input
From the first law
Therefore T)=-
4.3 The refrigerator (Der Kiihlschrank)
The refrigerator is a device which works
Hot reservoir
in an opposite manner to the heat engine.
It absorbs some heat at a low temperature Q
and rejects a larger amount of heat at a
higher temperature. Work has to be done
on the refrigerator for this to take place.
The principle involved is shown in Fig
4.6. Another statement of the second law
| Cold reservoir |
of thermodynamics based on the
refrigerator is possible and this is: Fig 4.6. Principle of the refrigerator
Second law of thermodynamics (second statement): It is not possible to have
a system which transfers heat from a cold body to a hot body without work
being done on the system.
4.4 Reversible and irreversible processes
(Umkehrbare und nichtumkehrbare Prozesse)
When a process is carried out, we can in many cases reverse the process and
bring back the system to its original state. A truly reversible process is one that
is carried out in such a way that both the system and its surroundings can be
restored to their original states without causing any changes in the rest of the
universe. All natural processes are unable to fulfil these conditions and are
therefore irreversible.
A reversible process must satisfy the conditions for mechanical, chemical and
thermal equilibrium. The process itself must be quasi-static which means that it
must pass through a series of thermodynamic equilibrium states. In addition, no
dissipative effects such as friction, viscosity, magnetic hysterisis, etc, should be
present. Since natural processes do not satisfy these conditions, it follows that a
4 The second law of thermodynamics 109
reversible process is an abstraction, which is nevertheless very useful for
theoretical purposes.
4.5 Entropy (Entropie)
It has been shown by Clausius that for any
reversible cycle j~¥~ = 0
R *
Let us consider a reversible cycle in which a
system first moves from an initial state i to a
final state/along a reversible path Rx. It then
returns along a reversible path R2 from/ to its
initial state i. For this cycle, we can write
Fig 4.7 Two reversible paths
jdQ = cdQ along R ,, = 0
1 2
f along R{ =
This shows that the integral from i to / does not depend on the path, but only
on the initial and final states. It follows that a function S exists whose change
is given by AS = S, -St = -^- along a reversible path.
This function S has been given the name entropy. The above integral defines
only a change in entropy, and does not define a value for the absolute entropy.
4.6 Changes in entropy (Entropieanderungen)
Changes in entropy of the universe have assumed an important place in
scientific thinking. When a system goes through a process, the change in entropy
of the system can be added to the change in entropy of the surroundings. This
total change can be called the change in entropy of the universe due to the
process. When a reversible process takes place, the entropy of the universe
remains unchanged. When an irreversible process takes place, the entropy of
the universe increases. Changes in entropy of the universe due to any kind of
process (meaning both reversible and irreversible) can be represented as follows:
£AS > o
4.7 Enthalpy (Enthalpie)
The first law of thermodynamics can be used to find the heat absorbed at
constant volume and constant pressure for a hydrostatic system.
(a) Heat absorbed at constant volume
(Zugefuhrte Warme bei konstantem Gasvolumen)
Using the first law of thermodynamics
dQ= dU + PdV
110 IV Thermodynamics
If V is constant, dV = 0 and \ mV
Therefore Q = Increase in internal energy
(b) Heat absorbed at constant pressure
(Zugefuhrte Warme bei konstantem Gasdruck)
Q = (U2 + P(V2 -V{)
Q = (U2 +PV )
2 -(UX+PVX)
Q = H2- where H = u + PV
In general we can write
H -U,+l °XV\ z= H2 = U2+P2V2 and H=U+PV
The function // is called enthalpy. This function is of special importance
because many thermal processes take place at constant pressure, particularly at
atmospheric pressure. Phase transitions like boiling, melting, sublimation take
place at constant pressure and the latent heat measured is equal to the change in
enthalpy. For an infinitesimal change we can write
dH = dU + PdV + VdP
Since dQ=dU + PdV
dH = dQ + VdP
For a constant pressure (or isobaric) process, dP = 0 and therefore
BT)P (dT)p
Integrating, we have
Hf -Hi = f.cpdT = Q
4.8 Phase transitions (Anderung der Aggregatzustande)
Matter normally exists in one of three phases, solid, liquid or vapour. When a
phase transition occurs, the temperature and pressure remain constant, while
the volume and entropy change. Phase transitions are usually reversible, and
one distinguishes between three types of first order transitions.
• Fusion (or melting) denotes a change from a solid to a liquid phase. The
reverse process (which is the change from a liquid to a solid) is called
solidification or freezing.
• Vapourisation denotes a change from a liquid to a gaseous phase. The
reverse process is called condensation. The term boiling refers to the
phase change which occurs when water changes into steam at normal
atmospheric pressure.
4 The second law of thermodynamics 111
• Sublimation refers to a direct change from a solid phase to a vapour
phase without going through an intermediate liquid phase.
Clear phase transitions between solid, liquid and vapour phases do not always
take place. In the case of mixtures and amorphous substances, intermediate
stages in a phase transition can occur. The phase in which a substance finds
itself depends on the cohesive (binding) forces present in the substance, and also
on the temperature and the pressure. When a solid is heated the atoms and
molecules are set into vibration. Further heating of the solid causes the bonds
between the atoms and molecules to be destroyed, and allows them to move
around in a container almost freely. The solid has now melted and is in a liquid
phase. Further supply of heat causes even larger movements in the atoms and
molecules until a point is reached where the particles are able to overcome all
forces between them and escape into free space. This corresponds to
vapourisation and the substance is now in a vapour phase.
4.8.1 Melting and freezing (Schmelzen und Erstarren)
A substance melts when its phase changes from solid to liquid. In the case of
pure substances, there is usually a definite temperature at which this occurs
called the melting point. The temperature remains constant during the melting
process. Impure substances melt within a range and not at a definite temperature.
4.8.2 Latent heat (or specific latent heat) of fusion (Schmelzwarme)
This is the term used for the amount of energy required to melt 1 kg of a
substance at the usual melting temperature. When a substance solidifies, the
same amount of heat is released from the substance.
There is usually an increase in the volume of a material when melting takes
place. The main exception is water which undergoes a decrease in volume when
its melts. The melting point of a solid, whose volume increases when it melts,
increases with increasing pressure. The reverse is true for substances like water.
4.8.3 Vapourisation and condensation (Sieden und ^Condensation)
The temperature at which the phase transition of a substance from the liquid to
the vapour phase takes place is very sensitive to the atmospheric (or other
external) pressure. Vapourisation of a substance takes place at a definite
temperature, provided the pressure is fixed. This is usually fixed at the standard
atmospheric pressure of 1.013 bar. The temperature in °C at which a substance
vapourises at a pressure of 1.01 bar is called the boiling point of the substance.
4.8.4 Latent heat of vapourisation (Verdampfungswarme) is the term used for
the amount of heat required to change 1 kg of a substance from the liquid phase
to the vapour phase at the boiling point of the liquid. The reverse process is
called condensation or liquefaction. Vapourisation involves an enormous
increase in the volume of the substance. At lower temperatures vapourisation
takes place only from the surface of the liquid and is called evaporation.
However the latent heat has to be supplied for evaporation to take place.
112 IV Thermodynamics
5 Ideal gases (Ideale Gase)
5.1 Equation of state for an ideal gas (Zustandsgleichung eines idealen Gases)
The thermodynamic states of a constant mass of gas can be represented by two
of the three coordinates P,V,T. When two of these coordinates are fixed, the
third one is also fixed. This is because of the existence of a relationship between
the three coordinates called an equation of state (see p 94). The behaviour of
gases has been studied over a long period of time, and the gas laws (due to
Boyle and Marriotte) and also due to (Charles and Gay-Lussac) can be com-
bined to give a single equation of state.
PV = mR.T
Pv=RiT where v = V/m is the specific volume
Here Rj is a constant corresponding to 1 kg of a gas. Its value depends on the
particular gas and its units are J / kg K.
If we consider a mole of a gas, the value of the constant is the same for all
gases. The constant used in this case is designated R and is known as the molar
universal gas constant. It has a value of R = 8.3144 J / mol. K and we can write
PV = nRT where n is the number of moles
The above equation of state holds not only for ideal gases, but also for real
gases when the pressure approaches zero. Experiments show that the behaviour
of all real gases approaches that of an ideal gas as the pressure approaches zero.
5.2 Specific heats of gases (Spezifische Warmekapazitat der Gase)
Two types of specific heat are useful in discussing the behaviour of an ideal gas,
Cp the specific heat at constant pressure
and cv the specific heat at constant volume
It can be shown that the difference between the specific heats is given by
The ratio of the specific heats is an important constant and is defined as
—£— = K (or sometimes termed y)
The value of the constant K depends on the atomicity of the gas, and is a func-
tion of the number of degrees of freedom of the molecules of the gas. Values
corresponding to different types of atomicity are given below.
Atomicity of the gas Degrees of freedom C
P c
v CplCy
1. Monatomic 3 5
2. Diatomic 5 7
3. Polyatomic n n+ 2 1+2
2 ' n
5 Ideal gases 113
5.3 Adiabatic (isentropic) process for an ideal gas
(Isentrope Zustandsanderung eines idealen Gases)
It can be shown for an ideal gas quasi-static adiabatic process
_,r 1 V-i
It can also be shown that
(a) the slope of an isothermal curve is —— = - —
\ov JT V
(b) the slope of an adiabatic curve is —-- = - K —
5.4 Changes of state of an ideal gas
(Zustandsanderungen eines idealen Gases)
A change of state of a gas involves a change in its thermodynamic coordinates.
It is useful to consider changes of a specific type, and some such changes corre-
sponding to unit mass (1 kg) of the gas are discussed below. It is convenient to
represent these changes on P,v and T,s diagrams.
5.4.1 Constant volume (isochoric) change (Isochore Zustandsanderung)
v = constant
Fig 4.8. (a) P vs v diagram (b) Tvs s diagram
When the volume is constant 1L-.
Heat gained or lost q = cv(T2-Tl)
Since there is no change in volume \Pdv = 0.
Change in the specific internal energy Au= c
Change in the specific enthalpy is Ah = < (T2 -
Change in the specific entropy is As = cvl
The external work done is \Pdv = 0.
114 IV Thermodynamics
5.4.2 Constant pressure (isobaric) change (Isobare Zustandsanderung)
Fig 4.9 (a) P vs v diagram (b) Tvss diagram
When the pressure is constant
V = T
2 \
Heat gained or lost q = cp (T2 -TO
Change in the specific internal energy AM -TO
= cv(T2
Change in the specific enthalpy Ah = cp(T2 -TO
Change in the specific entropy AS >
Specific external work done W = P(yt --v,)
5.4.3 Constant temperature (isothermal) change
(Isotherme Zustandsanderung)
• •
Fig 4.10 (a) P vs v diagram (b) Tvss diagram
When the temperature is constant
Heat gained or lost q = R/T 2 R Tln
= i p~2
Change in specific internal energy Au = 0
5 Ideal gases 115
Change in specific enthalpy A/z =
Change in specific entropy
Specific external work done W = RiTln-L = RiTln1^
5.4.4 Adiabatic (isentropic) change (Isentrope Zustandsanderung)
As = 0
Fig 4.11 (a) P vs v diagram (b) Tvs s diagram
3.J3.I -
When an adiabatic change takes place, there is no transfer of heat between a sys-
tem and its surroundings.
The heat change is zero q-0
Work done W = Aw = cv(T2 - Tx)
Since q =0, Change in specific entropy As = 0
Change in the specific enthalpy = cp(T2 - J )= n
5.5 Cyclic processes and heat engines
(Kreisprozesse und Warmekraftmaschinen)
Several types of heat engines are used in practice to convert heat energy into
work. In the analysis of these cycles it is assumed that friction, turbulence, etc.
can be neglected. Although this is not true in practice, the conclusions from
such studies are approximately valid and are used in evaluating the perform-
ance of heat engines.
5.6 The Carnot cycle (Der Carnot-Prozess)
The Carnot cycle is a reversible cycle of historical importance in that a Carnot
engine has the highest efficiency of all heat engines working between two heat
reservoirs at different temperatures. In practice all practical heat engines have
efficiencies which are well below that of an ideal Carnot engine. The stages in
116 IV Thermodynamics
the cycle are shown in the diagrams of Fig 4.12 (a) and (b). The Carnot cycle
consists of two isothermal and two adiabatic (isentropic) stages.
The stages in the cycle are as follows:
1 —> 2 Isothermal expansion at temperature Tj ( = T2)
2 —> 3 Adiabatic expansion resulting in a fall of temperature from T] to T3
4 Isothermal compression at temperature T3 (= T4)
1 Adiabatic compression resulting in an increase of temperature from
T 3 (=T4)toT,
Area = Work done
Fig 4.12 Carnot cycle (a) P vs v diagram (b) Tvs s diagram
The Carnot cycle is a reversible cycle. It can be shown that the heat absorbed
from the hot reservoir Qn (= QH) at a temperature 7j and the heat rejected into
the cold reservoir £>34 (=Qc) at a temperature T2, are in the ratio of their abso-
lute temperatures. This means that
Work done
The efficiency of a Carnot engine depends only on the temperatures of the res-
ervoirs. This is an idealized cycle which cannot be realized in practice. However
5 Ideal gases 117
its usefulness lies in the fact that it gives a value for the upper limit of efficiency
that a heat engine can reach.
5.7 The Otto cycle (Der Otto-Prozess)
The Otto cycle is mainly used in inter-
nal combustion petrol engines. In
these engines, a mixture of petrol and
air are compressed and ignited, to pro-
duce the power which is required to
drive the engine.
An analysis of the cycle can only be
made by making simplifying assump-
tions. The working substance is as-
sumed to be like an ideal gas, and all
processes assumed to be quasi-static.
Friction is assumed to be negligible. Fig 4 n The Otto c y d e
The Otto cycle consists of six processes. Four of these involve a motion of the
piston and are called strokes. The processes are described briefly below.
1. The induction (or intake) stroke 5 —> 1, in which a mixture of gasoline
vapour and air is sucked into the cylinder at atmospheric pressure Po due
to the downward movement of the piston.
2. The compression stroke 1—> 2, in which the piston moves upwards to
compress the mixture (adiabatically). This causes a considerable rise in
temperature. The temperature rises from 7j to T2.
3. The ignition process 2 —» 3 represents a constant volume (isochoric) in-
crease of temperature. This is brought about by the absorption of a quan-
tity of heat QH which is produced by the explosive combustion of the
fuel. The piston remains stationary during this process while the tem-
perature rises from T2 to T3.
4. The power stroke 3 —> 4 is a consequence of the hot gases expanding and
pushing the piston downwards. This is an adiabatic expansion which in-
volves a drop in temperature from T3 to T4.
5. The valve exhaust process 4 —»1 in which the exhaust valve opens and
allows some gas to escape. The pressure drops to the atmospheric pres-
sure value of PQ. The piston does not move during this process. This
represents a constant volume (isochoric) drop in temperature from TA
and a rejection of an amount of heat Qc .
6. The exhaust stroke 1 —» 5 involves the movement of the piston pushing
out all the remaining gases out of the cylinder. This represents a constant
pressure (isobaric) process at atmospheric pressure. The volume changes
from Vl to zero.
118 IV Thermodynamics
The amount of heat QH absorbed in the ignition process 2 —» 3 is given by
dT=cvCT3 -T2)
and the amount of heat Qc rejected in the exhaust process 4 —» 1 is given by
The thermal efficiency is r\ = 1 - Qc = 1 -
QH 3 ~T2
T - T
We can show that
The ratio r = , is called the compression ratio and we can write
1 . 1
! - •
5.8 The Diesel cycle
(Der Diesel-Prozess)
In the Diesel cycle, only air is initially Q
sucked in. This air is compressed adia-
batically until the temperature of the
air is high enough to ignite the fuel,
which is sprayed directly into the
combustion chamber of the cylinder.
The successive stages in the Diesel
cycle are described below. The rate of
supply of the fuel can be adjusted to
control the rate of combustion. Fig 4.14 The Diesel cycle
1. The induction (or intake) stroke 5 —> 1. Only air is sucked in.
2. The compression stroke 1 —» 2 . This involves the adiabatic compression
of air to a temperature that is high enough to ignite the fuel sprayed into
the cylinder after the compression.
3. The combustion stroke 2 —> 3. The fuel is sprayed in at such a rate that
the piston moves out during the combustion process which takes place at
constant pressure (isobaric).
The remainder of the cycle, power stroke, valve exhaust and exhaust stroke is
the same as for the gasoline engine.
If we write, expansion ratio r =77- and compression ratio rc = "
then it can be shown that
6 The transfer of heat 119
6 The transfer of heat (Warmeiibertragung)
Heat is energy in transit, and can flow from one part of a system to another, or
from a system to its surroundings. Heat transfer can take place in three different
ways, (1) conduction (2) convection (3) radiation.
6.1 Heat conduction (Warmeleitung)
Consider a thin slab of material which has a thickness Ax and a surface area A.
Let one surface of the slab be maintained at a temperature 6 while the other
surface is kept at a temperature 9 + Ad. If the quantity of heat Q that flows
perpendicular to the surfaces for a time r is measured, then it is found that
The rate of flow of heat — <x A —
r Ax
For a slab of infinitesimal thickness, we can write
dt dx
The derivative dOldx is called the temperature gradient. The negative sign is
used to ensure that the direction of heat flow should be coincident with the
positive direction of the x axis. This type of heat transfer is called heat
conduction and the constant K which is called the thermal conductivity has a
value which depends on the material.
A substance which has a large value of K is called a thermal conductor, while
one with a small value of K is called a thermal insulator. The values of K can be
measured for different substances for different ranges of temperature.
6.2 Heat convection (Warmeiibergang/ Warmekonvektion)
The transfer of heat by convection takes place in liquids or gases. When a fluid
is heated, some parts of the fluid acquire a different density in comparison with
other parts of the fluid, and a current (of fluid) flows due to the difference in
density. Such a current is called a convection current. A convection current
absorbs heat in one part of a fluid and moves it to a cooler part of the fluid
where it rejects the heat.
6.3 Thermal radiation (Warmestrahlung)
Thermal radiation is the term used to designate the radiation emitted by a body
by virtue of its temperature. The radiation consists of a continuous spectrum of
electromagnetic waves. The total energy radiated annd the distribution of
energy with wavelength are dependent on the temperature. As the temperature
of a body is increased, the total energy radiated also increases, and the
wavelength at which the maximum amount of energy is emitted becomes
The rate at which thermal radiation is emitted by a body depends on the
temperature and the nature of its surface. The total radiant power emitted per
unit area of a surface is called the emissive power of a surface. (Other names
like emittance, radiant flux density, or radiant excitance have also been given for
the emissive power). The units are kW / m2 at a given temperature.
120 IV Thermodynamics
When thermal radiation falls on a body equally from all directions (which means
isotropically), some of it is absorbed, some reflected and some transmitted. The
fraction absorbed is called the absorptivity a (or the absorptance). The
magnitude of this fraction depends on the temperature and the nature of the
Emissive power R = Total radiant power emitted per unit area
Absorptivity a = Fraction of isotropic radiation which is absorbed
6.4 Black body radiation and cavity radiation
(Schwarzkorperstrahlung und Hohlraumstrahlung)
An ideal body which absorbs all thermal radiation falling on it (a = l) is called
a black body. In practice some substances like lamp black (Lampenrufi)have an
absorptivity of nearly unity.
A hollow cavity (or box) with a small hole in one of its walls is a very good
approximation to a black body. Any radiation entering the cavity through the
hole is partly absorbed and partly reflected many times by the interior walls of
the cavity. Only a very minute fraction of this radiation can escape through the
hole again. This takes place regardless of the type of material used for the
walls. The result is that the cavity absorbs all the radiation falling on it, and the
radiation inside it is isotropic. If a small amount of radiation is allowed to
escape through the small hole in the cavity, this radiation is independent of the
material used for the interior walls and depends only on the temperature of the
cavity. This radiation called cavity radiation, can be assumed to be the same as
that from a black body maintained at the same temperature as the cavity.
6.5 Kirchhoffs law (Kirchhoffsches Gesetz)
If the emissive power of a black body is RB, then the emissive power of a
nonblack body R is & fraction of this. According to Kirchoff s law, this fraction
is equal to the absorptivity of the body. Therefore we can write
R = aRQ
6.6 The Stefan-Boltzmann law (Gesetz von Stefan und Boltzmann)
On the basis of experimental evidence, it was stated by Stefan in 1879 that the
heat transferred by radiation between a body and its surroundings was
proportional to the fourth power of the absolute temperature. This was derived
theoretically by Boltzmann, who was able to show that the emissive power of a
black body at any temperature T is equal to
This is known as the Stefan-Boltzmann law and the constant <r is called the
Stefan-Boltzmann constant. The constant has a value
a = 5.67 x 10 "8 W/m 2 (K) 4
V Machine elements (Maschinenelemente)
1 Limits and fits (GrenzmaPe und Passungen)
1.1 Measurement and inspection (Messen und Lehren)
In the past, it was the practice to make each component to precise dimensions
and assemble the components to form the final product. Each dimension of the
component was measured accurately using measuring instruments, and accepted
only when the dimensions were extremely close to the prescribed dimensions.
With the advent of mass production, it was no longer possible to manufacture
and measure each component to obtain an exact fit. The dimensions of mass
produced components varied from sample to sample and the measurement
procedure had to be replaced by a different procedure called inspection. The
main feature of this inspection procedure was to check if each dimension of a
sample lay between two prescribed limits, an upper limit and a lower limit.
The inspection procedure is simpler than the measurement procedure and can be
accomplished for example by using limit gauges. These gauges ensure that the
dimensions of a component always lie between prescribed limits.
This procedure guaranteed the interchangeability of components, regardless of
when and where the components were produced. Soon international standards
became desirable and necessary, and it has become the practice for
manufacturers to adopt the ISO Standards detailed below in Section 1.3.
1.2 Basic quantities (Grundbegriffe)
Some of the basic quantities used when choosing suitable limits and fits for
cylindrical holes and shafts are defined below and illustrated in Fig 5.1.
1. Basic size (NennmaP) is the theoretical size from which limits or deviations
are measured. The basic size is the same for both members (shaft and hole).
2. Upper (or high) limit (Hochstmap) refers to the maximum size that a
dimension in a component can have.
3. Lower (or low) limit (MindestmaP) refers to the minimum size that a
dimension in a component can have.
4. Deviation (AbmaP) refers to the algebraic difference between a given size
and the corresponding basic size.
5. Upper deviation (oberes AbmaP) is the algebraic difference between the
upper (or high) limit and the corresponding basic size.
6. Lower deviation (unteres AbmaP) is the algebraic difference between the
lower (or low) limit and the corresponding basic size.
7. Tolerance (Toleranz) is the difference between the upper and lower limits of
the dimensions of a component.
8. Fundamental deviation (GrundabmaP) is distance of the tolerance zone
from the basic size. This will be seen to be the distance of the lower or the
upper limits from the basic size, whichever lies closer.
122 V Machine elements
Basic size
Lower limit
Upper limit
Fig 5.1. Basic quantities related to the fit of a shaft and a hole
1.3 ISO standards for limits and fits (ISO Toleranzsysteme)
The ISO standards are based on the two following items:
(1) Fundamental tolerance (2) Fundamental deviation
1.3.1 Fundamental tolerance grades (Grundtoleranzgrade)
The fundamental tolerance is specified in terms of 20 tolerance grades. Each
tolerance grade has a number assigned to it. The numbers assigned are 01, 0,
and 1 to 18. The actual magnitude of the tolerance depends on both the
tolerance grade and the basic size. The basic sizes vary from lmm to 3150 mm
and are divided into 21 groups.
The tolerance grade which is to be used can be chosen freely by the designer
depending on the accuracy to which the work has to be carried out. The smaller
numbers correspond to smaller tolerances, while the larger numbers correspond
to larger tolerances assuming that the basic size remains the same. Tolerances
on components should be chosen to be as large as possible. This is because
small tolerances require expensive manufacturing and measuring equipment,
and lead to a higher percentage of rejected components. The tolerance grades
which are suitable for different types of applications are shown in Fig 5.2.
Tolerance »rac!es 01 to 4 5 toll 12 to 18
Type of Test gauges, Machine tools, Ordinary
application Standards, Manufacture of machines,
Instruments vehicles Consumer goods
Processes used Lapping, Honing, Turning, Milling, Pressing,
1 Superfinishing Grinding Drawing, Forging
Fig 5.2. Tolerance grades suitable for different applications
1 Limits and fits 123
1.3.2 Fundamental deviation (Grundabma(3)
The fundamental deviation determines the type of fit obtained when a shaft is
mated to a hole. If we have a hole that is close to the basic size, then the greater
the fundamental deviation of the shaft, the coarser will be the fit between hole
and shaft. The fundamental deviations are indicated by the following letters:
For holes: A B C D E F G H J J S K M N P R S T U V W X Y Z ZAZBZC
For shafts: abcdefghjjskmnprstuvwxyzzazbzc
The fundamental deviation is different for each of these letters and is illustrated
in Fig 5.3. The letters JS for holes and js for shafts correspond to tolerance
boundaries which are symmetrical relative to the zero line.
Holes Shafts)
CD Zero line H J X
Fig 5.3 Position of the tolerance boundaries for holes and shafts
1. A hole is described by an appropriate capital letter followed by a number
denoting the tolerance grade e.g H7
2. A shaft is described by an appropriate small letter followed by a number
denoting a tolerance grade e.g. p6
3. A fit is described by writing the hole symbol followed by the symbol for the
shaft e.g. H7/p6
1.3.3 Types of fits (Passungsarten)
1. Fit (Passung) - The term fit refers to the difference between the size of
the hole and the size of the shaft when both members have the same basic
2. Clearance fit (Spielpassung) - A clearance fit is obtained when the low
limit of a hole exceeds the high limit of a shaft which is to mate with the
3. Interference fit (Uberma|3passung) - An interference fit is obtained when
the high limit of the hole is smaller than the low limit of the shaft.
4. Transition fit (Ubergangspassung) - In a transition fit there can be either
a clearance or an interference between shaft and hole. In practice the
tolerances for transition fits are very small, and both the hole and shaft are
around the middle limit. Any interference that exists will be slight, and
hand pressure is usually sufficient to push the shaft into the hole.
124 V Machine elements
1.3.4 Systems of fits (Passungssysteme)
In order to keep manufacturing and inspection costs low, industry has largely
adopted either a hole basis system (based on a constant hole size) or a shaft
basis system (based on a constant shaft size).
1.3.5 Fundamental deviations for H holes and h shafts
(Grundabma|3e fur H Bohrungen und h Wellen)
All H holes and h shafts have zero deviation. The lower limit for H holes is the
same as the basic size. For shafts, the upper limit is equal to the basic size.
1.3.6 Hole basis system (Passungssystem Einheitsbohrung)
In the hole basis system only H holes are used. As mentioned above, the
fundamental deviation for all H holes is zero. For a given H hole, shafts with
the right fundamental deviation can be chosen to give any desired fit.
1.3.7. Shaft basis system (Passungssystem Einheitswelle)
In the shaft basis system, only h shafts are used. Corresponding to a given h
shaft, holes with the right fundamental deviation can be chosen to give any
desired fit.
1.3.8 Choice of suitable tolerance grades for holes on a hole basis system
(Auswahl von Einheitsbohrungen)
For ordinary work only six grades of holes are usually required as listed below:
H6 Internal grinding or honing H9 Boring with a worn lathe
H7 High quality boring, broaching H10 Good quality drilling
H8 Boring with a lathe, reaming Hll Standard drilling
1.3.9 Some preferred fits using the hole basis system (Auswahl von
(a) Clearance fits Paptoleranzfeldern)
1. Loose running fit H7/d8,H8/dlO, H l l / d l l
2. Easy running fit H6/e7, H7/e8, H8/e9
3. Running fit H6/f6, H7/f7, H8/f8
4. Close running fit H6/g5, H7/g6, H8/g7
5. Location fit (not for running) H6/h5, H7/h6, H8/h7
(b) Transition fit (c) Interference fit
1 Push fit H6/J5, H7/J6 1. Light press fit H6/p5. H7/p6
2. Easy keying fit H6/k5, H7/k6 2. Press fit H6/s5, H7/s6
3. Drive fit H7/n6, H8/n7 3. Shrink fit H6/u5, H7/u6
2 Rivets and riveted joints 125
2 Rivets and riveted joints (Niete und Nietverbindungen)
Riveting is mainly used when it is necessary to join two or more metal sheets (or
other components) permanently. Although it has been replaced to a large extent
by welding, it has however many advantages over welding. Among these
are that the
• microstructure of the metal
remains unchanged
• it is possible to join different
types of materials.
• on-site riveting is possible. (a) Half round (b) Countersunk
• process is easily controlled.
Disadvantages are that:
the material is weakened by
holes, weak joints,etc. (c) Oval (d) Flat round
working times are longer Fig 5.4 Some types of rivet heads
Riveting is still used to make firm and leakpr oof joints in ships, aircraft, steel
containers, boilers, etc. In addition to its use in joining steel sheets, it is also
used to join materials like copper, aluminium and their alloys.
2.1 Types of rivets (Nietformen)
Some of the types of rivets used are shown in Fig 5.4. Rivets with a half round
head are the most frequently used, but countersunk rivets must be used for
joints that need to have a flush surface.
| 1
(a) Sinjde row lap joint (b) Double row lap joint
pji [1 ink
(c) Single row butt joint (d) Double row butt joint
Fig 5.5 Some types of riveted joints
2.2 Types of riveted joints (Nietverbindunsarten)
Two types of joints are usually used, lap joints and butt joints. Lap joints are
used in boiler and container construction, while butt joints are used in steel
construction. Some examples of the types of joints used are shown in Fig 5.5.
126 V Machine elements
3 Screws and screw joints (Schrauben und Schraubenverbindungen)
Metal sheets and components can be joined by screws in several different ways
as shown in Fig 5.6.
1) Bolts and nuts (Schrauben und Muttern) are used when both sides of
the components to be joined are accessible (Fig 5.6(a)). If the parts are
subject to vibration, an additional part like a spring washer or a lock
nut is required to prevent the nut from becoming loose.
2) Set screws (Stellschrauben) are used (Fig 5.6(b)) when the use of a
bolt and nut is not possible. Set screws with normal heads can be used,
but it is often necessary to use set screws with countersunk heads.
Such screws are called socket screws (Fig 5.6(c)) and have a hole of
hexagonal form in the head of the screw, enabling them to be
tightened efficiently.
3) Studs (Stiftschrauben) are used for example (Fig 5.6(d)), when joining
parts to cast iron components. Cast iron has a low tensile strength and
excessive tightening of a set screw into a cast iron thread can cause the
thread to be damaged. In this case the studs are screwed into the
casting first, and the tightening is accomplished by using mild steel
nuts. Any damage caused will be to the nut or stud and not to the
casting. Studs can be used to effect gas-tight and water-tight joints in
cases when heavy pressures are present. A good example of the use of
studs is their use for holding down a cylinder head on a cylinder block
of an internal combustion engine. A thin gasket is placed between the
metal surfaces to make the joint gas and water-tight.
3.1 Screws, bolts and nuts (Schrauben und Muttern)
Screws together with bolts and nuts, are the most convenient devices used for
the nonpermanent joining of materials and components. A screw is the term
used for a device (like a wood screw) used alone for joining two parts. Bolts and
nuts on the other hand are used as a pair. The usage of terms is clearly different
from that in German where the term Schraube is used for both a screw as well
as a bolt.
A screw joint is made by screwing an external screw thread on an internal screw
thread. The screw thread is therefore the basis of the joining process. There are
many different kinds of screws, each made to a definite specification. Some of
the terms used in defining the specification of a screw are given below.
1) The angle of a screw thread is the angle between the two inclined faces of
the screw thread Fig 5.7 (a).
2) The pitch is the distance measured between any point on a thread and the
corresponding point on the next thread when measured parallel to the
axis of the screw Fig 5.7 (a).
3) The major diameter is the external diameter of the screw, and the minor
diameter is the core or smallest diameter of the screw.
3 Screws and screw joints 127
Fig 5.6 (a) Use of bolts and nuts Fig 5.6(b) Use of set screws
Fig 5.6 (c) Use of socket screws Fig 5.6 (d) Use of studs
128 V Machine elements
4) The depth of engagement is the radially measured distance over which the
two mating screw threads overlap (Fig 5.7 (b)).
5) One distinguishes between left hand and right hand screws depending on
which way they have to be rotated, when fastening takes place.
80 % depth
-Pitch engagement
Core diameter
Fig 5.7(a) Angle of a screw thread (b) Depth of engagement
3.2 Types of screw threads (Gewindearten)
Many types of screw threads have been used in the past, but with increasing
international cooperation, two types of screw threads are predominantly used for
most purposes today. These are the ISO metric screw thread and the (American)
unified (inch) screw threads. In addition to these, other screw threads are used
for special purposes like in the construction of drive and feed shafts for
machines and machine tools.
3.2.1 Unified screw threads ((American) Unified Gewinde)
These screw threads are mainly used in the U.S and Canada. The basic profile of
the unified screw thread is the same as that for the ISO metric thread. The series
of unified threads that are available are:
1) Coarse series UNC or UNRC
2) Fine series UNF or UNRF
3) Extra fine series UNEF or UNREF
4) Constant pitch series UN or UNR
5) Other selected UNS or UNRS
The following features are worth noting.
1) Both the UN and UNR threads have the same have the same profile which
is identical to that of the ISO metric threads.
2) The term UN thread applies to both the internal and external threads,
while the term UNR applies only to the external threads.
3) External UN threads may have either flat or rounded crests and roots.
4) Internal UN threads must have rounded roots, but may have flat or
rounded crests.
5) Internal UN threads must have rounded roots.
3 Screws and screw joints 129
3.2.2. ISO metric threads (Metrisches ISO Gewinde)
As mentioned before, the profile of the ISO metric thread is the same as the
unified thread. There are a number of metric thread series, some of which are
mentioned below.
1) ISO metric series - Covers thread diameters from lmm to 68 mm.
Intended for use in all types of bolts and nuts and other types of
mechanical fasteners.
2) ISO metric fine thread series - Covers thread diameters from lmm to
300mm. Used for mechanical fasteners, for ensuring water-tight and gas-
tight joints, for measuring instruments, etc.
3) ISO metric saw tooth thread - The saw tooth thread has a thread angle
of 33°. The unsymmetrical thread form makes unsymmetrical loading
possible. Used in the construction of collett chucks for lathes and milling
4) ISO metric acme thread (trapezoidal form) - Covers thread diameters
from 8mm to 300mm. Used in drives for machine tools, vices, valves,
presses, etc.
3.2.3 Other types of threads (Andere Gewindearten)
1) Whitworth pipe threads - This thread has an angle of 55 degrees and is
used in pipes and pipe parts where effective sealing is important.
2) Round screw thread - These threads have a thread angle of 35 degrees
together with rounded roots and crests. Used for example in clutch
3.2.4 Types of screws, bolts and nuts (Schraubenarten und Mutterarten)
1) Different types of heads - In addition to having different types of screw
threads, screws can also have different types of heads. Some of the types
of heads which are used are shown in Fig 5.8.
2) Taper screws - Screws which have a tapering form are not used with a
nut. Examples of these are wood screws and hardened self-tapping screws
used to join metals. The self-tapping screws are able to cut a thread in the
metal when they are screwed in.
3) Nuts - Nuts can also have different forms. Some of the available forms
are shown in Fig 5.9.
4) Thread inserts - Thread inserts are used with materials like soft metals,
plastics and wood where the thread strips off or is easily damaged. They
can also be used to repair damaged screw threads.
5) Locking devices - Locking devices are often necessary to prevent screws
and bolts from becoming loose. Some of the devices that can be used are
own in Fig 5.10.
130 V Machine elements
(a) Flat or cheese (b) Filister (c) Countersunk (d) Oval (e) Round
head head head head head
(f) Hexagonal (g) Socket (h) Set or grub (i) Philips
head head screw head
Fig 5.8 Some types of screw heads
nr~i j—in
(a) Hexagonal nut (b) Capped nut (c) Winged nut (d) Slotted or
castle nut
Fig 5.9 Some types of nuts
(a) Cotter or split pin (b) Locking plate (c) Spring washer
Fig 5.10 Some types of locking devices
4 Pins 131_
4 Pins (Stifle)
4.1 Uses of pins (Verwendung von Stiften)
Pins are removable fasteners. They are used are used as locating devices and as
fasteners for the transmission of small torques.
4.1.1 Locating pins (Papstifte)
Locating pins are used to locate (or secure) the position of two components
relative to each other. They facilitate the precise assembly of components and
prevent sideways movement due to lateral (sideways) forces.
4.1.2 Fastening pins (Befestigungsstifte)
Fastening pins are used to hold components together firmly so that they can
transmit forces and couples without becoming loose.
4.1.3 Overload protection pins (Abscherstifte)
Overload protection pins are used to prevent damage when components are
subjected to excessive forces or torques. If the forces or torques exceed certain
values, the/j/» breaks thereby ensuring that no damage is caused.
4.2 Types of pins (Stiftformen)
Pins can be classified according to their shape or form as cylindrical pins, taper
pins, roll pins, spiral pins, grooved pins, etc.
4.2.1 Cylindrical pins (Zylinderstifte)
Cylindrical pins are used as locating pins to join parts when strength and
accuracy are important, and when the parts that are joined need to be rarely
4.2.2 Taper pins (Kegelstifte)
Taper pins are usually made with a standard taper of 1: 50. The hole is usually
bored to the smallest diameter of the pin and then enlarged with a taper reamer
until the pin projects 4 mm above the hole when inserted by hand. The pin is
then hammered in until it is firmly fixed in the hole. The pin is elastically
deformed in this process and creates a strong joint which however is not strong
enough to resist shocks.
4.2.3 Roll pins (Spannstifte)
These are hollow cylindrical pins which have a slit along their length. They are
made of spring steel and heat treated before use. The outer diameter of the pin is
larger than the hole and becomes compressed when driven into the hole. These
can be used to join components and to ensure resistance against lateral forces.
4.2.4 Spiral pins (Spiral-Spannstifte)
These are rolled in the form of a spiral cylinder from heat treated spring steel
The outer diameter is slightly larger than the hole. The pins are rolled elastically
tighter when driven into the hole. These pins (due to their elastic properties) are
particularly suitable for use in joints which are subjected to shocks.
4.2.5 Grooved pins (Kerbstifte)
Grooved pins usually have three grooves along part or the whole of their length.
These are used in joints where great accuracy is not required, and where the
joints are rarely separated.
132 V Machine elements
5 Axles and shafts (Axen und Wellen)
5.1 Axles (Axen)
Axles are used as mountings and supports for wheels, pulleys, levers etc. and
are mainly subjected to bending loads. They are not used for the transmission
of torques. Axles can be used in a fixed position as for example in cranes. They
can also be used as moving components as for example in trains and other
5.2 Shafts (Wellen)
Shafts are rotating machine elements which carry gear wheels, pulleys,
couplings, etc. They are used to transmit torques and are subjected to both
bending and torsional stresses. Shafts are of different types like for example
fixed rigid shafts, shafts with joints in them and flexible shafts.
5.2.1 Rigid shafts (Starre Wellen)
These can be of many types like for example straight shafts, shafts with offsets
in them like crankshafts, uniform shafts or shafts with reduced cross-section in
certain places on the shaft. Shafts in machine tools called spindles are often
hollow to accommodate chucks, tools, workpieces, etc.
5.2.2 Crankshafts (Kurbelwellen)
These are used to convert reciprocating motion into rotary motion as for
example in engines or compressors with pistons in them.
5.2.3 Drive shafts (Getriebewellen)
These shafts often have their cross-sections reduced in certain places to enable
machine elements like gear wheels, pulleys, bearings, couplings, etc. to be easily
and accurately fitted on them.
5.2.4 Jointed shafts (Gelenkwellen)
These are used when the position of the end of a shaft can change as in the
drive shafts of cars. The use of universal joints allows complete flexibility in
these cases.
5.2.5 Flexible shafts (Biegsame Wellen)
These are used with small electrical devices which are fitted with high speed
low torque motors. They are particularly useful when the position of the device
driven by the motor (like a drill or a speedometer) changes its position often
relative to the motor. The shafts are usually made of several strands of steel
wire interwoven to give maximum flexibility. The interwoven strands are then
protected by covering them with a metal (or other type of) sheath.
5.3 Shaft to hub (or collar) connections (Welle-Nabe Verbindungen)
A shaft is mainly used to transmit rotary motion. This is done through machine
elements like gear wheels, pulleys, clutch plates, etc. which are mounted on the
shaft. The connection between the shaft and the machine element which is
responsible for the further transmission of the torque is called the shaft to hub
(or collar) connection. The hub is the usually the inner surface (or other part) of
the gear wheel or other machine element which fits on the shaft. Connections
5 Axles and shafts 133
can be of two types (1) those that depend on frictional forces and (2) those that
depend on mechanical fastening devices.
(a) Cylindrical press fit (fc>) Taper connection (C) Split collar connection
(d) Taper key connection Longitudinal pin
(f) Key connection (g) Splined connection
Fig 5.11 Shaft to hub connections
5.3.1 Shaft to hub connections which depend on frictional forces
(a) Cylindrical press fit connections (Zylindrischer PrePverbande)
This is a simple and cheap way of making shaft to hub connections (Fig
5.11 (a)). The shaft has a very slightly larger diameter than the hole into which it
fits. It can be pressed into the hole if sufficient force is used. Such a fit is called
an interference fit (see pi 15). The fitting can also be done by heating the hub,
so that the hole expands allowing the hub (or collar) to be slipped easily over the
shaft. On cooling the hub contracts, and grips the shaft firmly. Such connections
are permanent and are able to transmit large, variable and abruptly changing
torques and forces. This type of connection can be used for gear wheels, pulleys,
flywheels, couplings, etc.
(b) Taper connections (Kegliger PrePverband)
These are easily removable connections in which an outer taper on the shaft fits
into an inner taper in the hub (Fig 5.1 l(b)). They are pressed together using a
nut or a screw. The axial forces which are brought into play give rise to large
134 V Machine elements
normal forces which hold the components together. Taper connections are
capable of transmitting large, variable and abruptly changing torques. They can
be used for the same applications which were mentioned for the cyindrical press
connections. In addition they are also used in machine tool spindles and mounts
for ball bearings.
(c) Clamp connections with split or slit collar (Geteilte Nabe)
These connections are easily removable and can be moved along the axis or
rotated about the axis (Fig 5.1 l(c)). They are suitable for use with moderate
torques. For use with larger torques an additional rectangular key should be
fitted between the shaft and the collar.
(d) Taper key connections (Keilsitzverbindungen)
The shaft and the hub have slots cut in them, and a key with a slope of 1:100
along the length is pressed into the slots (Fig 5.11(d)). This causes the axes of
the shaft and the hub to be displaced, so that they are pressed against each
other. The result is an increase in the friction between the shaft and the collar
and which forces them to rotate together.
5.3.2 Shaft to hub connections that depend on mechanical devices
(a) Pin connections (Stiftverbindungen)
These are removable connections mostly suitable for the transmission of smaller
constant torques (Fig 5.1 l(e)). Tapered pins are mostly used, and these can be
fitted laterally or longitudinally.
(b) Key connections (Pa(3federverbindungen)
A rectangular key with parallel sides is fitted into slots cut in the shaft and hub
(Fig 5.1 l(f)). There is a space between the key and the top of the slot in the hub.
Such a connection is unsuitable for torques which are subject to abrupt changes.
For gear wheels which have to slide along the shaft, the keys are made with
sufficient tolerances to enable sliding. By using screws to fix the key on the
shaft or the collar, any axial movement of the key can be avoided. A key that is
fixed in this fashion is called & feather key.
(c) Splined connections (Profilwellen Verbindungen)
Splined connections are used for heavy duty couplings (Fig 5.1 l(g)). An axial
movement between the shaft and the hub is possible when splines are used. The
spline shaft has a number of longitudinal projections round its circumference.
These engage with corresponding recesses in the hub. These splined shafts can
have different profiles like involute (similar to those in gear wheels), parallel-
sided slots and splines, polygon profiles,etc.
6 Couplings 135
5.3.3 Axial locking devices (Wellensicherungen)
Many types of locking devices are available for preventing the axial movements
of shafts and machine elements like ball bearings, bushes, pulleys, etc.
a) Locking rings (Sicherungsringe)
These are made of spring steel and are round in shape. They exert uniform
pressure round the circumference of a slot or recess.
(b) Snap rings (Springringe)
These are used where a ring of uniform cross-section is required.
(c) Locking discs (Sicherungsscheibe)
These are used for small shafts in instruments and other devices.
(d) Cotter pins (Splint)
These are particularly useful in preventing bolts and nuts from becoming loose.
(e) Adjusting ring or set collar (Stellringe)
These are used to limit the axial movement of shafts or to allow the sideways
motion of moving elements like wheels and levers.
6 Couplings (Kupplungen)
The main purpose of a coupling is to transmit the torque from one shaft to
another shaft (or to another drive element). There are many types of couplings.
(a) Rigid coupling (b) Universal joint
Fig 5.12 Some Couplings
6.1 Rigid couplings (Starre Kupplungen)
Rigid couplings make a firm connection between a shaft and another drive
element. One form of rigid coupling is shown in Fig 5.12 (a). One of the shafts
has a cylindrical projection which fits into a corresponding cylindrical recess
on the other shaft. The shafts can be screwed together to be friction tight. When
the coupling has to be disconnected, the shafts must be moved apart in the axial
6.2 Flexible inelastic couplings (Flexible unelastische Kupplungen)
These are required to connect shafts which are misaligned laterally or
angularly. Universal joints (Gelenkkupplungen) can be used where very large
misalignments are present, and are particularly useful for connecting the engine
of a vehicle to the final drive axle. Two such joints are usually coupled through
sliding splined drive shafts, to allow both longitudinal and lateral movement of
the axle relative to the engine. One type of universal joint is shown in Fig
136 V Machine elements
6.3 Elastic couplings (Elastische Kupplungen)
Elastic couplings can tolerate considerable misalignment in the radial and
axial directions. They are also helpful in damping out vibrations. They are
most often used in compressors and pumps where sudden variations in
torque are experienced. Rubber parts and leaf springs are used as elastic
6.4 Clutches (Schaltbare Kupplungen)
Clutches are used when the coupling between the two shafts needs to be
engaged and disengaged, even when the shafts are rotating.
6.4.1 Claw-type clutches (Klauenkupplungen)
These clutches have two sets of claws which grip each other when the clutch
is engaged. No additional force is required to keep the clutch in the engaged
position when the shafts are coupled together. They have square jaws when
driven in both directions, or spiral jaws when driven in one direction.
6.4.2 Friction clutches (Kraftschliissige Schaltkupplungen)
Friction clutches reduce the coupling shock experienced, when engagement
takes place. They also slip when the torque exceeds a certain value, thereby
acting as safety devices. Single or multiplate clutches are available, and they
can be operated mechanically or electrically.
7 Belt and chain drives (Riemen- und Kettengetriebe)
7.1 Belt drives (Riemengetriebe)
These are friction drives which are used to transmit torque between two or
more shafts. They have many advantages some of which are:
• Shafts which are not parallel can also be included in a belt drive
• The transmission of torque is possible even at high speeds.
• They are elastic drives which help to dampen speed variations,
vibrations and noise.
• No lubrication is required.
Disadvantages are that:
• Some slip usually takes place with flat, V-belt or round belt drives.
• The high belt tension results in the bearings of the shaft being heavily
7.1.1 Some types of belts and pulleys (Riemen und Scheibenarten)
• Flat belts are made out of leather, or out of several layers of leather,
canvas and synthetic material.
• Textile belts are endless belts made of woven polyester or polyamide.
They operate with a minimum of vibration and noise and are
particularly suitable for driving internal grinding spindles.
7 Belt and chain drives 137
• Pulleys for flat belts (Riemenscheiben fur Flachriemen) are made of cast
iron, steel, light alloy or plastic. The surface of the pulley has to be
smooth, otherwise the slip in the belt causes the wear to become too
great. The outer surface of the pulley is slightly rounded to ensure that
the belt always remains in the centre.
• V-belts (Keilriemen) are endless belts with a trapezoidal cross-section,
and are made of rubber reinforced with polyester fibres. In flat belt drives,
the friction acts between the inside surface of the belt and the outside
surface of the pulley. The friction in V-belt drives acts between the outer-
side surfaces of the belt, and the inner-side surfaces of the pulleys.
• Ribbed V-belts (Mehrrippenkeilriemen) distribute the load uniformly
across the belt. They are used for widely separated axes and heavy loads.
7.1.2 Toothed belt drives (Zahnriemengetriebe)
The transmission of torque in toothed belt drives does not take place through
friction, but through the meshing of the teeth in the V-belt with the teeth in
the pulley. Toothed V-belt drives combine the advantages of flat or ordinary
V-belt drives with the slip-free operation of the chain drive. Toothed belt
drives are characterized by low belt tensioning and a consequent lowering of
the load on the bearings. They are particularly useful for shafts which need
to have an exact timing relationship between each other, as in the case of the
crankshaft (or the camshaft) of an internal combustion engine.
7.2 Chain drives (Kettengetriebe)
The transmission of torque and power from one shaft to another can also be
accomplished through chain drives. In this type of drive, special toothed
wheels called sprocket wheels are mounted on the shafts and an endless
chain is stretched over them. Some of the advantages of chain drives are:
• High efficiencies of 98 to 99 % even at low speeds.
• No slip takes place, and no initial tension is required.
• Chains can move in either direction.
• Heavy loads of up to 200 kW per chain are possible even at low
• Chains can link several shafts which are spaced wide apart.
• Idler sprockets can be used on either side of the chain. These can
compensate for slack, guide the chain round obstructions, or change
the direction of rotation of the shaft.
• Increased loads can be handled by using multiple chains.
Disadvantages are that with small numbers of teeth in the sprocket a polygon
effect is experienced, which hinders smooth operation of the drive. Speed
variations, noise and vibrations are the result. This effect can be reduced by
having more teeth and using multiple chain drives. The life of a chain is reduced
by inadequate lubrication, accumulation of dirt, shocks and vibrations.
138 V Machine elements
8 Bearings (Lager)
Bearings act as supports and guides for axles and shafts. Bearings are of
different types and can be classified according to their function.
1. Cylindrical journal bearings (Radiallager) which carry a rotating shaft
and have to resist radial forces.
2. Thrust bearings (Axiallager) which have to resist axial forces and
prevent longitudinal motion of the shaft.
3. Guide bearings (Fuhrungen) which guide a machine element along the
length of a machine without causing any rotatory motion of the machine
8.1 Plain bearings (Gleitlager)
In a plain bearing the shaft rotates in a
shell or a bush. In Fig 5.13 is shown how Gudgeon pin
a bush (gudgeon pin) and split shell
bearings are used in the connecting rod
of an automobile engine. Frictional forces
arise between the shaft and the bearing
and these must be kept to a minimum.
The frictional forces are minimized by
lubrication, a term which refers to the
process of maintaining a thin film of oil
between two surfaces which slide past
each other. Two types of lubrication are
normally used hydrodynamic lubrication Fig 5.13 Split shell bearings and
and hydrostatic lubrication. a gudgeon pin
8.2 The lubrication of plain bearings (Schmierung der Gleitlager)
8.2.1 Hydrodynamic lubrication (Hydrodynamische Schmierung)
In bearings which use the process of hydrodynamic lubrication, the oil film is
generated by the rotational motion of the shaft. When the shaft begins to rotate,
the two surfaces are not fully separated by an oil film. As the speed of rotation
increases, the oil which is in the unloaded side of the bearing will be forced into
the region where the gap between the surfaces is narrow. The increasing oil
pressure in the gap moves the shaft, thereby increasing the space between the
surfaces. This results in improved lubrication and a consequent reduction of the
frictional forces.
8.2.2 Hydrostatic lubrication (Hydrostatische Schmierung)
In bearings which have hydrostatic lubrication, oil is pumped into oil pockets in
the bearing. The oil flows from these pockets into the narrow gaps between the
surfaces. The oil pressure in the gap ensures that the shaft and the bearing are
not physically in contact with each other.
8 Bearings 139
8.2.3 Air lubricated bearings (Gleitlager mit Luft als Schmierstoff)
Lubrication with air as the lubricating medium (or lubricant) is used in special
applications like for example in measuring instruments. The frictional forces in
such bearings are extremely small.
8.2.4 Other methods of lubrication (Andere Schmierungsarten)
Bearings are provided with oil at low feed rates by such devices as wicks, felt
pads and drop-feed oilers. Another method of oiling is ring oiling, in which a
ring dips into an oil reservoir and rotates round the shaft, smearing it with oil.
8.2.5 Lubrication-free bearings (Wartungsfreie Gleitlager)
Among the bearings that do not need lubrication are:
• Bearings made of synthetic and plastic materials.
• Sintered material bearings which are impregnated with lubricant during
• Bearings with special layers which contain a solid lubricant.
8.3 Bearings with rolling elements (Walzlager)
Rolling-contact bearings have a number of rolling elements like steel balls or
steel cylinders which roll between an outer and an inner ring. Cages are used to
maintain a fixed distance between the rolling elements. The friction is less than
in a plain bearing. Particularly advantageous is the low friction at slow speeds
and when starting.
Among the rolling elements used are balls, cylindrical rollers, tapered rollers
and needle rollers. The rolling elements can be arranged in single or double
rows. The rolling elements and the surrounding rings are usually made of
hardened steel. Other materials like stainless steel, ceramics, Monel (a nickel
alloy) and plastics are used when corrosion has to be prevented. The advantages
and disadvantages of bearings with roller elements in comparison with plain
bearings are as follows:
Advantages Disadvantages
1. High load capacity at low speeds. 1. Sensitivity to dirt, contamination.
2. Low friction losses. 2. Sensitivity to shocks.
3. Low lubrication requirements. 3. Limited life and maximum speed.
4. Easy interchangeability due to 4. Relatively high level of noise
size standardization. generated.
5. Compensation for the bending of 5. Smaller load capacity for the same
shafts by the use of self-aligning size of bearing.
8.3.1 Ball bearings (Kugellager)
(a) Deep-groove or single row radial bearing (Rillenkugellager)
These are available as single (Fig 5.14(a)) or double row arrangements, and with
single or double row shields or seals. They are used for both radial loads, and
axial (thrust) loads of (up to 60 % of radial loads). Can be used at higher speeds
140 V Machine elements
than is possible with other types of bearings. These are the cheapest types of
bearings for the same load.
(b) Angular contact bearings (Einreihiges Schragkugellager)
These are suitable for use with combined radial and thrust loads or heavy thrust
loads in a single direction (Fig (5.14(b)). Should be used in pairs mounted as
mirror images of each other. The pairs are referred to as duplex bearings.
(c) Double row angular contact bearings (Zweireihiges Schragkugellager)
In this bearing, a pair of angular contact bearings are mounted in such a way that
they are mirror images of each other (Fig 5.14(c)). This may be considered to be
a composite duplex bearing.
(d) Internal self-aligning double row bearings (Pendelkugellager)
These bearings can be used for radial and axial (thrust) loads (Fig 5.14(d)).
These are self-aligning bearings which can withstand slight axial and angular
(a) Single row (b) Angular (c) Double row
radial contact angular contact
bearing bearing bearing
Fig 5.14 Different types of ball bearings
8.3.2 Roller bearings (Rollenlager)
(a) Cylindrical roller bearings (Zylinderrollenlager)
These bearings (Fig 5.15(a)) can be used with heavy radial and light thrust
loads. They can be used with large diameter shafts and have the highest speed
limits for roller bearings.
(b) Tapered roller bearings (Kegelrollenlager)
These bearings (Fig 5.15(b)) can be used with heavy radial and thrust loads.
They are only used in pairs arranged as mirror images of each other. They are
also available in double row form as duplex bearings.
(c) Spherical roller bearings (Pendelrollenlager)
These bearings (Fig 5.15(c)) have a self-aligning capability which enables them
to compensate for any bending or misalignment of the shaft. They are excellent
for heavy radial and moderate thrust loads.
(d) Needle bearings (Nadellager)
The rolling elements in these bearings (Fig 5.15(d)) are long in comparison to
their diameter and are very useful where space is a factor. They can be used
with or without an inner race. If used without an inner race, the shaft has to be
hardened and ground. They cannot be used for axial (thrust) loads.
9 Gears 141
1 -J-
(a) Cylindrical roller (b)Tapered roller (c) Spherical roller (d) Needle bearings
bearing bearing bearing
Fig 5.15 Different types of roller bearings
8.3.3 Thrust bearings
(a) Axial thrust ball bearings (Axial-Rillenkugellager)
These can only used with axial loads and with shafts which are perpendicular to
the bearing. A ball bearing for unidirectional loads is shown in Fig 5.16 (a).
Fig 5.16 (a) Axial thrust ball bearing (b) Axial thrust roller bearing
(b) Axial thrust roller bearings (Axial-Pendelrollenlager)
These bearings shown in Fig 5.16(b) are self-aligning and can compensate for
small shaft misalignments.
9. Gears (Zahnrader)
The coupling of two shafts which are rotating at the same speed or at different
speeds can be achieved in many ways. One way is by the use of gears or (gear
wheels), which are wheels with teeth cut in them. The ratio of the speeds of
rotation of the shafts is dependent on the ratio of the number of teeth in the
wheels. Both parallel and nonparallel shafts can be coupled by gear wheels.
9.1 Spur gears (Stirnrader mit Geradverzahnung)
Spur gears are the most commonly used types of gears and have teeth cut
parallel to the gear's axis of rotation. They are used to couple shafts which are
parallel to each other. The smaller wheel is called the pinion and the larger
wheel the gear. The teeth have involute profiles. Cycloidal teeth are used in
precision mechanical clocks, but not in gears used for the transmission of
power. Spur gears can have internal and external teeth as shown in Fig 5.17 (a)
and (b).
9.2 Helical gears (Stirnrader mit Schragverzahnung)
The teeth of a helical gear lie on a cylinder and are cut at an angle to the axis of
rotation of the gear (Fig 5.18(b)). The teeth on helical gears mesh with each
other progressively, and are therefore smoother and quieter in action than the
teeth on spur gears. A further advantage is that the life of the gears is longer for
the same loading than that of equivalent spur gears.
142 V Machine elements
Helical gears produce an axial thrust which is not present in spur gears and
provision has to be made to take this by using thrust collars or axial thrust
bearings. Involute profiles are usually used for helical gears.
Double helical (or herring bone) gears do not exert a thrust load and are
quieter in action. Helical gears are quite efficient although their efficiency is
lower than that of spur gears. They can be used to couple both parallel and
nonparallel shafts. They are very often placed in an oil bath as in the case of an
automobile gear box, so that the wear on the teeth will be a minimum.
9.3 Bevel gears (Kegelrader)
Bevel gears are most often used to couple shafts which are at right angles to
each other (Fig 5.18(a)). The teeth of these gears do not have an involute
profile. The teeth lie on a conical surface and the apex of the pinion and the
mating gear intersect at the point at which the axes of the gear shaft and the
pinion intersect. All types of bevel gears exert thrust and radial loads on their
support bearings in addition to the tangential loads which they transmit.
9.4 Worm and worm gears (Schneckengetriebe)
Worm gears are used for heavy duty work where a large reduction in speeds is
required (Fig 5.18(c)). They are used to couple shafts which are at right angles
to each other. The driving wheel is called the worm and the driven wheel the
worm gear. The worm has a form which is similar to the screw thread of a
cylindrical bolt. The screw thread meshes with the teeth on the worm gear
(wheel). The teeth on the worm wheel are cut at an angle to its axis of rotation.
9.5 Rack and pinion (Zahnstangengetriebe)
In this device, a flat piece of metal with teeth cut on it and called the rack,
meshes with a spur gear called the pinion (Fig 5.17 (c)). Rotation of the pinion
causes the rack to move in a straight line. This is an example of the conversion
of rotatory motion into linear motion. The drill feed mechanism of a drilling
machine uses a rack and pinion, as does the coarse feed mechanism of an
optical microscope.
9.6 Gear boxes (Zahnrad-Stufengetriebe)
It is quite often necessary to repeatedly change the ratio of the speeds of
rotation of two shafts called the gear ratio. Such changes are done in several
stages through several pairs of shafts and gears. A gear assembly which does
this smoothly and efficiently is called a gear box (Fig (5.18(d)). Gear boxes are
an integral part of machine tools and automobile engines. It must be noted that
only a few selected gear ratios can be obtained in this way. Intermediate values
of gear ratio cannot be obtained.
9.7 Continuously variable speed drives (Stufenlose Getriebe)
Drives in which the ratio of the output speed to the input speed can be varied
continuously cannot be constructed using gear wheels. However other types of
continuously variable speed drives are available. Among these are friction
drives, hydrostatic drives and electrical drives.
9 Gears 143
-— Centre distance
Fig 5.17(a) Spur gears
Fig 5.17(b) Involute epicyclic gearing Fig 5.17(c) Rack and pinion drive
144 V Machine elements
Fig 5.18(a) Bevel gears Fig 5.18 (b) Helical gears
Fig 5.18 (c) Worm and worm gear Fig 5.18 (d) Gear box fitted to a lathe
VI Joining processes (Verbindungsarten)
1 Adhesive bonding (Klebverbindung)
Materials which cannot be soldered or welded can be bonded by the use of
adhesives. This is usually better than using metal fasteners. Adhesives are used
to bond metals to nonmetallic materials like plastics, glass, wood, porcelain,
etc., or where welding is detrimental to the properties of the material. It is
particularly useful with very thin materials, which cannot be joined by welding
or with the help of metal fasteners. Adhesive bonding offers great advantages in
aircraft construction, because by using the method of sandwich construction,
very light components with excellent stiffness properties can be produced.
1.1 Adhesives (Klebstoffe)
The adhesives used are either phenol resins or epoxy resins. Sometimes rubber
dissolved in a solvent is also used.
1.1.1 Contact adhesives (Kontaktklebstoffe)
These adhesives based on rubber solutions are applied both surfaces. The
surfaces are exposed to air for a short time and then pressed together.
1.1.2 Resin based adhesives (Klebstoffe auf Kunstharzbasis)
These are usually composed of two components, a binder and a catalyser. The
two are mixed in equal parts just before use. The mixture is first applied to the
two surfaces which have to be joined, after which the two surfaces are pressed
together. It takes some time for the adhesive to harden, and the hardening time
can be shortened by increasing the temperature, or by adding an accelerator as a
third component to the mixture.
Cold-hardening adhesives harden at room temperature, while warm-hardening
adhesives harden only at high temperatures. There are also slow-hardening
adhesives as well as fast-hardening adhesives, which can both be used at room
1.2 Preparation of surfaces for bonding (Vorbehandlung der Oberflachen)
An adhesive bond can only be strong and effective when the surfaces to be
bonded are clean and free of oil and fat. Removal of dirt, oxide and paint
remnants can be done by chemical or mechanical methods. Chemical methods
have been said to produce better bonding in aluminium, magnesium and copper
alloys as also with glass and ceramics. Removal of fat, oil and wax is done by
using chemicals like perchloroethylene, methylchloride or acetone. Etching
particularly on metal surfaces is done by using dilute sulphuric acid.
1.3 The bonding process (Klebverbindungsprozess)
It is important to spread the adhesive evenly over the surface. When using a
rubber solution as an adhesive, the time at which the surfaces are brought
together under pressure after exposure to air is important for the strength of the
bond. With the other adhesives only one surface needs to be smeared with
adhesive. The surfaces can be brought together immediately thereafter.
146 VI Joining processes
2 Soldering (Loten)
Soldering is a process which is used to join two pieces of metal by a third metal
alloy called solder. The solder should have a lower melting point than the
objects being soldered. Some of the requirements and features of the process are
the following:
1. The solder is melted during the soldering process, but the metals being
joined are not melted unlike in welding, where localized melting takes
2. A solder must have the ability to wet the surfaces being joined, which
means that it is able to form an alloy with the metals. At the same time,
the solder must melt at a temperature well below the melting points of the
metals which are being soldered. Alloys of tin and lead satisfy these
requirements, because tin alloys readily with iron, with the copper alloys
and with lead. At the same time, tin-lead alloys melt at temperatures
between 183°C and 250°C, well below the melting points of the metals to
be joined.
3. A soft soldered joint lacks mechanical strength. It is desirable that the
objects to be joined be fastened to each other securely by flanging,
folding, twisting, spot welding, etc., to give the joint sufficient mechanical
strength. Soldering makes a joint gas-tight and water-tight. It also ensures
good electrical contact.
4. When two metal objects are joined to each other before soldering, there is
usually a gap between the surfaces into which the solder must flow. Only
then are the capillary forces large enough to make the solder flow into the
5. The working temperature of a solder is the temperature at which the
solder wets, flows, and alloys with the metal surface. The solder must be
in liquid form and not in the form of a paste. A good soldered joint is only
possible if those parts of the metal objects to be soldered and the solder
are all heated to the working temperature of the solder during the
soldering process.
6. Before soldering, it is necessary to clean the surfaces of the objects to be
soldered to remove fat, oxides and other substances like remaining paint,
etc. This is first done by scrubbing or other mechanical methods if
necessary. Further cleaning is done by coating the surfaces with a flux
before soldering. These are substances which clean the surfaces, and are
of two types, the first being acidic flux which is corrosive, and the second
being resin which is noncorrosive. The fluxes used in the workshop are
strongly acidic in character. Commonly used types are hydrochloric acid,
zinc chloride and acid paste. For electrical work a noncorrosive flux like
resin is required. The solder is usually in the form of a wire having a core
of resin.
2 Soldering 147
2.1 Soft soldering (Weichloten)
The working temperature for soft soldering is below 450°C. The parts to be
soldered and the solder are brought into contact and heated to the required
temperature. Heating may be carried out in many ways. A soldering iron is used
in sheet metal work and also in electrical work. The tip is made of copper and is
heated by electricity or gas. The copper tip conducts the heat quickly to the
soldering point which is heated together with the solder. The solder flows into
the joint and solidifies when the iron is removed. Other ways of heating are by
using a gas flame, by using an oven, by floating in a bath of molten solder, by
induction heating, etc. The solder may be fed into a joint by hand or placed on
the joint before soldering in the form of washers, rings, sheets, shims,etc.
3 Brazing (Hartloten)
Brazing is preferred to soldering when a tougher, stronger joint is required.
This is a versatile process and can be used to join virtually all metals. The
temperatures used for brazing are above 450°C, but below the melting temperat-
ures of the metals to be joined. Here again cleanliness of the surfaces is
essential, and the fluxes used are of the borax or fluoride type.
The types of solder used are (1) brazing solder (or spelt) which are copper-zinc
alloys (of the brass type) and (2) silver solder which is an alloy of silver, copper
and zinc. Silver solder has lower working temperatures of between 610°C and
For joining steel components, the brass (copper-zinc) type brazing solder is
used, while silver solder is used for metals like copper, brass and silver. The use
of a gaseous atmosphere to protect the components being brazed from oxidation
is often necessary. There are many ways of carrying out the brazing process.
Among these are dip brazing, furnace brazing, resistance brazing, etc.
4 Welding (Schweipen)
Welding is the term applied to a process of the joining of metals, by heating to
temperatures high enough to cause localized melting of the metals at the joining
points. This process may be carried out with or without the use of filler metals,
and with or without the use of pressure. This is different from soldering or
brazing, where any melting of the base metals does not takes place. Welding
produces strong joints which are almost as strong as the base metal, except in
cases of fatigue loading.
Many types of joints are possible. Among these are butt joints, tee joints (fillet
joints), lap joints, corner joints, etc. Examples of these are shown in Fig 6.1.
There are many types of welding processes and it is possible to group them in
many ways. Here they have been divided into two groups (1) Fusion welding
processes and (2) pressure welding processes.
4.1 Fusion welding (Schmelz-Schweipen)
In fusion welding processes, metals are joined by melting them locally at the
joining points without using pressure. A filler metal may or may not be used.
148 VI Joining processes
(1) Butt joints
(a) Square groove (b) Single V-groove (c) Single U-groove
(2) Fillett joints
(a) Single joint (b) Double joint
(3) Lap joints
(a) Single weld (b) Double weld
Fig 6.1 Some types of welded joints
4.1.1 Oxy-acetylene welding (Gasschmelzschweipen)
In oxy-acetylene welding, a mixture of oxygen and acetylene is burned in a
blowpipe. The temperature can be controlled varying the amounts of by gases
flowing through the pipe. The flame produced can exceed a temperature of
3000°C. This is well over the melting points of the metals being welded. The
regions of the metals at the joint melt, and mix with each other. The joint is
made stronger by the melting of a filler rod which is held close to the joint. A
small pool of metal is formed at the joint, and this pool solidifies when the flame
is removed forming a strong joint. The process is illustrated in Fig 6.2.
4.1.2 Electric arc welding (Metall-Lichtbogenschweipen)
In electric arc welding, an arc is maintained between the metals to be welded
and an electrode, or between two electrodes. Both direct and alternating
currents may be used. An alternating current welding installation uses a
transformer to supply the welding current. The transformer changes the high
voltage low current input from the mains supply, to a low voltage high current
source at the output terminals which are used for welding. The current flows
through Hat filler rod which also acts as an electrode.
The arc is produced between the tip of the filler electrode and the metal. Here
again the temperature can be above 3000°C, and small portions of the metal and
the filler rod are melted. Movement of the electrode causes the deposition of a
pool of metal along the path of the electrode. The type of set-up used is shown
in Fig 6.3.
4 Welding 149
Filler rod
Fig 6.2 Oxy-acetylene welding
6.3 Electric arc welding
150 VI Joining processes
4.1.3 Disadvantages of bare metal electrodes
(Nachteile der ungeschutzten Elektroden)
The welds produced by arc welding are considerably weakened by the
absorption of atmospheric oxygen and nitrogen. The absorption of atmospheric
gases makes the weld brittle and porous, and this is further worsened by the
rapid cooling of the molten metal. If the electric arc, the tip of the electrode and
the pool of molten metal can be shielded from the atmosphere, a much stronger
weld can be produced.
4.1.4 Shielded arc welding (Pulver-Schwei(3en)
In this type of welding, the metal electrode is covered with a coating. The
coating is a flux which has a higher melting point than the electrode. The
coating extends beyond the tip of the electrode during the welding process. The
melting of the flux coating produces a gaseous shield, which protects the weld
from atmospheric gases. In addition the melted coating forms on solidification,
an insulating layer of slag on the surface of the weld. This layer allows the weld
to cool slowly. An added advantage is that the vapourisation of the electrode is
reduced by the shielding effect, which results in a more economical use of the
welding electrode.
Welds produced by this process are strong, reliable and ductile. The automatic
welding of steel parts is possible by this process. Other applications are in the
welding of mild and alloy steels, stainless steels, and to a lesser extent in the
welding of nonferrous metals.
4.1.5 Submerged arc welding (Unter-Pulver-Schwei|3en)
This process is particularly suitable for the production of long continuous
welds. Flux in the form of powder is used, and is fed in front ofamoving head
which carries a bare wire coil which is the electrode. The flux has good heat
insulation and high electrical resistance. The arc is covered by the powder and is
completely isolated from atmospheric gases. The arc is also not visible. A slag is
built up above the weld, and this isolates it from atmospheric gases and
promotes slow cooling of the weld. The unused powder is sucked out and
reused. This is an efficient process which lends itself to automation. It is useful
for welding sheets of plain and alloy steels from 2 mm to 150 mm in thickness.
4.1.6 Welding using an inert gas shield (Schutzgasschwei(3en)
Welding is carried out in an inert gas atmosphere as a protection from
atmospheric gases. There are two types of inert gas processes, the tungsten
electrode process which uses a tungsten electrode that does not melt and the bare
wire electrode process which uses a wire electrode as a filler.
(a) The tungsten electrode process (Wolfram-Inertgas-Schweipen)
This process can be used with direct or alternating current supplies. Direct
current is used to weld alloy steels and also nonferrous metals and their alloys.
The bare tungsten electrode is surrounded by a tube through which argon gas
flows. The argon gas forms an inert shield which gives protection from the
4 Welding 151
atmosphere. A filler rod is used to improve the weld. As no flux is used, no slag
is formed resulting in a clean weld.
(b) The wire electrode process (Metall-Schutzgasschwei(3en)
In this process, an arc is formed between the metal parts being welded and a
metal wire electrode which also acts as a filler. The electrode melts and this
adds to the pool of metal formed by the melting of the base metals. Argon gas
flows through a tube which surrounds the wire forming & protective shield. The
wire is fed from a reel and the feeding rate is automatically controlled, so that
the gap of the arc between the tip of the wire and the parts being welded is kept
constant. The whole unit is mounted on a moving head which travels
automatically along the path of the weld. Long continuous runs can be achieved
using this process. This method is particularly useful for the production of clean,
slag-free welds in components made from stainless steel and nonferrous metals.
4.1.7 Electron beam welding (Elektronenstrahlschwei(3en)
In this process a filament of a metal like tungsten is heated to emit electrons.
The electrons are accelerated towards an anode which has a high positive
voltage relative to the filament. The number of electrons reaching the anode can
be controlled by a grid whose potential can be varied. The electrons pass
through a hole in the anode and then through a focusing coil and various
deflecting coils before reaching the workpiece. On striking the workpiece, the
kinetic energy of the electrons is transformed into heat which melts the portions
of the metal to be welded. The set-up has to be operated in a high vacuum to
prevent oxidation of the filament.
The extremely high energy density of the electron beam is effective in
producing narrow deep welds at high speed with minimum distortion. The welds
made are said to be stronger than those made by other welding processes. The
welds are also very pure, because they are made in a vacuum.
Disadvantages are the difficulty of aligning the beam with the joint to be
welded, and the difficulty of manipulating the filler metal in a vacuum. The cost,
complexity, and maintenance difficulties are also problems.
4.1.8 Laser beam welding (Laserschweipen)
A laser is an optical source which generates a monochromatic beam of coherent
light which usually has a very small cross-section. This highly concentrated
beam can be used as an energy source for welding. The beam is concentrated
through concave mirrors or lenses to the location where the welding has to take
A vacuum is not required for a laser welding operation, and this process has
many of the advantages of electron beam welding at a lower cost and at higher
rates of production. High speed production of narrow deep wells is possible and
complex welding operations using computer control are possible. Lasers can
also be used for cutting and scribing of metals and nonconductive materials like
ceramics. The main disadvantage is that the power output of lasers is limited.
152 VI Joining processes
4.2 Pressure resistance welding processes (Widerstandsprepschweipen)
All the processes mentioned so far produce fusion welds without the application
of pressure. In each case, a liquid pool of metal was formed between the two
parts to be joined, with the further addition of more liquid metal by the use of a
filler rod or an electrode. The process is continued along the joint and on
cooling the liquid metal solidifies and the two parts are welded together.
In pressure resistance welding, an electric current is made to flow through a
circuit of which the workpiece is a part. The resistance of the circuit is a
maximum at the interface of the parts being joined, and the heat generated is
sufficient to cause a local fusion of the metal. The parts to be welded are pressed
together at the same time, and a welded joint is produced without the use of a
filler material.
4.2.1 Spot welding (Punktschweipen)
In spot welding, metal sheets are held together under pressure and joined
permanently by welding them at individual spots. The size and shape of the
welds are controlled by the size and shape of the electrodes which are usually
circular. This method is usually used for welding thin metal sheets. The speed of
welding can be improved by using machines with multiple electrodes. This is a
cheap, rapid and efficient technique and each spot weld takes only a few
seconds to carry out. A typical set-up for spot welding is shown in Fig 6.4.
4.2.2 Seam welding (Rollennahtschweipen)
Seam welding is used when air-tight or water-tight seams are required. This is
achieved by making a succession of spot welds in such a way that the welds
overlap. The process is illustrated in Fig 6.5. The welding current is applied
intermittently by using timing devices while the sheets are pressed together by
revolving circular electrodes. The process is continuous and results in welds,
each weld overlapping its neighbours. Stitch welds can also be made using the
same equipment. Stitch welds are a series of welds separated by a constant
distance as shown in Fig 6.5.
4.2.3 Butt or upset welding (Abbrennstumpfschweipen)
This process is used to weld pieces of metal having approximately the same
cross-section. A good example is in the construction of a lathe tool. There is no
reason why the entire tool should be made of high speed steel, and a cheaper but
equally good tool can be made by welding two different types of steel. The
cutting end of the steel is made of high speed steel and butt welded to a shank
(or rear end) made of medium carbon steel.
Butt welding is achieved by bringing together the two parts to be joined, and
passing the welding current through the joint. When the joint reaches the
desired temperature, further pressure is applied and the welding current is
switched off. This technique can only be used with small areas of contact where
a good match between the surfaces exists. Special preparation of the surfaces
may be necessary.
4 Welding 153
Pressure Top electrode moves
away on completion
of weld
XX /
Pool of
Current on Current off
Fig 6.4 Spot welding
Pressure on circular
W\\ \\ \\ \ \ \ \ \ \ \
Seams of
± / /
\ \ \ \ \ \~\>i
/ /A
spot welds Stitch welding
Fig 6.5 Seam and stitch welding
VII Metal removal processes (Zerspanvorgange)
1 Basics (Grundbegriffe)
Metal removal processes use a metal cutting tool that moves relative to the
workpiece, and removes metal chips from it. Efficient metal removal is only
possible, if the tool has the optimum rake and clearance (or relief) angles as
shown for a lathe tool in Fig 7.10. The material which lies ahead of the tool is
sheared continuously. Chips are formed which become hard and brittle, and curl
away from the tool. Four basic types of chips can be identified.
1.1 Types of chips (Spanarten)
a) Continuous chips (Fliepspane) are long chips formed by the continuous
deformation of the workpiece ahead of the tool, and the smooth
movement of the chips along the face of the tool. Such chips are produced
when ductile materials are cut at high speed.
b) Discontinuous chips (Reipspane) are segmented chips produced by the
breaking of the metal which is ahead of the tool. Such chips are formed
when brittle materials are machined, or when ductile materials are
machined at very low speeds.
c) Serrated or inhomogeneous chips (Scherspane) have parts with large
and small strain. Chips of this type are produced when materials of low
thermal conductivity are machined. Chips produced from titanium alloys
are usually of this type.
d) Built-up edge chips (Scheinspane) arise when a piece of metal attaches
itself 'to the tool face, while the chip itself moves continuously along the
face. Such chips are produced at low speeds, and occur when there is a
large amount of friction between the chip and the tool.
1.2 Power consumption during the cutting process (Wirkleistung)
Power is consumed in the cutting process, and is mostly converted into heat.
Most of the heat is carried away by the chip, while the rest is shared between the
tool and the workpiece. The temperature of the interface between the tool and
the chip increases with cutting speed and feed. In general the use of cutting
fluids removes heat. The cooling effect of cutting fluids at the high speeds used
with carbide or ceramic tools has however been found to be negligible,
1.3 Tool wear (Werkzeugverschleip)
Wear on the tool is something that has to be compensated for. The tool wear
affects not only the tool, but also the dimensions of the machined workpiece.
Automatic compensation is effected in CNC machines, but in spite of this a
regular program for sharpening of tools is necessary. Various types of wear can
be identified on tools, like flank wear, crater wear, chipping, and the formation
of grooves called wear notches at the end of the tools.
1. Basics 155^
When metals are cut at high speeds, long spirals of chips can form and become
entangled with the tooling. Chip breakers are often introduced on the tool to
prevent this from happening. These cause the chips to break into small sections.
1.4 Materials for cutting tools (Schneidstoffe)
a) Carbon steels (Kohlenstoffstahl) are used for low speed applications.
They are inexpensive, but have largely been replaced by better types of
tool steels.
b) High speed steels (Schnellarbeitsstahl) are the most used alloy tool steels.
They have the ability to maintain their strength, hardness, and cutting
edge over long periods of time. This has led to their use in a variety of
cutting, drilling, reaming, broaching and other tools.
c) Cemented carbide (Hartmetalle) tools are made from metal carbides by
the use of powder metallurgy techniques. They have a high level of
hardness, high thermal conductivity, and low thermal expansivity. Their
elastic modulus is high, and they are not subject to plastic flow. They are
used in the form of small tips which are brazed or mechanically fastened
to a steel shank. Typical of the carbides used are tungsten carbide with
cobalt as a binder, or titanium carbide with nickel and molybdenum as
d) Ceramic or oxide (Schneidkeramik und Oxidkeramik) inserts are harder
than cemented carbides. Ceramic materials maintain their hardness and
wear resistance at temperatures of up to 1200°C. They are however brittle
and sensitive to variations in cutting forces. They are therefore used
without cooling, under conditions where cutting forces remain constant.
They can be used at higher cutting speeds than cemented carbide tools,
but are unsuitable for use with aluminium alloys. Oxides used are mainly
grains of corundum (aluminium oxide) which are bonded together by the
use of powder metallurgy techniques.
e) Polycrystalline diamond tools (Polykristalliner Diamant (PKD)) are
used where high dimensional accuracy and a good surface finish are
required. These tools are made by bonding a layer of polycrystalline
diamond on a carbide substrate. They are particularly helpful for use with
nonferrous metals which are not easy to machine with normal steel tools.
f) Polycrystalline cubic boron nitride (CBN) (Polykristallines Bornitrid)
(PKB)) is the next hardest material to diamond. Polycrystalline CBN is
bonded to a carbide substrate before being used in cutting tools. It is
useful in machining high temperature alloys and ferrous alloys. Diamond
and CBN are also used as abrasives for grinding.
1.5 Cutting fluids (Kuhlschmierstoffe)
Cutting fluids which consist of liquids or gases are allowed to flow over the tool
and workpiece to ensure smooth operation of the cutting proceses. Cutting
fluids have many functions. Among them are, keeping the work and tool cool,
ensuring lubrication which reduces power consumption and tool wear, providing
156 VII Metal removal processes
a good surface finish on the work, helping in the satisfactory formation of chips
and their removal, and preventing corrosion.
In most cases, the fluid is pumped from a sump and allowed to flow over the
cutting interface. Mist cooling is also used. In this type of cooling, water-based
fluids are dispersed as fine droplets in air.
Some of the main types of cutting fluids are the following:
a) Air drafts (Luftstrome) are used mainly to remove dust or small chips
during grinding, polishing and boring operations. A certain amount of
cooling is also obtained.
b) Emulsions (Wassermischbare Kuhlschmierstoffe) are produced by emuls-
ifying a soluble oil with water. The ratio of the oil to water is between 1 to
10 and 1 to 100. Emulsions contain additives, which reduce friction and
provide effective lubrication at the interface between tool and chip in a
machining operation. These are low cost cutting fluids, which are used for
practically all types of cutting and grinding operations.
c) Lubricating oils (Mineralolhaltige Kuhlschmierstoffe) are also used in
metal cutting operations. They are used in cases where lubrication is
more important than cooling. The oils usually used are mineral oils with
varying proportions of fat, sulphur and chlorine.
d) Solutions (Mineralolfreie Losungen) are cutting fluids which contain
various chemical agents such as amines, chlorine, nitrites, nitrates,
phosphates etc, in water. Most of these fluids are coolants although some
are lubricants.
2 The use of hand tools for metal removal
(Spannende Formgebung von Hand)
Most of the metal components and objects manufactured today are mass
produced using machines. However it is nearly always necessary to use hand
tools/or repairs, and also for the creation of models and prototypes.
2.1 Marking-out process (Vorbereitung durch AnreiBen)
Before work can be started on a piece of metal, it is usually subjected to a
marking-out process. In this process, suitable lines are scribed on the surface of
the metal, to help and guide the person who is working on the metal. Some of
the marking out tools are shown in Fig 7.2 (b).
The work is carried out on a very flat and level table which is made of cast iron
or hard stone. The lines are drawn on the surface using a hard scriber. Scribing
blocks, vernier height gauges with scriber inserts and other devices are used in
this process. Centre punches are used to mark points, and dividers are used to
scribe circles.
2.2 Holding and clamping devices (Spannelemente)
When working on a metal by hand, it is necessary to use devices which hold the
metal workpiece firmly in place. A vice holds an object firmly between its jaws
while work is being done on it. Other holding devices are toolmaker's clamps,
vee-blocks and angle blocks (See Fig 7.2 (a)).
2 Hand tools 157
Cylindrical rods and pipes are held in vee-blocks while work is being done on
them. Angle blocks have two faces at right angles to each other, and are used
when the position of the work has to be changed by 90°.
2.3 Measuring devices (MePgerate)
Measuring devices are required during the marking-out process, and also for
checking the dimensions of the work when it is finished. Vernier calipers can be
used to measure internal, external and depth dimensions to an accuracy of 1/100
cm. Micrometers are more accurate than vernier calipers, and can be used to
make similar measurements. Inside and outside calipers can be used to check the
dimensions of an object while machining is being done on it. Try squares are
used to check if two surfaces axe perpendicular to each other (Fig 7.2 (a) & (b)).
2.4 Hand tools (Handwerkszeuge)
Chisels are of many types and are used for removing metal from an object as
well as for shearing metal into two or more parts. Chisels can also used for work
on wood and other materials.
Saws are used to cut metals as well as other materials. Their construction
depends on the materials on which they are to be used. Hand saws are of many
types and include wood saws for cutting wood, hack saws for cutting metal, and
slitting saws for cutting slots in screw heads. Machine driven saws like hack
saws, band saws and circular metal saws save time and labour.
Files of various shapes are used for metal removal, and available types range
from coarse to fine. Scrapers can be used to remove very small amounts of
metal when a very flat surface is required.
Hammers are used for many purposes like shaping metal, hammering nails,
driving a chisel, etc. A hammer with a head made of wood or other soft material
is called a mallet.
Punches are of various types. A centre punch is used to mark a specific point
on a piece of metal. A pin punch is used to drive-in or remove pins and keys.
Drift punches are used to align two or more pieces of metal which are to be
joined together by bolts or rivets.
Taps are used for cutting internal screw threads, and dies are used for cutting
external screw threads. A tap and a tap wrench which holds the tap when it is
being turned to cut the thread are shown in Fig 7.1(b). Also shown are a circular
split die and a die stock (or holder) for the die.
2.5. Screw drivers, spanners and keys (Schraubenzieher und Schliissel)
Screw drivers are used to turn screws, which have a slit cut in their head. Offset
screw drivers are used for turning screws in awkward places. Pliers are used for
holding, gripping, turning, etc. A spanner or a wrench is a tool used for turning
nuts and bolts. There are many types of spanners like the ring spanner, socket
spanner, double-ended spanner, etc. Keys are special tools used for turning
screws. They can be inserted into slots which have been cut into the head of a
screw, after which the screw can be rotated. A screw with a hexagonal slot in its
head can be turned with a hexagonal key.
158 VII Metal removal processes
Rake angle
/ . /Point angle
Clearance angle
Chisel angles Flat chisel
B Mallet
Centre punch Offset screwdriver
Drift punch Pin punch
Fig 7.1 (a) Some hand tools
2 Hand tools 159
Ring Spanner Pliers
Tap holder Tap
Die holder Die
Fig 7.1 (b) Some hand tools
160 VII Metal removal processes
Vee-block Try square
Angle block Toolmaker's clamp
Fig 7.2 (a) Some clamping devices and a try square
2 Hand tools 161
Vernier height gauge Scribing block
Inside calipers Outside calipers
Fig 7.2 (b) Some marking-out and measuring equipment
162 VII Metal removal processes
3 Drilling, sinking and reaming (Bohren, Senken und Reiben)
Drilling, sinking , thread cutting and reaming are metal removal processes which
use multi-point cutting tools. Drilling machines may be used to carry out a large
variety of operations such as:
(1) Drilling (2) Boring (3) Counterboring (4) Countersinking (5) Reaming
(6) Grinding (7) Spot facing (8) Lapping (9) Tapping
3.1 Drilling and boring (Bohren und Aufbohren)
Precise drilling of a hole of the required size at the right location is not an easy
task. Accurate drilling of holes can be ensured by using jigs and fixtures. The
manufacture of jigs and fixtures requires extra care and precision and can only
be achieved by using specially designed machines \\kzjig borers.
A hole can be roughly drilled in a given location by first marking the location by
hand with a centre punch and then drilling at this location. A centre drill is first
used to drill a small hole, after which a twist drill is used to enlarge the hole to
the required size.
Precision drilling using a jig borer involves first clamping the workpiece on a
compound table which has two movements at right angles to each to each other.
The work is moved by using the lead screws on the compound table until the
position of the hole is precisely located under the drilling head, after which the
drilling can be done.
3.1.1 Twist drills (Spiralbohrer)
Twist drills are the most widely used types of drills. They are made from a
cylindrical piece of high speed steel. They consist of three main parts (a) the
body which is the cutting unit (b) the shank which is the part gripped by the
drilling machine chuck and (c) the tang which is found only in large tapered
shank drills (Fig 7.3 &Fig 7.4). Small drills have straight shanks which are held
in a self-centering chuck. Large drills have tapered shanks with a tang and are
directly inserted into the spindle of the drilling machine. Twist drills have two
spiral flutes which run along the body of the drill and also two lips or cutting
edges. To ensure that holes of the proper size are drilled, the drill should be
precisely ground so that (a) both lips have the same inclination to the drill axis
and (b) both lips have the same length. Centre drills (Fig 7.7) are small drills
with stiff points which are used to start a hole before a twist drill is used. Holes
produced by a twist drill are slightly oversized and have a rough inner surface.
3.1.2 Drills with inserted bits (Bohrer mit Schneidplatten)
Drills with inserted bits have a holder in which a tip of cemented carbide or
other hard material is clamped.
3.1.3 Boring bars (Bohrstangen)
Boring bars have inserted tips of hard material. The diameter of the hole that
can be bored is adjustable.
3.2 Reaming (Reiben) Reaming is a finishing process used to ensure that a hole
has the right size. The hole is drilled slightly undersize and then enlarged to the
correct size by using a reamer which removes only a small amount of metal.
3 Drilling, sinking and reaming 163
Fig 7.3 Parts of a twist drill
1. Slots for inserting
drifts, 2. Drill spindle,
3. Sleeve, 4. Drill
Fig 7.4 Drill, sleeve and spindle Fig 7.5 One type of machine reamer
164 VII Metal removal processes
Fig 7.6 Counter boring tool with Fig 7.7 A centre drill
typical application
60' 90c
Counterhead screw Rivet
Fig 7.8 Countersinking tool with typical application
3 Drilling, sinking and reaming 165
3.3 Counterboring and countersinking (Zylindersenken und Kegelsenken)
Counterboring is usually used to enlarge the top of a hole cylindrically to
accommodate the heads of bolts. The tool used is called a counterbore (Fig 7.6).
Deeper counterboring can also be carried out for other purposes. When a hole
has to have different diameters at different depths, special multidiameter drills
can be used. These have different diameters at different lengths of the drill, and
ensure that the different diameters are concentric.
Countersinking enlarges the top of a hole conically to accommodate the head of
a countersunk screw or rivet. The tool used is called a countersink (Fig 7.8).
3.4 Spot facing (Planansenken)
This is an operation which levels the surface around a hole that has been drilled
or counterbored to take the head of a screw.
3.5 Tapping (Gewindebohren)
This is the operation of cutting internal threads by means of a cutting tool
called a tap (Fig 7.1(b)). The tap has threads and flutes cut on it and has cutting
edges which are hardened and ground. A hole of the right size has to be drilled
before the tap is used. If the tap is now screwed into the hole, it cuts the required
internal thread. Exeternal threads are cut by using dies (Fig 7.1(b)).
3.6 Drilling machines (Bohrmaschinen)
Drilling machines usually have a column, a table, and a drilling head. The
workpiece is placed on the table. Both the drilling head and the table can be
moved up and down to accommodate different sizes of workpieces. The speed
of rotation of the drill and the rate of downward feed can be adjusted, as can the
depth of hole to be drilled.
3.6.1 Radial drilling machines (Schwenkbohrmaschinen) have in addition a
radial arm on which the drilling head is mounted. The radial arm can be rotated
to any position on the column, and in addition the head may move sideways on
the radial arm. The movements enable a hole to be drilled at any position on a
large workpiece. In some machines the drill head can be swung about a
horizontal axis perpendicular to the arm. This enables the drilling of holes at an
angle to the vertical.
3.6.2 Multiple drilling machines (Mehrspindelbohrmaschinen)
These are machines with several spindles which can drill several holes in a
workpiece simultaneously. They may be used to drill the same pattern of holes
in a large number of workpieces as part of a mass production program. Jigs may
be used to guide the drills.
3.7 Clamps, jigs and fixtures (Spannelemente und Vorrichtungen)
It is necessary to hold the work securely while drilling, and various types of
clamps are used for this purpose. Fixtures are used to ensure that holes are
drilled in the right locations, and jigs are used when the drills have also to be
guided into the holes.
Fig 7.9 Shows the different parts of a typical lathe
4 The lathe 167
4 The lathe and single point cutting tools
(Drehmaschine und DrehmeiBel)
The lathe is the most important of all machine tools, and is used for producing
components which are symmetrical about an axis. It can be used for machining
cylindrical external and internal surfaces, and also for the turning of conical and
tapered surfaces. In addition a lathe can be used to cut screw threads on an
already machined cylindrical surface.
The lathe is a versatile machine which is widely used in tool rooms to perform a
wide variety of work. The accuracy of the work done on a lathe depends on the
skill and experience of the operator. A lot of time is spent on tool setting, tool
changing etc., with the result that it is unsuitable for use in production work. It
is mainly used for the making of prototypes and spare parts. A typical lathe is
shown in Fig 7.9.
4.1 The size of a lathe (BaugroPe der Drehmaschine)
The specifications for the size of a lathe include the following items:
1. The height of centres (Spitzenhohe) measured above the lathe bed.
2. The length between centres (Spitzenweite) which corresponds to the
maximum length of work that can be mounted between lathe centres.
3. The maximum bar diameter (Spindelbohrdurchmesser). This is the
maximum diameter of bar stock (metal bars) that will pass through the
hole in the headstock spindle.
4.2 Parts of a lathe (Bauteile der Drehmaschine)
A lathe has a rigid bed with parallel guideways on which are mounted a fixed
headstock and a movable tailstock. In addition there is a carriage which can be
moved along the guideways of the bed, in a direction which is parallel to the
axis of rotation of the spindle. The headstock has a strong spindle which is
driven by a motor through a gearbox.
The speed of the spindle can be varied through a wide range, to suit the type of
work that has to be done. A lathe is also usually fitted with a lead screw which is
used for screw-cutting. The lead screw can be geared to the headstock spindle
through the gear box.
Knurling is another operation that can be carried out on a lathe. This is done by
using a knurling tool which consists of a set of hardened steel rollers mounted in
a holder. The rollers have a definite pattern of teeth cut on them. This creates a
diamond (or other) shaped pattern on the surface of the workpiece.
4.3 Lathe accessories (Drehmaschinen Zubehor)
Lathe accessories are used for supporting the work or holding the tool. They
include lathe centres, catch plates and carriers, chucks, collet chucks (or
colletts), face plates, angle plates, mandrels, steady and follower rests.
4.3.1 Lathe centres (Zentrierspitze)
The workpiece is held very often between a live centre (Mitlaufende
Zentrierspitze) on the spindle, and a dead centre (Einfache Zentrierspitze) on the
tailstock. A half centre allows the facing of the ends of a bar without removing
168 VII Metal removal processes
the centre. A rotating or frictionless centre can be fitted in the tailstock for
heavy work revolving at high speed. This type of centre is fitted with roller and
thrust bearings.
4.3.2 Carriers and catch plates (Mitnehmer und Mitnehmerscheibe)
A workpiece which is held between centres is usually driven by using carriers
(or driving dogs) and catch plates. Catch plates are attached to the end of the
headstock spindle and the carriers attached to the end of the workpiece by set
4.3.3 Chucks (Futter)
Chucks are some of the most important devices for holding a workpiece in a
lathe. The chuck is usually screwed-on to the nose of the lathe spindle. The
following are some of the most important types of chucks that are available:
1. Three jaw self-centering or universal chuck (Dreibackenfutter) - This
chuck is useful for holding round, hexagonal or other regular shaped
workpieces. The work is centered automatically (although the centering
may not be very accurate), because all three jaws move forward or
backward by an equal amount when the chuck is adjusted.
2. Four jaw chuck (Vierbackenfutter) - Here each jaw may be adjusted
independently and this chuck is particularly suitable for heavy and
irregular shaped workpieces.
3. Magnetic chuck (Magnetfutter) - These chucks are used for holding very
thin workpieces which cannot be held in an ordinary chuck. They can also
be used when the distortion caused by the jaws of an ordinary chuck is not
4. Collets or collet chucks (Spannzange) - These are small chucks that fit
into the headstock spindle and are used for holding bar stock (long bars
or rods). These chucks are particularly useful in cases where accurate
centering and quick setting are required.
5. Face plates (Planscheiben) - Face plates are circular plates which can be
fitted by screw threads to the nose of the lathe spindle. Face plates have
slots on them for holding work by bolts and clamps.
6. Mandrels (Drehdorne und Spanndorne) - A mandrel is used for holding
and rotating a workpiece that has a bore in it. The mandrel is mounted
between centres and the workpiece rotates with it. Many types of mandrel
are available.
4.3.4 Steady and follower rests (Feststehende und mitlaufende Setzstocke)
Steady and follower rests are used when turning long bars or other similar
workpieces. These rests prevent the bending of the bars which would be caused
by the cutting forces. The steady rest is bolted to the bed of the lathe, while the
follower rest is bolted to the saddle of the lathe. Care is required when adjusting
the pads of the rests. Excessive pressure is not required, and the workpiece
should be able to rotate with reasonable ease.
4 The lathe 169
4.3.5 Attachments for lathes (Zusatzgerate)
Attachments are additional devices used for specific purposes. They include
stops, thread chasing dials, and attachments for taper turning, milling, grinding,
gear cutting, knurling, etc.
4.4 Single point lathe cutting tools (DrehmeiBel)
The lathe uses a single point cutting tool for the removal of metal from a
workpiece. The action is similar to that of a chisel. The pointed part of the tool
is a wedge which presses on the metal and tears off a chip when the metal
moves relative to the tool. Efficient metal cutting is only possible if the cutting
tools are made of the right material and have the correct cutting angles ground
on the tip of the tool. A lathe cutting tool with the main cutting angles is shown
in Fig 7.10.
End cutting Nose angle
Side cutting
End face Side face
or flank
A:Top or front rake angle, B:Side rake angle
C:Front clearance or relief angle, D:Side clearance or relief angle
E:Side cutting angle, F:End cutting angle
Fig 7.10. Typical lathe tool showing the main cutting angles
4.5 Capstan and turret lathes (Revolverdrehmaschinen)
The tool room lathe is unsuitable for production work, but modified versions of
the lathe like the capstan and turret lathes have been used as mass production
machines. These machines have the same headstock and four way tool post as
the ordinary lathe. However the tailstock is replaced by a hexagonal turret and
each face of the turret can carry one or more tools. These tools may be used
successively to perform a series of different operations in a regular sequence.
The feed movements of each tool may be regulated by stops. Lead screws are
not fitted and the cutting of screw threads is done by using taps and dies. The
initial setting of tools is a skilled operation. Once this has been done a semi-
skilled operator can produce a large number of components in a short time.
170 VII Metal removal processes
1. Hexagonal turret, 2. Auxilliary slide, 3. Feed stop rod, 4. Lathe bed,
5.Handwheel for auxilliary slide, 6.Saddle
Fig 7.11 A capstan lathe saddle and components
4.6 Automatic lathes and screw machines (Drehautomaten)
Single and multispindle automatic lathes or screw machines as they are often
called have been in use for a long time. Mechanical devices like cams and stops
are used to enable the lathes to carry out a series of operations according to a
predetermined program. The setting-up time is long and such lathes are
unsuitable for small batch production.
5 Milling machines (Frasmaschinen)
A milling machine uses a multipoint tool to remove metal from a workpiece.
The use of multipoint tools enables the machine to achieve fast rates of metal
removal and produce a good surface finish.
5.1 Column and knee type of milling machines (Konsolfrasmaschinen)
These machines have a column and a projecting knee which carries the saddle
and work table. The work table has three independent movements, longitudinal,
transverse and vertical. Milling machines lack the rigidity required for heavy
production work and are mainly used in tool rooms and workshops.
5.2 The horizontal milling machine (Horizontal Frasmaschine)
A horizontal milling machine (Fig 7.12) has a horizontal spindle located in the
upper part of the column. It receives power from a motor through belts, gears
and clutches. The spindle projects slightly out of the column face and has a
tapered hole into which cutting tools and arbors may be inserted. An arbor is an
extension of the machine spindle. The overhanging arm which is fixed on top of
the column serves as a bearing support for the arbor. The arbor has a taper
shank which fits into the nose of the machine spindle.
5 The milling machine 171
International Taper spindle Starting lever
Speed dial Arbor steadies
Overarm pilot wheel
Overarm clamp nut Table feed lever (power)
Speed change lever Saddle clamp
Spindle reverse
Vertical feed
hand crank
Feed change lever
Knee Vertical feed lever (power)
Rear Dower hand lever Elevating screw
Fig 7.12 A horizontal milling machine
172 VII Metal removal processes
5.3 The vertical milling machine (Vertikal Frasmaschine)
The vertical milling machine has a column and knee similar to a horizontal
milling machine, but the spindle is perpendicular to the work table. The spindle
head which is clamped to the vertical column may be swivelled at an angle, thus
permitting the milling of angular surfaces.
5.4 The universal milling machine (Universal Frasmaschine)
The universal milling machine is a versatile machine which can perform a wide
variety of operations. It has a fourth table movement in addition to the
movements mentioned before. The table can be swivelled at an angle to the
milling machine spindle. It is also provided with a wide range of accessories
like dividing heads, vertical milling attachments, rotary tables, etc. These
accessories enable the machine to produce spur, spiral and bevel gears, twist
drills, and milling cutters.
5.5 Milling cutters (Fraswerkzeuge)
There are many types of milling cutters some of the most important of which are
given below.
1 Plain milling cutters (Walzenfraser) - Plain milling cutters have a cylindrical
shape and have teeth only on the circumferential surface. These cutters are used
for generating flat surfaces parallel to the axis of rotation of the spindle. The
cutter teeth can be straight or helical, depending on the size of the cutter.
2 Side milling cutter (Walzenstirnfraser) - These cutters have teeth on the
periphery and also on one or both of the cutter's sides. They are used for
removing metal from the side of a workpiece. Among the types available are
plain and staggered teeth types, and also half side milling cutters with teeth on
one side only.
3 Metal slitting saw (Schlitzfraser) - These are similar to milling cutters , but
have a very small width and are used for parting-off operations or for slotting.
4 Angle milling cutters (Winkel-Stirnfraser) - Angle milling cutters are avai-
lable as single or double angle cutters and are used to generate angles other
than 90°.
5 T-slot milling cutter (T-Nutenfraser) - These are cutters of special shape for
producing T-slots and dovetail slots.
6 Form cutter (Profilfraser) - These cutters are used to produce a surface that
has a definite form. Some of the types available are concave and convex milling
cutters, gear tooth cutters and thread milling cutters.
5.6 Types of milling processes (Frasverfahrensarten)
Milling processes may in general be divided into three types:
(1) Peripheral milling (2) Face milling (3) End milling which may be
considered to be a combination of face and peripheral milling.
5.6.1 Peripheral milling (Umfangs-Planfrasen) - In this operation, the mach-
ined surface is parallel to the axis of rotation of the cutter. Two types of
5 The milling machine 173
processes are possible, depending on the sense of rotation of the cutter relative
to the direction of movement of the workpiece. These processes are termed up
milling and down milling.
(a) Up milling (Gegenlauffrasen) is the conventional type of milling in which
the cutter is rotated against the direction of travel of the workpiece. The
thickness of the chip is small at the beginning and increases towards the end of
the cut. The upward cutting force tends to lift the workpiece from the table. Due
to the nature of the cutting forces, difficulty is experienced in feeding coolant at
the beginning of the cut. In spite of the disadvantages, it is used so often because
it is safer. It is particularly useful for milling castings containing particles of
sand, and also for milling welded joints.
(b) Down milling (Gleichlauffrasen) which is also called climb milling, is a
process in which the cutter is rotated in the same direction as the direction of
travel of the workpiece. The thickness of the chip and the cutting force are a
maximum when the tooth begins cutting, and a minimum when the tooth stops
cutting. In this case, the clamping of the work is easier and the chips are
disposed more easily. Coolants can be fed into the cutting zones, and this
reduces heat problems and gives a better surface finish. However down milling
cannot be used on machines having backlash. The backlash causes the work to
be drawn below the cutter at the beginning of the cut, and leaves the work free
when the cut is over. This results in vibration and damage to the workpiece.
5.6.2 Face milling (Stirn-Planfrasen) produces a flat machined surface perpend-
icular to the axis of rotation of the cutter. The main cutting is done by the
peripheral cutting teeth while the face cutting edges finish the work by
removing a small quantity of metal.
5.6.3 End milling (Stirn-Umfangs-Planfrasen) - This may be considered to be a
combination of peripheral and face milling. The milling cutter has teeth on the
periphery as well as on the end face.
6 Broaching (Raumen)
Broaching is a metal removal process in which a single tool having a definite
geometric shape is used. The tool which has multiple cutting edges is pushed or
pulled along the inner or outer surfaces of a workpiece. Only a small amount of
metal can be removed in this process, and it is necessary most of the metal
should have been removed previously by other machining processes. Broaching
is carried out when special profiles having a good surface finish, and good
dimensional accuracy are required. The work is carried out in a single operation
and high production rates with unskilled labour can be achieved.
6.1.1 Internal broaching (Innenraumen) is used to produce holes of various
shapes in cylindrical holes which have been previously made by drilling, boring,
casting, etc. For example keyways or splines may be cut by a broach in a
previously drilled hole. It is also possible to cut internal spirals in a workpiece,
174 VII Metal removal processes
by using special broaches and by rotating the workpiece during the broaching
process. This is similar to the cutting of screw threads by using taps.
6.1.2 External broaching (AuBenraumen) can be used to generate external
surfaces with profiles similar to those produced by other machining procedures.
7 Surface finishing processes (Oberflachenfeinbearbeitung)
Machined surfaces are usually rough, and may not meet the standards of surface
quality and dimensional accuracy required. Finishing operations are used to
bring the surfaces of the components to the required standard. Very little metal
is removed in a finishing operation, and previous machining operations should
have been carried out satisfactorily before the finishing processes are started.
7.1 Grinding (Schleifen)
Grinding is an operation that is carried out by using a rotating abrasive wheel to
remove metal from an object. Very high levels of dimensional accuracy and
surface finish can be achieved by grinding. Comparatively little metal is
removed usually 0.25 to 0.50 mm in most operations.
Grinding can also be used effectively to machine materials which are too hard to
be machined in any other way. Some of the grinding processes which are
normally in use are the following:
(1) External grinding including centreless grinding (2) Internal cylindrical
grinding (3) Surface grinding (4) Form grinding
7.1.1 External cylindrical grinding (AuPen-Rundschleifen) is used to grind a
cylindrical or tapered surface on the outside of the workpiece. The workpiece is
rotated between centres as it is moved lengthwise, while making contact with a
rotating grinding wheel which rotates at high speed.
7.1.2 Internal cylindrical grinding (Innen-Rundschleifen) is carried out in a
similar way to external grinding by using smaller grinding wheels that grind the
inner surfaces of the bored workpiece. The small wheels need to rotate at high
speeds for effective grinding.
7.1.3 Centreless grinding (Spitzenlosschleifen)
This is a method of external grinding Regulating Grinding
used to grind cylindrical, tapered and wheel wheel
formed surfaces that are not held
between centres. The set-up consists of
a work-rest which lies between a
grinding wheel and a regulating (or
back-up) wheel. The work is placed on
the work-rest, which moves forward
with the regulating wheel thus forcing ' Work rest
the work against the grinding wheel. F i g 7 {3 centreless grinding
7 Surface finishing processes 175
7.1.4 Surface grinding (Planschleifen) is an operation used to grind flat
surfaces. The grinding is carried out by using either the periphery or the end
face of the grinding wheel. The workpiece is given a reciprocating movement
below or on the end face of the grinding wheel.
7.1.5 Form grinding (Profilschleifen) uses grinding wheels which are specially
shaped to accurately finish surfaces which have been previously machined to a
special shape like gear teeth, spline shafts and screw threads.
7.1.6 Abrasive wheels (Schleifkorper)
Grinding wheels contain very small abrasive particles of a very hard material
like silicon carbide or aluminium oxide. The wheels are made by using a bond-
ing material which holds the abrasive particles together. The particles have
sharp edges and each wheel acts like a multi-tooth cutter which removes metal
from the workpiece. Different particle sizes and different kinds of bonding
materials are used to make a whole range of grinding wheels.
Silicon carbide wheels are useful for grinding materials of low tensile strength
such as cutting tool tips, ceramics, cast iron, brass, etc. Aluminium oxide wheels
are better suited for materials of higher tensile strength such as most kinds of
steel, wrought iron, tough bronzes, etc. Diamond wheels which are made by
impregnating a metal wheel with fine diamond particles are used for special
purposes like gem cutting.
7.2 Lapping (Lappen)
Lapping is a process which is used to produce geometrically true surfaces,
achieve high dimensional accuracy, secure a fine finish and obtain a close fit
between two surfaces. Very little material is removed (less than .01 mm), and
this method cannot correct for substantial errors inform.
The lapping process uses a lapping paste and a tool called a lap. The paste is
formed by mixing fine particles of an abrasive material with oil. The lap is made
of a relatively soft porous material like cast iron or copper. The paste is rubbed
into the lap, causing the abrasive particles to become imbedded in it. In the
lapping process, the work is rubbed with the lap in an ever changing path. Laps
can be operated by machine or by hand.
7.3 Honing (Honen)
Honing is a grinding process which is mostly used for finishing cylindrical
holes by means of bonded abrasive stones called hones. Honing can be used to
remove as much as 3 mm of material, but is normally used for removing less
than 0.25 mm. Honing is primarily used to correct errors in roundness, taper,
axial distortion, and tool marks in a previously machined workpiece.
The abrasive tool is in the form of aflat stone or stick called a hone. A few of
these stones are mounted round a metal cylinder to form a honing tool. This
tool is reciprocated axially while being in contact with the rotating workpiece.
Coolants are used to remove small chips and and keep temperatures uniform.
176 VII Metal removal processes
7.4 Superfinishing (Kurzhubhonen)
Superfinishing is a honing process which uses large bonded abrasive stones to
produce a surface of extremely high quality. A very thin layer of metal (less
than .02 mm) is removed in this process. It may be applied to the internal or
external surfaces of objects made of cast iron, steel or nonferrous alloys which
have been previously ground or machined.
In this process a stick containing a very fine abrasive is placed in a suitable
holder and applied to the surface of the workpiece with light pressure. The
abrasive holder is given an oscillating motion, while the workpiece is rotated or
given a reciprocating motion depending on the shape of the surface. A special
lubricant, usually a mixture of kerosene and oil is used to obtain a high quality
finish. Superfinishing is used for many types of components such as crankshaft
bearings, cylinder bores, pistons, valve stems, and other moving metallic parts.
7.5 Polishing and buffing (Polieren und Hochglanzpolieren)
Polishing is an operation which is used to remove scratches, pits, tool marks and
other defects from rough surfaces. In polishing the dimensional accuracy of the
polished surface is not important. Polishing wheels are made of leather, canvas,
felt or wool. The abrasive particles are glued to the surface of the wheel and the
wheel is rotated while the object to be polished is held against it until the
desired finish is obtained.
Buffing produces a much more lustrous surface than is obtainable by polishing.
Buffing wheels are made of felt, leather or pressed and glued layers of cloth.
The abrasive is mixed with a binder and is applied to the buffing wheel or to the
work. The wheels are rotated with a high peripheral speed of up to 40 m/s. The
abrasives used are iron oxide, chromium oxide, emery, etc. The binder is a paste
consisting of wax mixed with grease, paraffin, turpentine, etc.
7.6 Shot or grit blasting (Kornchenblasen)
Shot or grit blasting is a surface cleaning process in which abrasive or other
particles moving at high speed are made to strike the surface to be cleaned.
Rust, scales, burrs, etc, are removed and the surface acquires a matt appearance.
1.1 Shot peening (Verfestigungsstrahlung)
Shot peening is a process used to strengthen and harden a surface. In this
process, steel balls moving at high speed strike the surface which becomes
work hardened and fatigue resistant.
7.8 Barrel finishing (Trommelpolieren)
This process eliminates hand finishing and is therefore very economical in the
use of labour. The workpieces are placed in a many-sided barrel together with
abrasive materials (like stones, abrasives, etc) and a suitable liquid. When the
barrel is rotated for an appropriate amount of time, the mutual impact between
the workpieces and the abrasive materials removes surface irregularities.
VIII CNC machines (CNC Maschinen)
1 Introduction (Einfuhrung)
1.1 Development of CNC machines (Entwicklung der CNC Machinen)
The machining of metal components had been done in the past by using
conventional machine tools like lathes, milling machines, etc. and the accuracy
of the work done was dependent on the skill and experience of the operator. A
lot of time was taken for tool setting, tool changing, etc. The result was that
these machines were unsuitable for large scale production.
An improvement was made by using machines like capstan and turret lathes.
These had rotating turrets for rapid tool changing and adjustable stops which
allowed feed control. However the setting time was long, and these machines
were unsuitable for small batch production.
A further improvement was made by using single and multispindle automatic
lathes. These were able to produce large numbers of identical components
rapidly. The operations were carried according to a predetermined program and
were controlled by mechanical devices like cams and stops. However, the
setting time was long, and these were also unsuitable for small batch production.
A solution to this problem was found by developing machines that were able to
produce components automatically in accordance with a series of predetermined
instructions called a program. The use of a programmed computer to control a
machine tool, led to this form of automation being called computer numerical
control (CNC).
1.2 Features of CNC machines (Besonderheiten der CNC Maschinen)
CNC machines are capable of doing more than producing components
automatically. They possess the characteristics of extreme accuracy, repeat-
ability, reliability and high productivity. No setting or resetting of these
machines is required. All that one needs to do when a new component is
required is to write out a new program, which when used correctly, produces a
component that has precisely the dimensions called for in the program.
The program contains the control instructions which guide the machine, and the
geometric data required to produce the component. Extensive changes in the
structure and operation of existing machine tools had to be carried out before the
new CNC machines could be built. Some of the changes made are given below.
1. CNC machines have heavier structures with improved rigidity and better
damping characteristics. This gives them the ability to withstand large
cutting forces and ignore the thermal effects of the chips produced. The
machines are often placed in a tilted position thus allowing the chips to
slide down.
2. Bearings and spindles have zero play. All spindles, drive elements and
systems are dynamically balanced.
178 VIII CNC machines
3. Recirculating ball screw systems with low friction and zero backlash are
used. They have a mechanical efficiency of over 98 %.
4. A continuous indication of the position of the cutting tool on each axis is
produced and transmitted back to the axis drive, which continues to drive
the tool until the target position is reached.
5. Each tool is mounted in a holder (or adapter) and is preset to the correct
length. Tool length compensation is made for actual differences between
preset and actual tool length after the tool has been reground or changed.
6. A large number of tools are usually required and these are stored in disc,
ring, chain or other types of magazine.
7. Automatic tool changing systems enable a direct exchange of tools from
the magazine into the machine spindle. This done by using grippers in an
automatic tool change cycle.
8. Automatic workpiece changing systems are used to change workpieces.
The workpieces are clamped to pallets which can be accurately located
and clamped to the work holding surfaces of the machine. Pallett changing
installations carry the work to the machine and back again.
9. The main spindle and axis feed drives have servo (or other) motors with
continuously variable speed and feed rates. Load fluctuations are
compensated for to avoid speed variations. All motions are independent
of opposing forces due to cutting loads, friction or inertia.
1.3 Method of operation of a CNC machine
(Arbeitsweise einer CNC Maschine)
A CNC machine does the same kind of work that a skilled operator does, but it
does it without human intervention. The work is done automatically and with
more precision than the work done by an operator. The method of operation of a
CNC machine may be summarized as follows:
1. The machine is controlled by a program which is recorded on a paper
tape, magnetic tape or other data carrier. Information which controls the
relative motion between tool and workpiece, as well as geometric data
relating to the component is contained on the tape in digital form. The
tape is fed into the system to start the process.
2. A processing unit converts the data into electrical signals that the
machine tool can understand.
3. The data is stored in a memory unit until it is required for use.
4. The stored data is converted into machine movements by servo units on
the machine tool.
5. A measuring system measures the machine movements and feeds back
the measured values to a comparison unit. This unit compares measured
and target values and instructs the drive unit to continue the movement
until the target value is reached. In this way a closed loop feedback
control system ensures that target values are reached (Fig 8.1).
1 Introduction 179
25.173 unit 51.325
Actual value i
Target value
of position Zero of position
Machine Feed drive i
table lllllljll
•m I \
Path measuring device
Fig 8.1 Closed loop feedback control system for positioning
1.4 Path measuring systems (WegmeBsysteme)
The accuracy of a CNC machine is entirely dependent on the accuracy of its
path measuring system. Path measuring systems can be of different types
depending on the measuring process whether it is direct or indirect, absolute or
incremental, analog or digital.
j ^ - Direct path measurement' Incremental
Path measurement system
^ I n d i r e c t path measurement:;; "
-^- Incremental
1.4.1 Direct path measurement (Direkte Wegmessung)
In direct path measurement, measurements are made without the use of any
intermediate mechanical device. The linear movement of a milling machine
table can for example be measured directly by using an optical scale. The
accuracy of the measurement will depend on the accuracy of the scale.
1.4.2 Indirect path measurement (Indirekte Wegmessung)
In indirect path measurement, the measurements are carried out by using an
intermediate mechanical device. Mechanical devices like ball screws or rack and
pinions, need a rotary encoder or a resolver to generate an electrical signal.
1.4.3. Digital measuring systems (Digitale Meflsysteme)
Digital path measuring systems are usually based on optoelectricalprinciples. A
ruled scale is usually attached to the table and the movement of the scale can be
measured by using a detector. The smallest resolution of the scale is 5 urn.
However path increments of lum can be measured by using an electronic
1.4.4 Digital incremental path measuring systems
(Digital-inkrementale WegmeBsysteme)
In a digital incremental path measuring system, any point at which the carriage
is in when the system is started is taken as the zero point. However, the
programming of distances along the axes is only possible provided that a fixed
180 VIII CNC machines
reference point exists. This diff- Lamp
iculty is overcome by mounting Zero
another glass scale above the usual marks
glass measuring scale as shown in
Fig 8.2.When the machine is started,
it is made to move past the zero
reference point and generate a Linear
reference signal. All further movem- Photoelectric scale
ents are measured from this zero
reference point. Fig 8.2 Incremental path measuring system
1.4.5 Digital absolute path measuring systems
(Digital-absolute WegmeBsysteme)
In this type of measurement, all distances are measured from a special reference
point. A special glass scale is used with successive columns of squares which
are either black or transparent. Each column has five squares where the squares
are arranged vertically to correspond to successive binary digits. The columns
are so arranged horizontally that they correspond to successive decimal
numbers. This is shown in Fig 8.3.
Binary 2
Fig 8.3 Digital absolute path measuring systems
2 Geometrical basis for programming (Geometrische Grundlagen)
2.1 Coordinate system (Koordinatensystem)
A coordinate system with rectangular axes is used to describe the motion of
tools and workpieces. It is based on the "right hand rule", involving the thumb,
middle and index fingers of the right hand. The thumb indicates the direction of
the X axis, the index finger the Y axis, and the middle finger the Z axis.
2 Geometrical basis for programming 181
2.1.1 Choice of axes for machine tools (Anordnung der Koordinatenachsen)
Z axis - The direction of the main spindle axis is taken to be the Z axis.
X axis - The X axis is the larger of the two other axes and if possible horizontal.
Y axis - The Y axis is perpendicular to the ZX plane.
2.1.2 Secondary axes (Zusatzliche Achsen)
If extra axes are required parallel to the X,Y,Z axes, these are designated
U,V, W, with U parallel to X, V parallel to Y and W parallel to Z.
2.1.3 Rotational axes (Drehungen
um die Koordinatenachsen)
The designation of a rotational axis is
based on the linear axis about which
rotation occurs. A refers to rotation
about the X axis, B refers to rotation
about the Y axis, and C refers to
rotation about the Z axis. X
Fig 8.4 Rotation about the axes
2.2 Zero points and reference points (Nullpunkte und Bezugspunkte)
Fig 8.5 Shows some of the zero and reference points
2.2.1 Machine zero point M (Machinennullpunkt M)
The machine zero point is at the origin of the machine's coordinate measuring
system. This is fixed and cannot be moved. In most cases it lies on the spindle
axis of the machine. In practice the machine zero point should be automatically
reached, when the machine is switched on. It should also be possible to reach
zero by pressing a particular key, or by using an instruction in the program itself.
2.2.2 Machine reference point R (Referenzpunkt R)
With some CNC machines, it is not possible to reach the machine zero point. In
such cases, another more convenient point is adopted as the machine's reference
point. Instead of starting measurements along the axis from zero, measurements
are now made from the coordinates of the new reference point.
182 VIII CNC machines
2.2.3 Workpiece (or piece part) zero point W (Werkstiicknullpunkt W)
The workpiece zero point can be freely selected by the programmer. However
on a lathe or other turning machine, it usually chosen to be at the intersection of
the spindle axis with the left or the right edge of the workpiece.
2.2.4 Program zero point P (Programmnullpunkt P)
Coordinate values taken with reference to the machine zero point are not
suitable for use in programming. A program zero point is usually chosen with
reference to the piece part or the tool change point. All geometric data are
related to this point, so that the machining process can start and continue soon
after the piece part has been clamped on the machine.
2.2.5 Tool change point TCP (Not standardized)
(Werkzeugwechselpunkt WWP - nicht genormt)
This is not a standard point but is very often the starting point for the machining
process. This is often the same point as the program zero point.
2.3 Control modes (Steuerungsarten)
2.3.1 Point to point control (Punktsteuerung)
In this method of control, rapid traverse (or rapid movement) takes place on all
axes independently until the programmed target value has been reached.
Machining starts only when the target value has been reached. This type of
control is suitable for use on drilling, punching or spot welding machines.
2.3.2 Continuous path (or contouring) control (Bahnsteuerung)
In continuous path control, the cutter spindle can be moved very accurately
along any programmed path. The movement along the axes is coordinated by a
software package called an interpolator. The interpolator controls the
movement along all programmed axes simultaneously, so that the programmed
path is accurately followed. Simultaneous interpolation of all three axes is called
3-D control. If successive two axis interpolation in each of the three planes (XY,
XZ and YZ) is carried out, then this type of control is called 2 Vi-D path control.
2.4 Types of interpolation (Interpolationsarten)
2.4.1 Linear interpolation (Linearinterpolation)
With linear interpolation, the cutter
spindle axis is moved along a straight
line from one point to the other. If it is
required to move along a curved
profile as shown in Fig 8.6, the profile
can be broken-up into a large number *1 6»
of straight lines. The larger the number Fig 8.6 Approximation to a curve
of straight lines, the closer the approximation to the curve. When a very close
approximation is required, a very large number of points need to be calculated
and the volume data of data processing becomes enormous. However, the
amount of data processing can be reduced considerably by using other types of
interpolation like circular, parabolic or spline interpolation.
3 Drives for CNC machines 183
2.4.2 Circular interpolation (Zirkularinterpolation)
Circular interpolation is limited in its usefulness. It cannot be used to interpolate
simultaneous movement along three or more axes. It is also not possible to
include rotary axes in circular interpolation. It is principally used for paths
which are in the plane of'theprincipal machine surface.
3 Drives for CNC machines (Antriebe der CNC Maschinen)
Two types of drives are required for CNC machines, feed drives and main
spindle drives. Both DC and AC servomotors have been used for these drives.
3.1 Feed drives (Vorschubantriebe)
Separate feed drives are used to control the movement along each axis of a CNC
machine. The feed movements along the axes have to be extremely precise, with
as little deceleration and overshoot as possible. All movements should be
independent of opposing forces such as those due to cutting load, friction or
inertia. Positioning speeds should be as fast as possible, and movements should
be smooth and uniform without jumps or oscillations.
3.1.1 DC feed drives (Gleichstrom Vorschubantriebe)
DC motor drives are well established for feed drives, and motors fitted with
permanent magnets to provide the exciting field are usually favoured.
Continuously variable speeds are achieved by varying the armature voltage.
The speed is directly proportional to the armature voltage when the magnetic
field remains constant. A current regulator compensates for a drop in speed due
to static or dynamic loads by increasing the armature voltage.
3.1.2 AC feed drives (Wechselstrom Vorschubantriebe)
This type of drive uses a three phase synchronous motor. The stator which
produces the exciting field has a normal three phase winding while the rotor is
fitted with permanent magnets. When a three phase voltage is applied to the
stator winding a rotating field is created, whose frequency of rotation is
identical to the frequency of the applied voltage. The rotor which is a permanent
magnet rotates at the same frequency. The only way the rotor frequency can be
changed is by changing the frequency of the voltage applied to the stator. This
can be achieved by using an electronic device called a frequency converter
which generates a three phase voltage whose frequency can be varied
continuously. Such motors have several advantages over DC motors like the
absence of commutators and carbon brushes.
3.2 Main spindle drives (Hauptspindelantriebe)
3.2.1 DC main spindle drives (Gleichstrom Hauptspindelantriebe)
DC main spindle drives have a separate excitation winding in contrast to DC
feed drives which have fields generated by permanent magnets. Two operating
ranges of speeds are possible, one controlled by the armature voltage which
gives constant torque, and the other by changing the voltage applied to the field
winding which gives constant power. Armature control allows a speed ratio of
20 to 30, while field control allows a speed ratio of only 5 to 4.
184 VIII CNC machines
3.2.2 Three phase asynchronous (squirrel cage) motor drives
(Drehstrom Asynchron-KurzschluBlaufermotoren)
Three phase asynchronous motors with short-circuited rotors (squirrel cage
motors) have been used for many main spindle drives. In these motors a three
phase voltage is applied to the stator winding and this creates a rotating field.
The rotating field induces a voltage in the rotor, causing a current to flow,
which in turn causes the rotor to rotate. The frequency of rotation of the rotor
is however less than the frequency of rotation of the rotating field. In other
words there is a continuous slip which can vary with the load. This
disadvantage can be overcome by using frequency converters. Speed ratios of
1:100 can be achieved by using this method.
4 Tool and work changing systems for CNC machines
(Werkzeug und Werkstuck Wechselsysteme)
Turret Disc Chain
Fig 8.7 Different types of tool magazines
Chain type
tool magazine
Groove to fit
Double gripper
Fig 8.8 Tool holder (or adapter) Fig 8.9 Double gripper used for tool changing
4 Tool and work changing systems 185
4.1 Tool changing systems (Werkzeug Wechselsysteme)
In CNC machines the manual tool change system has been replaced by
automatic tool changers and tool magazines. The first automatic tool change
systems were the tool turrets used in capstan and turret lathes, in which each
turret had six or eight tools. CNC machines called turning centres still have
these turrets because they are cheaper than other systems. In machining centres,
the number of cutting tools required is much greater than with turning centres,
and disc, chain or rotary type magazines are used (Fig 8.7).
4.2 Tool holders or adapters (Werkzeughalter)
1. The cutting tool is fitted into a standard tool holder or adapter (Fig 8.8)
which can be positively locked into the machine spindle. The tool while it
is in its holder is preset to prescribed dimensions using a set-up which
can be far away from the machine.
2. A positive identification of the tool can be accomplished by having tool
encoding rings on the tool holder. More recently identifying has been
done by having a microchip enclosed within the tool holder body. By
using these systems, the tools can be used in any required sequence by
having the tool number in the program.
3. Tool holders have grooves or gripper slots (Fig 8.8) in them. These allow
automatic tool changers to change tools (together with their holders)
4.3 Automatic tool changing systems
(Automatische Werkzeugwechselsysteme)
An automatic tool change cycle is used to transfer tools from the magazine to
the spindle of the machine and back. Double grippers (Fig 8.9) which are able to
grip the tool in the spindle as well as the tool in the magazine simultaneously
are used. A typical cycle is as follows:
1. Location of the next tool required in the machine.
2. Removal of the last tool to be used from the spindle.
3. Insertion of a new tool into the machine spindle
4. Return of the used tool to the magazine.
4.4 Tool management (Werkzeugverwaltung)
Any program written for CNC machines is based on tools of given dimensions.
When the tools used in the machines do not conform to these dimensions, the
parts turned out on these machines will not have the right dimensions. It is
therefore essential that tools are kept in good condition, and corrections be
made to compensate for any deviations in tool dimensions.
1. Accurate presetting of tools (as mentioned) is a necessary first step.
2. Tool length compensation is necessary to allow for the difference in
actual length and desired length.
3. Tool diameter correction is necessary for cutting path corrections.
4. Tool wear compensation is used to compensate for tool wear without
changing the programmed offset data.
186 VIII CNC machines
5. Tool life monitoring is used to monitor the usage of each tool and
compare this with the permitted cutting life.
4.5 Automatic work(piece) changing systems
(Automatische Werkstlickwechselsysteme)
Automatic work changers enable the saving of the down time of the machine
tools caused by the loading and unloading of workpieces, clamping, aligning,
etc. This can be done far away from the machine without interrupting the
machining process.
1. Work storing platforms called pallets are used. These have special seating
faces which allow accurate location and clamping to the work tables of
the machine.
2. Pallets are transferred automatically from buffer stations to the machine
tool and back again, after the machining has been carried out.
3. Automatic work changers are necessary if several work stations are to be
integrated into a manufacturing cell or system.
5 Adaptive control for CNC maschines
(Maximierung der Leistung der CNC Maschinen)
In adaptive control, the objective is to achieve the maximum possible metal
removal rate within the capability of the machine. CNC machines fitted with
adaptive control are able to work closer to their design limits, without
overloading the machine or increasing the complexity of the program.
Adaptive control is a control system which monitors changes in cutting
conditions, and automatically adjusts the spindle speed and feed rate of a CNC
machine to produce a component at the lowest possible cost.
The programmer when writing a program sets the spindle speeds, feed rates, etc.
so that satisfactory machining will take place, even under the worst possible
conditions. This takes care of such unpredictable variations as tool wear,
variation in the quality of the materials, and variations in the dimensions of the
rough workpieces. The program is designed to ensure reliability, repeatability
and safety, but not maximum metal removal. Adaptive control however
automatically changes machining conditions to enable the machine to operate at
the limit of its capability at all times.
Adaptive control operates by measuring such quantities as torque, cutting
power and motor temperature, by installing sensors at suitable places on the
machine. The measurements are carried out continuously without interrupting
the machining process. The following changes are identified by adaptive control.
1. Changes in the hardness of the workpiece.
2. Wear of the cutting edges of the tool.
3. Changes in cutting depth.
4. Presence of air gaps in the path of motion.
Changes in machining conditions are immediately compensated for by changes
in spindle speed or feed rate.
6 Programming of CNC machines 187
6 Programming of CNC machines
(Programmieren von CNC Maschinen)
6.1 Part programming (Manuelles Programmieren)
The term part programming means the process of writing a program which can
be used to machine a piecepart (or workpiece) on a CNC machine. It does not
mean the writing of only apart of a program. A part program is written using a
language which the machine tool can directly understand. Computers are not
normally used. The usual aids used are pocket calculators and data tables.
A CNC part program consists of a sequence of blocks which instruct a CNC
machine to carry out a definite machining task. Such a program contains the
geometric data giving the dimensions and other characteristics of the piecepart
(or workpiece) to be machined. It also contains the path information, switching
and other instructions necessary to operate the machine.
6.2 Binary systems (Binaredarstellung)
Digital electronic systems are based on the binary system rather than the decimal
system because of the inherent simplicity and reliability of the binary system.
In the binary system each binary digit
or bit has only two states 0 or 1. Larger 2 2 21 2°
numbers can be represented in a binary
system by having a combination of
several bits as shown in the adjacent 8 4 2 1
Each position to the left corresponds to an increase in the power of two. Thus the
binary number 1010 corresponds to the decimal 8 + 0 + 2 + 0= 10. Large
numbers however require a very large number of bits when represented in the
binary system. For this reason a combination of the decimal and binary systems
called the binary-coded decimal system (BCD) has been devised. This uses a
smaller number of bits than a pure binary system. In the BCD system only the
numbers 0 to 9 are coded as binary, and then the decimal position is used in the
same way as in the decimal system. An example is given below.
0111 0010
7 2
The BCD system is ideally suited to
be used on the 8-track punched paper Code
tape shown in Fig 8.10, which is used channel
to feed data into CNC machines.
Other forms of data carriers like Transport
magnetic tapes and diskettes are also channel"
sometimes used instead of punched Code 2
Fig 8.10 8-track punched tape
188 VIII CNC machines
6.3 Program structure (Programmaufbau)
6.3.1 Words (Worter)
A word in a program is composed of alphanumeric characters. Each word has
two parts, an address which is an alpha character (a letter), followed by
numeric values. Each word is an instruction to the control system of the
machine to carry out a certain task. For example, instructions related to the type
of movement are assigned the character G. The word G 01 corresponds to linear
Address | Value
G 01
Each word can correspond to different kinds of instructions as follows:
1. Preparatory function path code - These are instructions relating to the
type of motion (G), like rapid traverse (movement) or linear interpolation.
2. Geometric instructions - These are instructions are concerned with the
relative movement between the tool and workpiece, for example the target
positional coordinates X, Y, Z.
3. Switching instructions - These are instructions like tool selection (T)
and miscellaneous instructions (M) which include items like coolant
supply on or off, and spindle on or off. Also included are correction
instructions for tool length, zero offsets and cutter radius compensation.
4. Technical instructions - These include items like spindle speed (S) and
feed rate (F).
5. Canned cycles - Instructions that recall parts of a program which are
repeatedly used. These are called canned cycles.
6.3.2 Blocks or sentences (Satze)
A block or a sentence is made up of a number of words. It starts with the
letter N and followed by a block or sequence number. The words are
arranged in a definite order. An example is shown below.
Block number Path instructions Technical instructions
Type of Target Feed Spindle Tool Misc:
motion position speed function
NOl G 01 X20 Y30Z45 F150 SI 200 T 0 2 M 0 7
6.3.3 Start and end of a program (Programmanfang und Programmende)
The program starts with the symbol % which is the start signal for the
program followed by a program number, for example % 0035. The end of the
program is signaled by using the symbols M 02 or M 30. The program itself
consists of a sequence of sentences which are instructions for tasks to be
carried out one after another.
6 Programming of CNC machines 189
6.3.4 Preparatory function path code G (Wegbedingung G)
The instructions concerning the motion of the tool relative to the workpiece are
specified by the preparatory function path code G, and the path information (or
geometric data). The path code determines the type of motion of the tool, for
example along a straight line, or along the circumference of a circle. The
instructions consist of the letter G and a two digit number.
The path code is followed by the geometric data, for example the coordinate of
the target point (X,Y,Z), or the position of the centre of the circle (I,J,K) and the
radius R. The distances can be given in absolute or incremental form. When
given in absolute form, the distances are related to the workpiece zero point. In
this case, the path traverse instruction G 90 has to be used. If the incremental
form is used, the instruction G 91 has to be used. A selected number of
preparatory function path code instructions are given below.
GOO Fast traverse, point to point G42 Cutter radius compensation
positioning - offset right
GOl Linear interpolation G53 Cancel zero offset
G02 Circular interpolation, G54 Zero shift
clockwise to 59
G03 Circular interpolation, G80 Cancel canned cycles
Anticlockwise G81 Canned cycles
G04 Dwell (stay) to 89
G06 Parabolic interpolation G90 Absolute input
G17 XY plane designation G91 Incremental input
G18 ZX plane designation G94 Feed rate in mm/min
G19 YZ plane designation G95 Feed rate in mm/ revolution
G40 Cancel cutter compensation G96 Feed rate for const, surface
G41 Cutter radius compensation speed
- offset left G97 Spindle speed in rev/min (rpm)
6.3.5 Miscellaneous functions M (Zusatzfunktionen M)
Miscellaneous functions (M) perform a number of additional tasks like starting
and stopping the spindle or feed, coolant flow on/off,etc. Both preparatory and
miscellaneous functions are generally classified as modal or nonmodal. Modal
functions remain effective in succeeding blocks until they are replaced by
another function code. Nonmodal functions are only effective in the block in
which they are programmed. A short list of these M functions is given below.
MOO Program stop M07 Coolant on
M02 End of program M09 Coolant off
M03 Spindle on, clockwise M13 Spindle (CW) + coolant on
M04 Spindle on, counterclockwise M14 Spindle (CCW) + coolant off
M06 Tool change M60 Piecepart (workpiece) change
190 VIII CNC machines
6.4 Tool compensation (Werkzeugkorrekturen)
6.4.1 Tool length compensation (Werkzeuglangenkorrektur)
Tool length compensation refers to the correction required when the actual tool
length is different from the preset tool length. The difference between these
must be entered into the tool compensation register of the CNC machine.
6.4.2 Tool path compensation
The path information in a CNC
program usually refers to the required
G41 G42
form or contour of the workpiece. The
centre of the cutting tool has to follow
a different path at a constant distance
from the contour of the finished
workpiece. The path traced by the axis
of a milling cutter is shown in Fig
8.11. A cutter offset equal to the
radius of the milling cutter is required.
The tool path must be precalculated by Fig 8.11 Milling cutter compensation
the CNC machine's computer.
The preparatory function path code instructions G 40, G 41 and G 42 are used
for tool path compensation. To choose the right code, the programmer has to
look in the feed direction of the tool and observe whether the tool lies to the left
or the right of the workpiece contour. The following codes are used depending
on the relative position of the workpiece and the direction of motion of the tool.
• G 41 when the tool lies to the left of the workpiece.
• G 42 when the tool lies to the right of the workpiece.
• G 40 cancels the cutter compensation.
6.4.3 Tool nose compensation (Schneidenradius-Korrektur)
The tips of single point cutting tools for
lathes, are usually rounded in order to
improve the surface finish of the mach-
ined component and reduce the wear on
the cutting tool. In such a case tool nose
compensation is required if the desired
contour is to be generated. A tool whose (a) (b)
nose is pointed, and one that has been
Fig 8.12 (a) Tool with a pointed nose and
rounded are shown in Fig 8.12 (a) & (b). (b) with a rounded nose
When the tool is rounded, it makes contact
with the workpiece at a point B which is
not the theoretical cutting point P.
6 Programming of CNC machines 191
Fig 8.13 Machining errors during Fig 8.14 Centre point C moves along a path normal to
a turning process the tangent contour of the workpiece
• In the case of feed along the axis {axial-feed shown at A in Fig 8.13) or
at right angles to the axis {cross-feed shown at E in Fig 8.13), no error is
made in the cutting process. This is because the contour generating
tangent through P is on the same straight line as the theoretical cutting
point P, and the straight lines are parallel to the X or Z axes.
• When the feed direction is not along the X or Z axis, the generated
contour is different from the required contour as shown at D in Fig 8.13.
The amount of error is dependent on the angle of inclination of the tool.
The desired shape of contour is machined when the centre point C of the
rounded nose of the tool travels along a path which is at a constant
distance BC normal to the target contour of the workpiece as shown in
Fig 8.14.
A detailed study of part programming procedure is beyond the scope of this
book. Those interested would be able to find details in the many comprehensive
books on this subject. See for example, Steve Krar and Arthur Gill: CNC
technology and programming (McGraw Hill).
6.5 Computer-aided programming (Rechnergestiitztes Programmieren)
6.5.1 Initial development (Entwicklungsverlauf)
After the introduction of the first CNC machines, it soon became apparent that
for complex machining tasks, a large volume of detailed data calculations had
to be carried out before the machining could be done as required. It was
necessary to precalculate the required data, obtain additional data from tables,
and to check that there was no danger of collisions between tools and
workpieces. In order to eliminate these difficulties and to save valuable time and
effort, new programming languages and methods were developed in which the
computer played a major role. The requirements that had to be met were the
1. The possibility of programming complex machining tasks in a simple
way. All detailed data required for carrying out a machining task must be
internally calculated by the computer from the basic geometric data
provided by the programmer.
192 VIII CNC machines
2. Freeing computer programmers from routine tasks like the detailed
calculation of points on profiles, the specification of feed rates and
spindle speeds, and the ensuring of collision-free operation of the
3. A programming language which is easy to learn and is user-friendly.
The first computer language developed for CNC machines was APT
(Automatically Programmed Tools). Many other languages have been
developed subsequently most of them based on APT. In Germany the
language that has been most frequently used has been EXAPT (Extended
Subset of APT). This language is capable of satisfying both geometrical and
technological requirements. In addition to languages like the above, which
can be used with any type of machine there are also other specific languages
which are designed for use with only one type of machine or control system.
6.5.2 Processors and postprocessors (Prozessoren und Postprozessoren)
The program which is written in a programming language like EXAPT is not
in a form which is suitable to control the machine tool. It is converted into a
suitable form in two successive stages by software conversion programs
called the processor and the post processor. The processor itself is language-
specific which means that a processor designed for APT cannot be used with
EXAPT. The postprocessor however has to be machine-specific and has to
generate a program which suits a specific machine.
The original program is first converted by the processor into an intermediate
form called CLDATA (Cutter Location Data,). This form is of a general type
and is not specific to any machine tool or controller. The processor, also
detects programming and geometrical errors and displays them on the screen.
In addition, it performs the necessary detailed calculations and calls up any
subroutines or canned cycles that may be required. Modern processors can
also display the progress of machining on the display screen.
The CLDATA which comes out of the processor is converted by the
postprocessor into a sequence of instructions specifically designed to
control the operation of a specific CNC machine tool. Different types or
makes of machines may need different post processors and specific machine
requirements will have to be strictly followed. Data relevant to the machine
itself are usually stored in a suitable form and can be called up when
required. Computer aided programming has the following advantages:
1. Use of an easy symbolic language to input geometric and technical
2. Reduction in geometric data input with all calculations being done by
the computer.
3. Computer plausibility checks on the correctness of program and data
4. Graphic display of the geometry of the part, and also a graphic
simulation of the cutting process.
IX Other manufacturing processes
(Weitere Fertigungsverfahren)
1 Bulk deformation processes (Massivumformprozesse)
Before metal products can be manufactured, the metal or alloy itself has to be
produced. The metal must have the chemical, physical and mechanical
properties that are required for manufacturing the desired product. Initially the
metal itself has to be produced from ores or scrap metal. This is done in
furnaces by melting and refining. The relatively impure metals or alloys, are
normally cast into ingots, billets or slabs. These are metals in their initial form.
Before they can be used for the manufacture of products, these cast metal forms
have to be transformed into secondary (intermediate or semi-fabricated)
products like metal sheets, wire and rods from which more complex products
can be manufactured. Secondary products are produced by bulk deformation
processes like rolling, drawing, extruding and forging in which large scale
plastic deformation is involved. Unlike in the sheet metal pressing and forming
processes where the changes in thickness are small, bulk deformation processes
cause large changes in diameter, thickness, or other dimensions of the metal.
1.1 Strain (or work hardening) caused by deformation (Kaltharten)
When a metal is plastically deformed, it is strained permanently and becomes
strain or work hardened. The metal becomes brittle, and heat treatment is
required to bring the metal back to a softer and more ductile state, before it can
be used to manufacture metal products.
1.2 Hot deformation processes (Warmumformprozesse)
In hot deformation processes, the metal is deformed after being heated to a
temperature that is above the recrystallisation temperature. The advantages of
the process are:
• The forces and power required to accomplish plastic deformation are
smaller because the metal flows more easily at high temperatures.
• Large deformations are possible without any danger of fracture. The
generation of complex shapes can be done without much difficulty.
• There is no work hardening and the components produced are very
strong and nonporous.
Disadvantages are the oxidation that takes place with me formation of scale on
the surface, and the low dimensional tolerances of the finished products.
Additionally, considerable amounts of energy are needed to heat the product
before it is deformed.
1.3 Cold deformation processes (Kaltumformprozesse)
Cold deformation is carried out at room temperature. This process has the
following advantages:
• The ability to generate products with better surface finish, closer
tolerances, and thinner walls.
194 IX Other manufacturing processes
• The metal object can be allowed to retain its strength in the strain
hardened state, or if preferred heat treated to bring it to a ductile state.
Disadvantages are that the flow stresses are high, requiring high tool pressure
and large amounts of power.
1.4 Rolling (Rollen)
Rolling is the most important of the bulk deformation processes. In flat rolling,
the thickness of a cast slab is reduced resulting in a product that is longer and
thinner, but only slightly wider. Cast slabs are initially rolled by hot rolling
processes. The sheets produced have poor dimensional tolerances and rough
surfaces. These sheets are relatively thick, and are used in such applications as
boiler making, ship building, and in the construction of welded machine frames.
Thinner sheets are produced by cold rolling the thick sheets produced by hot
rolling. Cold rolled sheets have closer tolerances and a better surface finish.
Shape rolling is used to manufacture rods, long bars, etc. each having a uniform
but different cross-section.
In processes like ring rolling (Fig 9.1(b)), and tube rolling (Fig 9.1(f)) which are
used to manufacture hollow products, pierced billets and centred mandrels are
used. Screws, taps, etc. can be produced by thread rolling processes. These
products have screw threads which are stronger than those produced by thread
1.5 Drawing (Ziehen)
In this process, the metal is pulled through a die whose cross-section gradually
decreases. Most wire types of circular, square or other cross-sections are
manufactured by drawing processes.
Many products like nails, screws, bolts and wire frames are made from metal
wires. Seamless tubes are also manufactured by drawing processes. Large
diameter tubes are usually manufactured by hot drawing, but small diameter
tubes below a certain diameter must be cold drawn.
1.6 Extrusion (Strangpressen)
The extrusion process can be used to produce long tubes and rods of uniform
cross-section. In this process, the metal is under pressure and is forced to flow
through a die. The cross-sections of the extruded products can have different
shapes and sizes, depending on the shape and size of the opening in the die.
• In direct or forward extrusion, the extruded metal and the punch which
pushes the metal move in the same direction (Fig 9.1(g)).
• In indirect reverse (or back) extrusion, the extruded metal and the punch
move in opposite directions (Fig 9.1(h)).
• Hot and cold extrusion processes are both possible, and the extrusion of
hollow products is carried out by using a centred mandrel (Fig 9.1(i)).
1 Bulk deformation processes 195
Fig 9.1 (a) Flat rolling Fig 9.1(b) Ring rolling Fig 9.1 (c) Form rolling
J Hi
Fig 9.1 (d) Wire drawing Fig 9.1 (e) Tube drawing Fig 9.1 (f) Tube rolling
Piston Pisto
Fig 9.1(g) Forward extrusion Fig 9.1(h) Reverse extrusion Fig 9.1(i) Extrusion of
hollow products
196 IX Other manufacturing processes
2 Forging (Schmieden)
Metal components can be produced in many ways, by casting, forging, cold
forming, welding, etc. Casting is probably the cheapest process available, but
cast components are often porous and also brittle, with the result that they break
Some metal components like crankshafts, connecting rods, spanners, etc. are
subjected to severe stress when in use. Such components are produced by
forging, because forged components are stronger than those produced by casting
or machining from solid bar material. This is because the grain structure in
these cases is different. Each grain in the metal is a crystallite (or a tiny crystal)
and the strength of the metal depends on the size, shape and orientation of the
grains. The difference in grain structure between a gear tooth that has been
machined and one that has been forged is shown in Fig 9.2.
Forging is a process which uses materials more economically, because the metal
is pressed into the final shape without any wastage as in a machining process.
However the dimensional accuracy of a forged component is poor.
Not all metals and alloys can be forged. Cast iron becomes very brittle when
heated to red heat, and breaks easily when struck with a hammer. Many steels
and other metals however remain ductile at high temperatures, and can be forged
into the required shape. Three ways in which metal objects can be forged are
given below.
2.1 Hand and hammer forging (Hand- und Hammerschmieden)
Over the centuries, blacksmiths produced small quantities of forged components
using hand tools. The red hot metal was forged into the required shape by the
blacksmith who was a highly skilled person. No dies were used in this process.
The forging of much larger components was possible by the use of large
mechanical hammers after the beginning of the industrial revolution. The
power required to operate large hammers became available, but a large degree of
skill was still required.
2.2 Drop forging (Gesenkschmieden)
Drop forging is the most commonly used method for the production of large
numbers of medium sized components. This process uses two half dies which
are kept in close alignment (Fig 9.3). The red hot metal billet is placed in the
cavity between the dies. If pressure is now applied to the top die, the metal is
forced to flow and take the shape of the cavity which exists between the dies,
when they are pressed together. The dimensional tolerances of the forged
component are usually poor, and the component usually needs to be subjected to
a succession of trimming and machining processes before it can be used.
2.3 Upset forging (Schmieden mit Axialdruck)
In this process, apart of the metal used to form the component is heated to red
heat, and axial pressure is applied to change the cross-section of the
component. Several stages are required to produce a component (Fig 9.4).
2 Forging 197
Forged Machined from bar
Fig 9.2 Difference in grain structure between a forged and a machined gear tooth
Finished forging
Fig 9.3 Drop forging produced by using split dies
198 IX Other manufacturing processes
Finished component
Fig 9.4 Several stages in the production of a socket spanner by the method of upset forging
3 The casting of metals 199
3 The casting of metals (Giefien)
Metal objects have been produced by the process of casting for thousands of
years. This is probably the cheapest and quickest way of producing a metal
object, particularly a large and complex one. There are many ways of producing
a casting, some of which are described below.
3.1 Sand casting (SandguB)
Sand casting was probably the oldest way of producing a metal casting. In this
method, the metal is melted and poured into a hollow space in a box filled with
sand. The box with its hollow space is called a mould, and the hollow space has
approximately the same shape and size as the object which has to be produced
as a casting. The production of a casting is usually done in four stages as
1. Making of the pattern
2. Making of the mould
3. Pouring in of the metal from the mould
4. Removal of the casting from the mould
The pattern is a replica of the object to be cast and is usually made from metal
or wood. It is slightly larger than the object to be cast. A wooden pattern is made
of two halves which can be joined together by using dowel pins (Fig 9.7).
Some castings are completely solid, while other castings are partly hollow.
Hollow castings are known as cored castings. The hollow part or core is
separately made as shown in Fig 9.6 and placed in the mould. A mould and a
core which are ready for the pouring in of the metal are shown in Fig 9.8.
The molten metal which is poured into the mould shrinks slightly on
solidifying. The pattern is usually made slightly larger than the final form of the
object to allow for shrinkage, and also so that the casting can be machined to
definite dimensions. These extra allowances in the size of the casting are called
shrinkage and machining allowances. Large and complex objects like engine
blocks, or beds of machine tools are usually made by the sand casting process.
3.1.1 Sands for moulds (Modellsand)
The cheapest sand used for moulds is silica sand (SiO2) and if its composition
and contamination level are carefully controlled, it is usable at the highest
casting temperatures including that for steel. Other special sands used are
zircon, chromite or olivine. The sands need to be bonded by using a bonding
agent or binder to withstand the pressure of the molten metal, and also the
erosion caused by the metal. The bonded sand must be sufficiently porous to
allow the gases present in the molten metal to escape. Sands are tested for
tensile and compressive strength, shear properties, porosity and compactability.
Green sand moulds are bonded with clay, but sometimes a binder like dextrine
is used which hardens the surface.
Dry sand cores are made from silica sand and a binder which is usually an oil
which hardens when heated.
200 IX Other manufacturing processes
Fig 9.5 Finished casting with a cored Fig 9.6 Method of producing cores
Half pattern
Fig 9.7 One half of a wooden pattern Fig 9.8 A mould ready for pouring in
3 The casting of metals 201
Carbon dioxide moulds use silica gel as a bonding agent. When the mould is
finished, carbon dioxide gas is passed through the sand. This produces a hard
mould which does not need baking.
Oil sands consist of sand mixed with a vegetable oil such as linseed oil, and
some cereal flour. On heating the oils form a polymer, which ensures high
strength bonding. These sands are particularly suitable for cores.
Shell moulding is a process which uses a synthetic resin binder and produces
castings with a smooth finish and close dimensional tolerances. The mixture of
sand and resin is placed over the metal pattern which is heated to a temperature
between 200°C and 260°C. The resin in the mixture forms a thin shell over the
pattern. When the shell has reached the required thickness, the sand is removed
by rotating the pattern which results in the sand being thrown out. The
remaining shell is cured on the pattern and then removed. Mating halves of the
shell are combined with a cement and surrounded with sufficient backing
material. The casting is now made by pouring the metal into the resin mould
3.2 Permanent mould casting (GieBen in Dauerformen)
In sand casting, the mould is destroyed after the casting has been made. In the
permanent mould casting processes, the mould can be used repeatedly. The
mould is made from a material which has the following properties:
1. A sufficiently high melting point to withstand erosion by the metal.
2. A strength that is high enough to prevent deformation under repeated use.
3. A high thermal fatigue resistance that prevents the formation of fatigue
4. A low level of adhesion to the molten metal. This prevents the metal from
welding itself to the mould.
Mould materials used are cast iron, alloy steels, molybdenum alloys and also
Coatings composed of refractory powder in a suspension are applied to the die
surface as protection for the surface and to reduce heat transfer.
Parting compounds consisting of graphite, silicone, etc. are used to reduce
adhesion and help ejection of the casting from the mould.
Metals suitable for casting by this method are alloys of zinc, aluminium,
magnesium and lead, certain bronzes and cast iron. The castings cool rapidly in
the permanent moulds, and therefore have a dense fine grained structure which
is free from blow holes or shrink defects. Better surfaces and closer tolerances
are obtained in comparison with sand castings.
3.2.1 Gravity die casting (GieBen mit Schwerkraft)
This process uses permanent moulds which are made as two halves which can
be assembled together during casting and moved apart for removal of the
casting. The molten metal is poured into the mould and fills it under the action
of gravity. Automatic machines have hydraulic actuators and automatic feed
systems to feed in the metal.
202 IX Other manufacturing processes
3.2.2 Pressure die casting (Druckgieften)
In this process, the molten metal is forced into the mould cavity by external
pressure. The metal is forced hard against the surface of the cavity producing a
very accurately made casting with an excellent surface finish. Such castings
are superior to those made by the gravity die casting process and do not need to
be subjected to further machining or finishing processes. There are two types
of pressure die casting processes (a) the hot chamber process and (b) the cold
chamber process
(a)The hot chamber process (Warmkammerverfahren)
The goose neck machine (Fig 9.8 (b)) used in this process, has a goose neck
which dips into the melting pot. The liquid metal is transferred to the mould
directly from the melting pot by a pump consisting of a cylinder and a plunger.
(b) The cold chamber process (Kaltkammerverfahren)
Here the metal is melted outside the machine and sufficient metal for each
casting is poured in manually or automatically into the shot chamber. The
plunger moves and pushes the molten metal into the mould. In all the above die
casting processes, the casting is ejected from the die after solidifying and the
machine automatically proceeds to make the next casting.
Fig 9.9 (a) Cold chamber pressure die Fig 9.9 (b) Hot chamber pressure die
casting casting
3.2.3 Centrifugal casting (SchleudergieBen)
In centrifugal casting, a portion of molten
metal is poured into a hollow water cooled Molten Water.jacket
metal tube (lined with refractory material) metal
which acts as a mould. The mould is
rotated at high speed, and the centrifugal
forces cause the molten metal to be
pressed tightly against the mould. The Refactory lining
metal solidifies quickly due to the water Fig 9.10 Centrifugal casting
cooling, and a sound dense casting in the
form of a tube is produced.
4 Shearing and blanking 203
4 Shearing and blanking (Scheren und Stanzen)
The terms cutting, shearing and blanking refer to some of the ways of separating
a sheet of material into parts.
4.1 The cutting process (Messerschneiden)
In a cutting process a knife whose cutting edge is shaped like a wedge is pressed
against a material to separate it into parts (Fig 1 l(a), (b) & (c)). This method of
separation can only used with soft materials like paper or leather.
4.2 Shearing (Scherschneiden)
This is the term applied to a process where the separation of the material takes
place between two cutting edges which pass each other (Fig 9.1 l(d)). Hand
shears are used for cutting pieces of material by hand. The cutting blades are
hollow ground so that when cutting takes place, the blades touch each other
only at one point. Guillotines are used for the cutting of large sheets, while
presses can be used for the blanking of complex forms.
U U II Lfr
1 I I I
(a) (b)
Fig 9.11 (a), (b) & (c) Cutting process
[) Fig 9.11 (d) Shearing process
4.2.1 Types of shearing operations (Verfahren beim Scherschneiden)
1. Blanking (Stanzen) refers to the removal of a piece of material of the
desired shape from a larger sheet. The removed piece is in this case more
important than the hole produced.
2. Piercing (Lochen) refers to the production of a hole of any shape in a
sheet of metal by the use of a punch and a die. The removed piece of
material is not important and is regarded as scrap.
3. Punching is a special kind of piercing where a circular hole is produced.
4. Notching (Ausklinken) refers to the removal of a piece of metal from the
edge of a metal sheet.
5. Lancing (Einschneiden) refers to the process of partially cutting through
a sheet of metal without removing any material.
6. Slitting (Abschneiden) refers to the operation of cutting a metal sheet
along a straight line parallel to its length.
7. Perforating (Perforieren) refers to the production of a regularly spaced
array of holes in a sheet of material.
204 IX Other manufacturing processes
8. Nibbling (Knabberschneiden, Nibbeln) refers to the use of repeated small
cuts in order to remove a piece of metal from a metal sheet.
9. Trimming (Beschneiden, Trimmen) is a term used to describe the
removal of excess material from a pressing (or pressed object).
4.3 Press tools (Schneidwerkzeuge)
Press tools (or die sets) consisting of punches and dies are used for the blanking
and piercing of large numbers of metal parts. The basic construction of one
type of press tool is shown in Fig 9.12.
Sliding pillars (Fiihrungssaule) are used to guide the punch precisely as it
moves downward into the die.
Stripper plate (Abstreifer) - The stripper plate is mounted above both the die
and the metal strip from which the blanks are produced. The stripper plate has
an opening large enough for the punch to pass freely through. As the punches
rise after the downward stroke, the metal may be lifted. The stripper plate
prevents the strip from rising too far.
Stops (Anlagestifte) are devices used to ensure that successive blanks cut from
the sheet have the optimum spacing. The stops are set in the right position to
ensure that the largest number of blanks can be cut from the sheet of metal. Two
types of stops that are frequently used are the button stop and the lever stop.
Pilots (Suchstifte) are rods which are used to ensure correct location of the
blank when it is fed by mechanical means. The pilot enters a. previously pierced
hole and moves the blank to the correct position.
Punch clearance (Schneidspalt) - The die has an opening to allow the punch to
pass through it. The opening is slightly larger than the punch and has the same
shape as the periphery of the punch. The gap or clearance between the punch
and the top or cutting edge of the die has to be carefully controlled. Its value
depends on the thickness and the shear modulus of the sheet which is being
blanked. The clearance varies between 0.5 % and 5 % of the sheet thickness.
4.4 Blanking (Stanzen)
Blanking can be done by using a press that is fitted with an appropriate die set.
The double blanking die set shown in Fig 9.12 consists of two punches and a
die. The punches which have sharp edges at the bottom are attached to a punch
holder which is fitted with two guide collars. The collars can move vertically on
two pillars attached to the die set. The punches are slightly smaller than the
holes in the die.
The metal in the form of strip is fed in from the right side, up to the small stop
stud. The punches now move down through the stripper plate, and two blanks
are punched from the strip. As the punches rise after the downward stroke, the
metal strip will be lifted, but is prevented from rising too far by the stripper
plate. The metal strip is next pushed forward by an appropriate distance
determined by the stop stud, and the punches move down to produce two more
blanks. The process can be continued as long as necessary.
4 Shearing and blanking 205
Guide Blanking
collar punches
^e stop Die with two holes Stripper
_^^^__^^_^ plate
O O O O \ __^- Metal strip with
O (~\r\f\* blanked holes
Fig 9.12 Blanking die set with two punches
Blanking Piercing
punch punch
Strip feed
Fig 9.13 Combined blanking and piercing using a follow-on die set
206 IX Other manufacturing processes
4.5 Follow-on (or progressive) die sets (Folgeschneidwerkzeuge)
A follow-on die set can be used to perform two or more operations simultan-
eously with a single stroke of the press. This is done by mounting separate sets
of punches and dies in two or more positions. The metal sheet or strip is moved
from one position to another, until the complete part is produced.
A two position die set used for the production of washers is shown in Fig 9.13.
The metal strip is fed in from the right into the first position, where a hole is
produced by the first die set in the first downward stroke of the ram. The metal
strip is advanced to the next position, the correct position being controlled by
the stop shown in the diagram. In the second stroke of the ram, the pilot enters
the already pierced hole and locates it correctly, while the blanking punch
moves down and shears the metal strip to produce a washer.
Although two strokes of the ram are needed to produce a washer, a complete
washer is delivered after each stroke of the ram due to the follow-on action.
4.6 Compound die sets (Gesamtschneidwerkzeuge)
In a compound die set two or more shearing operations are carried out at one
position of the press for each stroke of the ram. For example the follow-on die
set shown in the previous section could be replaced by a compound die set
which cuts the outside and the inside peripheries of the washer in one stroke.
This arrangement eliminates any undesirable displacements in position between
the inside and outside peripheries of the washer due to inaccurate feed
movements between the two strokes or due to sideways play of the metal strip in
the feed track.
Compound die sets are used in cases where the positional deviation between the
inside and outside peripheries must be kept within close limits. A good example
is the manufacture of precision mechanical components like multiple contacts
which are used in the mounts for semiconductor chips.
4.7 Combination die sets (Kombinierte Werkzeuge)
In a combination die set both shearing and nonshearing operations are
performed at one position for each stroke of the ram. For a combination die set
can carry out both blanking and drawing operations if blanking and drawing dies
are built into it.
5. Thermal cutting of metals (Thermisches Trennen)
5.1 Oxygen cutting II 1 I
(Autogenes Brennschneiden) \mlJir A
Oxygen cutting depends on the fact /yMt /) Stytene
that iron oxidizes rapidly in the / Tlf, // Oxygen only
presence of oxygen at a temperature / // //
of 816°C. This temperature is well I M V
below the melting point of iron.
Fig 9.14 Oxygen cutting
5 Thermal cutting of metals 207
This process can only be used only with iron and steel products which have a
low alloy content. It can be used to cut steel products such as sheets, bars, pipes,
forgings, castings, etc. The type of burner used is shown in Fig 9.14. A mixture
of oxygen and acetylene flows through the outer tube and when lighted
prewarms the metal at the cutting point. The stream of oxygen coming out of the
central tube hits the central spot. The steel is oxidized and the resulting slag is
carried away by the stream of oxygen and a narrow clean cut is produced.
5.2 Plasma cutting (Plasmaschneiden)
Plasma cutting is a process that can be used to cut alloy steels and nonferrous
metals. The oxides formed by these materials have melting temperatures which
are higher than the melting temperatures of the metals themselves. The type of
burner used is shown in Fig 9.15. This process uses a tungsten electrode.
Electrode • Lens
cooling Gasi
Focused laser beam
Fig 9.15 Plasma cutting Fig 9.16 Laser cutting
A pilot arc is first produced between the electrode and the nozzle by using a
high frequency source. If the gas is now allowed to flow past this arc, the gas
becomes ionized and an arc is now struck between the electrode and the
workpiece. This arc soon becomes a high density plasma jet with temperatures
of above 20,000 °C. The thin jet melts a thin portion of the metal and flushes it
away. Ordinary carbon steels are cut by using air or oxygen, while nonferrous
metals and stainless steels are cut by using a mixture of hydrogen and argon, or
hydrogen and nitrogen.
5.3 Laser cutting (Laserschneiden)
When the radiation from a laser beam is focused, the intensity can be great
enough to cause the melting of a metal (Fig 9.16). A lens is used to focus the
light from a laser beam to a spot having a diameter between 0.1 and 0.3 mm.
The energy density which reaches a level of about 107 W/cm2 quickly melts the
metal. The melted metal is carried away by a stream of gas. A 1 kW laser can
cut through lm thick steel sheets. Laser cutting is a process that can be used to
cut almost any type of metallic or nonmetallic material.
208 IX Other manufacturing processes
6 Bending and forming processes (Umformverfahren)
6.1 Introduction (Einfuhrung)
Many products are manufactured by bending and forming sheet metal into
various shapes. These are cold working operations in which the sheet metal is
plastically deformed. The sheet metal has to be stretched beyond the elastic
limit, but care has to be taken that the stretching does not go so far as to cause
cracking or fracture of the metals. Metals suitable for this kind of work are low
carbon steels, killed steels and alloys of copper or aluminium.
6.2 Forming by bending (Biegeumformen)
In some cases, simple bending of a metal sheet is all that is necessary to yield
the required product. Die sets in mechanical presses are used to bend small
pieces of metal into complicated shapes. Special presses with long beds called
press brakes are used for the bending of longer pieces of metal. The type of die
set used in a press brake is shown in Fig 9.17. Repeated bending (Fig 9.18) may
be used to produce more complex shapes. It may also be possible to form more
complex shapes by passing the strips or sheets through successive sets of rollers
with specially shaped wheels.
Fig 9.17 Die set for a press brake Fig 9.18 Repeated bending
using a press brake
Metal sheet
Fig 9.19 Stretch forming using a punch without a die
6 Bending and forming processes 209
Metal blank
Fig 9.20 Stretch drawing
6.3 Stretch forming (Streckziehen)
In the stretch forming process, the metal sheet is clamped round its periphery.
This process uses only a punch to stretch the clamped sheet (Fig 9.19). The
change in shape causes the sheet to stretch and become thinner. An example of
stretch drawing is shown in Fig 9.20.
6.4 Deep drawing (Tiefziehen)
In this process, the metal blank which is not clamped is allowed to draw into the
die. A number of stages are required satisfactory deep drawing. The first stage
which is shown in Fig 9.21 is called cupping.
Initially the pressure pad presses firmly on the die. When the punch moves
downwards, the blank is pushed into the cavity. The metal bends and flows
plastically when it is drawn into the cavity to form a cup. Any wrinkles formed
at this stage are ironed out by the pressure pad. Several stages of drawing are
required to produce deeper objects. Simultaneous blanking and drawing can be
carried out by using combination dies.
Metal blank
Fig 9.21 First stage in a deep drawing process (also called cupping)
6.5 Other forming operations (Weitere Umformverfahren)
• Beading is an operation which improves the appearance, safety, strength
and stiffness by folding over the edge of the metal sheet (Fig 9.22(a).
• Curling is a similar operation to beading in which the edges of a metal
sheet are curled or rolled over (Fig 9.22(b)).
210 IX Other manufacturing processes
Plunging is an operation in which a hole in a metal sheet is bent into a
shape suitable to take the head of a screw, by pressing a punch through
the hole (Fig 9.22(c)).
Flanging is an operation by which edges of various angles and widths
may be produced on flat or curved metal sheets or tubes (Fig 9.22(e).
Folding is an operation in which two sheets of metal are folded to form
interlocking joints (Fig 9.22(d) and soldered to make them water-tight.
Cold forming , coining and embossing are operations in which a piece of
metal placed between a punch and a die is subjected to a very high
pressure applied from both sides. The metal is forced to flow while in the
cold state and fills the space between the punch and the die.
(a) Beading (b) Curling (c) Plunging
(d) Folding (e) Flanging
Fig 9.22 Some bending and forming processes
6.6 Spinning (Drucken)
In this process, a thin sheet of metal is revolved at high speed and pressed
against a former which is attached to the spindle of a lathe. The metal is
supported through a pressure block at the tailstock. A special tool is used to
press the metal sheet so that it acquires the shape of the metal former (Fig 9.23).
Metal sheet
I Pressure block
Rotating former
Fig 9.23 Metal spinning
7 The coating of surfaces 211
7 The coating of surfaces (Beschichten)
7.1 Introduction (Einfuhrung)
Surface coatings are an important part of many products and a variety of
coatings are used for purposes of decoration, surface protection, improving
corrosion resistance, and for improving the wearing qualities of the surface.
It is at first necessary to clean the surface thoroughly so that it is free of dirt,
oil, grease, scale, oxides, etc. which affect the adhesion and the life of the
coatings. The different types of coatings may be divided into the following
1. Metallic coatings
2. Organic coatings
3. Inorganic coatings
4. Chemical conversion coatings
7.2 Metallic coatings (Metallische Uberziige)
Metallic coatings may be applied in many ways, by electroplating, hot
immersion, chemical deposition or by the spraying of hot metal (metallizing).
7.2.1 Electroplating (Galvanisieren)
In this process, a current is passed between two electrodes, an anode and a
cathode which are placed in a solution of a salt (or compound) of the metal
which forms the coating. The metal object to be plated is attached to the
cathode, while the metal which forms the coating is attached to the anode.
(a) Zinc plating is the cheapest and most commonly used form of
plating. It is mainly used to plate steel and iron objects, and is able to
provide them with good protection against corrosion.
(b) Cadmium plating is more expensive than zinc but has the advantage
of providing better corrosion protection under salty conditions.
(c) Nickel plating provides a surface which has excellent wear and
corrosion resistance and the ability to be joined by soldering or
(d) Tin plating provides a good surface, but is relatively expensive to
make. It is mainly used for coating tin cans, kitchenware and food
containers because of good tarnishing resistance, and also because of
the nontoxic nature of the oxides formed.
(e) Copper plating has decorative value, but has to be protected from
oxidation by a clear lacquer.
(f) Silver plating is used mainly for decorative purposes. Disadvantages
are its high cost and its susceptibility to tarnishing.
(g) Gold plating is used mainly for decorative purposes and for its
excellent resistance to tarnishing. It is used for plating jewellery,
watches, etc. and for plating electronic components and circuits.
(h) Chromium plating is used because of its decorative properties and
also for producing wear-resistant surfaces on tools, piston rings, etc.
212 IX Other manufacturing processes
7.2.2 Hot-dip coating (Schmelztauchuberziige)
This is a rapid and inexpensive process that is cheaper than electroplating. All
parts of the object to be coated including joints and crevices can be covered.
The commonest process is galvanizing (or hot-dip galvanizing), in which
thoroughly cleaned objects made of iron or steel are dipped in a bath of molten
zinc. Zinc gives electrochemical protection against rusting, and can be effective
in preventing rust even when part of the coating is removed. Aluminium, tin and
lead coatings can also be applied by the hot-dip method.
7.2.3 Metallizing (or thermal spraying) (Metall-Spritzuberztige)
In this process, metallic or sometimes nonmetallic coatings can be deposited by
spraying fine globules of the coating material on the object to be coated. The
metal is initially in the form of rod, wire or powder. The commonly used flame
spray process uses a spray gun that feeds the metal wire through a nozzle
surrounded by an oxy-acetylene flame. A stream of air breaks the molten metal
into globules and sprays it on the surface.
The sprayed metal is porous and can absorb oil. Bearing surfaces from Babbitt
metal can be built by metal spraying. Sprayed coatings are used for building up
worn components, for corrosion protection and for improving the wearing
qualities of the surfaces. Paper and cloth are coated with sprayed metal for use
in electrical capacitors.
7.3 Organic coatings (Organische Uberziige)
Organic coatings may be divided into three classes - paints, varnishes and
lacquers. These usually have three main constituents:
• A vehicle binder (or filmogen) like a drying oil or a resin.
• A pigment
• A thinner
In addition other ingredients (often called additives) like plasticizers, catalysts,
emulsifiers, antifoamers and thickeners are added as required.
Pigments may be natural or synthetic, organic or inorganic, opaque or
nonopaque. Inorganic pigments like white zinc oxide or titanium oxide, red iron
oxides or red lead (for rust prevention), yellow iron oxide or zinc yellow, blue
ultramarine, etc. are used in addition to organic dyes.
7.3.1 Paints (Lacke)
a) Oil paints contain oil as a vehicle, and are mainly used for exterior
surfaces. They need a relatively long time for drying.
b) Enamel paints are harder, glossier and smoother than other types of
paints. This arises from the use of resin or varnish as the vehicle. Enamels
are widely used as organic coatings in the metal processing industry,
because of their availability in a large range of colours, their resistance to
corrosion, and their ease of application.
c) Baked enamels have a harder finish, which is more abrasion resistant
than typical air-drying enamels.
7 The coating of surfaces 213
d) Bituminous paints are used to protect metal and masonry where there is
no objection to their black colour. They contain hard asphalts cooked with
drying oils.
7.3.2 Varnishes (Klarlacke)
A varnish is a mixture of resin and drying oil dissolved in a volatile thinner.
Varnishes may be clear or may contain a dye, but they do not hide a surface
when applied to it. The addition of a pigment produces an enamel which hides
the surface.
a) A spirit varnish is a solution of resin alone in a thinner, for example
shellac varnish.
b) An oleoresinous varnish consists of a mixture of resin and drying oil
dissolved in a thinner.
c) A spar varnish is made of a mixture of phenolic resin, dehydrated castor
oil and linseed oil dissolved in a thinner.
7.3.3 Lacquers (Schnell trocknende Lacke)
Present day lacquer refers to quick drying coatings which contain cellulose
acetate, cellulose nitrate, or cellulose acetate butytrate. In addition they contain
resins, plasticizers and solvent.
7.3.4 Special paints (Speziallacke)
Numerous types of paints are produced which are required for a special purpose,
have a special finish, and have special ingredients and formulas. Among these
are paints resistant to chemicals, emulsion paints, powder coatings, fire-retardant
paint, marine paint, fungicides, wood preservatives, crackle finish paint, hammer
finish paint, etc.
7.4 Inorganic coatings (Anorganische tjberzuge)
Inorganic coatings mainly contain refractory materials. They have an attractive
finish and also good resistance to corrosion and oxidation. They have surfaces
which are hard, rigid, abrasion resistant, and thermally insulating. They can also
resist high temperatures.
a) Porcelain enamels have surfaces with the strength and stability of steel
combined with the beauty and usefulness of glass. They are durable, easy
to clean, and have good colour stability.
Porcelain enamels can be applied in many ways, by dipping, by manual
and electrostatic spraying, flow coating and by the application of dry
powder. The coated objects are fired at temperatures of about 600°C.
Conveyer equipment can be used for successive operations like spraying,
dipping, drying and firing. Very often a single coat is sufficient, and this
is usually of good quality and inexpensive to make.
b) Ceramic coatings are particularly useful as protection for surfaces that
are subjected to elevated temperatures. In addition to protecting metal
surfaces from oxidation and corrosion, ceramic coatings increase their
strength and rigidity.The materials used in the coatings are mainly silicate
214 IX Other manufacturing processes
powders, but carbides, silicides and phosphates may also be used. The
coatings may be applied by spraying, dipping, flow coating, etc.
7.5 Chemical conversion coatings
(Beschichten durch chemisches Abscheiden)
Chemical conversion coatings are produced when a film is deposited on the
surface as a result of a chemical reaction. The most important types of coatings
are described below.
a) Phosphate coatings are mainly used as a base for the application of
paint or enamel. The surface is treated with a dilute solution of
phosphoric acid and other ingredients to form a mild protective layer of
crystalline phosphate. This process is widely used in the automobile and
electrical appliance industries.
b) Chromate dip coatings are used as an added corrosion protection for
zinc or cadmium coated steel sheets. They are also used for protecting
objects made of nonferrous metals like aluminium and magnesium. The
coatings are very thin and also as a base for painting. The object to be
coated is dipped in a solution of chromic acid mixed with other acids and
salts. The chemical reaction produces a protective film containing
chemical compounds. Coloured coatings can be produced by adding
suitable organic dyes.
c) Anodic coating refers to the process of forming an oxide coating on the
surfaces of metals like aluminium and magnesium. Here the object whose
surface is to be anodized is made the anode in an electrolytic bath
containing chromic and other acids. An oxide coating is formed which
protects the metal from corrosion and acts as a base for painting. This
process is widely used in the aircraft industry. Excellent coloured
coatings may be produced by immersing the coated objects in warm dye
solutions and then sealing the dye in the porous coatings by dipping in
dilute nickel acetate.
8 The manufacture of plastic goods
(Herstellung der Kunststoff Produkte)
8.1 Introduction (Einfuhrung)
Plastic products are of recent origin, but they are being increasingly used,
particularly as replacements for metal products. This is because they are cheap,
light, easy to manufacture, and easy to maintain.
Processes used in the manufacture of plastic goods are very cost-effective,
because products having complicated shapes can be produced in a single
operation, with no further work having to be done on them. However the dies
used in these processes have to be very precisely made and must have an
excellent finish. This makes the dies very expensive to make, and the processes
can only be profitable if large quantities of goods are produced. The raw
materials used in manufacturing these goods are usually in the form of powder
granules or liquid. The plastic materials which are most commonly used are of
8 The manufacture of plastic goods 215
two types, thermoplastics which can be moulded several times, and
thermosetting plastics which can be moulded only once.
8.2 The injection moulding process (SpritzgieBen)
This is a process that is used for the manufacture of thermoplastic goods and is
probably the most widely used process in the manufacture of plastic products.
The raw material which is in the form of granules, is fed into a heated
plasticizing chamber through a screw feed mechanism (Fig 9.24).The raw
material is first heated, compressed and degassed, until it is in a soft state. The
screw feed mechanism is next given a sudden push forward. This forces the soft
plastic through an injection nozzle into a two piece mould.The mould is next
cooled rapidly, causing the plastic in the mould to harden quickly. When the
plastic has hardened, the mould opens, and the finished component is ejected
from the mould.
8.3 The extrusion process (Extrudieren)
The extrusion process is commonly used for the production of bar, tube, sheet,
etc. from thermoplastic materials. Extrusion machines have screw feed mechan-
isms similar to those fitted be to injection moulding mchines. The soft plastic is
forced through a die (which has the desired cross-section) in the form of a
strand, and is hardened by cooling in a stream of air. Bars, sheets, tubes, etc. are
semifabricated products which are used to fabricate more complicated
8.4 Thermoforming processes (Warmumformen)
Open container like objects can be made by thermoforming processes from
thermoplastic sheets which are heated to temperatures of between 60° and 90°C.
a) In the vacuum forming process, the sheet is clamped round its periphery
and heated. When the sheet has become soft, a vacuum is applied from
below and the sheet is drawn into the female die. On cooling the plastic
sheet has the form of the die (Fig 9.25).
b) In pressure assisted vacuum forming, air pressure is applied from above in
addition to the vacuum applied from below (Fig 9.26).
8.5 Extrusion blow moulding (Druckumformen)
In this process, extruded pieces of soft plastic tubing are pinched off and welded
to the bottom of a die (Fig 9.27). Air at high pressure is blown into the soft tube
causing it to expand and take the shape of the mould. The moulded object
hardens on cooling and is removed by separating the two halves of the die.
8.6 Compression moulding (Formpressen)
This process is used for the moulding of objects made from thermosetting
plastics. An appropriate amount of raw material in the form of granules is first
introduced into a heated mould. When the material has softened, a plunger
moves down and compresses the material as shown in Fig 9.28. Continued
heating and pressure lead to the formation of a hard object, which is finally
ejected from the mould. Objects made from thermosetting plastics remain
permanently hard and cannot be softened and moulded again.
216 IX Other manufacturing processes
Two piece
Granules of
Z mould Heater
raw material
— Ram
Soft Feed Hydraulic
plastic screw cylinder
Fig 9.24 Diagram of an injection moulding machine
Plastic sheet Pressure Heater
after forming
Clamp •
Vacuum Vacuum
Fig 9.25 Vacuum forming Fig 9.26 Pressure assisted vacuum forming
8 The manufacture of plastic goods 217
Air pressure
Extruded[ Extnruding
tube »
Pinched-off tube welded to
bottom of forming die
Fig 9.27 Extrusion blow moulding
Plastic I |C~ 1 1
granules I 1 ^Punch
., .—«
• •
Heater Formed
Ejector product
(a) Filling (b) Compression operation (c) Ejection operation
Fig 9.28 Compression moulding
List of symbols (Only the symbols used in this book have been listed)
Symbol Units Englisch Deutsch
a m/sz acceleration Beschleunigung
A m2 area Fla'che, Flacheninhalt
c J/kgK specific heat capacity spezifische Warmekapazitat
C J/K heat capacity Warmekapazitat
d m, mm diameter Durchmesser
E J energy Energie
E NW Young's modulus or modulus Elastizitatsmodul
of elasticity
F N force Kraft
f 1/s frequency Frequenz
f mm deflection Durchbiegung
g m/s2 acceleration due to gravity Fallbeschleunigung
G N/mmz modulus of rigidity or Schubmodul
shear modulus
h m height Hohe (allgemein)
H J enthalpy Enthalpie
I mm4 second moment of an area Flachenmoment 2.Grades
h mm4 polar second moment of an Polares Flachenmoment
area 2.Grades
J kgm2 moment of inertia Tragheitsmoment
k m radius of gyration Tragheitsradius
k 1 coefficient of restitution StoBzahl
I m, mm distance, length Abstande, Lange
m kg mass Masse
M Nm moment Moment
P W,kW power Leistung
P N/m2,Pa pressure Druck
Q J heat Warme
qm kg/s mass flow Massenstrom
m7s volume flow Volumenstrom
r m,mm radius, radius of gyration Radius, Tragheitsradius
Rt J/kgK special gas constant spezielle Gaskonstante
R J/mol.K universal gas constant universelle Gaskonstante
s m, cm, displacement (vector) Weglange
mm distance (scalar)
S mmJ elastic section modulus Widerstandsmoment W
S J/K entropy Entropie
t s time Zeit
T s period Periodendauer
List of symbols 219
T Nm twisting torque Torsionsmoment
T K Kelvin temperature Kelvin-Temperatur
u m/s initial velocity Anfangsgeschwindigkeit
U J internal energy Innere Energie
V m/s velocity Geschwindigkeit
V m2/s kinematic viscosity Kinematische Viskositat
V 1 Poisson's ratio Poisson-Zahl
V 1 safety factor Sicherheit
V mm3 volume Vo lumen
w m/s average velocity of fluid flow Stromungsgeschwindigkeit
W J work Arbeit
a 1 coefficient of contraction Kontraktionszahl
a 1/K coefficient of linear Langenausdehnungs-
expansion koeffizient
fi 1/K coefficient of areal expansion Flachenausdehnungs-
7 1/K coefficient of volume Volumenausdehnungs-
expansion koeffizient
y 1 shear strain Schubverformung
s 1 longitudinal strain Dehnung
C 1 resistance number for bends Widerstandszahl fur
and valves in pipes Krummer und Ventile
n 1 efficiency Wirkungsgrad
n Ns/m2 dynamic viscosity Dynamische Viskositat
6i rad angle of rotation Drehwinkel
°,rad angle Winkel
e °C Celsius temperature Celsius-Temperatur
K 1 isentropic exponent Isentropenexponent
X 1 tube flow resistance Widerstandszahl fur
coefficient Rohrleitungen
M 1 coefficient of friction Reibungszahl (Reibzahl)
M 1 coefficient of discharge AusfluBzahl
P angle of friction Reibungswinkel
P kg/mJ density Dichte
P mm radius of curvature Krummungsradius
a N/mmz normal stress Normalspannung
X NW shear stress Tangentialspannung
1 coefficient of velocity Geschwindigkeitszahl
9 °,rad angle of twist Verdrehwinkel
CO rad/s angular velocity Winkelgeschwindigkeit
Vocabulary 1
Englisch Deutsch Englisch Deutsch
ability FShigkeit appropriate passend, geignet
abrasion Abrieb, Abnutzung arbitrary beliebig
abrasive particles Schleifkorner arbor Fraserdorn
abrasive wheels Schleiflcorper arc Bogen, Lichtbogen
abrupt plotzlich area Oberflache
absorb v aufnehmen, armature Anker
absorbieren arrangement Ordnung, Einrichtung
absorptivity Absorptionskraft assembly Montageablauf
acceleration Beschleunigung assign v anweisen, zuteilen
accessible zuganglich associate v verbinden, angliedern
achieve v ausfuhren, erzielen assume v annehmen
acquire v erwerben, erlangen assumption Annahme
act v wirken at right angles rechtwinklig
action Wirkung attachments Zusatzgerate
actuator Stellglied attract v anziehen
adaptive control Maximierung der automatic lathes Drehautomaten
Leistung average value Durchschnittswert
additives Zusatzstoffe avoid v vermeiden
adhesion Anhanglichkeit axial locking devices Wellensicherungen
adhesives Klebstoffe axis Achse
adiabatic adiabate backlash Flankenspiel
adjacent angrenzend, neben ball bearings Kugellager
adjust v regulieren barrel finish v trommelpolieren
adjusting ring Stellringe basic size NennmaB
or set collar bead v bordeln, falzen
advantage Vorteil beam Trager, Tragbalken
adverse entgegenwirkend bearing Lager
align v anordnen bearings with Walzlager
alignment Anordnung, rolling elements
Anpassung behave v sich benehmen
allowable stress zulassige Spannung behaviour Verhalten, Benehmen
alloy Legierung belt drive Riemengetriebe
angle Winkel bend v biegen
angle milling cutters Winkel-Stirnfraser bending process Biegeumformen
angular impulse Drehimpuls bending moment Biegemoment
angular velocity Winkel- bevel gears Kegelrader
geschwindigkeit billet Knuppel
anneal v weichglilhen binder Bindemittel
apparent weight scheinbares Gewicht blank v stanzen
appear v erschneinen blast furnace Hochofen
appearance Aussehen blow StoB
appliance GerSt, Apparat bolts (with nuts) Schrauben (mit
application Anwendung Muttern)
apply v anwenden boring bars Bohrstangen
approach v sich nahern boundary condition Randbedingung
Enghsch/Deutsch 221
brass Messing chucks Futter
braze v hartloten circuit Schaltung
or hard solder v clamps Klemme,
break Bruch Spannelemente
breakdown v abbrechen claw-type clutches Klauenkupplungen
breaking strength Bruchfestigkeit clearance angle Freiwinkel
brittleness Sprodigkeit clearance fit Spielpassung
broach v raumen clinker Klinker, Schlacke
buckle v knicken clockwise Uhrzeigersinn
buff v hochglanzpolieren clutches schaltbare
bulk deform v massivumformen Kupplungen
buoyancy Auftrieb coarse grob
bush Lagerbuchse coarse grain grobkornig
butt joint Stumpfnaht coating Oberzug, Schicht
butt weld v Abbrennstumpf- coat v beschichten
schweiBen coefficient of StoBzahl
cam Nocken restitution
cantilever Freitrager coke Koks
carbon Kohlenstoff collets (or collet Spannzange
carbon content Kohlenstoffinhalt chucks)
carbon steel Kohlenstoffstahl collide v stoBen
carburize v aufkohlen collision Stofi, Kollision
carriage Werkzeugschlitten column Druckstab, Saule
carrier Mitnehmer column and knee Konsolfrasmachinen
case hardening Einsatzstahle type of millimg
steels machines
cast alloys GuBlegierungen combination die sets kombinierte
cast iron GuBeisen Werkzeuge
catch plates Mitnehmerscheibe combine v kombinieren
cause v verursachen commutator Kommutator
cavity Hohlraum compact kompakt, fest
centre drill Zentrierbohrer compare v vergleichen
centre of gravity Schwerpunkt compel v zwingen, notigen
centre of mass Massenmittelpunkt compensate v entschadigen,
centreless grinding Spitzenlosschleifen component Bestandteil
(process) composed of v bestehen aus
centrifugal casting SchleudergieBen composite materials Verbundwerkstoffe
(process) compound die sets Gesamtschneid-
centroid Flachenschwerpunkt werkzeuge
chain drive Kettengetriebe compound table Rechtecktisch
chamber Kamraer compressible komprimierbar
change of phase Anderung des compression Verdichtung
Aggregatzustandes compression formpressen
change of state Zustandsanderung mould v
channel Rille compression stress Druckspannung
charcoal Holzkohle compressor Kompressor
chemical analysis chemische Priifungen conclusion Endergebnis
chemical reaction chemische Reaktion concrete Beton
chisel MeiBel condensation Kondensation
choose v wahlen
222 Vocabulary 1
condition Bedingung, dead centre Zentrierspitze
Voraussetzung decelerate v verz6gern
conically kegelformig decorative dekorativ
connecting rod Pleuelstange deep draw v tiefziehen
consider v nachdenken, defect Mangel, Defekt
iiberlegen deficiency Mangel, Schwache
consideration Erwagung deflection Durchbiegung
contact Beriihrung deflection angle Neigungswinkel
contain v enthalten deform v verformen
contamination Verunreinigung deformation Verformung
content Inhalt degree of freedom Freiheitsgrad
continuity equation Kontinuitats- density Dichte
gleichung depend (on) v abhangen (von)
continuous ununterbrochen deposit v ablagern
continuously stufenlose Getriebe deprive v entziehen
variable speed depth Tiefe
drives description Beschreibung
contour Kontur design v entwerfen
conventional herkommlich desirable wiinschenswert
conversion Umwandlung destroy v zerstoren
conveyor F6rderband deteriorate v sich verschlechtern
coolant Kuhlflussigkeit determination Entschlossenheit
correspond (to) v entsprechen determine v bestimmen
corrosion Korrosion detrimental schadlich
corrosion resistant korrosionsbestandige development Entwicklung
steels Stahle deviation Abweichung
cost-effective kostengiinstig diameter Durchmesser
cotter pins Splint diathermic diatherm
counterboring zylindrische Senkung die Schneideisen
(process) differ (from) v abweichen (von)
countersinking Kegelsenkung dimension Dimension
(process) direction Richtung
countersunk screw Senkschraube discontinuity Unterbrechung
couple Kraftepaar disengage v loskuppeln, befreien
couplings Kupplungen disperse v zerstreuen
crack RiB, Schlitz displace v verdrangen
crankshaft Kurbelwelle displacement geradlinige
create v erzeugen (vector) Weglange,
critical load kritische Last (compare with Verschiebung
critical value kritische Zahl distance (scalar))
cross-section Durchschnitt dissipate v zerstreuen,
curl v rollbiegen verwenden
curvature Krummung distance (scalar) Weglange
cut Messerschneiden distortion Verformung
cycle Kreislauf, Zyklus distribute v verteilen
cyclic process Kreisprozess disturbance Stoning
cylinder Zylinder dowel pin Diibel
cylinder block Zylinderblock down mill v gleichlauffrasen
damage v schaden, beschadigen draw v ziehen
damping Dampfung drill v bohren
Englisch/Deutsch 223
drive Getriebe evaluate v berechnen, bewerten
drive shafts Getriebewellen evaporate v verdampfen
ductile dehnbar, biegbar evidence Aussage, Zeugnis
dye Farbstoff exceed v uberschreiten
ease Leichtigkeit excitation winding Erregerwicklung
economical wirtschaftlich exhaust Auspuff
eddy current Wirbelstrom expansion Ausdehnung
effect Wirkung experience Erfahrung
effective wirksam, erfolgreich express v ausdrilcken, auBern
efficiency Wirkungsgrad expression Ausdruck, Formel
eject v hinauswerfen extension Dehnung,
elastic elastisch Verlangerung
elastic section Widerstandsmoment extensive ausfilhrlich,
modulus umfassend
elastic curve Biegelinie extent Bereich, Strecke
elastomers Elastomere external auBerlich
electric arc welding Metall- external broaching AuBenraumen
LichtbogenschweiBen (process)
electron beam Elektronenstrahl- external cylindrical AuBenrundschleifen
microanalysis analyse grinding (process)
electron beam Elektronenstrahl- extract v ausziehen
welding schweiflen extrude v strangpressen,
electroplate v galvanisieren verdrangen
element Element extrusion blow Druckumformen
elementary forces Teilkrafte moulding process
eliminate v beseitigen, entfernen face mill v stirnplanfrasen
elongation Ausdehnung, face plates Planscheiben
emboss v einpragen facilitate v erleichtern
emission Ausstrahlung, fastener Befestigung
Emission fastening device Befestigungsgerat
empirical empirisch fastening pins Befestigungsstifte
enamel Email fatigue strength Dauerfestigkeit
enclose v einschlieBen fatigue tests Dauerfestigkeits-
end mill v stirnumfangs- prlifung
planfrasen feature Besonderheit
engage v betatigen, einkuppeln feed Vorschub
engine mechanischer Motor feedback Ruckkopplung
(Das Wort engine ist felt Filz
nicht fur elektrische fibre-reinforced faserverstarkte
Motoren benutzt) materials Verbundwerkstoffe
enlarge v vergroBern fibre Faser
ensure v sichern file Feile
envelope Decke, Hiille filler metal SchweiBstab
environment Umgebung fillers Fullstoffe
equal gleich fillet joint Kehlnaht
equation of state Zustandsgleichung final state Endzustand
equilibrium Gleichgewicht fine grain feinkornig
equivalent gleichwertig fine grained schweiBgeeignete
erosion Erosion, Abnutzung welding steels Feinkornstahle
etch v atzen, kupferstechen
224 Vocabulary 1
first moment of an Flachenmoment glass Glas
area 1. Grades globules Kugelchen
fits Passungen glossy glanzend
fixed axis feste Achse gradient Neigung, Gradient
fixtures Vorrichtungen gradual allmahlich
flakes Flocke grain structure Gefuge
flame harden v Flammenharten grains, crystallites Korner, Kristallite
flange Flansch granules Kornchen
flat belts Flachriemen graphically graphisch
flexible shafts biegsame Wellen grind v schleifen
float v schwimmen grinding wheel Schleifstein
flux FluBmittel g»P greifen
foam Schaum gripper Greifer
follower rest mitlaufender groove Nut, Rille
Setzstock grooved pins Kerbstifte
follow-on die set Folgeschneid- guide v fuhren, steuern
werkzeuge guideways FUhrungen
force Kraft gypsum Gips
forge v schmieden hack saw Bugelsage
form Form hard cast iron HartguB
form v formen, bilden hard wearing verschleififest
form cutter Profilfraser hardness Harte
form grind v profilschleifen hardness tests Harteprtlfungen
former Former, Gestalter headstock Spindelstock
formula Formel heat capacity Warmekapazitat
four jaw chuck Vierbackenfutter heat engine Warmekraftmaschine
fraction Bruch, Bruchteil heat resistant warmebestandig
fracture Bruch heat resistant steels warmfeste Stahle
fragment Splitter, Bruchstilck heat treatment Warmebehandlung
free cutting steels Automatenstahle height Hohe
freeze v frieren helical gears Stirnrader mit
friction Reibung Schragverzahnung
friction clutches Reibungskupplung hemispherical hemispharisch
fuel Brennstoff high speed steels Schnellarbeitsstahle
fundamental GrundabmaB hole basis system Passungssystem
deviation Einheitsbohrung
fundamental Grundtoleranzgrade homogeneous homogen, gleichartig
tolerance grades hot-dip coating Schmelztauch-
fusion Schmelzen uberzuge
fusion weld v schmelzschweiBen identical identisch
gap Spalt, Offnung idler Leerlaufrolle
gasket Dichtung ignition Ziindung
gear box Zahnrad- illustrate v erlautern, darstellen
stufengetriebe, impact StoB
Zahnrad- impact test Kerbschlag-
schaltgetriebe biegeversuch
gears Zahnrader impair v schwachen
general purpose allgemeine Stahle imperfection Mangel, Fehler
steels improve v verbessern
generate v erzeugen impulse KraftstoB
Enghsch/Deutsch 225
impure unrein, gemischt join v verbinden
in accordance with ubereinstimmen mit jointed shafts Gelenkwellen
inclination Neigung key Schlussel
inclined plane schiefe Ebene key connections PaBfeder
indentation Einschnitt Verbindungen
independent unabhangig keyway Keilnut
indication Anzeige, Andeutung kinetic energy kinetische Energie
indispensable unentbehrlich knurl v randeln
individual einzel lack Mangel
individually einzeln laminated materials Schichtverbund-
induction Induktion werkstoffe
induction harden v induktionsharten lamination Schichtung
inert gas weld v schutzgasschweiBen lance v ausschneiden
inertia Tragheit lap joint Uberlappnaht
infinitesimal unendlich kleine laser cut v laserschneiden
influence EinfluB latent heat of fusion Schmelzwarme
ingot GuBblock latent heat of Verdampfungswa'rme
ingredient Bestandteil vapourization
initial state Anfangszustand lateral seitlich
initially am Anfang lathe Drehmaschine
injection mould v Spritzgiefien lathe centres Zentrierspitze
input Eingang lathe tool DrehmeiBel
insert v einsetzen layer Schicht
inspect v priifen lead screw Leitspindel
installation Anlage leakproof lecksicher
instruction Anweisung, Befehl lengthwise der La'nge nach
insulate v isolieren liftv aufheben
intensity Intensitat, Starke limestone Kalkstein
interchangeability Auswechselbarkeit limit Grenze, Grenzwert
interference fit UbermaBpassung limit gauges Grenzlehren
intermittent mit Unterbrechungen limits GrenzmaBe
internal broaching Innenra'umen line of action (of a Wirklinie der Kraft
(process) force)
internal cylindrical Innenrundschleifen liquid lubricants flilssige
grinding (process) Schmierstoffe
internal energy innere Energie live centre mitlaufende
interpolator Interpolator Zentrierspitze
intersection Schnittpunkt load Last, Belastung
introduce v einfiihren load capacity Belastbarkeit
inverse umgekehrt locating pins PaBstifte
investment casting FeingieBen location Lage, Stelle
process locking devices Losdrehsicherunge
involve v verwickeln locking discs Sicherungsscheibe
irregularity Unregelma'Bigkeit locking rings Sicherungsringe
irreversible nicht umkehrbar longitudinal strain Dehnung
isolate v isolieren loosen v lockern, auflockern
isotherm Isotherme losses Verluste
isotropy Isotropie low temperature kaltzaher Stahl
jaw Backe steel
j'g Vorrichtung lower deviation unteres AbmaB
226 Vocabulary 1
lower limit MindestmaB modulus of Elastizitatsmodul
lubricants Schmierstoffe elasticity
lubricating greases Schmierfette modulus of rigidity Schubmodul
lubrication Schmierung molten geschmolzen
lubrication free wartungsfreie moment Moment
bearing Lager moment of a couple Drehmoment
lustrous glanzend moment of inertia Tragheitsmoment
machine frame Maschinengestell momentum Impuls
machining Bearbeitungszugabe monitor v uberwachen
allowance motion Bewegung
macromolecules Makromoleklile mould GieBform
magazine Magazine mounting Befestigungsschelle,
(for tools) (fur Werkzeuge) Gestell
magnetic chuck Magnetfutter multipoint tool mehrschneidiges
magnetic particle magnetische Werkzeug
tests ReiBpriifungen necessary notig
magnitude GroBe needle bearings Nadellager
maintain v beibehalten, needle-shaped nadelartig
instandhalten neglect v vernachlassigen
malleable hammerbar, neutral axis neutrale Achse
geschmeidig neutral surface neutrale Schicht
malleable cast iron Tempergufi nibble v knabberschneiden
mallet Holzhammer nitride v nitrieren
mandrel Drehdorn, Spandorn nitriding steels Nitrierstahle
manometer Manometer nodular cast iron GuBeisen mit
manufacture v fertigen, herstellen Kugelgraphit
mass Masse nonferrous metals Nichteisenmetalle
matter Material, Substanz normalizing Normalgluhen
measurement Messung (process)
measure v messen notch Kerbe, Einschnitt
melt v schmelzen oblique schrag
melting point Schmelzpunkt obstacle festes Hindernis
membrane Membran offset Versetzung
metacentre Metazentrum omit v auslassen, weglassen
metal chips Spane opaque undurchsichtig
metal slitting saw Schlitzfraser opposite entgegengesetzt
metallizing (or Metall- optical spectrum optische
thermal spraying) Spritziiberzuge analysis Spektralanalyse
metallographic metallographische ore Erz
analysis Untersuchungen oscillate v schwingen
method of sections Schnittverfahren outflow AusfluB
mild steel Baustahl output Ausgang
milling cutters Fraswerkzeuge overhanging arm Gegenhalter
milling machine Frasmaschine overlap v uberlappen
misalignment Fluchtfehler overload v iiberbelasten
mixture Mischung overload protection Abscherstifte
models Muster pins
modification Abanderung, overturn v umkippen
Modifikation oxidation Oxydierung
modify v abandern
Englisch/Deutsch 227
oxy-acetylene Gasschmelz- polygon Vieleck, Polygon
welding schweifien porous poros
oxygen Sauerstoff possess v besitzen
oxygen cutting autogenes possible moglich
(process) Brennschneiden potential energy potentielle Energie
paints Lacke power Leistung
part Teil power consumption Wirkleistung
particle-reinforced teilchenverstarkte predict v vorhersagen
materials Verbundwerkstoffe preparation Vorbehandlung
parting-off process Abtrennung preserve v bewahren
path Weg press drilcken, pressen
path measurement Wegmessung press tools Schneidwerkzeuge
pattern (for casting) Modell pressure Druck
pendulum Pendel pressure pad PreBplatte
penetrate v eindringen pressure resistance Widerstands-
perforate v perforieren welding process preBschweiBen
perform v leisten, ausfuhren prestressed concrete Spannbeton
performance Leistung prevent v verhindern
period Periode previously vorher
periodically regelmafiig profile Profil, Kontur
peripheral milling Umfangs-Planfrasen project v werfen
(process) property Eigenschaft
periphery Umkreis, Peripherie, protect v schiitzen
Rand, Grenze provide v zur Verfiigung stellen
perpendicular rechtwinklig pulley Rolle
physical quantity physikalische GroBe punch Stanzwerkzeug
piece part Werkstiick punch clearance Schneidspalt
(or workpiece) purpose Zweck, Absicht
pierce v lochen quantity Menge, Anzahl
pig iron Roheisen quench v abschrecken
pigments Pigmente, Farbstoffe quenching and Vergutungsstahle
pilot Suchstift tempering steels
pin connections Stiftverbindungen race (in a bearing) Laufring
pin-ended gelenkig gelagert rack and pinion Zahnstangengetriebe
pins Stifle radial drilling Schwenkbohr-
pitch Teilung machines maschine
plain bearing Gleitlager radian rad (Radiant)
plain milling cutter Walzenfraser radiation Strahlung
plane Ebene radioactive radioaktiv
plasma cutting Plasmaschneiden radius of curvature Krummungsradius
(process) radius of gyration Tragheitsradius
plasticity Plastizitat rake angle Spanwinkel
plastics Kunststoffe rapid traverse positionieren im
plausibility Glaubwiirdigkeit Eilgang
plunger Druckkolben ratio Verhaltnis
plywood Sperrholz reaction Rilckwirkung
point of inflection Inflexionspunkt ream v reiben
polar second polares Flachen- recess Nische, Ausschnitt
moment of an area moment 2.Grades reciprocal Kehrwert
polish v polieren
228 Vocabulary 1
reciprocating pendelnde Bewegung roll v rollen
motion roll pins Spannstifte
rectangular rechtwinklig roller bearings Rollenlager
recycling Wiederverwertung rolling resistance Rollreibung
reduce v vermindern rotate v rotieren, sich drehen
reference points Bezugspunkte rotation Rotation
refine v raffinieren rotational motion Drehbewegung
refractory feuerfest rotor Rotor, Drehteil
refractory materials feuerfester Baustoff rubber Gummi
refrigerator Kaltemaschine rust Rost
regain v wiedergewinnen safety factor Sicherheitsfaktor
regardless ungeachtet sample Muster, Exemplar
regulating wheel Regelscheibe sand core Kern
regulator Regler satisfactory zufriedenstellend
reinforced concrete Stahlbeton saw Sage
reject v ablehnen scale (formed on a Schuppe,
relationship Beziehung, metal surface) Metalloxydschicht
Verhaltnis scrap Schrott
release v entlassen scratch v kratzen
reliability Zuverlassigkeit screw (see also bolt) Schraube
remain v bleiben screw joints Schrauben-
remove v entfernen, beseitigen verbindungen
repeat v wiederholen screw thread Gewinde
replace v ersetzen seam welding Rol lennahtschweiBen
represent v darstellen (process)
representation Darstellung seamless tube nahtlosgezogenes
require v erfordern, brauchen Rohr
reservoir Speicher, Behalter second moment of Flachenmoment
resin Harz an area 2.Grades
resistance Widerstand section Schnitt, Sektion
resolution of forces Zerlegung von select v auswahlen
Kraften self-centering chuck Dreibackenbohrfutter
respond v reagieren, antworten sense of rotation Sinn der Rotation
restore v restaurieren separate v trennen
resultant Resultierende sequence Reihenfolge
retain v behalten set screws Stellschrauben
revealv offenbaren, enthiillen set-up Aufbau, Anlage
reverse v umkehren, umdrehen shade v schraffieren
reverse Gegenteil shaft Maschinenwelle
reversible umkehrbar shaft basis system Passungssystem
rhombus Rhombus Einheitswelle
ribbed V-belts mehrrippen shaft to hub Welle-Nabe
Keilriemen connections Verbindungen
rigid body starre Korper shank Bohrerschaft
rigid couplings starre Kupplungen shape Form, Gestalt
rigid shafts starre Wellen sharpen v scharfen
rigidity Festigkeit, Stabilitat shear modulus Schubmodul
riveted joints Nietverbindungen shear strain Schubverformung
rivets Niete shear stress Schubspannung
rod Rundstab shielded arc welding Pulver-SchweiBen
Englisch/Deutsch 229
shear v scheren spring steels Federstahle
shot or grit blasting Kornchenblasen spring washer Unterlegscheibe
(process) sprocket wheel Kettenrad
shot peering Verfestigungs- spur gears Stirnrader mit
(process) strahlen Geradverzahnung
shrink v schrumpfen stability StabilitSt
side milling cutter Walzenstirnfra'ser stable stabil
similar ahnlich stainless steels nichtrostende Stahle
simplify v vereinfachen state v aussagen, ausstellen
single load Einzellast state Zustand
sink v sinken state of rest Zustand der Ruhe
sinter v sintern static friction Haftreibung
sine function, Sinusfunktion stator Stator
sinusoidal function steady rest feststehende
skill Geschick(lichkeit) Setzstocke
slab Platte steel castings StahlguB
slag Schlacke steel for electrical Stahle fur elektrische
slenderness ratio Schlankheitsgrad machines Maschinen
sliding friction Gleitreibung stiffness Steifheit
sliding pillars Ftihrungssaule straight gerade
slit Schlitz straight line gerade Linie
slit v abschneiden strain Verformung
slope Neigung strain harden v kaltharten
slot Spalte, Nut strand Strang, Draht
Schlitz stream filaments Strom faden
snap rings Springringe stream tubes StromrOhre
soft solder v weichloten streamline flow laminare Stromung
solder v loten streamlines Stromlinien
solid lubricants Festschmierfette stress Spannung
solution Losung stress relieve Spannungsarmgluhen
spanner Schraubenschliissel stretch v strecken
Steckschlussell stripper plate Abstreifer
specific heat spezifische submerged arc Unter-Pulver-
capacity Warmekapazitat weld v SchweiBen
specification Spezifizierung subsequent folgend, nachtraglich
specimen Exemplar, Muster substitute v ersetzen
speed (scalar) Geschwindigkeit substitute Ersatz
(compare velocity) substrate Unterschicht
speed of rotation Drehzahl successive folgend,
(in revolutions per hintereinander
minute (rpm)) suck in v einsaugen
spin v drticken, spinnen sufficient genug, ausreichend
spiral pins Spiral- Spannstifte suitable geeignet, passend
spline Keil summary Kurzfassung
splined connections Profilwellen superfinish v kurzhubhonen
Verbindungen support v tragen, unterstiltzen
split (or slit) collar geteilte Nabe support Trager, Stutze
spot face v planansenken surface OberflSche
spot weld v punktschweiGen surface finish Oberflachen-
spray v spritzen beschaffenheit
230 Vocabulary 1
surface grind v planschleifen tool steels Werkzeugstahle
surface harden v harten von tools Werkzeuge
Oberflachenschichten toothed belt drives Zahnriemengetriebe
surround v umgeben torque Drehmoment
surroundings Umgebung torsion Verdrehung, Torsion
swing v schwingen toughness Zahigkeit
switch v einschalten transfer v iibertragen
swivel v drehen, schwenken transfer of heat Warmeubertragung
tailstock Reitstock transform v verwandeln
taper Verjiingung transformer Transformator
taper connection kegliger PreBverband transition Ubergang
taper pins Kegelstifte transition fit Ubergangspassung
taper shank Kegelschaft transmission Ubertragung
taper roller Kegelrollenlager transverse forces Querkrafte
bearings transverse loading Querkraftbiegung
tap v gewindebohren transverse section Querschnitt
tap Gewindebohrer treat v behandeln
target value Sollwert triangle Dreieck
task Aufgabe trim v beschneiden, trimmen
tear v zerreifien T-slot milling cutter T-Nutenfraser
temper v anlassen tube Rohr
tend neigen, streben tubular rohrformig
tendency Tendenz, Richtung tungsten Wolfram
tensile stress Zugspannung tungsten electrode Wolfram-Inertgas-
term fachlicher Ausdruck, process SchweiBen
Bezeichnung turret Revolverkopf
thermal cutting thermisches Trenn- twist v drehen, umdrehen
(process) verfahren twist drill Spiralbohrer
thermoform Warmumformen ultimate tensile Zugfestigkeit
thermoplastics Thermoplaste strength
thermosetting Duroplaste unbalanced unausgeglichen
plastics undergo v erleben
thinner Verdtinner uniform gleichmaBig, konstant
thread inserts Gewindeeinsatze uniform motion gleichfSrmige
three jaw self- Dreibackenfutter Bewegung
centering (or unique einzigartig
universal) chuck universal joints Gelenkkupplungen
thrust (or axial Axialkraft unsatu rated ungesattigt
force) unstable unsicher, labil
tighten v befestigen up milling process Gegenlauffrasen
tip Spitze upper deviation oberes AbmaB
tolerance Toleranz upper limit HOchstmaB
tool holder Werkzeughalter, upthrust Auftrieb
MeiBelhalter valid gultig, rechtskraftig
tool length Werkzeuglangen- value Wert
compensation korrektur vapour Dampf, Dunst
tool nose Schneidenradius- vapourization verdunsten,
compensation Korrektur verdampfen
tool path Werkzeugbahn- variation Veranderung
compensation korrektur varnishes Klarlacke
Englisch/Deutsch 231
V-belts Keilnemen
velocity (vector) Geschwindigkeit
(compare with
speed (scalar))
vernier caliper MeBschieber
versatile vielseitig
vertical deflection Durchbiegung
vessel GefaB
virtually eigentlich
viscosity Viskositat
visible sichtbar
wall Wand
washer Unterlegscheibe
water-tight wasserdicht
wavelength Wellenlange
weak schwach
wear VerschleiB
wear resistance VerschleiBfestigkeit
wedge Keil
weight Gewicht
wick Docht
width Breite
wire Draht
wire electrode Metall-
process SchutzgasschweiBen
with reference to, beziiglich
with respect to
withstand v aushalten
wood Holz
work Arbeit
work harden v kaltharten
work rest Werkstiickauflage
working conditions Arbeitsbedingungen
worm and Schneckengetriebe
worm gear
wrench (American Schraubenschlussel
wrought alloys Knetlegierungen
wrought iron Schmiedeeisen
X'ray and gamma Rontgen- und
ray tests Gammastrahlen-
X'ray fluorescence Rontgenfluoreszenz-
analysis analyse
yield strength , yieldStreckgrenze
stress, yield point
zero point Nullpunkt
Vocabulary 2
Deutsch Englisch Deutsch Englisch
abandern modify v Aufgabe task
abbrechen breakdown v aufheben Iiftv
Abbrennstumpf- butt weld v aufkohlen carburize v
sehweiBen absorbieren absorb v
abhangen (von) depend(on)v aufnehmen,
ablagern deposit v Auftrieb buoyancy,
ablehnen reject v upthrust
Abrieb, Abnutzung abrasion Ausdehnung expansion
Abscherstifte overload protection Ausdruck, Formel expression
pins ausdriicken, aiiBern express v
abschneiden (to) slit v AnsfliiB outflow
abschrecken quench v ausfiihren, erzielen achieve v
Absorptionsgrad absorptivity ausfiihrlich extensive
Abstreifer stripper plate Ausgang output
Abtrennung parting-off process aushalten withstand v
abweichen (von) differ (from) v auslassen, weglassen omit v
Abweichung deviation Auspuff exhaust
Achse axis Aussage evidence
adiabate adiabatic aussagen, ausstellen state v
ahnlich similar ausschneiden lance v
allgemeine Stable general purpose steels Aussehen appearance
allmahlich gradual AuBenraumcn external broaching
am Anfang initially process
Anderung des change of phase AuBenrundschleifen external cylindrical
Aggregatzustandes grinding process
Anfangszustand initial state auBerlich external
angrenzend, neben adjacent Ausstrahlung emission
Anhanglichkeit adhesion auswahlen select v
Anker armature Auswechselbarkeit interchangeability
Anlage installation ausziehen extract v
anlassen temper v autogenes oxygen cutting
Annahme assumption Brennschneiden process
annehmen assume v Automatenstahle free cutting steels
anordnen align v Axialkraft thrust (or axial force)
reagieren respond v Backe jaw
anwcisen, zuteilen assign v Baustahl mild steel
Anweisung, Befehl instruction Bearbeitungs- machining allowance
anwenden apply v zugabe
Anwendung application Bedingung, condition
Anzeige, Andeutung indication Voraussetzung
anziehen attract v befestigen tighten v
Arbeit work Befestigung fastener
Arbeitsbedingungen working conditions Befestigungsgerat fastening device
atzen, kupferstechen etch v Befestigungsschelle, mounting
Aufbau, Anlage set-up Gestell
Deutsch/Englisch 233
Befestigungsstifte fastening pins Dampf, Dunst vapour
behalten retain v Dainpfimg damping
behandeln treat v darstellen represent v
beibehalten maintain v Darstelluug representation
Belastbarkeit load capacity Dauerfestigkeit fatigue strength
beliebig arbitrary Dauerfestigkeits- fatigue tests
berechnen, evaluate v p lulling
bewerten Decke, Hiille envelope
Bereich, Strecke extent dehnbar, biegbar ductile
Beriihrung contact Dehnung longitudinal strain
beschichten coat v dekorativ decorative
Beschleunigung acceleration der Lange nach lengthwise
beschneiden trim v diatherm diathermic
Beschreibung description Dichte density
beseitigen, entfernen eliminate v Dichtung gasket
besitzen possess v Dimension dimension
Besonderheit feature Docht wick
Bestandteil ingredient, Draht wire
component Drehautomaten automatic lathes
bestehen aus composed of v Drehbewegung rotational motion
bestimmen determine v Drehdorn, mandrel
betatigen, engage v Spanndorn
einkuppeln drehen, schwenken swivel v
Beton concrete drehen, umdrehen twist v
bewahren preserve v Drehimpuls angular impulse
Bewegung motion Drehmaschine lathe
Beziehung relationship Drehmeiliel lathe tool
beziiglich with reference to, Drehmoment moment of a couple
with respect to torque
Bezugspunkte reference points Drehzahl speed of rotation
Biegelinie elastic curve (in revolutions per
Biegemoment bending moment minute (rpm))
biegen bend v Dreibackenfutter three jaw self-
biegsame Wclleii flexible shafts centering (or
Bindemittel binder universal) chuck
bleiben remain v Dreieck triangle
Bogen, Lichtbogen arc Druck pressure
bohren drill v drttcken, pressen press v
Bohrerschaft shank driicken, spinnen spin v
Bohrstangen boring bars Druckkolben plunger
bordeln, falzen bead v Druckspannung compression stress
Breite width Druckstab, Saule column
Brennstoff fuel Druckumformen extrusion blow
Bruch break, fracture moulding (process)
Bruch, Bruchteil fraction Diibel dowel pin
Bruchfestigkeit breaking strength Durchbiegung deflection
BUgelsage hack saw durchgehen traverse v
chemische chemical analysis Durchmesser diameter
Priifungen Durchschnitt cross-section
chemische Reaktion chemical reaction Durchschnittswert average value
234 Vocabulary 2
Duroplaste thermosetting plastics Erregerwicklung excitation winding
Ebene plane erscheinen appear v
Eigenschaft property ersetzen replace, substitute v
eigentlich virtually Ersatz substitute
eindringen penetrate v Erwagung consideration
einfache Zentrier- dead centre erwerben, erlangen acquire v
spitze Erz ore
EinfluB influence erzeugen create v, generate v
einfiihren introduce v Exemplar, Muster specimen
Eingang input fliissige Schmier- liquid lubricants
einpragen emboss v stoffe
Einsatzstahle case hardening steels Fahigkeit ability
einsaugen suck in v Farbstoff dye
einschalten switch v Faser fibre
einschlieBen enclose v faserverstarkte fibre-reinforced
Einschnitt indentation Verbundwerkstoffe materials
einsetzen insert v Federstahle spring steels
einzeln individual Feile file
Einzellast single load FeingicBcn investment casting
einzigartig unique (process)
elastisch elastic feinkornig fine grain
Elastizitatsmodul modulus of elasticity fertigen, herstellen manufacture v
Elastomere elastomers feste Achse fixed axis
Elektronenstrahl- electron beam festes Hindernis obstacle
analyse microanalysis Festigkeit, Stabilitat rigidity
Elektronenstrahl- electron beam Festschmierfette solid lubricants
schweiBen welding feststehender steady rest
Element element Setzstock
Email enamel feuerfest refractory
empirisch empirical feuerfester Baustoff refractory materials
Endergebnis conclusion Filz felt
Endzustand final state Flachenmoment first moment of an
entfernen, beseitigen remove v 1. Grades area
entgegengesetzt opposite Flachenmoment second moment of an
entgegenwirkend adverse 2. Grades area
enthalten contain v Flachenschwer- centroid
entlassen release v punkt
Entschlossenheit determination Flachriemen flat belts
cntschadigcn, compensate v flammharten flame harden v
ersetzen replace v Flankenspiel backlash
entsprechen correspond to v Flansch flange
entwerfen design v Flocke flakes
Kiitvvicklung development Fluchtfehler misalignment
entziehen deprive v FluBmittel flux
Erfahrung experience folgend successive
erfordern, brauchen require v nachtraglich subsequent
Erhaltung conservation Folgeschneid- follow-on die set
erlautern, darstellen illustrate v werkzeuge
erleichtern facilitate v Forderband conveyor
Erosion, Abnutzung erosion Form form
Deutsch/Englisch 235
Form, Gestalt shape Giefiform mould
Formel formula Gips gypsum
formen, bilden form v glanzend glossy,
Former, Gestalter former lustrous
formpressen compression mould v Glas glass
Frasmaschine milling machine Glaubwiirdigkeit plausibility
Fraswerkzeuge milling cutters gleich equal
Fraserdorn arbor gleichformige uniform motion
Freiheitsgrad degree of freedom Bewegung
Freitrager cantilever Gleichgewicht equilibrium
Freiwinkel clearance angle gleichlauffrasen down mill v
frieren freeze v gleichmaBig, uniform
fiihren, steuern guide v konstant
Fiihrungen guideways gleichwertig equivalent
Fiihrungssaule sliding pillars Gleitlager plain bearing
Fullstoffe fillers Gleitreibung sliding friction
Futter chucks graphisch graphically
galvanisieren electroplate v greifen grip v
Gasschmelz- oxy-acetylene Greifer gripper
sehwcilkn welding (process) Grenze, Grenzwert limit
GefaB vessel Grenzlehren limit gauges
Gefiige grain structure GrenzmaBe limits
Gegenhalter overhanging arm grob coarse
Gegenlauffrasen up milling process grobkornig coarse grain
Gegenteil reverse GroBe magnitude
geeignet, passend suitable GrundabmaB fundamental
gelenkig gelagert pin-ended deviation
Gelenkkupplungen universal joints Grundtoleranzgrade fundamental
Gelenkwellen jointed shafts tolerance grades
genug, ausreichend sufficient giiltig, rechtskraftig valid
gerade straight Gummi rubber
gerade Linie straight line GuBblock ingot
geradlinige displacement (vector) GuBeiscu cast iron
Weglange (compare with GuBeisen mit nodular cast iron
distance) Kugelgraphit
Gerat, Apparat appliance GuBlegierungen cast alloys
Gesamtschneid- compound die sets Haftreibung static friction
werkzeuge hammerbar, malleability
Geschick(lichkeit) skill geschmeidig
geschmolzen molten Harte hardness
Geschwindigkeit speed (scalar), Hartepriifungen hardness tests
velocity (vector) HartguB hard cast iron
geteilte Nabe split (or slit) collar hartloten braze v
Getriebe drive or hard solder v
Getriebewellen drive shafts harten von surface harden v
Gewicht weight Oberflachen-
Gewinde screw thread schichten
gewindebohren tap v Harz resin
Gewindebohrer tap hemispharisch hemispherical
Gewindeeinsatze thread inserts herkommlich conventional
236 Vocabulary 2
hinauswerfen eject v Kerbschlag- impact test
hochglanzpolieren buffv biegeversuch
Hochleistungs- heavy duty Kerbstifte grooved pins
Hochofen blast furnace Kern sand core
Hochstmafi upper limit Kettengetriebe chain drive
Hone height Kettenrad sprocket wheel
Hohlraum cavity kinetische Energie kinetic energy
Holz wood K la i lack varnish
Holzhammer mallet Klauenkupplungen claw-type clutches
Holzkohle charcoal Klebstoffe adhesives
homogen, homogeneous Klenime clamps
gleichartig Klinker, Schlacke clinker
identisch identical knabberschneiden nibble v
Impuls momentum Knetlegierungen wrought alloys
Induktion induction knicken buckle v
induktionsharten induction harden v Knuppel billet
Inflexionspunkt point of inflection Kohlenstoff carbon
Inhalt content Kohlenstoffinhalt carbon content
innenraumen internal broach v Kohlenstoffstahl carbon steel
innere Energie internal energy Koks coke
Innernrundschleifen internal cylindrical kombinieren combine v
grinding (process) kombinierte combination die sets
instandhalten maintain v Werkzeuge
Intensity, Starke intensity Kom imitator commutator
Interpolator interpolator kompakt, fest compact
isolicrcn insulate v, Kompressor compressor
isolate v komprimierbar compressible
Isotherme isotherm Kondensation condensation
Isotropie isotropy Konsolfrasmachinen column and knee type
Kalkstein limestone millimg machines
Kaltemaschine refrigerator Kontinuitats- continuity equation
kaltharten strain harden v, gleichung
work harden v Kontur contour
kaltzaher Stahl low temperature steel Kornchen granules
Kammer chamber Kornchenblasen shot or grit blasting
kegelformig conically (process)
Kegelrader bevel gears Korner, Kristallite grains, crystallites
Kegelrollenlager taper roller bearings Korrosion corrosion
Kegelschaft taper shank korrosions- corrosion resistant
kegelsenken countersink v bestandige Stahlc steels
Kegelstifte taper pins kos ten g tins tig cost-effective
kegliger taper connection Kraft force
PreBverband Kraftepaar couple
Kehlnaht fillet joint Reibungskupplung friction clutches
Kehrwert reciprocal KraftstoB impulse
Keil wedge, spline kratzen, Kratzer scratch
Keilnut keyway Kreislauf, Zyklus cycle
Keilriemen V-belts Kreisprozess cyclic process
Keilsitzverbindung taper key connection kritische Last critical load
Kerbe, Einschnitt notch kritische Zahl critical value
Deutsch/Englisch 237
Kriimmung curvature nicht fur elektrische
Kriimmungs radius radius of curvature Motoren bcnutzt)
Kiigelchen globules Mehrrippen- ribbed V-belts
Kugellager ball bearings keilriemen
Kiihlfliissigkeit coolant mehrschneidiges multipoint tool
Kunststoffe plastics Werkzeug
Kupplungen couplings MeiBel chisel
Kurbelwelle crankshaft Membran membrane
Kurzfassung summary Menge, Anzahl quantity
kurzhubhonen superfmish v messen measure v
Lacke paints messerschneiden cut v
Lage, Stelle location Messing brass
Lager bearing Mefischieber vernier caliper
Lagerbuchse (bearing) bush Messung measurement
laminare Stromung streamline flow Metall-Lichtbogen- electric arc welding
laserschneiden laser cutting v schweifien process
Last, Belastung load metallographische metallographic
Laufring race (in a bearing) Untersuchungen analysis
lecksicher leakproof Metall-Schutzgas- wire electrode
Leerlaufrolle idler scliweiBen process
Legierung alloy Metall-Spritz- metallizing or
Leichtigkeit ease iiberzuge thermal spraying
leisten, ausfiihren perform v Metazentrum metacentre
Leistung power Mindestmafi lower limit
Leitspindel lead screw Mischung mixture
lochen pierce v mit Unter- intermittent
Iockern, auflockern loosen v brechungen
Losdrehsicherung locking devices mitlaufende live centre
loskuppeln, befreien disengage v Zentrierspitze
Losung solution mitlaufender follower rest
loten solder v Setzstock
Magazine (fur magazine Mitnehmer carrier
Werkzeuge) (for tools) Mitnehmerscheibe catch plates
Magnetfutter magnetic chuck Modell pattern (for casting)
magnetische magnetic particle moglich possible
ReiBpriifungen tests Moment moment
Makromolekiile macromolecules Montageablauf assembly
Mangel defect, deficiency Muster, Exemplar sample
imperfection nachdenken, consider v
Manometer manometer uberlegen
Maschinengestell machine frame nadelartig needle-shaped
Maschinenwelle shaft Nadellager needle bearings
Masse mass nahtlosgezogenes seamless tube
Massenmittelpunkt centre of mass Rohr
massivumformen bulk deform v Neigung, Steigung, inclination.slope,
Material, Substanz matter Gradient gradient
Maximierung der adaptive control Neigungswinkel deflection angle
Leistung NennmaB basic size
mechanischer Motor engine neutrale Achse neutral axis
(Das Wort engine ist neutrale Schicht neutral surface
238 Vocabulary 2
nicht umkehrbar irreversible Pleuelstange connecting rod
Nichteisenmetalle nonferrous metals plotzlich abrupt
nichtrostende Stahle stainless steels polares Flachen- polar second moment
Niete rivets moment 2.Grades of an area
Nietverbindungen riveted joints polieren polish v
Nische, Ausschnitt recess poriis porous
nitrieren nitride v positionieren im rapid traverse v
Nitrierstahle nitriding steels Eilgang
Nocken cam potentielle Energie potential energy
Normalgliihen Normalizing PreBplatte pressure pad
(process) Profil, Kontur profile
notig necessary Profilfraser form cutter
Nut, Rille groove profilschleifen form grind v
oberes AbmaB upper deviation Profilwellen- splined connections
Oberflache surface, Verbindungen
surface area, priifen inspect v
Oberfliichen- surface finish pulverschweiBen shielded arc weld v
beschaffenheit punktschweiBen spot weld v
Oberflachenfein- surface finishing Querkraftbiegung transverse loading
bearbeitung processes Querkrafte transverse forces
offenbaren, reveal v Querschnitt transverse section
enthiillen rad (Radiant) radian
optische optical spectrum radioaktiv radioactive
Spektralanalyse analysis raffinieren refine
Ordnung, arrangement Randbedingung boundary condition
Einrichtung randeln knurl v
Oxydierung oxidation raumen broach v
passend, geignet appropriate Rechtecktisch compound table
PaBfeder-Verbind- key connections rechtwinklig at right angles,
ungen perpendicular,
PaBstifte locating pins rectangular
Passungen fits regelmaBig regular, periodical
Passungssystem hole basis system Regelscheibe regulating wheel
Einheitsbohrung Regler regulator
Passungssystem shaft basis system regulieren adjust v
Einheitswelle reiben ream v
Pendel pendulum Reibung friction
pendelnde reciprocating motion Reihenfolge sequence
Bewegung Reitstock tailstock
perforieren perforate v restaurieren restore v
Periode period Resultierende resultant
physikalische GroBe physical quantity Revolverkopf turret
Pigmente, pigments Rhombus rhombus
Farbstoffe Richtung direction
planausenken spot face v Riemengetriebe belt drive
Planscheiben face plates Rille channel
Plasraaschneiden plasma cutting RiB, Schlitz crack
process Roheisen pig iron
planschleifen surface grind v Rohr tube
Platte slab rohrformig tubular
Deutsch/Englisch 239
rollbiegen curl v schmelzschweifien fusion weld v
Rolle pulley Schmelztauch- hot-dip coating
rollen roll v uberziige
Rollenlager roller bearings Schmelzwarme latent heat of fusion
Rollennaht- seam welding Schmiedeeisen wrought iron
schweiBen (process) schmieden forge v
Rollreibung rolling resistance Schmierfette lubricating greases
Rontgen- und X'ray and gamma ray Schmierstoffe lubricants
Gammastrahlen- tests Schmierung lubrication
priifungen Schneckengetriebe worm and worm gear
Rontgenfluoreszenz- X'ray fluorescence Schneideisen die (for thread
analyse analysis cutting)
Rost rust Schneidenradius- tool nose
Rotation rotation Korrektur compensation
rotieren, sich drehen rotate v Schneidspalt punch clearance
Rotor, Drehteil rotor Schneidwerkzeuge press tools
Riickkopplung feedback Sclniellarbeitsstahle high speed steels
Riickwirkung, reaction Schnitt, Sektion section
Sage saw Schnittpunkt intersection
Sauerstoff oxygen Schnittverfahren method of sections
schaden, damage v schraffieren shade v
beschiidigen schrag oblique
schadlich detrimental Schraube screw (see also bolt)
schaltbare clutches Schrauben- screw joints
Kupplungen verbindungen
Schaltung circuit Schrauben (mit bolts (with nuts)
scharfen sharpen v Muttern)
Schaum foam Schraubenschliissel spanner,
scheinbares Gewicht apparent weight Steckschliissell wrench (american)
scheren shear v Schrott scrap
Schicht layer schrumpfen shrink v
Schichtung lamination Schubmodul modulus of rigidity
Schichtverbund- laminated materials Schubspannung shear stress
werkstoffe Schubverformung shear strain
schiefe Ebene inclined plane Metalloxydschicht, scale (formed on a
Schild, Schirm shield Schuppe metal surface)
Schlacke slag schiitzen protect v
Schlankheitsgrad slenderness ratio SchutzgasschweiBen inert gas welding
schleifen grind v process
SchleifkSrner abrasive particles schwaelien impair v
Schleifkorper abrasive wheels SchwciBstab filler metal
Schleifstein grinding wheel schweifigeeignete fine grained welding
SchleudergieBen centrifugal casting Feinkornstiihle steels
process Schwenkbohr- radial drilling
Schlitzfraser metal slitting saw maschine machines
Schlitz slit, slot Scliwerpunkt centre of gravity
SchlusscI key schwimmen float v
Schmelzen fusion (process) schwingen oscillate v,
schmelzen melt v swing v
Schmelzpunkt melting point seitlich lateral
240 Vocabulary 2
Senkschraube countersunk screw Stahlbeton reinforced concrete
sich benehmen behave v Stiihle fur elektri- steel for electrical
sich nahern approach v sche Maschinen machines
sich verschlechtern deteriorate v StahlguB steel castings
Sicherheitsfaktor safety factor stanzen blanking process
sichern ensure v Stanzwerkzeug punch
Sicherungsringe locking rings starre Korper rigid body
Sicherungsscheibe locking discs starre Kupplungen rigid couplings
sichtbar visible starre Wellen rigid shafts
sinken sink v Stator stator
Sinn der Rotation sense of rotation Steifheit stiffness
sintern sinter v Stellglied actuator
Sinusfunktion sinusoidal function, Stellringe adjusting ring
sine function or set collar
Sollwert target value Stellschrauben set screws
Spalt, Offnung gap Stifte pins
Spalte, Nut slot Stiftverbindungen pin connections
Spiinc metal chips stirnplanfrasen face mill v
Spannbeton prestressed concrete Stirnrader mit helical gears
Spannelemente clamps, clamping Schragverzahnung
devices Stirnrader mit spur gears
Spannstifte roll pins Geradverzahnung
Spannung stress stirnumfangs- end mill v
Spannungsarm- stress relieving planfrasen
gliihen (process) Stiirung disturbance
Spannzange collets (or collet StoB blow, impact
chucks) StoB, Kollision collision
Spanwinkel rake angle stoBen collide v
Speicher, Bchalter reservoir StoBzahl coefficient of
Sperrholz plywood restitution
spezifische specific heat capacity Strahlung radiation
Warmekapazitat Strang, Draht strand
Spezifizierung specification strangpressen, extrude v
Spielpassung clearance fit verdrangen
Spindel spindle strecken stretch v
Spindelstock headstock Streckgrenze yield strength, yield
Spiral-Spannstifte spiral pins stress, yield point
Spiralbohrer twist drill Stromfaden stream filaments
Spitze tip Stromlinien streamlines
Spitzenlosschleifen centreless grinding StromrBhre stream tubes
process Stufenlosegetriebe continuously variable
Splint cotter pins speed drives
Splitter, Bruchstiick fragment Stumpfnaht butt joint
Springringe snap rings Suchstift pilot
spritzen spray v Teil part
spritzgieBen injection mould v teilchenverstarkte particle-reinforced
Sprodigkeit brittleness Verbundwerkstoffe materials
Stab (rund) rod Teilkrafte elementary forces
stabil stable Teilung pitch
Stabilitat stability TemperguB malleable cast iron
Deutsch/Englisch 241
Tendenz, Richtung tendency unrein, gemischt impure
thermisches Trenn- thermal cutting unsicher, labil unstable
verfahren Unterbrechung discontinuity
Thermoplaste thermoplastics unteres Abmal.l lower deviation
Tiefe depth Unterlegscheibe washer, spring
tiefziehen deep draw v washer
T-Nutenfraser T-slot milling cutter Unter-Pulver- submerged arc weld v
Toleranz tolerance SchweiBen
tragen, unterstiitzen support v Unterschicht substrate
Trager, Stiitze support ununterbrochen continuous
Tragbalken beam Veranderung variation
Tragheit inertia verbessern improve v
Tragheitsmoment moment of inertia verbinden join v
Tragheitsradius radius of gyration Verbundwerkstoffe composite materials
Transformator transformer verdampfen evaporate v
trennen separate v Verdampfungs- latent heat of
trommel polieren barrel finish v warme vapourization
iiberbelasten overload v Verdichtung compression
iibereinstimmen mit in accordance with verdrangen displace v
tibergang transition Verdrehung, torsion
Lfbergangspassung transition fit Torsion
iiberlappen overlap v Verdunner thinner
Cberlappnaht lap joint verdunsten vapourize v
UbermaBpassung interference fit vereinfachen simplify v
uberschreiten exceed v Verfestigungs- shot peening
iibertragen transfer v strahlen (process)
Ubertragung transmission verformen deform v
iiberwachcn monitor v Verformung deformation,
iiberzug, Schicht coating distortion
Uhrzeigersinn clockwise vergleichen compare v
umdrehen twist, rotate vergrofiern enlarge v
Umfangs-Planfrasen peripheral milling Vergiitungsstahle quenching and
(process) tempering steels
umgeben surround v Verhalten behaviour
Umgebung environment, Verhaltnis ratio
surroundings verhindern prevent v
umgekehrt inverse Verjiingung taper
umkehrbar reversible Verlangerung elongation
umkehren reverse v Verluste losses
umkippen overturn v vermeiden avoid v
Umkreis, Peripherie periphery vermindern reduce v
Uinwan dlung conversion vernachlassigen neglect v
unabhangig independent VerschleiB wear
unausgeglichen unbalanced verschleiBfest hard wearing
undurchsichtig opaque VerschleiBfestigkeit wear resistance
unendlich klein infinitesimal Verse tzung offset
unentbehrlich indispensable verteilen distribute v
ungeachtet regardless Verunreinigung contamination
ungesattigt unsaturated verursachen cause v
UnregelmaBigkeit irregularity verwandeln transform v
242 Vocabulary 2
verwerfen reject v korrektur compensation
verwickeln involve v Werkzeugstahle tool steels
verzogern decelerate v Wert value
Vieleck, Polygon polygon Widerstand Resistance
vielseitig versatile Widerstands- elastic section
Vierbackenfutter four jaw chuck moment modulus
Viskositat viscosity Widerstands- pressure resistance
Vorbehandlung preparation preBschweiBen welding process
vorher previously wiedergewinnen regain v
vorhersagen predict v wiederholen repeat v
Vorrichtungen jigs, fixtures Wiederverwertung recycling process
Vorschub feed Winkel angle
Vorteil advantage Winkel- angular velocity
wahlen choose v geschwindigkeit
Walzenfraser plain milling cutter Winkel-Stirnfraser angle milling cutters
Walzenstirnfriiser side milling cutter Wirbelstrom eddy current
Walzlager bearings with rolling Wirkleistung power consumption
elements Wirklinie der Kraft line of action (of a
Wand wall force)
Warmebehandlung heat treatment wirksam effective
warmebestandig heat resistant Wirkung effect
Wiirmekapazitat heat capacity Wirkungsgrad efficiency
WSrmekraft- heat engine wirtschaftlich economical
maschine Wolfram tungsten
Warmeubertragung transfer of heat Wolfram-Inertgas- tungsten electrode
warmfeste Stable heat resistant steels SchweiBen welding process
warmumformen thermoform v wiinschenswert desirable
wartungsfreie lubrication free Zahigkeit toughness
Lager bearing Zahnrader gears
wasserdicht water-tight Zahnrad- gear box
Weg path schaltgetriebe
Weglange distance (scalar) Zah n riemengetriebe toothed belt drives
Wegmessung path measurement Zahnstangen- rack and pinion
weichgliihen anneal v getriebe
weichloten soft solder v Zentrierbohrer centre drill
Welle-Nabe shaft to hub Zentrierspitze lathe centres
Verbindungen connections Zerlegung von resolution of forces
Wellenliinge wavelength Kraften
Wellensicherungen axial locking devices zerreifien tear v
werfen project v zerstoren destroy v
Werkstiick piece part zerstreuen disperse v
(or workpiece) ziehen draw v
Werkstiickauflage work rest zufriedenstellend satisfactory
Werkzeugbahn- tool path zuganglich accessible
korrektur compensation Zugfestigkeit ultimate tensile
Werkzeuge tools strength
Werkzeughalter tool holder Zugspannung tensile stress
MeiBelhalter Lathe tool holder zulassige Spannung allowable stress
Werkzeugschlitten carriage Ziindung ignition
Werkzeuglangen- tool length
Deutsch/Englisch 243
Zusatzgerate attachments
Zusatzstoffe additives
Zustand state
Zustand der Ruhe state of rest
Zustandsanderung change of state
Zustandsgleichung equation of state
Zuverlassigkeit reliability
Zweck, Absicht purpose
zwingen compel v
Zylinder cylinder
Zylinderblock cylinder block
zylindrisch senken counterbore v
acceleration 20 bronze 83 CNC machine operation
adaptive control for CNC buckling 51 178
machines 186 buckling of columns tool changing systems for
additives 94,95 63 CNC machines 184
adhesive bonding 145 buffing 176 work changing systems
adhesives 145 bulk deformation for CNC machine 184
adiabatic 98 processes 193 CNC machines 177
adiabatic work 105 buoyancy 37 coating of surfaces 211
allowable stress 53 butt or upset welding coefficient of restitution
alloy 73 152 34
aluminium and its alloys cold deformation
85 C processes 193
angular impulse 32 cantilever 59, 63 collinear impact 32
angular motion 24 capstan and turret lathes column with one fixed
angular velocity 24 169 and one free end 65
annealing 75 carburizing 76 column with one fixed
anodizing of aluminium Carnot cycle 116 end and one pin
86 case hardening 76 connected end 66
apparent weight 37 cast iron 81 column with two fixed
austenite 65 grey or lamellar cast ends 66
automatic lathes 170 iron 81 components 12
axial load 63 hard cast iron 82 composite materials 92
axial locking devices malleable cast iron 81 composition of forces 11,
134 nodular cast iron 81 25
axle types 132 white cast iron 81 compression moulding
casting of metals 199 215
Celsius scale 100 compression stress 48, 63
cement 89 computer aided
barrel finishing 176
cemented carbides 89 programming 192
bearing types 138
cementite 73 concrete 89
belt drives 136
centre of gravity 14 conservation of angular
bending 51
centre of mass 14 momentum 32
bending loads 54
centrifugal casting 202 conservation of energy
bending moments 55, 59,
centroid 14, 58 27,62
ceramic materials 88 conservation of mass 41
bending processes 208
chain drives 137 conservation of
Bernoulli equation 42
changes of state of an momentum 28
blanking 203
ideal gas 112 continuity equation 41
body projected at an
channel 53 continuous path control
oblique angle 23
chemical analysis 96 182
bolts 126
chemical conversion continuously variable
boring 162
coatings 214 speed drives 142
brass 82
clamping devices 156 control modes for CNC
brazing 147
clamps 162 machines 181
breaking strength 52
clutches 136 copper and its alloys 82
brittleness 70, 75
CNC machine drives 177 copper-based bearing
broaching 173
alloys 87
Index 245
copper-nickel alloys elastic section modulus 57 friction 15,26
76 elasticity 70 friction in belts 18
core (sand core) 198 elastomers 84 friction in pulleys 18
counterboring 162 butyl rubber 92 friction in screws 17
countersinking 162 nitrile rubber 92 furnaces 72
couple 9, 25, 31, 54 polyurethane rubbers 92 fusion 110
couplings 135 silicon rubber 92 fusion welding 147
creep 71 synthetic rubber or
critical temperature 73 Butadienne 92 G
curvature 57, 61 electric arc welding 148 gases 35
cutting fluids 203 electron beam gear types 141
cyclic processes 104 microanalysis 97 geometrical basis for
electron beam welding programming CNC
D 151 machines 180
deceleration 21 electroplating 211 glass 89
deep drawing 208 energy 27 grain structure 73, 77, 196
deflection 62, 63 enthalpy 109 graphite 72, 81
deflection of beams 61 entropy 109 gravity 22
deformation 33, 54 entropy of the universe gravity die casting 201
density 35 109 grinding processes 174
determination of equation of state 102 grinding wheels 93
deflection by integration equilibrium 9, 13, 14,47,
61 49 H
deviation 121, 123 Euler's formula 64, 65 hand tools 156, 157
diathermic 98, 105 extrusion of metals 194 hard magnetic materials
die sets 205 extrusion of plastics 215 79
diesel cycle 118 hardening 73, 75
displacement 10, 20, 103 hardness tests 96
dissipative effects 108 fatigue 54, 71, 77, 78 harmonic motion 24
drawing of metal 194 fatigue tests 97 heat capacity 106
drill types 162 ferrite 73 heat engine 108
drilling 162 fibre reinforced materials heat reservoir 107
drilling machines 162 92 heat treatment 73
drop forging 196 fillers 94, 95 holding devices 156
ductility 70 first law of holes 123, 124
dynamic loading 53 thermodynamics 105 honing 175
dynamic pressure 43 first moment of an area 56 honing tools 93
dynamic viscosity 40 fits 121, 123, 124 Hooke's law 49
dynamics 20 fixtures 162 horizontally projected
flame hardening 76 body 23
floating bodies 37 hot deformation processes
eddy current tests 97 fluid dynamics 39 193
efficiency 26 fluids 35 hydrostatic pressure 35
elastic and inelastic flux (soldering) 146 hydrostatic system 102
impacts 33 force 9, 47, 103 hydrostatics 35
elastic bodies 47 forging 196
elastic curve 63 forming by bending
elastic deformation 47, 208 ideal gases 112
52,70 fracture 47, 70 impact test 95
elastic limit 47, 52 free body 47, 59 impact 32, 71
246 Index
impulse 28 magnesium alloys 86 nuts 126
induction hardening 76 magnetic particle tests 97
injection moulding malleability 70 o
of plastics 215 mandrels 168 oblique impact 32
inspection 121 manometer 44 optical spectrum analysis
interchangeability 121 marking out process 96
internal energy 105 156 Otto cycle 117
iron 72 martensite 73, 75, 77 outflow of liquids 45
iron ore 72 materials for cutting tools oxy-acetylene welding
irreversible process 108 155 148
isotherm 99 measurement 121 oxygen cutting 206
measurement of
J temperature 100 P
jigs 162 measuring devices 157 paints 212
joining processes 145 mechanics 9 parallel axis theorem
metacentre 38 30,59
metal chip types 154 parallelogram of forces 11
metal removal processes particle reinforced
Kelvin scale 101
154 materials 92
kinematic viscosity 40
metallographic analysis Pascal's principle 35
kinematics 20
97 path measuring systems
kinetic energy 28
method of sections 47 for CNC machines 179
microstructure 73 pattern 199
L perforating 203
mild steel 75, 77,
lacquers 213 phase transitions 110
milling cutters 172
laminar flow 41 piercing 203
milling machines 170
laminated materials 93 pig iron 72
milling processes 172
lancing 203 pin-ended columns 63
modulus of elasticity
lapping 175 pins and pin types 127
laser beam welding 151 plane of symmetry 55
modulus of rigidity 50, 68
laser cutting 207 plasma cutting 207
moment of inertia 29
latent heat 111 plastic deformation
moment-area method 63
lateral deflection 63 4, 52, 70
momentum 28
lateral strain 51 plasticity 70
mould 199
lathe 167 plastics 90
lathe accessories 167 plywood 89
lathe chucks 167 N
necking 52 point to point control
lathe cutting tools 169 182
lathe parts 167 neutral axis 55
neutral surface 55 Poisson's ratio 50
lead and its alloys 84 polar moment of an area
limits 121 Newton's laws 27
Newtonian fluid 39 59,69
longitudinal strain 49 polishing 176
longitudinal stress 49 nibbling 204
nickel and its alloys 84 power 26
lubricants 93 precious metals 87
lubricating grease 94 nitriding 77
nonuniform motion 20 press tools 204
lubrication 138 pressure 35
normal forces 35
normal stress 48, 56 pressure die casting 201
M normalizing 75 pressure resistance
Mach number 41 notch 53 welding 152
macroscopic 98 notching 203 prestressed concrete 89
Index 247
principle of Archimedes shaft to hub connections heat resistant steels 79
37 132 low temp, steels 79
programming of CNC shafts 123, 124, 132 nitriding steels 78
machines 187 shear forces 35,49 quenching and
punching 203 shear modulus 68 tempering steels 78
pure bending 53 shear strain 50, 67 spring steels 78
shear stress 39, 49, 60, 67 stainless steels 79
shearing process 203 steel castings 80
quasi-static process 103 shielded arc welding 150 steel for electrical
quenching 75 shot blasting 176 machines 79
shot peening 176 tool steels 80
R shrinkage 199 strain 47, 48, 52
radius of curvature 57, 61 sinking 162 strain harden 52, 73, 193
radius of gyration 30, 59 sinter materials 87 stream filaments 40
reaming 162 slenderness ratio 64 streamlines 40
recrystallization 73 sliding friction 16 stream tubes 40
reference points 181 slitting 203 strength 51, 62
refining 77 soft magnetic materials 79 strength of materials 47
refrigerator 108 soft soldering 147 stress 47,48, 52
reinforced concrete 89 soldering 146 stress relieving 73
resins 91 soldering alloys 84 stretch forming 208
resistance coefficient 46 solid lubricants 94 studs 126
resolution of forces 11 specific heat capacity 106 sublimation 111
restoring couple 38 specific heats of gases submerged arc welding
resultant 9 112 150
reversible process 108 speed 20 superfinishing 176
Reynold's number 41 spindle drives for CNC surface hardening 75
rivets 125 machines 183 synthetic oils 93
rolling process 194 splines 53
rolling resistance 16 spot facing 162
rotational kinetic energy spot welding 152 tangential force 31,32
31 sprocket wheels 137 tapping 162
rotational motion 29 stability of floating bodies temperature 98
38 tempering 73
stable equilibrium 38 tensile stress 48, 52
state of a system 98 tensile test 58
safety factor 53
static friction 15 testing of materials 71, 95
safety margin 47
static pressure 43 thermal cutting 206
sand casting 199
statics 9 thermal efficiency 108
scrap 72
steady flow 40 thermal equilibrium 98
screws 125
steels, thermal expansion 101
screw locking devices
carbon steel thermal spraying 212
129, 130
case hardening steels 78 thermodynamic
screw terms 126
corrosion resistant steels coordinates 98
screw thread types 128
79 thermodynamic
seam welding 152
fine grained welding equilibrium 102
second law of
steels 78 thermodynamic systems
thermodynamics 107
free cutting steels 78 102
second moment of an area
general purpose steels thermoforming of plastics
78 215
set screws 126
248 Index
thermoplastics 90
thermosetting plastics 91
tin and its alloys 84 wear resistance 75
titanium and its alloys 86 welding 147
tolerance 121 welding using an inert
tool holders 185 gas shield 150
tool length compensation white metal bearing
190 alloys 87
tool magazines 185 wire electrode process
tool nose compensation 151
190 wood 89
tool path compensation work 25, 31, 103
190 work done by a gas 104
tool wear 154 work harden 52, 73, 193
torque 67 wrought iron 72
torsion 67
total pressure 43 X'ray and gamma ray
toughness 70, 75, tests 97
transfer of energy 103 X'ray fluorescence
transverse force 48 analysis 97
transverse load 54, 60
transverse loading 60
triangle of forces 11
yield strength 52
trimming 204
yield stress 53
triple point of water 100
tungsten electrode process
150 z
turbulent flow 41 zero points 181
types of interpolation 182 zeroth law 99
ultimate strength 53
ultimate tensile strength
unbalanced force 103
uniform acceleration 21
uniform motion 20
unstable equilibrium 38
upset forging 196
upthrust 37
vapourization 110
varnishes 303
velocity 20
venturi tube 44
vertically projected body
viscosity 40
Abscherbeanspruchung Carnot-Prozess 115 schweipen 151
51 Chemische Priifungen 95 Elektrostahlverfahren 72
Abscherspannung 49 Geometrische Grundlagen Energie 27
Allgemeine Stahle79 (fur CNC Maschinen) 180 Energie Erhaltungssatz 27
Aluminium und Enthalpie 109
Aluminium Legierungen D Entropie 109
85 Dauerfestigkeitspriifung Erster Hauptsatz 105
Anderung der 97 Extrudieren 215
Aggregatzustande 110 Dichte 35
Anlassen 75 Diesel-Prozess 118
Anorganische Uberzttge Drehbewegung 24 Fahrwiderstand 17
213 Drehimpuls 32 Fertigungsverfahren 193
Antriebe der CNC Drehmaschine 167 Festigkeit51
Maschinen 182 Drehmaschinen Zubehor Festigkeit bei
Arbeit der Gewichtskraft 167 dynamischer Belastung 53
26 Drehmaschinen Festigkeit bei statischer
Arbeitsweise einer CNC Zusatzgerate 169 Belastung 52
Maschine 178 DrehmeiBel 167 Festigkeitslehre 47
Arten des Gleichgewichts Druck Ausbreitungsgesetz Festschmierstoffe 94
14 35 Feuerfeste Steine 88
Aufkohlen 76 Druckbeanspruchung 51 Flachenmoment 1.Grades
Auftrieb 37 Drucken210 58
AusfluB aus einem Gefa'B DruckgieBen 202 Flachenmoment 2.Grades
43 Druckumformen 215 58
Autogenes Druckverteilung durch Flachenschwerpunkt 58
Brennschneiden 205 Gewichtskraft der Flammharten 76
Axen 132 Flussigkeit 35 Folgeschneidwerkzeuge
Axial-Rillenkugellager Durchbiegung eines 206
141 Freitragers 61 Formpressen 215
Durchbiegung von Frasmaschinen 170
B Tragern 61 Fra'sverfahrensarten 172
Beanspruchungsarten 51 Dynamik der Fraswerkzeuge 172
Bernoullische Flussigkeiten 39 Freier Fall 22
Druckgleichung 42 Dynamik 20 Fullstoffe 93
Beschichten 311 Futter 168
Beschichten durch E
chemisches Abscheiden Edelmetalle 87
214 Eigenschaften der Galvanisieren 311
Beschleunigung 20 Flussigkeiten und Gase 35 Gasschmelzschweipen
Beton 89 Einsatzharten 76 148
Biegebeanspruchung 51 Eisen und Stahl 64 Gerader zentrischer StoB
Biegeumformen 208 elastischer StoB 33 32
Blei und Blei- Elastomere 92 Gesamtschneidwerkzeuge
Legierungen 84 Elektronenstrahl- 206
Bohren 162 analyse 97 Geschwindigkeit 20
Bohrmaschinen 165 Gesenkschmieden 196
250 Stichwortverzeichnis
Gesetz von Stefan und Ideale und nichtideale Kupplungen 135
Boltzmann 120 Flussigkeiten 39 Kurzhubhonen 176
Gewindearten 128 Impuls 28
Gewindebohren 165 Impulserhaltungssatz 28 L
GieBen 199 Induktionsharten 76 Lacke212
GieBen in Dauerformen Innere Energiefunktion Lager 138
201 105 Lagerwerkstoffe 87
GieBen mit Schwerkraft Integrationsmethode fur Lappen 175
201 die Bestimmung von Laserschneiden 207
Gleichfbrmige Bewegung Durchbiegung 61 Laserschweipen 151
20 Interpolationsarten 182 Leistung 26
Gleichgewichst- Loten 146
bedingungen 13 K Machsche Zahl 41
GleichmaBig Kaltumformprozesse 173
beschleunigte Bewegung Kautschuk 92 M
21 Keramische Stoffe 88 Magnesium und
Gleitlager 138 Kerbschlagbiegeversuch Magnesium Legierungen
Gleitreibung 16 95 86
Graphische Methoden 13 Kerbwirkung 53 Magnetische
Grenzma|3e 121 Kettengetriebe 137 Rifiprufungen 97
GrundabmaP 123 Kinematik 20 Maschinenelemente 121
Grundgleichungen der Kirchhoffsches Gesetz Massenmittelpunkt 14
Stromung41 120 Massivumformprozesse
Grundtoleranzgrade 122 Klarlacke213 193
GuBeisen81 Klebverbindung 145 Mechanik 9
Knickbeanspruchung 51 mechanische Arbeit 25
H Knickung 63 mechanische
Haftreibung 15 Kombinierte Werkzeuge Eigenschaften 70
Handwerkzeuge 157 206 Messen und Lehrenl21
Harmonische Bewegung Kontinuitatsgleichung 41 Messerschneiden 203
24 Kornchenblasen 176 Messing 82
Harten 75 Krafte beim StoB 32 Messung der Temperatur
Harteprufungen 96 Kraftedreieck 11 100
Hartloten 147 Kraftepaare 9 Metallische Uberziige211
Hartung von Krafteparallelogramm 11 Metall-Lichtbogen
Oberflachenschichten 75 KraftstoB 29 Schweipenl48
Herstellung der Kreisprozesse 104 metallographische
Kunststoff Produkte 214 Kreisprozesse und Untersuchungen 97
Herstellung von Eisen 72 Warmekraftmaschinen Metall-Spritziiberziige
Hohlraumstrahlung 120 115 212
Honen 175 KrUmmung 57 MePgerate 157
Hookesches Gesetz 49 Krummungsradius 57 Momente 9
HorizontalerWurf23 Kugellager 139 Momentenflachen
Hydrostatik 35 Kiihlschmierstoffe 155 Methode 62
Hydrostatische Krafte 37 Kuhlschrank 108 Muttern 126
Hydrostatische Systeme Kunststoffe 90
103 Kupfer und N
Kupferlegierungen 82 Newtonsche
Kupfer-Nickel Grundgesetze 27
IdealeGase 112 Legierungen 84 Nichteisenmetalle 82
Stichwortverzeichnis 251
nichtmetallische Revolverdrehmaschinen Schubspannungen in
Werkstoffe 88 169 einem Kreiszylinder 68
nichtumkehrbare Reynoldssche Zahl 41 Schubverformung 50
Prozesse 108 Riemengetriebe 136 SchwarzkOrperstrahlung
Nickel und Nickel Rollen 194 120
Legierungen 84 Rollenlager 140 Schweipen 147
Nietformen 125 Rollreibung 16 Schwerpunkt 14
Nietverbindungen 125 Rontgen- und Schwimmende Korper 38
Nitrieren 77 Gammastrahlenprufungen Seilreibung 18
Normalgliihen 75 97 Senken 162
Nullpunkte und Rontgenfluoreszenz- Senkrechter Wurf 22
Bezugspunkte 181 analyse 97 Sicherheitsfaktor 53
Rotation eines Korpers 29 Sieden und
O Rotationsenergie 31 Kondensation 111
Oberflachen- Sinterhartmetallkarbide
feinbearbeitung 174 88
Optische Spektralanalyse SandguB 199 Sinterwerkstoffe 87
96 Satz von Steiner 30 Spanarten 154
Organische Uberzuge 212 Sauerstoff- Spannelemente 156, 165
Otto-Prozess 117 Blasverfahren 72 Spannende Formgebung
Schaltbare Kupplungen von Hand 156
136 Spannung 48
Passungen 121 Scheren 203 Spannungen und
Passungsarten 124 Schleifen 174 Verformungen im
Plasmaschneiden 207 Schleifkorper 175 elastischen Bereich 56
Poisson's Zahl 50 SchleudergieBen 202 Spannungsarmgluhen 73
Polieren 176 Schmelzen und Erstarren Speziallacke213
111 spezifische
Prinzip von Archimedes
37 Schmelz-Schweipen 147 Warmekapazitat der Gase
Programmieren von CNC Schmelztauchiiberziige 112
Maschinen 187 212 spezifische
Punktschweipen 152 Schmelzwarme 111 Warmekapazitaten 107
Schmieden 196 Spritzgie6en215
Schmierfette 94 Stabe fflr
Schraierstoffe 93 Leistungsiibertragung 69
Quasi-statische Prozesse
Schmierung der Gleitlager Stahlerzeugung 64
138 StahlguB 80
Querkraftbiegung und
Schneidstoffe 155 Stahlsorten 77
Schubspannung 59
Schneidwerkzeuge 204 Stanzen 203, 204
Schnell trocknende Lacke Statik 9
R StationSre und
Raumen 173 nichtstationare Stromung
Schnittverfahren 47
Reiben 162 40
Schrauben 126
Reibung 15 Steinersche
Schraubenarten und
Reibung beim Schrauben Verschiebesatz 59
Mutterarten 129
17 Stifle 131
Reibung in Flaschenziigen StoB 32
19 StoBzahl 26
Reibung in Rollen 18 Strangpressen 186
Schubgleitungen in einem
Reibungsarbeit 26 Streckziehen201
Kreiszylinder 68
252 Stichwortverzeichnis
Stromfaden 40 Verdampfungswarme 111 Werkzeug- und
Stromlinie 40 Verdrehbeanspruchung 51 Werkstiick-
Stromrohre 40 Verdrehung 67 Wechselsysteme 184
Stufenlose Getriebe 142 Verfestigungsstrahlen 176 Werkzeugverschleip 154
Verformung 49 Widerstande in
Verformungen in einem Rohrleitungen 46
Temperaturkonzept 99 Trager 55 Widerstandsprep-
TemperguB 82 Viskositat 40 schweipen 152
Thermisches Vorrichtungen 165 Wirbelstromprlifungen 97
Gleichgewicht 98, 102 Wirkungsgrad 26
w Wurf schrag nach oben 23
Thermisches Trennen 206
Thermodynamik 98 Walzlager 139
thermodynamische Wanddruckkraft 35
Systeme 98 Warmeausdehnung 101 Young's Modulus 53
thermodynamische Warmebehandlung
Systeme und Arbeit 102 der Stahle 73 z
Thermoplaste 90 Warmekapazitat 105 Zahnrader 141
Tiefziehen 209 Warmekraftmaschine 108 Zahnrad-Stufengetriebe
Titan und Titan- Warmestrahlung 119 142
Legierungen 86 Warmeiibergang 119 Zement 89
Torsion in einem Warmekonvektion 119 Zerlegen von Kraften 11
Kreiszylinder 67 Warmeiibertragung 119 Zerspanvorgange 154
Tra'ger mit gleich Warmumformen 215 Ziegelsteine 88
bleibendem Querschnitt Warmumformprozesse Ziehen 194
54 193 Zink und Zink-
Tragheitsmoment 29 Wartungsfreie Gleitlager Legierungen 84
Tragheitsradius 33 139 Zinn und Zinn-
Trommelpolieren 176 WegmeBsysteme 179 Legierungen 64
Weichgluhen 75 Zinnbronze 83
U Weichloten 147 Zugbeanspruchung 51
Umformverfahren 208 Wellen 132 Zugversuch 95
umkehrbare Prozesse 108 Welle-Nabe zulassige Spannung 53
unelastischer Stofi 33 Verbindungen 132 Zusammensetzen
ungleichformige Wellensicherungen 134 von Kraften 11
Bewegung 21 Werkstoffe 70 Zusatzstoffe 94
Werkstoffeigenschaften Zustand eines Systems 98
V 70 Zustandsa'nderungen eines
Venturirohr 44 Werkstoffprufung 71, 95 idealen Gases 113
Verbindungsarten 145 Zustandsgleichungen 102
Verbundwerkstoffe 92 zweiter Hauptsatz 107
This is only a small selection from the large number of books available in
English. New editions of these books are published frequently and it is very
difficult to keep track of these changes. For this reason, the edition number and
year of publication are not given below.
1. Avallone and Baumeister : Marks' Standard Handbook for Mechanical
Engineers (McGraw-Hill)
2. Kutz: Mechanical Engineer's Handbook (John Wiley)
3. Dubbel: Taschenbuch fur den Maschinenbau (Springer)
4. Alfred Boge: Techniker Handbuch (Vieweg)
5. Rothbart: Mechanical Design Handbook (McGraw-Hill)
6. Meriam and Craig: Engineering Mechanics, Vol. I: Statics,
Vol II: Dynamics (John Wiley)
7. Beer and Johnston: Vector Mechanics for Engineers: Statics,
Dynamics (McGraw-Hill)
8. Beer and Johnston: Mechanics of Materials (McGraw-Hill)
9. Riley and Sturges: Statics and Mechanics of materials (John Wiley)
10. Shames: Mechanics of Fluids (McGraw-Hill)
11. Young, Munson and Okiishi: A Brief Introduction to Fluid Mechanics
(John Wiley)
12. Oertel: Introduction to Fluid Mechanics (Vieweg)
13. Degarmo, Black and Kohser : Materials and Processes in Manufacturing
(John Wiley)
14. Schey: Introduction to Manufacturing Processes (McGraw-Hill)
15. Wark: Thermodynamics (McGraw-Hill)
16. Moran and Shapiro: Fundamentals of Engineering Thermodynamics
(John Wiley)
17. Zemansky and Dittman: Heat and Thermodynamics (McGraw-Hill)
18. Schigley, Mischke and Budynas: Mechanical Engineering Design
19. Collins, Staab and Busby: Design of Machine Elements and Machines
(John Wiley)
20. Krar and Oswald: Technology of Machine Tools (McGraw-Hill)
21. Thyer: Computer Numerical Control of Machine Tools (Industrial Press)
22. Kief and Waters: Computer Numerical Control (McGraw-Hill)
23. Bollinger and Duffle: Computer Control of Machines and Processes
(Addison- Wesley)
24. Krar and Gill: CNC Technology and Programming (McGraw-Hill)
25. Kalpakjian: Manufacturing Engineering and Technology
26. Kalkapjian: Manufacturing Processes for Engineering Materials
Appendix 1
Alternate word forms in English
English is a language that is used and spoken all over the world, with the
consequence that english words can be found in many other languages. On the
other hand, english has also acquired words from other languages, like for
example "Guru" or "Mantra" from Sanskrit, and "Angst" or "Eigenfunktion"
from german. With increasing globalization, it is possible that many regional
forms of english may be created in the future, similar to that of american
english, which can be considered to be a regional form of english.
In this book the british kind of english has been used, and as is well known, the
word forms are closer to the latin than the word forms used in american english.
Readers who use american textbooks may want to know something about the
difference between british and american word forms, and also about the
difference between the british and american pronounciation of a given word.
The difference in most cases is small, and examples are given below to illustrate
a few cases where a difference does exist. Those interested in knowing more,
should refer to the dictionaries mentioned below.
A few examples of differences in spelling
• Some words which end in "we" like stabilise can also be written as
stabilize. The word form stabilise is more commonly used in Britain .
• Words ending in "o«r" in british english like vapour and colour are
written in american english as vapor and color.
• The word centre in british english is written as center in american
• In some cases the singular forms are the same, while the plural form
may be different. Examples are singular forms like radius and index
which are the same in british and american english. These have the
plural forms radii and indices in british english (following the latin
plural forms), while the american forms are radiuses and indexes.
Differences in technical terms
In most cases the British and American technical terms are the same. Only in
rare cases is there an outright difference. A few cases are quoted below.
• The hand tool which is called a spanner (Schliissel) in british english
is termed a wrench in american english.
• The measuring device gauge (Lehre) in british english is written gage
in american english. Both forms are pronounced in the same way.
• The measuring devices called slip gauges (Endmasse) in british
english are called gage blocks in american english.
• The fuel used in automobiles called petrol (Benzene) in british
english is called gasoline or gas in american english.
Alternate word forms in English 255
• The word car (Auto) is normally used for a motorized vehicle in
british English. This word is less used in american english, where the
word automobile is more common.
• The word engine (Motor) is used in british english for mechanical
devices (or drives) which convert the energy of a fuel into mechanical
energy. Common examples are the internal combustion engine, the
steam engine and the jet engine. In american english, the word motor
is more commonly used for the engine of an automobile, although
words like jet engine and steam engine are used in the same way as
in british english. The word engine is only applicable to mechanical
devices and should not be used for electric motors.
• Abbreviations like AC (alternating current - Wechselstrom), DC
(direct current - Gleichstrom) and rpm (revolutions per minute-
Drehzahl ) are sometimes differently written like for example A.C,
D.C or r.p.m. However I think that the abbreviations AC, DC and
rpm are the ones that are most frequently used.
I would advice all those interested in improving their English to use an
English/English Dictionary. A good example is the
"Oxford Reference Dictionary"
(published by the Oxford University Press) which gives long explanations for
each word, and considers many aspects of each given word like its origin,
alternate forms, synonyms, etc.
Even more helpful may be one of the new electronic dictionaries on CD-ROM,
like for example the
"Cambridge Advanced Learners Dictionary on CD-ROM"
(published by the Cambridge University Press)
This dictionary gives the written word forms in both British and American
English. The reader can also (by using a series of mouse clicks) listen to the
British and American pronounciations of the words, and can record his (or her)
own pronounciation of a word, and replay it.
This dictionary is full of other helpful features, like the different meanings of
words, examples of sentences using the words, common errors made by users,
related words, synonyms, exercises and many other features that are too
numerous to mention here. I would whole-heartedly recommend such a
dictionary, because I think it is not expensive and is excellent value for money.
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SpreadsheetControl.SelectionChanged Event
Fires when the selection changes in an active worksheet.
Namespace: DevExpress.XtraSpreadsheet
Assembly: DevExpress.XtraSpreadsheet.v21.2.dll
public event EventHandler SelectionChanged
Event Data
The SelectionChanged event's data class is EventArgs.
Handle the SelectionChanged event to perform any actions each time a user selects cells, rows, columns, or drawing objects in the SpreadsheetControl’s UI.
Set the WorkbookEventOptions.RaiseOnModificationsViaAPI property to true to raise the SelectionChanged event when the selection is changed in code.
spreadsheetControl.Options.Events.RaiseOnModificationsViaAPI = true;
Use the following API members to specify the selection:
The example below shows how to use the SelectionChanged event to calculate the average, count, numerical count and sum for non-empty selected cells.
spreadsheetControl1.SelectionChanged += (s, e) =>
int count = 0;
double sum = 0.0;
int numericCount = 0;
double average = 0.0;
Worksheet worksheet = spreadsheetControl1.ActiveWorksheet;
Range selectedCells = worksheet.Selection.Intersect(worksheet.GetDataRange());
if (selectedCells != null)
foreach (Cell cell in selectedCells.ExistingCells)
if (cell.Value.IsNumeric)
sum += cell.Value.NumericValue;
if (numericCount > 0)
average = sum / numericCount;
See Also
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Symbol for Smooth Transition Between Pitches?
• Mar 2, 2021 - 20:10
Is there a notation symbol that indicates a continuous change in pitch between two notes?
I'm not talking about legato, I'm trying to indicate sliding your finger up or down the violin to transition smoothly between two notes.
If this exists, what does it look like?
And does it exist in Musescore?
Edit: I might be looking for "Portamento"
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Essay 5 paragraph
How to Write an Effective 5-Paragraph Essay: Formulas for
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BCCC Tutoring Center Outline for a Five-Paragraph Essay
Sep 03, 2019 · The 5 paragraph essay is really small, so warp from original topic is a big breakdown of the rule. You must focus on the exact theme, create thesis statements, and use them during the whole essay. Besides, your conclusions should also be connected with the introduction and body; use fair and strong arguments. more
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May 22, 2021 · A Persuasive Essay Has 3 Components . Introduction: This is the opening paragraph of your essay. It contains the hook, which is used to grab the reader's attention, and the thesis, or argument, which you'll explain in the next section. Body: This is the heart of your essay, usually three to five paragraphs in length. Each paragraph examines one more
Sample 5 Paragraph Argumentative Essay | PDF
May 21, 2021 · Essays religion science; profile essay of a police officer; Although students learning mathematics it influences decisions to determine whether the statements below are examples of a group of students, as of this book have nothing to contribute to under a paragraph 5 write to how a essay with thesis stand that there appear to be told what to say. more
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Five Paragraph Essay Sample The Hazards of Moviegoing Introductory paragraph (Hook) (Thesis) (Blueprint) I am a movie fanatic. When friends want to know what picture won the Oscar in 1980 or who played the police chief in Jaws, they ask me. My friends, though, have stopped asking me if I want to go out to the movies. more
5 Paragraph Argumentative Essay Examples and Writing Tips 2021
A five paragraph essay is quite a popular college assignment. As you get from its name, it is a paper, which consists of five paragraphs: introduction, three arguments with supportive data, and conclusions, where you sum all the results of your work. Using this simple outline you will be able to cover every issue without missing anything out. more
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What Is a Five Paragraph Essay? - Essay Writing Service
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5 Paragraph Essay: Guide, Topics, Outline, Examples | EssayPro
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Essays in love alain and example 5 paragraph essay college 7. Use history, especially case examples or 2. 6. ) for humanists, education should be included in the curriculum, such as the american clark blaise, she and her accountant. Pepi leistyna, arlie woodrum, and stephen j. more
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Tim and Moby explain the structure of five-paragraph essay, including details about the introduction, the body paragraphs, and the conclusion. Which topic sentence supports the claim that everyone should learn computer programming? Coding is an ok essential twenty-first-century skill. more
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Feb 11, 2020 · In this post, we discuss how to write a five-paragraph essay that works, regardless of subject or topic, with a simple—but effective—plan for completing a successful essay. As a parent of five children (three now in high school), I've helped brainstorm and edit my fair share of essays. more
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The Basic Five Paragraph Essay: Format and Outline Worksheet Below is the pattern or format used to write a basic five-paragraph essay. Because it allows you to present information and ideas clearly and logically, it is applicable to many styles of essay for many types of academic disciplines. There is an Outline worksheet on the back of this page more
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Apr 13, 2021 · Below are some of the steps to take in writing a 5 paragraph argumentative essay: Choose a good argumentative essay topic. Also, endeavor to conduct good research. Furthermore, write out your argumentative essay outline. Additionally, carry out a careful and adequate editing. Some 5 Paragraph Argumentative Essay Examples. Below are some 5 paragraph argumentative essay … more
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The 5 Paragraph Essay Outline. Don’t know the 5 paragraph essay structure? It’s pretty simple. Here’s the basic outline you should follow: Paragraph 1: Introduction; Paragraph 2: First Main Point; Paragraph 3: Second Main Point; Paragraph 4: Third Main Point; Paragraph 5: Conclusion; Now let’s discuss what should go in each paragraph. more
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How a Virtual Assistant can help manage incoming and outgoing phone calls
Property Management Assistant can definitely help you answering calls and handle inbound inquiries, and simply take a certain message and send emails for some details. You have the right to have your Property Management Virtual Assistant answer calls during office hours, or you can or even have them handle the
Leave a Reply
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| 0.840125 |
Data Set Calculator | Number Sieve || German: Datensatzrechner | Zahlensieb || Imprint & Privacy
Data Set Calculator
Calculations with a data set of numbers*. Enter numbers separated by space or line break into the upper field, each of which you want to perform the same calculation. Determine a value x to calculate with. Then click the according button. Calculated can be basic arithmetic operations, powers, logarithms and trigonometric functions (enter as radiant). E.g. the square root can be calculated with a^x and x=0.5. deg2rad turns degrees into rad. ↑ transfers the values from the lower field to the upper. To round the numbers of a set, determine the amount of decimal places and calculate *1.
If you used a different separator (e.g. ;) in your data set, you can search and replace it here (replace with space).
*Maximum 10000 characters | ©Jumk.de Webprojects
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| 0.999299 |
A team is a group of individuals with different skills and abilities working together to achieve a common goal or vision. Teamwork makes it easier to accomplish a task that would not have been done well within a short time when handled individually. Teamwork creates a platform to combine ideas, skills, talents and leadership to accomplish a project or job. When required to write a teamwork essay, you should remember that teamwork is the ultimate key to success. With the analogy in mind, your essay needs to be directed to prove the success that comes with teamwork.
What is teamwork essay?
A teamwork essay is focused on addressing matters related to working as a group. Such an essay should cover the aspects of teamwork, the advantages and disadvantages of teamwork, among other perspectives. You can use a teamwork essay example to know what such an essay entail. Here are some points on the importance of teamwork that you could highlight in your essay to emphasize that teamwork is the ultimate key to success.
1. Improvement of employee relations
Teamwork promotes employee relations in a workplace environment. You could look through any teamwork essay example and realize there are few chances that an essay could lack such importance of teamwork. Through interactions in teams, employees bond with one another as they build trust and feelings of being valued by realizing that they have contributed to achieving a particular goal. With better employee relations, remember that your essay should shed light on the increased cohesion among team members.
1. Learning opportunity
A teamwork essay sample should address the issues around learning opportunities created by individuals working as a team. A team is made of individuals with different skill sets, mental abilities, capabilities and knowledge. Teamwork creates cooperation where new individuals get to improve their skills by learning from experienced parties. Through teamwork, team members can challenge each other’s ideas till they arrive at a common solution to a problem, eventually ensuring the completion of a job. It would be best to highlight the aspect of rapid understanding of concepts resulting from teamwork in your teamwork essay.
1. Work efficiency
Promoting work efficiency through teamwork is another aspect to cover in your teamwork essay that will be relevant and an additional point to your paper. Efficiency when working in teams is achieved by team members coming together to perform tasks faster and efficiently. Cooperation when working in teams reduces workload as responsibilities are shared between the team members.
However, it is essential to remember that conflicts and disagreements are unavoidable when working in groups. Conflicts can be good as they provide a platform where ideas are presented and debated upon. Through such debates, the best solutions to problems are reached.
Any teamwork essay sample has vital points that are to be considered in writing. It is not challenging to write on how teamwork is an ultimate key to success based on actual life incidences that prove that many are better than one. The key points to focus on should be how ideas and responsibilities are shared when working in teams, the bonds that result from teams and how teams create learning opportunities for individuals.
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Question: What state granted women’s full suffrage 1893?
Which nation first granted women’s suffrage in 1893?
First in the world
Although a number of other territories enfranchised women before 1893, New Zealand can justly claim to be the first self-governing country to grant the vote to all adult women.
Which states had the vote for women’s suffrage?
Tennessee played a pivotal role in the passage of the 19th Amendment, which granted women the right to vote in 1920. By that summer, 35 of the 36 states necessary had ratified the amendment. Eight states had rejected the amendment, and five had not voted.
When was women’s suffrage granted in the US?
When was the first female vote?
Which states granted women’s suffrage first?
1869: The territory of Wyoming is the first to grant unrestricted suffrage to women. 1869: The suffrage movement splits into the National Woman Suffrage Association and the American Woman Suffrage Association.
THIS IS IMPORTANT: What did Wollstonecraft mean by virtue?
What states were the first states to allow for women’s suffrage?
Wyoming. On December 10, 1869, Territorial Governor John Allen Campbell signed an act of the Wyoming Territorial Legislature granting women the right to vote, the first U.S. state or territory to grant suffrage to women.
Why did Wyoming grant women’s suffrage?
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Individual Page
Marriage: Children:
1. William Daniel Thompson: Birth: 3 OCT 1962. Death: 3 OCT 1962
2. Person Not Viewable
3. Person Not Viewable
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What Are NFTs and How Can They Be Used in Decentralized Finance? DEFI Explained
So what are NFTs all about? And how can they be used in decentralized finance? You’ll find answers to these questions in this video.
💛 Gitcoin ► https://gitcoin.co/grants/1158/finematics-defi-education
Okay, so let’s start with what NFTs actually are. NFTs stand for non-fungible tokens and they are one of the types of cryptographic tokens that can represent ownership of digitally scarce goods such as pieces of art or collectibles.
“Non-fungible” is not a very popular word so let’s see what it really means.
In economics, fungibility is the characteristic of goods or commodities where each individual unit is interchangeable and indistinguishable from each other.
Although NFTs can be implemented on any blockchain that supports smart contract programming, the most noticeable examples are ERC-721 and ERC-1155 standards on Ethereum.
When it comes to DeFi, NFTs can unlock even more potential for decentralized finance. Currently in DeFi, the vast majority of DeFi lending protocols are collateralized. One of the most interesting ideas is to use NFTs as collateral. This means that now you’d be able to supply an NFT representing a piece of art, digital land or even a tokenised real estate, as collateral and borrow money against it.
📖 Post ► https://finematics.com/what-are-nfts-and-how-can-they-be-used-in-defi
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Infrared What Does Nm Mean?
IR or Infrared wavelengths are measured in ‘nm’ or nanometers, which are used to specify the wavelength of electromagnetic radiation near the visible part of the light spectrum. The main advantage of the 940nm wavelength is that the IR LED’s do not produce any visible glow.
What is nm in infrared?
Infrared radiation (IR), sometimes referred to simply as infrared, is a region of the electromagnetic radiation spectrum where wavelengths range from about 700 nanometers (nm) to 1 millimeter (mm).
Is 850 nm light visible?
The 850 nm wavelength is standard for most applications, including CCTV. The light source does produce a faint red glow at direct exposure, but otherwise it is not visible to the naked eye.
What is the nm range of IR?
Infrared radiation (IR), also known as thermal radiation, is that band in the electromagnetic radiation spectrum with wavelengths above red visible light between 780 nm and 1 mm.
What does nm wavelength mean?
NOTE: Wavelengths of visible light are measured in nanometers (nm). A nanometer is a unit of length equal to one billionth of a meter.
Can humans see 850 nm?
A typical human eye will respond to wavelengths from about 390 to 750nm (nano metres). Infra Red light in the 850nm wavelength is hard to see with the naked eye – but not impossible.
You might be interested: Question: What Is The Basic Difference Between Ultraviolet Visible And Infrared Electromagnetic Radiation?
What is 1550 nm wavelength?
1550nm -. 5dB of loss/ km. This is the second window of opportunity for single- mode transmission. This wavelength is used for extremely long distance high bandwidth applications.
What is the difference between 850nm and 940nm IR?
All cameras are most sensitive to 850nm infra-red, delivering superior surveillance footage at night. 940nm delivers virtually invisible covert lighting but does result in reduced performance ( typically up to 40% less ) and requires a very sensitive camera.
What is mid IR range?
Mid-IR region from 4000-400 cm1 (~2.5-25 µm wavelength)
Can infrared be harmful?
Medical studies indicate that prolonged IR exposure can lead to lens, cornea and retina damage, including cataracts, corneal ulcers and retinal burns, respectively. To help protect against long-term IR exposure, workers can wear products with IR filters or reflective coatings.
What does 532 nm mean on a laser?
Wavelength: 532 nm Second Harmonic Generation (SHG) lasers use a 532 nm wavelength. This laser light is visible to humans, appearing green, and is produced by transmitting a 1064 nm wavelength through a nonlinear crystal. As the light passes through the crystal, it’s wavelength is reduced by half.
What does nm measure?
A nanometer is a unit of measurement for length just as you have with meters and centimeters. A nanometer is one billionth of a meter, 0.000000001 or 109 meters. The word nano comes from the Greek word for “dwarf.” The term nanoscale is used to refer to objects with dimensions on the order of 1-100 nanometers (nm).
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Project Grants Landing Page
Project Grant Library
What is Required to Feed Our Community?
SEEQS, Oʻahu
Our project wasn’t simple. The goal was to feed a community, hence our “What does it take to feed a community?” essential question. There was a twist, though. We could only use food that we grew, and the only things we could buy were staple ingredients; stuff that we couldn’t make. We spent a whole school year working on every aspect of what it would take to feed others. We first split up into groups, each covering different things that would be needed. For example, the Field rotation focused only on the field and making those plants grow, and then we rotated and a different group would come to the field.
The four groups were Field, Garden Beds, Aquaponics, and closing the circle, also called nutrient management. The second semester we split off into four different groups that would focus more on the event, they were Event Planning, Chef & Artist Corner, Field & Garden Beds, and Water.
We stayed in these groups and worked on our independent projects. The Field 2 was a mini projects, and the meditation and tea garden was another, but people also continued with previous projects, like the Aquaponics. These all led up to our final event in May, for example the meditation and tea garden group made tea and grew herbs. Other groups preserved food that was harvested early on in the year, such as kabocha squash and flint corn. Some students worked on researching and testing recipes, and others made plans on how to organize the event as a whole. Together, we cooked and served all our food at the Rusty Fork Cafe!
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Teaching Children Home & School Routines
• Situation
The Watson Institute has received a number of questions from parents searching for resources to teach their child how to complete various tasks with greater independence or how to set routines for their child. For example, one parent noted that her daughter had difficulty staying focused while getting ready for bed in the evenings. She was looking for a resource to help her stay focused and be more independent. Another parent asked about teaching their son to brush his teeth before bedtime and incorporate that into his daily morning and evening routines.
We’ve also heard from educators looking for ways to support their students with exceptionalities who may have difficulty following along during activities or particular classes.
• Summary
A mini-schedule provides a picture or word sequence for each step of a routine or task. This can promote independence for your child and decrease the amount of assistance or prompting you need to give. The type of mini-schedule you use (whether visual or text/checklist) will be dependent upon your child or student’s needs and preferences.
Identify a motivator/reinforcer that your child/student may have or do after they have completed the mini-schedule. Add the motivator to the schedule as a reminder of what they will be working towards.
• Definition
A mini-schedule is a visual schedule or visual sequencing of events for a short period of time, NOT an entire day. It can be in picture, object, word, or numeral format. A mini-schedule’s purpose is to give a sense of time and when an activity will end.
• Quick Facts
• Child's Age: 3-5, 6-10, 11-13, 14-17, 18+
• Planning Effort: Moderate
• Difficulty Level: Easy
• Pre-requisites
Ability to understand pictures, words, and objects. Ability to understand delayed gratification/rewards. Knowledge of the steps of the class or activity. Materials to depict the steps in picture or written format. Materials to model the project. Knowledge of the steps of the class or activity.
• Process
1. Identify the steps for the task at hand; i.e. brushing your teeth or participating in physical education class.
2. Gather the materials to make the visual representations of each step if you are using a visual mini-schedule.
3. Make the schedule using pictures/words/objects.
4. Present it to your child/student.
5. Model and demonstrate how to use the mini-schedule during the task.
6. Positively reinforce the child for using the mini-schedule with their preferred item or activity.
7. Over time you can work with your child/student to promote independence by prompting them less and using fewer verbal supports. Let them follow the pictures or text on the schedule with less prompting.
• Documents and Related Resources
website about visual schedules
setbc.org (website resource for pictures/icons)
do2learn.com (website – resource for pictures)
visualaidsforlearning.com (website)
Mini-Schedule Gym (image)
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Program Manager:
Dr. Russ Tremayne
(208) 732-6885
Focus Area Advisor:
Jacob McCue
(208) 732-6252
Program Overview:
The study of History provides the student with an understanding of and ability to interpret the past.
Completion of the following courses is designed to result in an associate degree, and meets the general education requirements at all Idaho public universities. Course selection should be coordinated to meet requirements for your intended transfer institution.
Many historians become teachers but others become professional editors, work in museums or archives, or take positions with state or federal government agencies. History also provides an excellent preparation for law school.
Program Outcomes:
Upon successful completion of the History program, a student will be able to:
1. Demonstrate knowledge of the theoretical and conceptual frameworks of History.
2. Develop an understanding of self and the world by examining the dynamic interaction of individuals, groups, and societies as they shape and are shaped by history, culture, institutions, and ideas.
3. Utilize discipline specific approaches from the field of History, such as research methods, inquiry, or problem-solving, to examine the variety of perspectives about human experiences.
4. Evaluate how reasoning, history, or culture informs and guides individual, civic, or global decisions.
5. Understand and appreciate similarities and differences among and between individuals, cultures, or societies across space and time.
Career Information:
Sample Career Opportunities: Historians
*Talk to an advisor for additional career choices
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ODM2 Working Group ODM2 Variable Name Controlled Vocabulary A vocabulary for describing the name of Variables. https://en.wikipedia.org/wiki/Michaelis%E2%80%93Menten_kinetics Added to support Critical Zone Observatory (CZO) data use cases. The Michaelis constant is the substrate concentration at which the reaction rate is half of Vmax. Vmax represents the maximum rate achieved by the system, at saturating substrate concentration Michaelis constant Wikipedia
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Support for deaf children aged 0 to 5 years: Guide
Hitchins, A. Lewis, S. Holmans, A. Grover, A. Wakefield, T. Cormier, K. Rowley, K. Macsweeney, M. | View as single page | Feedback/Impact
Use of signs
If a child has a hearing loss their parents may wish to communicate with them using a sign language. Sign languages are visual languages using the hands, face and body - they are different from spoken languages and have their own linguistic structure. British Sign Language (BSL) is the language of the UK’s Deaf community, who often describe themselves as Deaf with a capital D to emphasise their deaf identity. Deaf children who are exposed to a sign language like BSL from a young age can acquire the language following very similar language milestones as hearing children who learn a spoken language. See here for a conversation in BSL with a 2 year-old deaf child and her mother.
Many children will be fitted with hearing aids or cochlear implants soon after they are identified as deaf, giving them the potential opportunity to develop spoken language. However, using sign language can help with understanding speech and can also be particularly useful at times when a deaf child is not using hearing aids or cochlear implants. Some deaf children may stop using sign language as their spoken language develops. However, for many deaf children sign language remains their primary means of communicating, or retains an important role in their lives. Action on Hearing Loss estimate that there are at least 24,000 people across the UK who use their main language, although this is likely to be an underestimate. The NDCS have a range of family support resources for accessing BSL,
For more information see BSL section of this MESHGuide.
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Placement test
You can use our free-of-charge placement test to determine your current language skills and find out which course will help you to achieve your goals. The test takes between 20 and 30 minutes to complete.
After assessment of the test, we will contact you to discuss the result and advise you without any commitment on your part.
We look forward to hearing from you!
Start test
Correct placement allows us to ensure that you learn your target language efficiently.
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Mike Loniewski
Myth #3
The secrets of the forest are revealed in the exciting conclusion to Myth. With ancient evil poised to strike, Sam finds himself in the clutches of the Ogre Guard. Meanwhile, Anne and Giant plot his rescue with a fallen warrior of old. But can they reach Sam before he's sacrificed to the Witch Queen's tomb?
This comic book is currently unavailable
54 printed pages
Original publication
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There are many approaches to model building. The following was used with church leaders in order to construct the Discipleship model.
Collecting Initial Thoughts
Participants were asked to consider how they might categorise people in the church in terms of the effect they have on the growth and life of the church. They were further asked why people join and leave the church. See handout sheet 1. Although a number of these responses have not been used the main aim was to get people thinking about how different elements are identified and how one may cause another. Later in the process, these questions were made more specific. See July Issues.
System Dynamics Elements Used in Modelling
Participants were shown how one particular model, loosely based on the Limited Enthusiasm Model, was built. This also introduced them to the concepts of stocks, flows, converters and connectors. The full presentation can be downloaded, with the four elements in System Dynamics. Essentially there are:
• Stocks. Also called accumulations. These measure quantity. What is accumulated stays there unless there are processes that change its quantity. For example, the number of people who belong to a church at any given time could be a stock. It is a static view of the system – what is there now, rather than what happens over time.
• Flows. Also called rates. These measure change. How many people are converted per year could be a flow. It is a dynamic view of the system, that is, how things change over a period.
• Connector. These control change, though linking one element to another. Connectors capture the process of cause and effect. If the people who belong to church cause (that is they are involved in the process of) conversion, then there is a connector from church to conversion. The more in the church, the more conversions
• Converter. These convert one type of quantity into another so that elements of different types can be linked together. Thus they can appear in causal chains. There are special converters that interface with the boundary of the model and have values that are set from outside. These are the parameters.
It is important to understand that any system has a static view (the stocks – what is there now), a dynamic view (the flows – how things are changing) and a causal view (the connectors – what causes what). People possess these three views of a system, but often they are in conflict with each other without them realising it. One purpose of a system dynamics model, and its simulation, is to highlight these conflicts and guide people to a resolution and a better understanding of the system.
Calibration and Parameters
The first model described in some detail was the discipleship model. With the basic stocks of the system constructed from discussions over three meetings the group assigned values to the stocks and to the parameters that control the flows, based on realistic guesses. Thus a static and dynamic view of the system was identified. The causal view was left on hold. A worksheet was constructed with the initial guesses for the parameters. The first guess gave a wide discrepancy between static and dynamic views – note the big difference between the first guess and the second which is where the stocks are calibrated to the flows (attached sheet). Participants were either overestimating the number of spiritually mature people in the church, or underestimating the process to spiritual maturity, or both.
A blank parameter worksheet is available.
Once there are satisfactory calibrations of a model, various experiments can be conducted, in the form of “what ifs”. For example, for the discipleship model, one experiment could be “what if there were a sudden influx of converts?”. How would the balance of new converts to “discipled” to “mature” behave? How long would it take to settle back down?
Feedback Loops
With a better understanding of how a model behaves, various control issues can be investigated. This is where causal loops become important, where making a change has an effect which in turn affects the original change. In the case of the discipleship model, there are at least two loops of interest.
• How does the lack of mature Christians affect the resourcing of the church programme, in particular those resources that help generate mature Christians? Does there need to be a minimum number of mature people for a church to avoid a downward spiral in its numbers?
• How does the number of discipled Christians affect the church’s quality and the perception of that quality by potential joiners? Could a church achieve a critical mass, so that by increasing its fraction of discipled believers, it would have such a positive impact that an upward spiral of growth would result?
Soft or Unquantified Variables
Soft variables are those for which no clear or easy measures exist. In that sense, they are unquantified, even though they have an informal sense of measure. For example, the quality of the church is a soft variable. There is no easy way to measure it, but people have a sense of what is a great church, good church, mediocre and poor. There is quantity but without specific numbers. Most models require such variables.
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What is Virtual Vaccine
virtualvaccine.me takes the improvements made in contacttrace.com.au each week, internationalises them and make it available to different countries for customisation.
virtualvaccine.me is a global domain, so in theory will work everywhere, but further local customisation will allow Citizen Assisted Contact Tracing to fit into the cultures and laws of a country perfectly.
For example, some countries might decide to create different customisations for each state, instead of one set of customisation for the whole country.
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Registration Dossier
Diss Factsheets
Ecotoxicological information
Long-term toxicity to aquatic invertebrates
Currently viewing:
Administrative data
Link to relevant study record(s)
Description of key information
The estimated freshwater invertebrate 21-day NOELR (Lowest Observed Effect Loading Rate) value is 2.144 mg/l based on reproduction.
Key value for chemical safety assessment
Additional information
The aquatic toxicity was estimated using the Petrotox model, which combines a partitioning model used to calculate the aqueous concentration of hydrocarbon components as a function of substance loading with the Target Lipid Model used to calculate acute and chronic toxicity of non-polar narcotic chemicals. Petrotox computes toxicity based on the summation of the aqueous-phase concentrations of hydrocarbon block(s) that represent a hydrocarbon substance and membrane-water partitioning coefficients (KMW) that describe the partitioning of the hydrocarbons between the water and organism.
Categories Display
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Technical Article
High Performance Flybuck
January 19, 2018 by Florian Mueller
This article discusses the different methods that can be used to improve the performance of a Flybuck converter in a wide input voltage or power level range.
A Flybuck is an alternative to a Flyback for low power applications because it is a low-cost, simple to use an isolated topology. Just synchronous buck and coupled inductor windings are needed to create isolated outputs. Furthermore, a Flybuck typically achieves softer switching compared to a Flyback topology. This can eliminate the need for a snubber circuit and lowers Electromagnetic Interference (EMI).
Improve the Performance of Flybuck
But how can we improve the performance of a simple Flybuck further? This article presents three different methods, which can be used individually or simultaneously. First, using an inverting topology will influence the duty cycle range and therefore will improve performance and efficiency in many applications. Second, adding a synchronous rectifier will reduce the secondary side losses and will improve the output voltage regulation. The last method will improve the output voltage regulation further by adding an optocoupler to regulate the output voltage.
Figure 1 shows a simplified schematic of an inverting Flybuck with the optocoupler and secondary synchronous rectification.
Simplified schematic of a high-performance Flybuck
Figure 1: Simplified schematic of a high-performance Flybuck
In a Flybuck, the minimum input voltage must always be higher than the primary output voltage. Very often this results in a high duty cycle for a low input voltage. That is a disadvantage in many Flybuck applications because high duty cycles will increase peak currents a lot. Therefore with large amounts of leakage inductance, the Flybuck is probably not usable with a duty cycle higher than 60%.
Fortunately, there is another alternative. An inverting BuckBoost can be used instead of a Buck since this will lead to a lower duty cycle in many applications. Of course, it is only attainable if a positive voltage on the primary side is not needed because the BuckBoost is generating a negative primary voltage.
Every synchronous Buck controller can be used for realizing an inverting BuckBoost that generates a negative output voltage. It is just a simple trick needed to get the controller working. In a standard Buck, the output voltage is connected to the inductor and the return line is connected to GND. For an Inverting BuckBoost, simply connect the device ground to the negative output (instead of to GND) and connect an additional capacitor between the input and the negative output. (see Figure 1). In this configuration, the Buck controller will generate a negative output voltage. Care must be taken about the maximum VDD voltage rating of the controller. After the output is in regulation, the controller is referenced to the negative output. Therefore, the maximum VDD voltage seen by the controller is the voltage difference between the input and the output voltage. Please note that the UVLO will not work properly because it is much lower in this configuration.
Secondary Side Synchronous Rectifier
There are different methods to drive secondary side synchronous rectifiers. You can add a separate Gate drive transformer to drive the secondary synchronous FET. If a primary controller is used with external primary MOSFETs then the driving signal could be taken from the primary side.
Another method is to use a secondary-side synchronous controller, which is expensive but typically leads to perfect control of the FET. A simpler and cheaper way than both these methods is to add a gate drive winding to the Flybuck transformer. This “self-driven” technique only costs a few cents, but unfortunately, this simple method has a drawback. The timing cannot be controlled perfectly which may result in a short shoot-through current. This will increase the power dissipation and reduce efficiency. The circuit should be verified in the lab to ensure safe operation under all conditions. Nevertheless, a self-driven synchronous rectifier will improve the efficiency and the output voltage regulation compared to an output diode. Figure 1 shows the simple circuit of a self-driven synchronous FET (highlighted in brown).
Optocoupler Feedback
In primary side control, the secondary output voltage is regulated through the coupling of the primary side voltage. The secondary output is controlled only by the primary output and the transformer. Voltage drops of the output rectifier or parasitic elements like leakage inductance, a resistance of the windings, layout or other components cannot be compensated. Therefore, typically only an output voltage regulation of about 5% to 10% can be achieved. When better regulation is needed, an optocoupler can be used for regulating the secondary output voltage.
How does the regulation of the output voltage work?
Figure 1 shows the simplified circuit of an optocoupler regulated design. An error amplifier (U3) such as the TL431 is used together with an optocoupler to provide feedback loop isolation. A small variation of the output voltage due to the line or load changes is sensed by the input of the error amplifier and compared to an internal voltage reference. Differences between the divided down output voltage (R7, R8) and the voltage reference are converted into an error current.
This error current signal is transferred to the primary side through the optocoupler. On the primary side, the controller (U1) is regulating the negative primary voltage. Similar to the secondary side, a resistor divider (R3, R4) is used to measure and compare the output voltage with the internal voltage reference of the controller. In other words, there are two feedback paths, one on the primary side and one on the secondary side. Combining these two feedback paths is simply done by connecting the Opto-transistor to the primary side resistor divider (see Figure 1).
The Opto-transistor is in parallel to the high side resistor (R3), therefore, the effective resistance can only be decreased. For this reason, the primary side resistor divider must be chosen carefully. In order that the secondary loop can control both directions (increasing and decreasing the output voltage) the primary loop itself must regulate a higher primary voltage (absolute value) than required. This means that the primary side voltage divider must be set for a higher absolute value of the negative output voltage. Therefore, the secondary loop has the ability to increase and decrease the output voltage which is needed during transients.
A Rising Popularity
The Flybuck topology is particularly prevalent in applications with a wide input voltage range or a wide power level range, the performance of a Flybuck is sometimes not sufficient. The presented methods showed ways to improve the behavior of this isolated topology.
A practical example of an inverting Flybuck with optocoupler feedback and synchronous rectification is shown in the PMP30197 reference design from Texas Instruments. The peak efficiency is above 92% (see Figure 2) and the load regulation is better than 1.5%. All technical documents such as Schematic, Test report, BOM or Gerber Files can be downloaded here.
Efficiency Reference Design PMP30197
Figure 2: Efficiency Reference Design PMP30197
About the Author
Florian Mueller was born in Rosenheim, Germany, in 1976. He received his degree in electrical engineering from the University of Haag. After working for several years as a freelancer in the field of electrical engineering, he joined TI in 2011 and is working in the European Power Design Services Group, based in Freising, Germany. His design activity includes isolated and non-isolated DC/DC and AC/DC converters for all application segments.
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Regulation of liver glycogen synthase phosphatase activity by ATP-Mg
Daniel P. Gilboe, frank q Nuttall
Research output: Contribution to journalArticlepeer-review
10 Scopus citations
The kinetics of a synthase phosphatase reaction inhibited by ATP-Mg in a liver glycogen particle preparation were complex. In the presence of a physiological concentration of ATP-Mg, synthase phosphatase activity in the glycogen particle follows a biphasic course. Initially, the reaction was inhibited but later the reaction rate accelerated. The reaction was inhibited but the rate was constant in the presence of ATP-Mg with the addition of a physiological concentration of glucose 6-phosphate (Glc 6-P). Therefore, in most subsequent experiments Glc 6-P was added. The concentration of ATP-Mg at which 50% maximal inhibition (I0.5) occurred was approximately 0.1 mm in preparations obtained from rats given glucagon prior to being killed. In preparations from animals given glucose, the I0.5 was increased to 2.0 mm. The maximum inhibition was little changed in preparations from glucose- or glucagon-treated animals. Thus, administration of glucose in vivo reduced the sensitivity of the synthase phosphatase to ATP-Mg inhibition. Complexes of ATP with paramagnetic ions such as Co2+ and Mn2+ were less inhibitory than complexes with diamagnetic ions, including Ca2+ and Mg2+. Magnesium complexes of adenosine tetraphosphate and 5′-adenylimidodiphosphate also were inhibitory. Inhibition was independent of phosphorylase a and not a nonspecific, polyvalent anion effect. The best explanation for the distinctive effects of ATP-Mg in preparations from glucagon- and glucose-treated animals is that the respective treatments promote and stabilize different forms of synthase D or possibly synthase phosphatase with different affinities for ATP-Mg. These forms are interconvertible, as previously suggested, in studies employing EDTA (20).
Original languageEnglish (US)
Pages (from-to)34-45
Number of pages12
JournalArchives of Biochemistry and Biophysics
Issue number1
StatePublished - Aug 15 1986
Dive into the research topics of 'Regulation of liver glycogen synthase phosphatase activity by ATP-Mg'. Together they form a unique fingerprint.
Cite this
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i How do i mask an image in photoshop? - GuideAnimation
How do you apply a layer mask?
Add a layer mask to hide part of a layer
• In the Layers panel, select the layer or group.
• To create a new layer mask, select the area in the image and click the New Layer Mask button in the Layers panel
• A layer mask with the selection revealed is created by clicking the New Layer Mask button.
• Option-click (Mac) or Alt-click (Windows) the Add Layer Mask button
What is the difference between clipping mask & layer mask?
In contrast to layer masks, clipping masks hide portions of an image using multiple layers, whereas layer masks use just one layer. It is a shape that masks other artwork and reveals only what lies within.
How do you add a layer mask in photoshop?
Photoshop Essentials.com - Adobe Photoshop tutorials and training. Where everyone can learn Photoshop! P
How do i quickly remove a background in photoshop?
In the "Layers" panel on the right side, add a new layer. Under "Layers," deselect "Layer 1," and select the "Background" layer with your photo as the icon image. 3. When you select that layer, you will see the option "Remove Background" in the "Quick Actions" panel.
What is the difference between layer mask and clipping mask procreate?
Clipping masks are layers placed above your original artwork. Clipping mask layers clip all work placed on them to the layer directly below them. Using a clipping mask in Procreate is similar to using one in Photoshop.
How do i use the mask tool in photoshop?
How to Select and Mask in Photoshop
1. Choose Select > Select And Mask.
2. Press Ctrl+Alt+R (Windows) or Cmd+Option+R (Mac).
3. Now, in the Options bar, select and mask a selection tool, such as Quick Selection, Magic Wand, or Lasso.
What does a layer clipping mask do?
Create a clipping mask by doing one of the following:
• When holding Alt (Option in Mac OS), position the pointer over the line dividing two layers in the Layers panel (the pointer changes to two overlapped
• Select the top layer of a pair of layers you want to group, and choose Layer - Create Clipping Mask.
What are the two types of layer masks?
Photoshop has two types of masks: layer masks and clipping masks. You'll find that they are fairly similar in theory, but wildly different in application. Below, we'll not only learn what these two masks are, but also learn how to use them.
What is the use of clipping mask in Photoshop?
In Photoshop, clipping masks are a powerful way to control layer visibility. In that sense, clipping masks are similar to layer masks. While the end result may look similar, clipping masks and layer masks are very different. Black and white are used in layer masks to show and hide parts of the layer. But a clipping mask controls the visibility of a layer by using its content and transparency.
What is a clipping mask in?
This is an object whose shape masks other artwork in a way that only areas within the mask's shape are visible, thus clipping the artwork to the mask's shape. Clipping masks and masked objects are referred to as clipping sets. Clipping sets can be made from a selection of two or more objects or from all objects in a group or layer.
What is the Mask tool in Photoshop?
You can create two types of masks:
• The layer masks are bitmap images that are edited using the painting or selection tools.
• Vector masks can be created with a pen or shape tool and are independent of resolution.
• Layer and vector masks are nondestructive, which means you can go back and edit them later without losing the pixels they hide.
• More items
What is a mask tool?
1. Make sure there is a white border around the layer mask thumbnail. If there is no white border, click the layer mask thumbnail.
2. Open the Brush Picker in the Options bar and choose the brush's size and hardness.
3. In the Toolbar, press D to set the default colors as white and black. Next, press X to switch the colors, so black becomes the foreground color.
4. Over the image, paint a black layer mask. The layer mask hides the layer with the mask, so you can see the layer below or the checkerboard pattern that represents transparency.
What is a layer mask procreate?
This layer mask allows you to conceal or reveal parts of the layer below (the primary layer). If you are editing the mask, you can only use black, white, or gray. To remember which color you need: White reveals and black conceals.
How many types of masks are there in photoshop?
Photoshop offers five methods of masking: Pixel Masks, Vector Masks, Quick Masks, Clipping Masks and Clipping Paths, all of which define pixel opacities without affecting the original data.
Does procreate pocket have alpha lock?
In the Layers panel, tap a Layer to bring up Layer Options, then tap Alpha Lock. Two fingers can be used to activate Alpha Lock by swiping left-to-right across a layer. A checkered background in the layer thumbnail indicates Alpha Lock is active.
Where is the add layer mask button?
What is a layer mask and what does it do? Layer masks allow us to control the transparency of a layer by adding something to that layer. Photoshop also offers other ways to control a layer's transparency. The Opacity option in the Layers panel is one way to adjust transparency. The Eraser Tool is another common way to add transparency to a layer. So what makes layer masks so special? S
How do i lock an image in procreate?
1. To access the Layers Panel, tap on the icon at the top left of your Procreate toolbar that looks like two squares stacked on top of each other.2. Delete a Layer Take your pointer finger or your apple pencil and select the layer you wish to delete. It will turn blue once selected.
What does alpha locking a layer do?
Alpha Lock allows you to lock a layer's transparency (or alpha) in Procreate. Once you apply Alpha Lock to a layer, you will only be able to paint within what already exists on the layer (the alpha). Start by blocking out a shape in a new layer or find the layer to which you want to apply the brush.
What is the difference between layer mask and clipping mask?
As with layer masks, clipping masks also allow you to hide portions of an image, but these masks are created with multiple layers, whereas layer masks use a single layer. In the art world, a clipping mask is a shape that hides other artwork and reveals only what it contains.
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Coral reef ecosystems are not only biologically rich but also a source of natural beauty, and they provide countless services to the coastal communities they support. If a reef degrades or is destroyed, the services it once provided will be reduced or eliminated, possibly forever. Coral reefs provide spawning and nursery grounds for economically important fish populations to thrive. Coral reefs help protect coastal communities from storm surge and wave erosion, which can increase as sea levels rise.
But do you know your sunscreen cream is killing sea creatures like corals?
As the research shows, most sunscreen products often contain chemical substances such as benzophenone and octyl methoxycinnamate, which can seriously interfere with the reproduction and growth cycle of corals, resulting in coral bleaching. These ingredients will be affected by human activities at sea, bathing, and washing faces. It is discharged from the seawater and sewage system, flows into the sea and is absorbed by corals. So corals will be harmed by the sunscreen cream that people wear.
Our show ‘sea sustainability’ calls on everyone to avoid using chemical sunscreen cream, instead, you can use physical sun protection. And please do not throw rubbish or put polluted water into the sea. Maybe you can ride a bike instead of driving a car to reduce carbon emissions. So the climate won’t change so fast. By the way, stop excessive amounts of fishing and cultivated coral can help corals as well.
Yumeng Wu
An undergraduate student at the University of Queensland, majors in the Bachelor of Communication.
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On The Edge!
Tag: Ivy-lee
The Ivy Lee Method: For Maxing your productivity.
James Clear in his post about how to improve productivity using the Ivy lee’s method and why it works the way it works
The Ivy Lee Method
1. At the end of each work day, write down the six most important things you need to accomplish tomorrow. Do not write down more than six tasks.
5. Repeat this process every working day.
Read about how this works and why it works like no other from here.
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Submitted Surnames Starting with Y
Ya Japanese
From Japanese ya, meaning "night". Note that other kanji interpretations and meanings could be possible.
Yabe Japanese
From the Japanese 矢 (ya) "arrow" and 部 (be) "region," "division," "part."
Yaben Basque
It means under the rushes or bracken.
Yablokov Russian
From Russian яблоко (yabloko) meaning "apple", used as a nickname for a ruddy person or a gardener who received a plentiful harvest.
Yabsley English
It is believed to be a derived spelling of Abboldesi, a place now more commonly known as Abbotsley or Abbotsleigh. However, the original surname had nothing to do with "Abbots" in any spelling, and derives from to the Olde English pre 7th Century personal name "Eadbeald" meaning "Prosperity-bold".
Yabuki Japanese
A famous bearier of this surname, Nako Yabuki from IZONE.
Yabusaki Japanese
From the Japanese 八 (ya) meaning "eight", 武 (bu) which was a traditional unit of measurement approximately equal to 90 centimeters, and 崎 (saki) meaning "cape, peninsula".
Yacob Amharic
From the given name Yacob.
Yacoob Arabic
From the given name Yaqub.
Yacoub Arabic
From the given name Yaqub.
Yada Japanese
From the Japanese 矢 (ya) "arrow" and 田 (da or ta) "rice paddy."
Yadav Indian, Hindi, Marathi, Gujarati, Bengali, Telugu, Kannada, Punjabi, Nepali
From Sanskrit यादव (yadava) meaning "descendant of Yadu", Yadu being a legendary king in Hindu mythology who was believed to be an ancestor of Krishna.
Yaeger German
Yaeger is a relatively uncommon American surname, most likely a transcription of the common German surname "Jaeger/Jäger" (hunter). The spelling was changed to become phonetic because standard English does not utilize the umlaut.
Yafai Arabic
Meaning unknown.
Yagami Japanese
From Japanese 八 (ya) meaning "eight" and 神 (kami) meaning "god".
Yager German
Americanized form of JÄGER, meaning "hunter."
Yagi Japanese
This can also be read as Yanagi meaning "Willow".
Yagira Japanese
Yaguchi Japanese
From Japanese 矢 (ya) meaning "arrow" and 口 (kuchi) meaning "mouth"
Yahia Arabic
From the given name Yahya.
Yahiaoui Arabic (Maghrebi)
From the given name Yahya.
Yahya Arabic, Urdu
From the given name Yahya.
Yahyaoui Arabic (Maghrebi)
From the given name Yahya.
Yakhin Bashkir, Tatar
From the given name Yakhya.
Yakimov Russian
Means "Son of Yakim".
Yakobashvili Georgian, Jewish
Alternate transcription of Iakobashvili chiefly used by Georgian Jews.
Yakovenko Ukrainian
Derived from the given name Yakov.
Yakovleva Russian
Feminine form of Yakovlev.
Yakubovich Russian, Belarusian
Derived from the given name Yakub.
Yakumo Japanese (Rare)
This surname combines 八 (hachi, ya, ya'.tsu, ya.tsu, you) meaning "eight", 耶 (ja, ya, ka) meaning "question mark" or 家 (ka, ke, ie, uchi, ya) meaning "expert, family, home, house, performer, professional" with 雲 (un, kumo, -gumo) meaning "cloud."... [more]
Yalaoui Arabic (Maghrebi)
Algerian family name possibly derived from Arabic يَعْلَى (yaʿlā) or يَعْلَ (yaʿla) both meaning "exalted, high".
Yalçın Turkish
From the given name Yalçın.
Yam Hebrew
From the given name Yam.
Yama Japanese
Yama means "Mountain".
Yamabe Japanese
From Japanese 山 (yama) meaning "mountain" and 部 (be) meaning "part, section".
Yamadaev Chechen
Means "son of Yamad", possibly from a form of the given name Ahmad.
Yamadera Japanese
"Mountain temple".
Yamagata Japanese
From Japanese 山 (yama) meaning "mountain" and 形 (gata) meaning "shape, form" or 縣 (gata) meaning "county, district".
Yamagishi Japanese
From Japanese 山 (yama) meaning "mountain" and 岸 (kishi) meaning "beach, shore, bank".
Yamaha Japanese (Rare)
This Japanese surname is more found in Brazil than Japan, because of Japanese immigrants who immigrated from Japan to Brazil. Notable bearer of this surname: Torakusu Yamaha (Japanese entrepreneur who was the founder of the Yamaha Corporation).
Yamahashi Japanese
In basic words, this is Hashiyama backwards. A notable bearer is Masaomi Yamahashi ,he's a voice actor.
Yamakawa Japanese
From Japanese 山 (yama) meaning "mountain, hill" and 川 (kawa) meaning "river, stream".
Yamamizu Japanese
山 (Yama) means "Mountain" and 水 (Mizu) means "Water". Check the notes if necessary.
Yamamura Japanese
From Japanese 山 (yama) meaning "mountain" and 村 (mura) meaning "town, village".
Yamanaka Japanese
From Japanese 山 (yama) meaning "mountain" and 中 (naka) meaning "middle".
Yamane Japanese
From Japanese 山 (yama) meaning "mountain" and 根 (ne) meaning "root".
Yamano Japanese
From Japanese 山 (yama) meaning "mountain" and 野 (no) meaning "field, wilderness".
Yamaoka Japanese
From Japanese 山 (yama) meaning "mountain" and 岡 (oka) meaning "hill, ridge".
Yamasato Japanese
This surname combines 山 (san, sen, yama) meaning "mountain" and 里 (ri, sato) meaning "league, parent's home, ri (unit of distance - equal to 3.927 km), village," 県 or 縣 - outdated variant of 県 - (ken, ka.keru) meaning "county, district, subdivision, prefecture," the last meaning reserved for 県.... [more]
Yamashiro Japanese
From Japanese 山 (yama) meaning "mounain, hill" and 城 (shiro) meaning "castle".
Yamatani Japanese
Yama means "Mountain" and Tani means "Valley". Testuo Yamatani was film director.
Yamato Japanese
From the given name Yamato.
Yambao Filipino
Possibly from Vietnamese iàm-báu meaning "treasure."
Yameen Urdu, Bengali, Dhivehi
Variant transcription of Yamin.
Yamikawa Japanese
From Japanese 闇 (Yami) meaning "darkness" 川(Kawa) meaning "river", the name basically means "Dark river"
Yampilskiy Ukrainian (Rare)
This was used by people originating from any of various Ukrainian settlements by the name of "Yampil".
Yan Chinese (Russified)
Russified form of Yang used by ethnic Chinese living in parts of the former Soviet Union.
Yanagi Japanese
From Japanese 柳 (yanagi) meaning "willow".
Yanagida Japanese
Yanagi (柳) means "willow", ta/da (田) means "ricefield", ta changes to da because of rendaku. Mikio Yanagida (柳田幹雄) from Btooom! is a notable character bearing this surname.
Yanagihara Japanese
From Japanese 柳 (yanagi) meaning "willow" and 原 (hara) meaning "field, plain".
Yanagimoto Japanese
Yanagi means "Willow" and Moto means "Source, Root, Origin."
Yanagisawa Japanese
From Japanese 柳 (yanagi) meaning "willow" and 沢 (sawa) meaning "marsh".
Yanai Japanese
From the Japanese 矢 (ya) "arrow" and 内 (nai or uchi) "inside."
Yandarbiev Chechen
Means "son of Yandarbi".
Yandarbiyeva Chechen
Feminine spelling of Yandarbiyev.
Yandarov Chechen
Possibly from the given name Yandar, which is of uncertain meaning, perhaps of Turkic or Iranian origin.
Yáñez Spanish
Patronymic of JUAN.
Yang Korean
This surname originated in China and refers to ‘bridge’.
Yaniv Hebrew
From the given name Yaniv.
Yankovic Slovene, Slovak, Serbian, Croatian, Polish
Americanized form of Janković, or perhaps Jankowicz.
Yankovich Serbian, Croatian, Slovene
Americanized spelling of Janković or Jankovič.
Yannotta American
Possibly a variant of Iannotta.
Yanqi Chinese
Yanqi is/ was a county of China. It is also the surname of Mao Yanqi, also known as VAVA.
Yantorno Italian
Derived from the word torno which in Italian means "around".
Yao Chinese
From Chinese 姚 (yáo) meaning "handsome, elegant".
Yaoyorozu Japanese (Rare)
From Japanese 八 (ya) meaning "eight", 百 (o) meaning "one hundred", and 万 (yorozu) meaning "ten thousand"
Yap Chinese (Hakka), Chinese (Hokkien)
Hakka and Hokkien romanization of Ye.
Yaqoob Arabic
From the given name Yaqub.
Yaqub Arabic, Urdu
From the given name Yaqub.
Yarbrough Anglo-Saxon
The ancient roots of the Yarbrough family name are in the Anglo-Saxon culture. The name Yarbrough comes from when the family lived in either the parish or the hamlet called Yarborough in the county of Lincolnshire... [more]
Yarchi Hebrew
From Hebrew יָרֵחַ (yareach), meaning "moon".
Yarden Hebrew (Rare)
From the given name Yarden, which is named after the Jordan 2 River. ... [more]
Yardeni Hebrew (Modern)
Means "of Jordan 2" in Hebrew.
Yardley English
Habitational name for someone from any of the various locations in England named Yardley, derived from Old English gierd meaning "branch, twig, pole, stick" and leah meaning "wood, clearing".
Yardy English
The most likely origin of this surname is that it was used to denote someone who held a piece of land known as a "yarde", from the Middle English word "yerd".
Yarish American
Anglicized form of Jaroš.
Yarmolenko Ukrainian
Regional name for someone from Yarmolyntsi, an urban-type settlement in Ukraine.
Yaroshevitz Jewish
Ashkenazi Jewish form of Yarrow.
Yaşar Turkish
From the given name Yaşar.
Yaseen Arabic, Urdu
From the given name Yasin.
Yasenov Bulgarian
Means "son of Yasen".
Yasin Arabic, Urdu, Bengali
From the given name Yasin.
Yasmin Bengali, Urdu
From the given name Yasmin.
Yassin Arabic
From the given name Yasin.
Yasuhiro Japanese
From Japanese 安 (yasu) meaning "peace, quiet" combined with 央 (hiro) meaning "centre, middle". Other Kanji combinations are possible.... [more]
Yasui Japanese
Yasu (安) "Relaxed, Cheap" and I (井) "Well, Mineshaft ".
Yasuki Japanese
Yasu means "Relax, Cheap" and Ki mean "Tree". Yasuki is also a first name.
Yasunishi Japanese
Yasu means "Peace,Quiet" and Nishi means "West". See Anzai for alternative,but similar meaning.
Yasuraoka Japanese (Rare)
安 (Yasu) means "Cheap, Low, Inexpensive, Rested, Peaceful, Relax".良 (Ra) means "Good, Excellent", and 岡 (Oka) means "Ridge, Hill". A notable bearer is Akio Yasuraoka, he was a composer in his earlier days.
Yasuyama Japanese
安 (Yasu) means "Peaceful, Rested, Relax, Cheap, Low" and 山 (Yama) means "Mountain". Check notes if necessary.
Yatteau French (Acadian)
I was always told it was French
Yaun Dutch (Americanized)
Americanized form of Jahn.
Yavorov Bulgarian
Means "son of Yavor".
Yavuz Turkish
Means "stern, tough" in Turkish.
Yaw Irish, English, Chinese
Irish: reduced and altered Anglicized form of Gaelic Mac Eochadha Chinese : Cantonese variant of Qiu.
Yaxley English
Meant "person from Yaxley", Cambridgeshire and Suffolk ("glade where cuckoos are heard").
Yaylacıoğlu Turkish
Means "descendant of the nomad" from Turkish yaylacı meaning "nomad, highlander, transhumant".
Yazaki Japanese
Ya means "Arrow" and Zaki means "Peninsula, Promontory, Cape". A notable bearer is Tomonori Yazaki, a film actor.
Yazbeck Arabic
Variant transcription of Yazbek.
Yazıcı Turkish
Means "writer" or "clerk" in Turkish.
Yazzie Indigenous American, Navajo
Derived from the Navajo word yázhí meaning "little".
Ybanez Spanish (Philippines)
Unaccented variant of Ybañez.
Ybiricu Basque (Latinized, Modern)
It means ford the river (cross or pass the river).
Ye Chinese
From Chinese 葉 (yè) meaning "leaf".
Yeager English, Irish, Scottish
Anglicized form of German Jäger.
Yeardley English
Means "enclosed meadow" in Old English, from Old English g(e)ard (“fence, enclosure”) + lēah (“woodland, clearing”).
Yeats English
Scottish and northern English variant spelling of Yates.
Yee Chinese (Taishanese)
Taishanese romanization of Yu 2.
Yefet Hebrew
From the given name Yefet. (see Japheth)
Yefimov Russian
Means "son of Yefim".
Yefimova Russian
Feminine form of Yefimov.
Yefimovich Russian
Grigori Yefimovich who is best known as "Rasputin" was a Russian peasant, mystic and private adviser to the Romanovs (Tsar Nicholas II and his wife Tsarina Alexandra in the early 20th century).
Yefremov Russian
Means "son of Yefrem"
Yegorov Russian
Means “son of Yegor”.
Yeh Chinese
Variant romanization of Ye.
Yehia Arabic
From the given name Yahya.
Yehya Arabic, Uyghur
From the given name Yehya.
Yelich Serbian (Anglicized, Rare)
Yelich is an Anglicized spelling of the last name Jelić.
Yelley English (British)
The surname Yelley was first found in Oxfordshire where they held a family seat as Lords of the Manor. The Saxon influence of English history diminished after the Battle of Hastings in 1066. The language of the courts was French for the next three centuries and the Norman ambience prevailed... [more]
Yellman English
Yellman comes from the English words yell and man creating Yellman. The last name Yellman was also given to a person who consistently yelled a lot.
Yellow English
Nickname for someone who has yellow hair; wore yellow clothing or has a yellow complexion
Yelnats Literature
Invented by Louis Sacher for his novel "Holes". The name was created because it is Stanley spelled backwards. Stanley Yelnats IV is the main character in the novel.
Yemelyanov Russian
Means "son of Yemelyan".
Yemelyanova Russian
Feminine spelling of Yemelyanov.
Yemen Arabic
From the Given Name YEMEN.
Yeo Chinese (Hokkien)
Hokkien romanization of Yang.
Yeoh Chinese (Hokkien)
Hokkien romanization of Yang.
Yeong Korean
Korean form of Yang, from Sino-Korean 楊 (yeong) meaning "willow".
Yerbabuena Spanish (Latin American)
From Spanish yerba buena meaning "good herb"
Yerkes German (Americanized)
Americanized spelling of German and Dutch Jerkes, a patronymic from the personal name Jerke.
Yermolaev Russian
Variant transcription of Yermolayev.
Yermolayev Russian
Means "son of Yermolai".
Yesayan Armenian
Means "son of Yesay".
Yesmin Bengali
Variant of Yasmin.
Yesua Indonesian
From the given name Yesua, a variant of Yeshua. This surname is found among Indonesian populations.
Yetman English
"gate keeper"
Yett English
Derived from the Old English word geat, meaning gate.
Yetts English
Variant of Yates
Yeukai Shona
Yeukai means "Remember". This name is given as a call to remember a particular event or to remember one's origins.
Yevdokimov Russian
Means "son of Yevdokim".
Yevdokimova Russian
Feminine spelling of Yevdokimov.
Yevstigneyeva Russian
Feminine transcription of Yevstigneyev.
Yewdale English
Derived from Yewdale, which is the name of a village near the town of Skelmersdale in Lancashire. Its name means "valley of yew trees", as it is derived from Middle English ew meaning "yew tree" combined with Middle English dale meaning "dale, valley".... [more]
Yiannopoulos Greek
Means son of Yianni, a famous bearer of this name is Milo Yiannopolous (1983-).
Yick Chinese (Cantonese)
Cantonese romanization of Yi.
Yiğit Turkish
From the given name YİĞİT.
Yiğitoğlu Turkish
Means "son of Yiğit".
Yıldırım Turkish
From the given name Yıldırım.
Yıldız Turkish
Means "star" in Turkish.
Yin Chinese
Transferred from the given name Yin.
Yíng Chinese (Rare)
From the name of the royal house of the Qin Dynasty from the ancient Chinese state also known as Qin.
Ying Chinese
From Chinese 应 (yīng) referring to the ancient state of Ying, which existed during the Zhou dynasty in what is now Henan province.
Yip Chinese (Cantonese)
Cantonese romanization of Ye.
Yiu Chinese (Cantonese)
Cantonese romanization of Yao.
Ylvisåker Norwegian (Rare)
Meaning unknown. Famous bearers of this name are the Norwegian comedy duo "Ylvis" consisting of brothers Vegard (b. 1979) and Bård Ylvisåker (b. 1982).
Ymffrostgar Medieval Welsh
A historic Welsh surname, meaning a brag or boastful person, later shortened to Ffrost and again to Frost.
Yoakam German (Anglicized)
Americanized form of Joachim.
Yoakum English (American)
Americanized version of Jochim
Yocum German (Anglicized), English
Americanized form of Jochum, a Low German form of the given name Joachim.
Yoffe Hebrew, Jewish
Eastern Ashkenazic variant of Jaffe.
Yohanan Assyrian, Indian (Christian), Malayalam, Jewish
From the given name Yohanan, used by Malayalam-speaking Saint Thomas Christians and Cochin Jews.
Yohe Medieval English
The Yohe surname comes from the Old English word "ea," or "yo," in Somerset and Devon dialects, which meant "river" or "stream." It was likely originally a topographic name for someone who lived near a stream.
Yoho American (Anglicized)
American Anglicized spelling of Swiss surname 'Joho'
Yoichi Japanese (Rare)
This surname is used as 与市 with 与 (yo, ata.eru,, kumi.suru, tomoni) meaning "bestow, participate in, give, award, impart, provide, cause, gift, godsend" and 市 (shi, ichi) meaning "city, market, town."... [more]
Yoichien Japanese (Rare)
Made up of 与 (Yo) "Give, Award, Participate", etc. 市 (Ichi) "In City, Market" or "Town". Anything along those lines. 園 (En) means "Garden". The source is in the notes.
Yoichimae Japanese (Rare)
与 (Yo) "Provide, Give, Award, Participate", 市 (Ichi) " Town, Market, City", etc. and 前 (Mae) "Front, Forward". The source is in the notes.
Yokohama Japanese
Yoko ("Beside") + Hama ("Beach, Seashore").
Yokoi Japanese
From Japanese 横 (yoko) meaning "side, beside, next to" and 井 (i) meaning "well, mine shaft, pit".
Yokomizo Japanese
Check notes if needed. 横 (Yoko) means "Beside" and 溝 (Mizo) means "Groove, Trench, Gutter, Gully, Drain, Ditch, Gap". A notable bearer is Seishi Yokomizo, a Japanese novelist in the Showa Period.
Yokomura Japanese
横 (Yoko) means "Beside" and 村 (Mura) means "Village, Hamlet". Check the source if needed.
Yokoshima Japanese
From Japanese 横 (yoko) meaning "side, beside, next to" and 島 or 嶋 (shima) meaning "island".
Yokota Japanese
From Japanese 横 (yoko) meaning "side, beside, next to" and 田 (ta) meaning "field, rice paddy".
Yokotake Japanese
From Japanese 横 (yoko) meaning "side, beside, next to" and 竹 (take) meaning "bamboo".
Yokotani Japanese (Rare)
From Japanese 横 (yoko) meaning "next to, beside" combined with 谷 (tani) "valley".
Yokote Japanese
Yoko ("Beside") + Te , this is the Japanese word for hand. This surname means "Beside a Hand". Michiko Yokote is an example. She wrote the Pichi Pichi Pitch manga and did screenwriting for Masamune-kun's Revenge.
Yokoyama Japanese
From Japanese 横 (yoko) meaning "side, beside, next to" and 山 (yama) meaning "mountain".
Yokoyama Japanese
A Japanese surname with a combination of Yoko and Yama
Yomohiro Japanese (Rare)
This is a very rare surname with the kanji of all four directions: (東西北南) "East, West, North, and South", in that order. Yomo literally means "Four directions" and Hiro means "Extension".
Yomtov Hebrew (Modern)
Means "good day", derived from Hebrew יום (yom) means "day" and טוב (tov) means "good".
Yonaga Japanese
From Japanese 夜長 (yonaga) meaning "a long night".
Yonah Jewish
Hebrew for "dove" יונה
Yonamine Japanese
From the Japanese 與 or 与(yo) "together with," 那 (na) "what" and 嶺 (mine) "peak," "summit."
Yone Japanese
Yo (与) means together.... [more]
Yoneda Japanese
From the Japanese 米 (yone or kome) "rice" and 田 (ta or da) "rice paddy" or 多 (ta or da) "many."
Yoneichi Japanese
Yone (米) means rice.... [more]
Yonezawa Japanese
From the Japanese 米 (yone or kome) "rice" and 澤 or 沢 (zawa or sawa) "swamp."
Yong Chinese (Hakka)
Hakka romanization of Yang.
Yong Korean
Korean form of Long from Sino-Korean 龍 (yong).
Yonge English
Variant of Yong
Yonover English (British)
The surname Yonover was first found in Somerset where they held a family seat as Lords of the Manor.
Yoosuf Dhivehi
From the given name Yoosuf.
Yorath Welsh
Derived from the Welsh given name Iorwerth.
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Total Number of words made out of Stover = 71
Stover is an acceptable word in Scrabble with 9 points. Stover is an accepted word in Word with Friends having 10 points. Stover is a 6 letter medium Word starting with S and ending with R. Below are Total 71 words made out of this word.
Anagrams of stover
1). voters 3). strove 4). troves
5 letter Words made out of stover
1). verso 2). store 3). roset 4). rotes 5). roves 6). servo 7). stove 8). voter 9). verts 10). tores 11). torse 12). trove 13). verst 14). overt 15). overs 16). votes
4 letter Words made out of stover
1). rove 2). orts 3). vest 4). vert 5). erst 6). sore 7). sort 8). roes 9). tors 10). ores 11). tore 12). rots 13). veto 14). rote 15). over 16). rest 17). eros 18). rets 19). vets 20). revs 21). vote 22). toes 23). rose 24). voes
3 letter Words made out of stover
1). ers 2). oes 3). rev 4). vet 5). tor 6). voe 7). toe 8). res 9). ret 10). roe 11). ose 12). rot 13). ser 14). ort 15). set 16). sot 17). ore 18). ors
2 letter Words made out of stover
1). to 2). er 3). so 4). oe 5). os 6). or 7). et 8). es 9). re
Stover Meaning :- Fodder for cattle- especially straw or coarse hay.
Find Words which
Also see:-
1. Words that start with Stover
2. Vowel only words
3. consonant only words
4. 7 Letter words
5. Words with J
6. Words with Z
7. Words with X
8. Words with Q
9. Words that start with Q
10. Words that start with Z
11. Words that start with F
12. Words that start with X
Word Finder Tools
1. Scrabble finder
2. Words with friends finder
3. Anagram Finder
4. Crossword Solver
Words made from adding one letter at the End of stover
Words made after changing Last letter with any other letter in stover
Note There are 2 vowel letters and 4 consonant letters in the word stover. S is 19th, T is 20th, O is 15th, V is 22th, E is 5th, R is 18th, Letter of Alphabet series.
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Tragedies of Child Marriage: How will you help?
The issue of child marriage is global. Countries such as Niger, Central African Republic, and Chad have the most child marriages globally with over 60-70% of girls being married before the age of 18 and approximately 30% married before the age of 15.
3 min read
Tragedies of Child Marriage: How will you help?
40.3 million people are enslaved globally, 15.4 million of which are forced into marriage. Each year, 12 million children under 18-years-old are married annually, and nearly one million of those children are under 15-years-old.
It’s unfortunately not uncommon for a girl to be given away to a man potentially twice or three times her age. For these girls, there are many expectations, the expectation to resolve her family's poverty, to gain approval from religious leaders, to avoid birthing a child out of wedlock after being assaulted; to stop wars, and create alliances. A child is meant to fix all this through marriage, and often without a choice.
The issue of child marriage is global. While many may recognize its prevalence in South Asia, countries such as Niger, Central African Republic, and Chad have the most child marriages globally with over 60-70% of girls being married before the age of 18 and approximately 30% married before the age of 15. However, child marriage is not just an issue in developing countries, it is also an issue and a neglected subject in countries such as the United States and Canada, and urgently needs to be recognized.
More than 207,000 minors have been legally married in the U.S over the last 15 years; many of whom are married before they reach the age of sexual consent. Until 2015, children aged 12 could obtain a marriage license in Alaska, Louisiana, and South Carolina. A 13-year-old could marry in 14 states including, Florida, New Jersey, Kentucky, Texas, Washington, and 9 others. Meanwhile, child marriages in Canada have been even more unnoticed, having licensed over 3,380 children to marry in the past 18 years. Over a thousand in Ontario alone, nearly 800 in Alberta, and hundreds in most provinces and territories.
So, when does child marriage become slavery? Children who marry to an older adult, and/or children married under 15, have a high possibility of experiencing slavery if the child does not and/or cannot give consent to the marriage, there is a sense of ownership over the child through violence, abuse, forced labor/domestic chores and/or engagement in non-consensual sexual relations and if the child cannot end or leave the marriage. It should be noted that although child marriages affect 84% girls, 16% affects boys, whose cases are equally as important.
In many child marriages, non-consensual sexual relations are all too common, putting children at a higher risk for HIV/AIDS and making childbirth a leading cause of death among 15-19-year-olds in developing countries. More often than not, law enforcement cannot charge the adult with statutory rape if they are married to a minor as the same acts that would be statutory rape outside of marriage are made lawful within. Not to mention, young girls who become mothers are generally at a higher risk for health complications. Additionally, girls in these situations are more likely to stop attending school at a young age, giving them little to no opportunities to find jobs to support themselves or their families.
The International Labour Office (ILO) outlines several strategies for ending child marriages; suggesting a coordinated enactment of various policies to protect vulnerable groups. However, there is no single solution. Regardless, every individual has a role in creating a change and the first step is raising awareness. The youth need to be empowered; girls need to know that opportunity exists, that they can pursue a career, that there is a life for them beyond marriage. Laws need to be changed, loopholes closed, minimum age of marriage raised, vulnerable groups protected, patriarchy dismantled and equality despite differences; the solution exists through changing many different aspects of society.
Child marriages are not limited to developing countries. Child marriages are happening everywhere, on a daily basis; it is happening in your country and it would be shameful to ignore it, knowing something can be done to end it. As members of a “free and just” society, it is our duty to draw attention to this atrocity and our silence makes us complicit to the tragedies created by child marriage. Here is how you can be part of the change; how will you help?
Take Action
Freedom United
End Slavery Now
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Also known as the religion of chaos discordianism was originally created as a prank religion by two young hippies kerry thornley and greg hill in the 1960 rsquo s the movement was later made world famous by the american author robert anton wilson who based the philosophy of his iconic satirical sci fi books the illuminatus.
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The SCEAS System
Navigation Menu
1. Xiaochun Xiao (4 paper(s) during 2008-2009)
2. Leqiu Qian (2 paper(s) during 2008-2009)
3. Gendu Zhang (2 paper(s) during 2008)
4. Huan Wang (1 paper(s) during 2009)
System created by [] © 2002
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Derivatives of Polynomial Functions
Here we explore the first derivative of polynomial functions up to order 4. The general function considered is. The function is initially created with and the other constants equal to zero, that is a parabola. The point A is a point on the curve and the point D represents the value of the derivative at the point A. The black line is the tangent to the curve at the point A. With your mouse you can move the point A along the curve and notice also that the tangent changes slope. At the same time, the point D moves and its motion is traced, in other words, D traces out the derivative of , that is . There are several things you can do here: 1. Change the value of and see how this changes the derivative. 2. Change the value of and see what effect this has on the derivative. 3. Increase the order of the polynomial by change the values of and . To remove an unwanted trace, simple adjust the zoom on the screen. The reset button at the top right will reset the initial parabola example.
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Provocation: Is the UAV control ratio the right question?
Peter A. Hancock, Mustapha Mouloua, Richard D. Gilson, James Szalma, Tal Oron-Gilad
Research output: Contribution to journalArticlepeer-review
17 Scopus citations
Unmanned aerial vehicle (UAV) are multifunctional, reprogrammable machines use to gather information from remote locations and then send back information to the controlling individual. Today, there are attempts to search for the ratio between operators and vehicles that will prove most efficient and effective. Presently, the ratio is around unity of 1:1, UAV:operator. However, design aspirations are for ratios that significantly exceed unity, as 4:1 or perhaps hundreds of UAVs to a single operator. The 1:1 ratio is more preferable, but the pressure to achieve an even greater personal ratio is destined for sensory input conflict, central decision-processing overload, and response confusion and interference.
Original languageEnglish
Pages (from-to)7+30-31
JournalErgonomics in Design
Issue number1
StatePublished - 1 Jan 2007
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The difference between the Amati and Ghirlanda relations
Amir Levinson, David Eichler
Research output: Contribution to journalArticlepeer-review
38 Scopus citations
We point out that the beaming correction commonly inferred from the achromatic breaks in the afterglow light curve is biased in situations where the isotropic equivalent energy is affected by factors other than the spread in opening angles. In particular, it underestimates the beaming factor of sources observed off-axis. Here we show that both the slopes and scatters in the Amati and Ghirlanda relations, and the difference between them, are quantitatively consistent with a recently proposed model in which the Eiso-v peak relation, as originally derived by Amati et al., is due to viewing angle effects. The quantitative difference between them confirms the relations between opening angle and break time suggested by Frail et al.
Original languageEnglish
Pages (from-to)L13-L16
JournalAstrophysical Journal
Issue number1 II
StatePublished - 10 Aug 2005
• Black hole physics
• Gamma rays: bursts
• Gamma rays: theory
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Tag: colombia
Since the arrival of the novel coronavirus to Colombia, armed groups in several parts of the country have imposed curfews, lockdowns, and other measures to prevent the spread of the virus. To enforce their rules, the groups have… Read More
Track / Trace
At-home rapid tests can be an extremely useful tool for allowing life to proceed semi-normally. How do you manage that risk? The answer is to test again. It is worrisome! The fact that the residents died despite being… Read More
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Specializing in Children with Emotional and Developmental Challenges
Phone 818-248-6414
From Struggles to Super-Powers: Helping Your Child Grow
From Struggles to Super-Powers: Helping Your Child Grow
As parents, we have many goals for our child. Overall, these goals are about managing the challenges in their lives, so they can ultimately be happy and successful. These can sound like: “I want him to turn in his homework.” I want her to clean up her room.” “I want her to have friends.” “I want him to learn how to solve problems for himself.” “I want her to be able to regulate her emotions and not yell at us or hide in her room all day.” These are all important and reasonable goals. After all, knowing what you want for your child and helping him get there is the job of parenting. Ideally, each of the hurdles are managed, and things move forward. The problem is when your child stumbles in making progress on these goals.
Along the way, parents look for and try many strategies. You may look at consequences, thinking that if they are strong enough, the behavior will come into line. This may include intensifying reminders (i.e., nagging), checking over work, or removing privileges. This approach may yield improvement toward getting your child to do what is expected but may also have the unintended consequence of increasing resentment. If progress is not made, frustration rises for both you and your child. As the frustration takes root, things can begin to feel futile. You may feel like a bad parent, and your child may feel, at best, misunderstood and, at worst, like a failure.
The path forward is to shift from trying to get your child to do what is expected to looking at what is getting in their way. This reorientation is important as it redirects your assumption that your child is capable but lacks motivation to exploring challenges behind the behavior. Whether it is about a specific task such as organizing their things, completing steps in a process, or managing the expression of their emotions, your child may not yet have the ability to do these things as expected. The shift from “she should know better” to “she is trying to manage, and doesn’t know how” increases your compassion and decreases the tension as it opens the door to new questions and approaches.
As you begin to look at your child through different eyes, it becomes possible to look for the difficulties in the way of getting things done. Consider visiting out of town relatives as an example of a goal. Embedded in this goal are many steps, including picking a date, figuring out how you’re going to get there, and packing for the visit. Breaking down this goal into steps makes it more doable. However, there are elements that underlie these steps. You may have memories of the last time you visited that colors your motivation. If you had a joyful experience, your motivation is likely to be high as compared to the hesitancy you may feel if your last visit was filled with tension and conflicts. This emotional history may inform how you structure the time you spend with your relative. Health challenges will also have a role in your planning. If you have back issues or a health condition that makes being in crowds a health risk, these considerations must be built into your planning. While the ultimate goal is to travel, working through these process questions guides you in your decision making. When this lens is applied to your child’s ability to complete a task, many variables get unearthed.
Shifting to exploring the challenges that interfere with accomplishing goals is powerful. This shift alone allies you with your child in exploring the processes that are interfering with their ability to meet and master goals. This journey begins with your curiosity, noticing how your child is currently managing.
Looking back at a challenging moment in a neutral way begins the shift to reflection. There are many things to reflect on and learn about; thoughts, emotions, body sensations, and overall health. Any one of these or a combination can make a significant difference in how we manage at any one moment in time. We are complicated beings with lots going on inside. The capacity to reflect is supported by mindfulness, the practice of bringing attention to the moment in a non-judgmental way. This practice of observing and describing in a non-judgmental way helps decrease assumptions and interpretations that often get in the way by escalating tensions.
As with anything new, reflecting and finding words to describe the elements of experience may feel awkward at first, but given time and practice, it gets easier. For us as parents, it opens the door to looking more clearly at ourselves as we reflect on what was going on for us in the moment. Being curious with your child and prompting them to reflect sets the stage for you to listen and them to learn more about themselves. For your child, it opens the door to self-awareness.
Helping your child build self-awareness is a like a super-power. As your child learns to look at what is going on for him when he didn’t turn in his homework or pick-up her room or when she yells at you, the door opens for your child to consider what could have happened differently. Reflection allows you and your child to recast behaviors as a means to manage a problem. This more open perspective helps you look at what works well and what makes things worse. Noticing the difference and the components that underlie each provides lots of information.
By building links between circumstances, emotions, and actions, your child can develop foresight to support planning for future success. This awareness can grow insight to guide behavior the next time they face a similar challenge. The movie Inside Out charmingly depicts the internal world of the “control panel” where emotions assert their influence. Attending to this internal world opens the door to unlock self-compassion, curiosity, creativity, and effective problem-solving.
As the capacity for reflection emerges, growth becomes sustainable and generalizable. In other words, it stops the “whack-a-mole” that parents often experience when one challenge is met, and another emerges. The gift to your child of supporting their access to who they are and what makes them “tick” is rewarding. As they acquire this capacity, they become resourceful and resilient, finding their personal internal levers of drive and self-control. With this broadened perspective, you can see your child’s behavior in a different light and share a loving, patient, and collaborative process as your child learns who they are and what is getting in their way. As a parent, this is holy grail– walking along your child’s side in a warm and connected relationship, supporting them on their journey as they learn to achieve academically, professionally, and interpersonally.
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"Evening Glow" Baroque Pearls
A hint of a pink glow resides in these peachy baroque pearl beauties. Naturally texured and very satiny, they resemble the summer glow of an evening sunset.
10-13 mm. peach-pink baroque bead nucleated Pearls
14k yellow gold JBG clasp system (includes either "U" or "S" catch)
18" length
The "U" catch is used to suspend pendants; the "S" catch is used to wear the pearl strand by itself.
Item # 325-00227
$1,695.00 SOLD
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Does An Elephant Have Blubber?
Does An Elephant Have Blubber? Elephant seals have a thick layer of blubber that keeps them warm in the deep, cold sea. By the end of breeding season in March, adult elephant seals of both sexes will have lost about 40% of their weight through blubber metabolism.
What animals have blubber? Blubber is a thick layer of fat, also called adipose tissue, directly under the skin of all marine mammals. Blubber covers the entire body of animals such as seals, whales, and walruses—except for their fins, flippers, and flukes.
Do Elephant seals have fur? Elephant seals are shielded from extreme cold more by their blubber than by fur. Their hair and outer layers of skin molt in large patches. The skin has to be regrown by blood vessels reaching through the blubber.
What was elephant seal blubber used for? Northern elephant seals and the hunt for blubber
All that blubber was once used as fuel for lamps, and demand for it nearly wiped out every elephant seal on the North American coastline. In 1892, a tiny population of northern elephant seals was rediscovered near Mexico, and from those the population bounced back.
Does An Elephant Have Blubber – Related Questions
Why is elephant skin so thick?
Elephants need a thick skin to hold together their mass respectively their inner pressure. This can be compared with buying bread: If 1 kg of bread is bought, it is wrapped in tissue-paper. If 20 kg of bread are bought, a thick and strong paper bag is needed to hold together the bread parcel.
Which animal has a hump on its body?
A camel is an even-toed ungulate in the genus Camelus that bears distinctive fatty deposits known as “humps” on its back. Camels have long been domesticated and, as livestock, they provide food (milk and meat) and textiles (fiber and felt from hair).
Are Penguins blubber?
Whales, seals and some penguins have thick layers of fat (or blubber). These fat layers act like insulation, trapping body heat in.
What is the female elephant called?
A male elephant is called a bull. A female elephant is called a cow. A baby elephant is called a calf.
Do elephant seals eat penguins?
Penguins are frequently killed and eaten by predators like fur seals, leopard seals, elephant seals, and other ground and marine predators.
Do elephant seals eat sharks?
Great white sharks are among the most fearsome predators in the ocean. But elephant seals can intimidate them with their massive size. They can eat all kinds of large prey – including tuna, rays, other sharks, dolphins, whales, seals, sea lions, sea otters and birds.
What is bigger an elephant seal or a walrus?
Among the most amazing of pinnipeds are the elephant seals. They are the biggest of pinnipeds – bigger even than walruses – there being a record of a giant male Southern elephant seal that was between 6.5 and 6.8 m long and weighed over 4000 kg (Carwardine 1995).
What do you call a baby elephant seal?
Are elephants afraid of mice?
How much do elephants poop a day?
Elephants defecate between eight and 10 times every day, and there are six or seven boli (poop) in a pile. That breaks down to about one pile per elephant every two hours!
What is the baby elephant?
A baby elephant is called a calf. Calves stay close to their mothers. They drink their mother’s milk for at least two years. The calf likes to be touched often by its mother or a relative.
How did a camel get a hump?
Scientists have found fragments of a camel’s leg bone from over 3.5 million years ago in the Canadian Arctic. These early camels were nearly twice the size they are now – over 3m tall – and evolved their fat-filled hump to help them survive the cold.
Why camel has a hump?
The humps function the same way—storing fat which can be converted to water and energy when sustenance is not available. These humps give camels their legendary ability to endure long periods of travel without water, even in harsh desert conditions. As their fat is depleted, the humps become floppy and flabby.
Which animals has three hearts?
The giant Pacific octopus has three hearts, nine brains and blue blood, making reality stranger than fiction.
Do polar bears have blubber?
Underneath their fur, polar bears have black skin which absorbs the heat of the sun, and below the skin is a thick, 4-inch layer of blubber. This blubber layer is particularly beneficial while polar bears swim, keeping them warm in the cold water and increasing buoyancy.
Can penguins fly?
No, technically penguins cannot fly.
Penguins are birds, so they do have wings. However, the wing structures of penguins are evolved for swimming, rather than flying in the traditional sense. Penguins swim underwater at speeds of up to 15 to 25 miles per hour .
Which animal is not cold blooded?
When I was a kid, I was taught that the animal kingdom could be divided into two groups. Warm-blooded animals, such as mammals and birds, were able to maintain their body temperature regardless of the surroundings. Cold-blooded animals, such as reptiles, amphibians, insects, arachnids and fish, were not.
How do elephants drink?
Elephants don’t drink with their trunks, but use them as “tools” to drink with. This is accomplished by filling the trunk with water and then using it as a hose to pour it into the elephant’s mouth. Elephants can swim – they use their trunk to breathe like a snorkel in deep water.
Can a seal mate with a penguin?
Male and female penguins mate via an opening called a cloaca, and the seals are thought to have actually penetrated the penguins in some of the acts, which were caught on film by [research team leader William A. Haddad]. In three of the four recorded incidents the seal let the penguin go.
Who eats leopard seals?
The only natural predator of leopard seals is the killer whale.
Do Orcas hunt elephant seals?
At Sea Lion Island, the main killer whale target are the elephant seals. Although killer whales are routinely observed chasing sea lions, penguins, and even steamer ducks, they concentrate on elephant seals, that is probably the species that guarantees the best return for the effort.
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How Big Is A Triceratops Compared To An Elephant?
How Big Is A Triceratops Compared To An Elephant?
Are dinosaurs bigger than elephants? Many of the dinosaurs of the Mesozoic Era (about 252 million to 66 million years ago) were longer and more massive than modern elephants, hippopotamuses, and rhinoceroses. The largest dinosaurs of the era were the sauropods, a collection of four-legged herbivorous species that possessed long necks and tails.
Can an elephant beat a Triceratops? Even though an Elephant is powerful, it will struggle to defeat a Triceratops because the dinosaur was nearly twice as heavy as the elephant and the Triceratops. Triceratops is also more used to fighting than elephants because elephants rarely have to fight predators because they are larger than all animals.
How big is a Triceratops compared to a rhino? The Triceratops is around 3 metres tall at the shoulder and weighs around 11,000 kilograms, while the White Rhinoceros is around 1.8 metres tall at the shoulder and weighs around 3200 kilograms. Triceratops is an example of a horned, beaked cerapod (ceratopsian) and was herbivorous and had a neck frill.
How Big Is A Triceratops Compared To An Elephant – Related Questions
What size is a Triceratops?
Paleontologists estimate that the body length of Triceratops approached 9 metres (30 feet). The largest adults are thought to have weighed 5,450–7,260 kg (approximately 12,000–16,000 pounds).
How tall is a Triceratops?
7.9 to 9 meters (25.9 to 29.5 ft) in length, 2.9 to 3.0 meters (9.5 to 9.8 ft) in height, and 6.1 to 12.0 metric tons (6.7 to 13.2 short tons) in weight. The most distinctive feature is their large skull, among the largest of all land animals.
Is argentinosaurus bigger than a blue whale?
Yes, while the Argentinosaurus (Argentinosaurus huinculensis) is longer at 115 feet (compared to the blue whales ruler-stretching 89 feet), the long-necked dinosaur of the Late Cretaceous is a lightweight at just a mere 80 or so tons.
How much did a triceratops weigh?
The massive Triceratops cut a formidable figure in the prehistoric landscape, stretching up to 30 feet long and weighing six to eight tons. Stout legs helped this quadruped support all that weight as it ambled through the underbrush of North America.
What was the biggest land animal ever?
The blue whale is believed to be the largest animal to have ever lived. The largest land animal classification is also dominated by mammals, with the African bush elephant being the largest of these.
Who would win T rex or triceratops?
The plant-eating dinosaurs of the late Cretaceous period weren’t the smartest bunch. As a general rule, carnivores tend to have more advanced brains than herbivores, meaning Triceratops would have been far outclassed by T. Rex in the IQ department.
How big can an elephant be?
Facts about Elephant Size
The average African elephant will grow to between 8.2 to 13 feet (2.5 to 4 meters) from shoulder to toe and weigh between 5,000 to 14,000 lbs. (2,268 to 6,350 kilograms), according to the National Geographic. Male elephants can grow to be significantly larger than their female counterparts.
How big is a stegosaurus?
Stegosaurus usually grew to a length of about 6.5 metres (21 feet), but some reached 9 metres (30 feet). The skull and brain were very small for such a large animal. The forelimbs were much shorter than the hind limbs, which gave the back a characteristically arched appearance. The feet were short and broad.
Is Triceratops related to rhinos?
Are Triceratops related to rhinos? Rhinos and Triceratops are not related to any degree. Despite the similarities in the two, such as their horns and thick skins, rhinos are mammals, and no dinosaurs are mammals. It makes rhinos more close to humans than dinosaurs.
Which reptile alive today is a descendant of the dinosaurs?
Tuatara Lizards. All lizards and reptiles are closely related to dinosaurs, but none more so than tuatara lizards. The last surviving animal within the Sphenodontia family, these lizards, native only to New Zealand, were around when dinosaurs walked the Earth.
Which dinosaur is the strongest?
Tyrannosaurus, meaning “tyrant lizard”, from the Ancient Greek tyrannos, “tyrant”, and sauros, “lizard” is a genus of coelurosaurian theropod dinosaur. It also had a tremendous bite force, the strongest of any dinosaur and living terrestrial animal. Its bite force reached up to 12,800 pounds.
How tall and wide is a Triceratops?
The Triceratops had a length between 26′-29.5′ (7.9-9 m), stood at a height of 9.5′-10′ (2.9-3 m), and had a width of 6.7′ (2 m). A typical Triceratops weighed between 13,500-26,500 lb (6.1-12 metric tons).
How big is a Triceratops brain?
Triceratops also had a small brain, given its large body size. It likely would have been approximately a walnut and a half, Morhardt said.
Do Triceratops lay eggs?
Triceratops like most dinosaurs are believed to have laid eggs in small clutches in a nest and guarded by the female until they were ready to hatch.
Was anything bigger than a Megalodon?
When it comes to size, the blue whale dwarfs even the largest megalodon estimates. It’s believed blue whales can reach a maximum length of 110 feet (34 meters) and weigh up to 200 tons (400,000 pounds!).
Are blue whales bigger than sauropods?
Sauropods can’t beat the largest animal on earth: the blue whale (Balaenoptera musculus). Blue whales weigh over 130 tons more than the weight of giant sauropods. However, some sauropods can have longer lengths than blue whales.
Does Triceratops eat meat?
Triceratops were herbivores, meaning they ate plants and not animals or meat. The Triceratops had rows and rows of teeth as well as a sharp hard beak, allowing them to slice and crush all sorts of vegetation.
How many eggs does a Triceratops lay?
As far as paleontologists can tell, female dinosaurs laid anywhere from a handful (three to five) to a whole clutch of eggs (15 to 20) at a single sitting, depending on the genus and species.
What’s bigger than a blue whale?
The spiral Siphonophore spotted by the team of scientists aboard the Schmidt Ocean Institute’s Falkor research vessel has been estimated to be 150-feet-long, which is an approximate 50 feet longer than a blue whale – widely held to be the largest animal to have ever existed.
What was the fastest dinosaur?
A: The fastest dinosaurs were probably the ostrich mimic ornithomimids, toothless meat-eaters with long limbs like ostriches. They ran at least 25 miles per hour from our estimates based on footprints in mud.
Did Triceratops fight each other?
There was no sign that these lesions were caused by disease or by the attack of a predator, but they were consistent with the idea that individual Triceratops fought each other by locking horns. Centrosaurus is thought to have evolved from an ancestor with Triceratops-like brow horns.
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Bottom-up Processing – Dictation in TESOL
For those of us who have studied or taught in traditional language learning classrooms, we are likely familiar with dictation as a form of assessment.
For lower levels, word lists are often used. The teacher simply reads out a list of pre-taught terms, and students copy down what they hear and have memorized.
Correction focuses on the spelling of the new terms and possibly identifying the part of speech. This is a bottom-up type of processing whereby students are listening for single morphemes and syllables, and copying out the full words they hear.
Why do the Dictations?
Dictations force students to memorize words and are one means of assessing vocabulary development and spelling.
Students need to develop their listening skill and control of spelling patterns so starting with single sounds, then syllables, then multi-syllable words is what can be done for lower levels.
Dictations are easy to create and conduct. There is little prep time, no worksheet needs to be created, and once students know what to do, dictation is an easy and fast means of assessment.
From simple word lists, students can be asked to copy out phrases, sentences and longer passages, so that they develop the ability to process longer spoken passages of speech.
These longer forms of dictation are typically read at normal speed, students are given time to write their responses and the whole sentence may be read two or three times in its entirety to allow students to add to their responses or make corrections.
The sentences need to be level-appropriate and teachers should be clear in what they are assessing.
What Do We Assess in a Dictation?
For word lists, the simplest grading is to give just one mark for a perfectly spelled word. What about with whole sentences and longer passages? Will we assess all spelling, all punctuation and will each incorrect answer get an equal percentage deducted from a grade?
Will we only focus on correcting the keywords or phrases that have been the target for the dictation? Will we penalize students if they get the actual sentence incorrect, yet they use correct grammar? What if they use grammatical constructions which are more complex than what was dictated?
These questions will be considered in the next article: Dictogloss Examined.
Developing Fluency in Listening
With longer dictations, what usually happens is the good students use good coping strategies to copy what they hear as quickly as possible.
They skip what they cannot write and can usually fill in any missing parts when the passage is read a second time. They listen for the keywords and are able to fill the gaps with the function words. This is what we train students to do in note-taking and it is the end goal of developing fluency in listening.
What happens to the weaker students when doing a long dictation? We see them writing feverishly as soon as the teacher begins to speak.
They try to copy word for word, they often get overwhelmed and stop. They are not trying to understand the text, they are only listening for single words.
Weaker students have not developed the ability to ignore or skip over the function words and focus only on the important content words.
This is a conscious strategy that must be developed over time, and with practice, it becomes an unconscious skill.
This is what it means to be a fluent listener.
A fluent listener does not hear every sound, every syllable, they hear the main content words and are able to get the meaning of the overall message from not only the words used but also the tone of voice and other non-verbal clues a speaker may use.
I have had students who have been very fluent users of spoken English. They can understand rapid native speech and respond fluently when engaged in conversations.
However, their linguistic competence in spelling and writing was at a beginning level. What happens to these students when they must do a traditional dictation? They fail miserably because they cannot spell, they cannot sound out words and reproduce what they hear in writing.
To be able to assess the listening abilities of these types of students we need to assess their top-down processing, how well they can listen globally, and get the main meaning from a passage.
If we require them to write responses and their writing skills are undeveloped, then we are penalizing them for their weaker writing skills, not assessing their listening skills.
Teach English in Canada or go abroad with TESL Canada certification. Our 250-hour TESOL Diploma is recognized by TESL Canada at their Professional Standard 2.
Related Articles:
Dictogloss Examined
Integrating Skills Through a Group Dictation
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Who made the first law in ancient Greece?
Who made the first law in Greece?
Draco (/ˈdreɪkoʊ/; Greek: Δράκων, Drakōn; fl. c. 7th century BC), also called Drako or Drakon, was the first recorded legislator of Athens in Ancient Greece. He replaced the prevailing system of oral law and blood feud by a written code to be enforced only by a court of law.
Who wrote the laws in ancient Greece?
The Law in Ancient Greece. The traditions of Athens and Sparta say that the laws were given to them by Solon and Lycurgus, legendary figures who served as leaders of their city-states long ago. The two traditions agree that the laws are made by the Assembly and approved by the Senate.
What was the first law of ancient Greece?
The earliest Greek law to survive is the Dreros inscription, a seventh century BC law concerning the role of kosmos.
Who wrote the first law in Athens?
Draconian laws, traditional Athenian law code allegedly introduced by Draco c. 621 bce. Aristotle, the chief source for knowledge of Draco, claims that his were the first written Athenian laws and that Draco established a constitution enfranchising hoplites, the lower class soldiers.
IT\'S FUNNING: Was Sparta jealous of Athens?
Who invented laws?
By the 22nd century BC, the ancient Sumerian ruler Ur-Nammu had formulated the first law code, which consisted of casuistic statements (“if … then …”). Around 1760 BC, King Hammurabi further developed Babylonian law, by codifying and inscribing it in stone.
Who started rule of law?
The Rule of Law was first originated by Sir Edward Coke, the Chief Justice in England at the time of King James I. Coke was the first person to criticise the maxims of Divine Concept. He strongly believed that the King should also be under the Rule of Law. The Rule of Law doctrine was later developed by A.V.
Who created Draco’s law?
Enforced by Draco near the end of the 7th century BC . It was written in response to the unjust interpretation and modification of oral law by Athenian aristocrats .
Draconian constitution
Created c. 620 BC
Author(s) Draco
Signatories Athenian aristocracy
How were laws made in ancient Greece?
Laws were passed through a process called nomothesia (νομοθεσία) or “legislation.” Each year the Assembly met to discuss the current body of laws. Any citizen could propose a change in the laws, but could only propose the repeal of a law if he suggested another law to replace the repealed law.
Who rules ancient Greece?
From about 2000 B.C.E. to 800 B.C.E., most Greek city-states were ruled by monarchs—usually kings (the Greeks did not allow women to have power). At first, the Greek kings were chosen by the people of the city-state. When a king died, another leader was selected to take his place.
IT\'S FUNNING: Is Montenegro worth going to?
When and where was the Greek law created?
In 620 B.C.E., Draco, the first creator of laws in Ancient Athens, replaced these family feuds with a written code that was designed to be enforced by a court of law. The first law that Draco wrote established that the penalty for murder was exile out of the country.
What is the law in Greece?
Greece is a civil law country, and thus jurisprudence is not considered as a source of law. The Constitution is the supreme law of the land, although article 28 of the Greek Constitution provides that international conventions ratified by Greece as well as EU legislation shall prevail over any other provision of law.
When was the Greek law written?
Written laws appear in the Greek world ca. 650 BC, and they quickly become a fixture of civic life in many (although not all) Greek cities.
What came first law or crime?
Laws are made in reaction or response to crime. Obviously, crime come first and not laws. Article 7 of the Human Rights Act states that you cannot be charged with a criminal offence for an action that was not a crime when you committed it.
Who was Draco Greek?
Draco, also spelled Dracon, (flourished 7th century bc), Athenian lawgiver whose harsh legal code punished both trivial and serious crimes in Athens with death—hence the continued use of the word draconian to describe repressive legal measures.
What is the earliest written law?
IT\'S FUNNING: What were the terms of Athens surrender in the Peloponnesian War?
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If you've done all the heavy work and attracted the best prospects ready to engage your professional service, transforming these leads to clients in your database shouldn't be so difficult or time-consuming. You can automate this stage in your client intake process with workflows to save yourself precious time and effort.
Automating lead conversion to matter
To automate the conversion of lead to matter via workflow:
1. Navigate to Automation on the left side-bar menu
2. Click Add
3. Enter a workflow name and description
4. Select Intake form submitted as the trigger, choose the desired intake form, then tap Continue
5. Choose Convert to Matter as a new action and set it up
6. Choose Create Invoice as a new action, tap Next, setup it up, and click Save to wrap up the process
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Scenario 8 | Education homework help
Chapter 8 Scenario: Protecting Children’s Safety
Objective and scenario
To develop and evaluate an action plan for children’s safe use of a climbing structure on the playground.
You recently accepted a position as an assistant teacher at a large early childhood program in your local community after completing your degree and certification requirements. The head teacher suggested that you spend your first week as an observer so that you become familiar with the safety policies and procedures that teachers are expected to follow with the children.
One day while you are observing during outdoor time, you notice that several children are gathered around a 4-foot-high climbing dome located in one corner of the large playground. Two children have managed to climb up and are standing on top of the structure. Another child is throwing bark chips at the two children. There are no teachers present in the area.
Focus assignment
1. Prepare a one-page outline that identifies the typical developmental characteristics of three-to six-year-olds, safety concerns associated with this age group, and general measures that adults must take to protect children’s safety. Develop a set of safety rules for children to follow when playing on the climbing dome.
2. Be sure to read the REFLECTION section below to guide your thinking. Write your reflection response after you have completed your plan.
1. For each item in your action plan:
a. Explain how this item addresses the issues in the scenario.
2. Describe and justify how your action plan would improve teaching and learning in the scenario.
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The Young Elites Wiki
This article is about the term. For other uses, see The Young Elites (disambiguation).
"The Elites exist only because of an imbalance between the mortal and immortal realms. The blood fevers themselves were ripples in our world caused by an ancient tear between those realms. our existence defies the natural order, defies Death herself."
A Young Elite is a survivor of the blood fever who gain mysterious powers afterwards.
A decade after the blood fever swept through the nation, most survivors - all of whom were children - gained strange markings during their time of illness, and some gained mysterious powers. Those with visible markings became known as malfettos. When people close to malfettos or people who have family members who are malfettos began having strange accidents or sometimes even dying, people began to believe that malfettos were bad luck, and they began being treated like second-class citizens. What people didn't originally know was that the blood fever gifted some of these children with strange abilities, and the children with these powers became known as Young Elites. The Inquisition Axis believes that Young Elites are dangerous and vengeful and will destroy the nation. Thus, they seek to destroy them before they can do so. It is pointed out by Violetta Amouteru that a Young Elite's body is not designed to wield the powers of the gods, and that, therefore, all Young Elites will die at a young age as a result of their powers. But then, the Young Elites and Adelina's crew voyaged to the realm of the gods, and returned their powers. Their markings disappeared, and they looked like what they would've as a normal human.
Known Young Elites
See also
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Amber Chime | Tierra Zen
Campana de Viento Ámbar
Amber Chime
In stock
38,00 €
You can find a representation of the sun on the amber-coloured stone of this sacred windchime.
Woodstock has used the golden ratio to tune the tubes of this chime in order to get an harmonious sound. Also called divine proportion, this ratio was discovered by the Greeks and it can be found all around in nature, within flowers, minerals or even within the human body.
Amber is a fossilised resin that comes from the secretion of specific coniferous trees. Its colour varies from transparent to opaque and from light to dark, similar to the colour of this windcatcher. Formerly known as the tears of the sun, it is meant to warm the heart.
This wind chime carries a lifetime tuning guarantee.
Listen to its sound:
Technical specifications:
53 cm overall length, 4 square bronze aluminium tubes, cherry finish ash wood, stone accents
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You are here
Tuning the auxin transcriptional response.
TitleTuning the auxin transcriptional response.
Publication TypeJournal Article
Year of Publication2013
AuthorsPierre-Jerome E, Moss BL, Nemhauser JL
JournalJournal of experimental botany
Date Published2013 Jun
KeywordsDimerization, Gene Expression Regulation, Plant, Indoleacetic Acids, Plant Growth Regulators, Plant Proteins, Signal Transduction, Ubiquitin-Protein Ligases
<p>How does auxin provoke such a diverse array of responses? This long-standing question is further complicated by a remarkably short nuclear auxin signalling pathway. To crack the auxin code, several potential sources of specificity need to be evaluated. These include: specificity of interactions among the core auxin response components, specificity resulting from higher order complex dynamics, and specificity in interactions with global factors controlling protein turnover and transcriptional repression. Here, we review recent progress towards characterizing and quantifying these interactions and highlight key gaps that remain.</p>
Alternate JournalJ. Exp. Bot.
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AEL Projects:
Accounting for Uncertainty in Mobile AR Systems
AIBAS: Adaptive Intent-Based Augmentation System
Alice's Adventures in New Media
AR Scene Graph
Augmented Office Environments
Augmented Reality for Poultry Inspection
Butterfly Effect
DART: The Designers Augmented Reality Toolkit
Four Angry Men
Live-Virtual Training Integration
Media Design for Augmented Reality
Presence and Aura in AR Experiences
Sweet Auburn
The Real-World Wide Web
The Voices of Oakland
Three Angry Men
projectpic missing ARCraft
ARCraft is a real-time AR strategy game. Users compete against each other in their "real life" environments, using virutal military units. Using head tracking and wand-based interaction, each player navigates his or her fighting force around obsticles while hunting for the enemy.
Our research goal is to investigage how people can use AR to work together (or against each other) in a shared virutal space while maintaining remote physical spaces. For example, how can we represent a single work (combat) area when the viewers are in radically different environments (room size, furniture, etc).
Related Links
Related People
Brendan Hannigan
Szymon Swistun
Related Resources
Go to the main Georgia Tech site
Go to Georgia Tech GVU site
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From education to employment
Canvas Headline banner Jan to Mar 2022
Why digitisation can create more inclusive and diverse university populations
Dave Sherwood, CEO and founder at BibliU
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In 2020, the inequalities at the heart of the Covid-19 pandemic and the BLM movement put a sharper spotlight on systemic racism, causing societies from across the world to reflect on their own roles in perpetuating social inequality. For far too long, efforts from every sector, discipline or industry have fallen short in creating equal access to inclusion and opportunity.
In 2021, we all are all accountable for deepening our understanding of systemic failures and creating meaningful solutions. This will be the only way to lead real change, including across the education sector.
When looking at what actionable strategies need to be urgently deployed, particularly as the pandemic rages on to exacerbate this inequality, technology has a crucial part to play. There needs to be a stronger emphasis on how digitisation of resources need not be a further enabler of disparities in accessing education, but instead the key to unlocking access for all. Technology can prove itself the mother of opportunity in setting a new precedent in inclusion – let’s unpack how.
Pricing out inclusivity
As it stands, when students step into the further education scene, they face a tidal wave of financial challenges when looking to access the necessary educational resources. Each lecture, seminar and overall curriculum demands a wealth of information to keep on track and succeed, yet many students often aren’t made aware of the high costs of course materials on top of rising tuition fees.
On average, students can expect to budget between £450 and £1070 for books and equipment per year. With many students already under an increasingly tighter budget while at university, those from disadvantaged backgrounds are under severe financial stress, with many unable to foot the cost of physical textbooks. Without financial support, disparities set in from the start of a student’s journey, subsequently cause greater anxiety around how their grades might suffer as a result.
The presence of this inequality in higher education has taken an even larger hit, with the pandemic exacerbating barriers to access. The abrupt shutdown of universities and libraries has meant students have had to shift to online learning. Students who can only access content through borrowing books from libraries they couldn’t otherwise afford will be hit hardest. Without a coordinated effort to tailor content to meet the needs of all students, the effect on their studies will be long-lasting and serve to continue denying equal opportunity.
Many organisations are taking great strides in providing better financial support for under-represented groups through bursaries and scholarships to tackle the issue. Technology can offer substantial gains in this work to ensure that it isn’t dealt with as a quick-fix, but rather, provides a roadmap for how to shake up the system as it stands. Institutional partnerships with integrated platforms are paramount to ensure that collaboration takes place at scale to future-proof EdTech strategies. Bringing highly detailed analytics at both a macro- and micro-level to provide a holistic overview of student accessibility and performance will open up greater opportunities to increase engagement. Without consistency across the entirety of an institution, digital integration will only go so far, it requires platform’s that take into account the human element when collating new insights and functionality around this area.
BibliU is one such platform that enables universities to bring textbooks online and allow students to access essential course materials within their own learning environment, thereby removing the issue of hidden textbook costs.
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Pathways to inclusive learning
The technology landscape continues to be populated with innovative use-cases that, when applied, provide a gateway to improve inclusion and engagement for all students, regardless of background.
In order to have a far-reaching impact, the process of designing and delivering programmes of study to break down barriers that students face needs to be sped up and made more widely available. A key route to success is to bring efficiency to online provision connecting a community of organisations working towards tackling equality, diversity and inclusion.
One startup innovating in the apprenticeships sector is The Apprenticeship Hack, a platform providing a blended learning approach so students feel as empowered to pursue the same opportunities as others and take charge where they see the need for structural and organisational improvement.
Tools like BibliU are geared towards making it easier for universities to adopt resources that make education more accessible for a diverse student population. By reducing the complexity of providing digital course materials, including Open Education Resources and textbooks, universities will be more effectively empowered to make the switch, which is especially critical for BAME students who are disproportionately impacted by the cost of education.
Tailoring to specific student needs
For too long, students with disabilities have been put off from pursuing higher education, with many course materials failing to meet individual needs. New assistive technologies must be taken advantage of to ensure such students have access to the same opportunities as others.
Therefore, investments should be made in tools like Good Feel, which converts musical scores into braille, and text-to-speech software for those with poor sight, as well as speed-readers for those with neurological disabilities. BibliU’s text-to-speech and speed-reader, alongside synchronised online annotations, mean students who learn differently have access to the assistive technology they need to do so.
All levels of the higher education system must take an active role in their commitment to building a more progressive and equal environment. In order to do so, the right type of infrastructure needs to be in place and must adapt in real-time to the needs of students. Now is the time to leave piecemeal approaches behind and instead take decisive and collaborative action from all key players across the higher education sector.
Dave Sherwood, CEO and founder at BibliU
Recommend0 recommendationsPublished in Exclusive to FE News
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5 months ago
Scientists Find 15,000-Year-Old Unknown Viruses Trapped In Tibetan Glacier
2 min read 397 Shares
Monit Khanna
Monit KhannaUpdated on Jul 22, 2021, 11:59 IST
Scientists studying glaciers have discovered viruses from around 15,000 years old from the two ice samples they've collected from the Tibetan Plateau in China, most of which are unknown to humans to date.
15000 year old viruses Representational image: Getty Images
Also Read: Hidden Gene Found In COVID-19 Virus Could Help Us Fight Pandemic Better
The findings (published in the journal Microbiome) could help scientists better understand how viruses have evolved over the centuries. The scientists were also able to create a new ultra-clean method for analysing microbes and viruses in ice without contaminating it.
Researchers analysed ice cores that were taken in 2015 from the Guliya ice cap in western China. These were taken from the summit of Guliya -- around 22,000 feet above sea level.
These cores were made up of layers of ice that got accumulated every year while trapping things in them. These layers sort of formed timelines that scientists have now used to understand more about climate change, microbes, viruses and gases throughout history.
Dating the core using a combination of conventional and novel techniques, the analysis revealed that the ice was nearly 15,000 years old. However, along with this, they discovered genetic codes for 33 viruses -- four of those viruses have already been identified by the scientific community -- and at least 28 of them are novel, which means unknown to humans.
Also Read: Ultrasound Kills Coronavirus, Next Step Is Using It As Covid-19 Treatment
According to researchers, they might have survived at the time they got frozen, actually because of the ice.
15000 year old viruses Representational image: Getty Images
The viruses don’t really share a common universal gene, so scientists haven’t really been able to name them just yet. To compare the novel viruses with the known ones, scientists compared gene sets that are catalogued in scientific databases, especially for known viruses.
Also Read: Viruses Play Key Role In Our Ability To Reproduce And Survive, Study Finds
The four viruses that seem familiar actually belong to virus families that typically infect bacteria. The researchers found the viruses in concentrations far lower than their normal levels when detected in soil or ocean.
Researchers’ analysis sheds light on the fact that the viruses likely originated with soil or plants and is not animal or human-based.
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Start a conversation, not a fire. Post with kindness.
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Language - Urdu
Language > Urdu
Urdu (undefined ALA-LC: ) (also known as Lashkari, locally written لشکری)—or, more precisely, Modern Standard Urdu—is a Persianised standard register of the Hindustani language. It is the official national language and lingua franca of Pakistan. In India, it is one of the 22 official languages recognized in the Constitution of India, having official status in the six states of Jammu and Kashmir, Telangana, Uttar Pradesh, Bihar, Jharkhand and West Bengal, as well as the national capital territory of Delhi. It is a registered regional language of Nepal.
Apart from specialized vocabulary, spoken Urdu is mutually intelligible with Standard Hindi, another recognized register of Hindustani. The Urdu variant of Hindustani received recognition and patronage under British rule when the British replaced the local official languages with English and Hindustani written in Nastaʿlīq script, as the official language in North and Northwestern India. Religious, social, and political factors pushed for a distinction between Urdu and Hindi in India, leading to the Hindi–Urdu controversy.
According to Nationalencyklopedin's 2010 estimates, Urdu is the 21st most spoken first language in the world, with approximately 66 million speakers. According to Ethnologue's 2017 estimates, Urdu, along with standard Hindi and the languages of the Hindi belt (as Hindustani), is the 3rd most spoken language in the world, with approximately 329.1 million native speakers, and 697.4 million total speakers.
Urdu, like Hindi, is a form of Hindustani. It evolved from the medieval (6th to 13th century) Apabhraṃśa register of the preceding Shauraseni language, a Middle Indo-Aryan language that is also the ancestor of other modern Indo-Aryan languages. Around 75% of Urdu words have their etymological roots in Sanskrit and Prakrit, and approximately 99% of Urdu verbs have their roots in Sanskrit and Prakrit. Because Persian-speaking sultans ruled the Indian subcontinent for a number of years, Urdu was influenced by Persian and to a lesser extent, Arabic, which have contributed to about 25% of Urdu's vocabulary. Although the word Urdu is derived from the Turkic word ordu (army) or orda, from which English horde is also derived, Turkic borrowings in Urdu are minimal and Urdu is also not genetically related to the Turkic languages. Urdu words originating from Chagatai and Arabic were borrowed through Persian and hence are Persianized versions of the original words. For instance, the Arabic ta' marbuta ( ة ) changes to he ( undefined ) or te ( undefined ). Nevertheless, contrary to popular belief, Urdu did not borrow from the Turkish language, but from Chagatai, a Turkic language from Central Asia. Urdu and Turkish borrowed from Arabic and Persian, hence the similarity in pronunciation of many Urdu and Turkish words.
Arabic influence in the region began with the late first-millennium Muslim conquests of the Indian subcontinent. The Persian language was introduced into the subcontinent a few centuries later by various Persianized Central Asian Turkic and Afghan dynasties including that of Mahmud of Ghazni. The Turko-Afghan Delhi Sultanate established Persian as its official language, a policy continued by the Mughal Empire, which extended over most of northern South Asia from the 16th to 18th centuries and cemented Persian influence on the developing Hindustani.
The name Urdu was first used by the poet Ghulam Hamadani Mushafi around 1780. From the 13th century until the end of the 18th century Urdu was commonly known as Hindi. The language was also known by various other names such as Hindavi and Dehlavi. Hindustani in Persian script was used by Muslims and Hindus, but was current chiefly in Muslim-influenced society. The communal nature of the language lasted until it replaced Persian as the official language in 1837 and was made co-official, along with English. Hindustani was promoted in British India by British policies to counter the previous emphasis on Persian. This triggered a Hindu backlash in northwestern India, which argued that the language should be written in the native Devanagari script. This literary standard called "Hindi" replaced Urdu as the official language of Bihar in 1881, establishing a sectarian divide of "Urdu" for Muslims and "Hindi" for Hindus, a divide that was formalized with the division of India and Pakistan after independence (though there are Hindu poets who continue to write in Urdu to this day, with post-independence examples including Gopi Chand Narang and Gulzar).
There have been attempts to "purify" Urdu and Hindi, by purging Urdu of Sanskrit words, and Hindi of Persian loanwords, and new vocabulary draws primarily from Persian and Arabic for Urdu and from Sanskrit for Hindi. English has exerted a heavy influence on both as a co-official language.
Bahrain (البحرين ' ), officially the Kingdom of Bahrain (مملكة البحرين '), is an island country in the Persian Gulf. The sovereign state comprises a small archipelago centered around Bahrain Island, situated between the Qatar peninsula and the north eastern coast of Saudi Arabia, to which it is connected by the 25 km King Fahd Causeway. Bahrain's population is 1,234,571 (c. 2010), including 666,172 non-nationals. It is 765.3 km2 in size, making it the third-smallest nation in Asia after the Maldives and Singapore.
Bahrain is the site of the ancient Dilmun civilisation. It has been famed since antiquity for its pearl fisheries, which were considered the best in the world into the 19th century. Bahrain was one of the earliest areas to convert to Islam, in 628 CE. Following a period of Arab rule, Bahrain was occupied by the Portuguese in 1521, who in turn were expelled in 1602 by Shah Abbas I of the Safavid dynasty under the Persian Empire. In 1783, the Bani Utbah clan captured Bahrain from Nasr Al-Madhkur and it has since been ruled by the Al Khalifa royal family, with Ahmed al Fateh as Bahrain's first hakim.
India (ISO: ), also known as the Republic of India (ISO: ), is a country in South Asia. It is the seventh largest country by area and with more than 1.3 billion people, it is the second most populous country as well as the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, and the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west; China, Nepal, and Bhutan to the northeast; and Bangladesh and Myanmar to the east. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives, while its Andaman and Nicobar Islands share a maritime border with Thailand and Indonesia.
The Indian subcontinent was home to the urban Indus Valley Civilisation of the 3rd millennium. In the following millennium, the oldest scriptures associated with Hinduism began to be composed. Social stratification, based on caste, emerged in the first millennium BCE, and Buddhism and Jainism arose. Early political consolidations took place under the Maurya and Gupta empires; later peninsular Middle Kingdoms influenced cultures as far as Southeast Asia. In the medieval era, Judaism, Zoroastrianism, Christianity, and Islam arrived, and Sikhism emerged, all adding to the region's diverse culture. Much of the north fell to the Delhi Sultanate; the south was united under the Vijayanagara Empire. The economy expanded in the 17th century in the Mughal Empire. In the mid-18th century, the subcontinent came under British East India Company rule, and in the mid-19th under British Crown rule. A nationalist movement emerged in the late 19th century, which later, under Mahatma Gandhi, was noted for nonviolent resistance and led to India's independence in 1947.
Oman (عمان ' ), officially the Sultanate of Oman''' (سلطنة عُمان ), is an Arab country on the southeastern coast of the Arabian Peninsula in Western Asia. Its official religion is Islam.
Holding a strategically important position at the mouth of the Persian Gulf, the country shares land borders with the United Arab Emirates to the northwest, Saudi Arabia to the west, and Yemen to the southwest, and shares marine borders with Iran and Pakistan. The coast is formed by the Arabian Sea on the southeast and the Gulf of Oman on the northeast. The Madha and Musandam exclaves are surrounded by the UAE on their land borders, with the Strait of Hormuz (which it shares with Iran) and Gulf of Oman forming Musandam's coastal boundaries.
"Faith, Unity, Discipline"
national_anthem =
United Arab Emirates
The United Arab Emirates (UAE; دولة الإمارات العربية المتحدة '), sometimes simply called the Emirates (الإمارات '), is a country in Western Asia at the southeast end of the Arabian Peninsula on the Persian Gulf, bordering Oman to the east and Saudi Arabia to the south, as well as sharing maritime borders with Qatar to the west and Iran to the north. The sovereign constitutional monarchy is a federation of seven emirates consisting of Abu Dhabi (which serves as the capital), Ajman, Dubai, Fujairah, Ras Al Khaimah, Sharjah and Umm Al Quwain. Their boundaries are complex, with numerous enclaves within the various emirates. Each emirate is governed by a ruler; together, they jointly form the Federal Supreme Council. One of the rulers serves as the President of the United Arab Emirates. In 2013, the UAE's population was 9.2 million, of which 1.4 million are Emirati citizens and 7.8 million are expatriates.
Human occupation of the present UAE has been traced back to the emergence of anatomically modern humans from Africa some 125,000 BCE through finds at the Faya-1 site in Mleiha, Sharjah. Burial sites dating back to the Neolithic Age and the Bronze Age include the oldest known such inland site at Jebel Buhais. Known as Magan to the Sumerians, the area was home to a prosperous Bronze Age trading culture during the Umm Al Nar period, which traded between the Indus Valley, Bahrain and Mesopotamia as well as Iran, Bactria and the Levant. The ensuing Wadi Suq period and three Iron Ages saw the emergence of nomadism as well as the development of water management and irrigation systems supporting human settlement in both the coast and interior. The Islamic age of the UAE dates back to the expulsion of the Sasanians and the subsequent Battle of Dibba. The UAE's long history of trade led to the emergence of Julfar, in the present day emirate of Ras Al Khaimah, as a major regional trading and maritime hub in the area. The maritime dominance of the Persian Gulf by Emirati traders led to conflicts with European powers, including the Portuguese and British.
Urdu (English) Lingua urdu (Italiano) Urdu (Nederlands) Ourdou (Français) Urdu (Deutsch) Língua urdu (Português) Урду (Русский) Urdu (Español) Język urdu (Polski) 乌尔都语 (中文) Urdu (Svenska) Limba urdu (Română) ウルドゥー語 (日本語) Урду (Українська) Урду (Български) 우르두어 (한국어) Urdu (Suomi) Bahasa Urdu (Bahasa Indonesia) Urdu (Lietuvių) Urdu (Dansk) Urdština (Česky) Urduca (Türkçe) Урду (Српски / Srpski) Urdu keel (Eesti) Urdčina (Slovenčina) Urdu nyelv (Magyar) Urdu jezik (Hrvatski) ภาษาอูรดู (ไทย) Urdujščina (Slovenščina) Urdu (Latviešu) Γλώσσα Ούρντου (Ελληνικά) Tiếng Urdu (Tiếng Việt)
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World Water Day 2021
Lauren Moriarty & Monalisa Booysen
22 March 2021
Valuing Water
World Water Day takes place March 22nd every year, and has since 1993. This day focuses on themes highlighting the importance of freshwater resources as coordinated by the United Nations, where this year’s theme is “Valuing water”. World Water Day aims to support the Sustainable Development Goal number 6 of water and sanitation for all by the year 2030, through raising awareness and taking action against the water crisis experienced around the world. There are approximately 2.2 billion people around the world that are living without proper sanitation and access to clean drinking water.
Water makes up approximately 75% of the planet, however, this is not all freshwater which is a highly sought after commodity. Due to its limited resource the use and abstraction process of freshwater can have damaging impacts on freshwater ecosystems. The value of water is however, more than the price but rather the context to which people themselves value its uses and importance, such that it is essential in improving the health and welfare of populations as well as reducing disease and increasing productivity. Understanding these uses and value of our global freshwater resources enable us to practice sustainable use and protect this finite resource for everyone.
So how can you make small changes that add up to make a big impact?
• Fix any leaks asap! Billions of litres of water are wasted by fault pumps and poor maintenance.
• Choose shower over bathing where possible, it uses approximately 50% less water
• Use of grey water and rainwater can help in garden and home practices
• Don’t let the taps run!
• Try install water-saving tools such as low flush toilet systems and eco-friendly washing techniques.
Human Rights and Water
It is everyone’s right to have access to the basic essentials which include water for sanitation and safe drinking water in a sufficient quantity and quality. This was recognised as a human right by the United Nations General Assembly on the 28th of July 2010.
“The human right to safe drinking water entitles everyone, without discrimination, to have access to sufficient, safe, acceptable, physically accessible, and affordable water for personal and domestic use.” - United Nations Committee on Economic, Social and Cultural Rights in General Comment 15 drafted in 2002
Water can mean many different things to different people - economically, socially, culturally, in daily living, education, health, the natural environment and many other aspects are all important to take into consideration while trying to raise awareness and protect this precious resource. Only by acknowledging and celebrating the value of water to our lives and all its benefits can we then truly manage and safeguard it for the future. Water is an intrinsic part to everyone’s life, where water and sanitation are vital to protect individual's health and wellbeing. Water also has an important socio-cultural impact in people’s lives, whether it be culturally or recreationally. However, our natural freshwater resources and ecosystems are facing great threats from degradation such as those caused by agricultural practices which has the largest demand on these freshwater resources, climate change and the way we manage, and supply water further threatens to endanger these valuable ecosystems.
So what does water mean to you and how are you speaking up about water practices in your local area?
IMG 20210322 83614
Beautiful view of the Groot River from a canoe -2021/03/22
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What is an airport?
It is a large space dedicated to several operations: takeoff and landing aircraft, the embarkation and disembarkation of passengers and goods.
An aircraft can operate at airports with the construction of long flat tracks. Use is made of these tracks at each takeoff and landing.
An airport has normally at least one terminal. It is a building where passengers check in their luggage and board a plane.
The terminal is often divided into two parts: departures and arrivals.
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Station: Dollarville, MI
Dollarville was founded about 1882 as a townsite and mill of the American Lumber Company. This was a station on the Detroit, Mackinac and Marquette (later DSS&A) on their line between St. Ignace and Marquette, two miles west of Newberry. [MPN]
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Think you’ll never have a stroke? Think again!
Someone in the United States has a stroke every 40 seconds. Every 4 minutes, someone dies of stroke. Every year more than 795,000 people in the United States have a stroke. Stroke is the leading cause of serious long-term disability. Stroke reduces mobility in more than half of the stroke survivors age 65 and over. [...]
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Q1) Paytm Money has appointed whom as its new Chief Executive Officer ?
1. Varun Sridhar
2. Pravin Jadhav
3. Amit Nayyar
4. Sameer Nigam
Q2) International Day of Friendship is observed every year on which date?
1. 31 July
2. 29 July
3. 30 July
4. 28 July
Q3) Who has been honoured with “Karamveer Chakra Award” instituted by United Nations and International Confederation of NGO (iCONGO)?
1. Sandeep Maheshwari
2. Vivek Bindra
3. Ujjwal Patani
4. Sunil ydv SS
Q4) Power Finance Corporation has signed an agreement with which IIT for Training, Research, and Entrepreneurship Development in Smart Grid Technology?
1. IIT Madras
2. IIT Kanpur
3. IIT Delhi
4. IIT Guwahati
Q5) Which Bank has taken possession of Reliance Centre, the headquarters of the Anil Dhirubhai Ambani Group (ADAG) in Mumbai?
1. Yes Bank
2. ICICI Bank
3. HDFC Bank
4. Axis Bank
Q6) Ministry of Human Resource Development has been renamed as _______?
1. Ministry of Knowledge
2. Ministry of Education
3. Ministry of Academics
4. Ministy of Learning
Q7) A fleet of five French-manufactured Rafale multi-role combat jets landed at which Air Force base of India?
1. Pathankot
2. Jorhat
3. Ambala
4. Bathinda
Q8) Which district has topped the list of aspirational districts ranked by government think-tank Niti Aayog for the February-June 2020 period?
1. Bahraich
2. Nawada
3. Ri-Bhoi
4. Bijapur
Q9) Green-Ag project, which is funded by Global Environment Facility (GEF), has been launched in which state recently?
1. Assam
2. Karnataka
3. Mizoram
4. Nagaland
Q10) ICRA Ltd has appointed whom as the Managing Director and Group Chief Executive Officer of the credit rating agency for three years?
1. Rohit Karan Sawhney
2. Ananda Bhoumik
3. N Sivaraman
4. Tarun Bansal
Q11) Dubai-based Indian-origin author Avni Doshi is among the 13 authors longlisted for the prestigious 2020 Booker Prize for her which novel?
1. Burnt Sugar
2. Deadly Shadows
3. A Girl to Remember
4. Hunted by the Sky
Q12) The UK India Business Council (UKIBC) has signed an MoU with which state government to improve industrial development?
1. Madhya Pradesh
2. Sikkim
3. Karnataka
4. Gujarat
Q13) Which state has announced a new Entrepreneurship Development Programme to address the issues of shortage of working capital?
1. Karnataka
2. Kerala
3. Andhra Pradesh
4. Telangana
Q14) Which has become the first DGCA-approved drone training school of the country?
1. Hyderabad Flying Club
2. Chennai Flying Club
3. Pune Flying Club
4. Bombay Flying Club
Q15) Which is the first city in the entire Northeast region to get a manhole cleaning robot ‘BANDICOOT’ ?
1. Dispur
2. Guwahati
3. Gangtok
4. Imphal
Q16) Asian Development Bank has approved USD _________ million (about Rs 22 crore) grant to India from its Asia Pacific Disaster Response Fund?
1. USD 3 million
2. USD 2 million
3. USD 4 million
4. USD 1 million
Q17) Union Government has approved an MoU between India & which country on cooperation in traditional medicine, homeopathy?
1. Australia
2. Zimbabwe
3. Canada
4. United States
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December grants include exploring ocean data through sound and math interventions
UO researchers received 43 new grants contracts and awards in December, including a grant from Vanderbilt University to study the effects of combined attention and academic interventions for kindergarten children with significant difficulties in mathematics and a grant from Woods Hole Oceanographic Institution for exploring ocean data through sound. For a full list of awards, see the December Awards Report from the Office of the Vice President for Research and Innovation.
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Welcome to the Chu Lab!
Our translational epilepsy laboratory at MGH uses anatomical and non-invasive and invasive physiological imaging techniques to study normal development, cognitive function, and seizures in epilepsy. Through this work, we aim to identify biomarkers to predict symptoms, understand the relationship between brain rhythms and symptoms, and develop treatments to improve them.
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Mind Matters Natural and Artificial Intelligence News and Analysis
TagPaul Sutter
multiverse conceptual illustration
In an Infinity of Universes, Is Another You Reading This Article?
Maybe. But the recent science evidence is not especially encouraging
It is generally believed that the early universe widely inflated. So, reporting on a recent article submitted to Journal of Cosmology and Astroparticle Physics, Stony Brook astrophysicist Paul Sutter points out: First off, they found that eternal inflation wasn’t nearly as common as originally thought. Their explanation for why cosmologists had thought eternal inflation was generic was because those earlier cosmologists had studied only a limited set of models. They found that many viable inflation models (“viable” here means they didn’t obviously contradict observations) didn’t lead to an eternally inflating scenario. Paul Sutter, “How real is the multiverse?” at Space.com (December 16, 2021) Cosmologists line up on both sides: Prominent proponents of the multiverse have included well-known cosmologists such as Max Tegmark and…
Concept of robots replacing humans in offices
Will Humans Ever Be Fully Replaceable by AI? Part 1
We must first determine, what is a person and what is the nature of the universe in which a person can exist?
The title question has been around for quite some time. In this discussion, I would like to take an ontological look at this question. What is the essential nature of being a person? To fully replace humans, what must AI machines become capable of? IF we want to consider the possibility of making humans obsolete, we need to know what is the essence of humanity? What is the ontological nature of a person? What characteristics define being a person? Even before we can address the essential nature of a person, we must identify the essential nature of the universe in which that person exists. What is the universe? How many dimensions does it have? Can the universe, or in it…
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News tagged with nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO− 3 and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a formal charge of -1. This results from a combination formal charge in which each of the three oxygens carries a −2⁄3 charge, whereas the nitrogen carries a +1 charge, all these adding up to formal charge of the polyatomic nitrate ion.
In organic chemistry a nitrate (not to be confused with nitro) is a functional group with general chemical formula RONO2 where R stands for any organic residue. They are the esters of nitric acid and alcohols formed by nitroxylation. Examples are methyl nitrate formed by reaction of methanol and nitric acid, the nitrate of tartaric acid, and the inaccurately-named nitroglycerin (which is actually an organic nitrate compound, not a nitro compound).
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How do I set up File upload questions?
File upload questions ask students to answer a question by uploading one or more files from their computer.
Note: Students must upload files from their computer; they may not attach links to cloud-hosted files like Google Docs or Google Sheets. Buzz enforces a filesize upload limit of 100MB.
After students upload a file, they can remove it or download it by clicking the buttons on the attached-file card.
Note: Because Practice questions activities are meant to give students immediate feedback to respond to, File upload questions are not available in them.
Create File upload questions
File upload questions can be added to assessments.
1. Add the Assessment activity.
2. Add a File upload question to the activity.
3. Follow the directions, below.
Question content
1. Specify how many Points the question is worth.
1. This section pictures and explains the default visual editor; select the Text editor to create and edit questions with the advanced Text editor.
1. Feedback for When answer is correct (irrelevant for this question type).
2. Feedback for When answer is incorrect (irrelevant for this question type).
3. Feedback that is Always delivered.
To manage the question's Interaction:
• You can specify the Maximum allowed files the student can upload. You can allow up to 5 files per question. The default is 1.
• You can specify the Allowed file extensions you allow the student to upload. Separate file types with a space and don't include the dot (e.g., pdf xls doc).
Note: Buzz enforces a filesize upload limit of 100MB.
Learn more: How do I vary attempt limits by question?
Objective mastery
1. Use the Filter field to search for specific objectives.
Use the Score card to:
1. Indicate if you want the question to count as Extra credit.
2. Provide a Rubric to use for grading the question.
Companion Material
1. Pointing to existing resources in the course.
2. Uploading new files (PDFs only).
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Enable Javscript for better performance
Location Diaries: The long night- Cinema express
Location Diaries: The long night
Published: 02nd September 2019
For director Shanthkumar's Magamuni, hero Arya shot in the hills near Pollachi for nearly a week. To reach this remote location, he had to trek up a hill every day. If it was hard for him, it was harder for the technical team, which had to carry heavy camera and lighting equipment, including a jimmy jib.
While they managed it a few times, it became impossible to repeat the feat every day. “We then hit upon an idea and decided to leave the equipment on the hill,” says Arya. “The crew put up a tent and took turns to stay there every night after shoot. It was tough, given the remoteness of the location and how cold the hilly area was.” This idea apparently saved them a lot of time and energy. “We moved to different hills, and each time, repeated this exercice several times!”
Logistics management played a crucial role in another segment of the shoot as well. For an important sequence, Arya and Indhuja had to travel to a location around three hours from Chennai. “The shoot was to occur in a tiny 100 square feet house. It was so small that even a small camera crew could barely fit inside. We felt quite claustrophobic about being there,” says Arya. “But that was exactly why Shanthakumar chose that house. We did a few performance-oriented scenes and the claustrophobia actually helped us perform better.”
In fact, Arya and Indhuja realised the importance of the cramped house so much that they decided not to step out for a break. “When it was time to pack up, we concluded that breaking the scene would destroy the claustrophobic, tired feeling important for those scenes. Instead of travelling to Chennai and returning the next day, we shot for 28 hours continuously and completed all the scenes on the same day. It was extremely tiring, but we are happy with the outcome.”
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Which is your favourite time travel film in Tamil?
Indru Netru Naalai
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What is guided discovery in CBT
New concepts can often feel overwhelming when we first start learning or trying different types of approach.
Commonly asked questions by people learning about Cognitive Behaviour Therapy (CBT) can include:
• What is guided discovery?
• Is it about the therapist directing the client?
• Is ‘Socratic dialogue’ the same thing as guided discovery?
• How do I offer guided discovery?
What is guided discovery and how can it help?
Guided discovery can be one of the most beneficial interventions used within CBT. In a nutshell, guided discovery is a process that a therapist or counsellor uses to help their client reflect on the way that they process information. Through the processes of answering questions or reflecting on thinking processes, a range of alternative thinking is opened up for each client. This alternative thinking forms the blueprint for changing perceptions and behaviours.
A woman stares thoughtfully out of a window A useful analogy for guided discovery is to think about going to an optician’s for an eye test. The optician may initially put a contraption on their clients head with a range of lenses on it. Initially, their clients cannot see through this contraption very well (for example, what they perceive may be a blur). The optician then sets about gradually removing or replacing lenses. Through a process of trial, error and feedback from the client, each individual begins to see more clearly.
Guided discovery works in exactly the same way. Instead of using optical lenses, the CBT therapist helps the client use lenses of perception. Perceiving information is a different way allows each client to access a range of choices in their life, ostensibly, to see their life through different lenses. When we view life in a different way our emotional reaction to events also shifts. These types of continued conscious re-evaluations in CBT are very important because they lay the foundations of future ‘automatic thinking’ and make relapse less likely.
Why is guided discovery used?
Used by cognitive therapists, guided discovery is a two-way, collaborative process that can help clients learn to develop different interpretations of their problems. Through collaboration, this can assist in creating and fostering a positive therapeutic relationship, whilst getting clients to focus on not only the problem, but also the solution.
Considered to be a productive way of helping clients to engage with and consider their unique problems or concerns, guided discovery in CBT does require a genuine interest from the therapist to understand their client’s point of view.
Is guided discovery CBT right for me?
Now that you know more about guided discovery, it’s important to consider if it may be the right type of therapy for you. Learning more about what to expect from CBT can be a good next step. It’s important to remember that there is no ‘right’ or ‘wrong’ approach when it comes to seeking help and support. If one method doesn't work for you, there are many other approaches available.
To find the right counsellor or therapist for you, use our advanced search to discover trained professionals offering in person, online, and telephone sessions.
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Aging Signs
aging signs concerns
The aging process is not kind to the skin.
Over time, aging can cause skin sagging, fine lines and wrinkles, age spots, and poor skin texture. These result from collagen and elastin depletion as well as sun exposure over the years.
Recommended Treatments
The face, neck, hands, arms, and legs are typically the first areas to show signs of aging, but aging skin occurs everywhere on the body. Signs of aging develop gradually and are permanent unless treated with professional anti-aging treatments.
While aging is inevitable, certain treatments can delay or minimize aging signs. Dr. Patrick Bitter, Jr., has dedicated his life to developing effective treatments to reduce the signs of aging. The FotoFacial® is an anti-aging skin treatment that Dr. Bitter himself invented. FotoFacial® treatments for the face and body counteract signs of aging and recapture smooth, tight, firm, evenly toned, and unmarked skin.
The FotoFacial® is clinically proven to restore skin elasticity by causing aged cells to behave like young cells. Additionally, Dr. Bitter offers the 30 Minute Miracle Facelift known as the Y LIFT®, a procedure that provides structural volumizing to dramatically improve facial contours.
Lastly, Dr. Bitter uses injectable fillers and BOTOX Cosmetic to correct volume loss, erase moderate to severe wrinkles and folds, and enhance facial contours for a more youthful and refreshed appearance.
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Exoplanet atmospheres
The chemical composition of exoplanetary atmospheres can tell us much about the physical (and potentially life bearing) conditions on these worlds. The most successful method for measuring chemical composition of an exoplanetary atmosphere is the transit spectroscopy method. When an exoplanet passes in front of its host star from our point of view, a small fraction of the stellar light passes through the exoplanetary atmosphere, where molecules absorb light of some wavelengths while light of other wavelengths can pass through unhindered. By measuring the fraction of stellar light able to penetrate the atmosphere at different wavelengths, the chemical composition of the atmosphere can be inferred.
However, the fraction of stellar light that passes through a transiting exoplanet's atmosphere is very small, which constrains both the telescopes/instruments that can be used and the planetary system that can be observed. The on-going search for exoplanets helps us to find the best-suited systems for transit spectroscopy.
Animation showing how planet atmosphere absorbs some light.
As the planet moves in front of the star, its brightness decreases. This planet has an atmosphere that absorbs blue and green light efficiently while letting red light pass through. By measuring the brightness decrease at different wavelengths, the wavelength dependent transmittance of the atmosphere can be obtained. Image credit: Erik Aronson
Model of light transmitted through planet atmospheres.
Modeled transmittance of three types of exoplanets in the near-infrared spectral region. Atmospheric transmittance is characterized by the amount of blocked stellar light, here characterized by additional perceived planetary radius (eclipsing height) due to absorption in the atmosphere. Top panel: Earth-twin. Middle panel: Hot Venus-like super Earth. Bottom panel: Hot Jupiter. Image credit: Erik Aronson
Artistic representation of exoplanets infront of their star.
Visual representation of a few of the currently known most promising exoplanet systems for transit spectroscopy, with Jupiter, Neptune and Earth included for comparison. Image credit: Erik Aronson
Contact: Nikolai Piskunov, Ulrike Heiter, Ansgar Wehrhahn
Last modified: 2021-12-21
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• Carrie Palmer Weber Middle School
Technology Education Port Washington UFSD
S.T.E.M. - Integrating Science, Mathematics, Engineering and Technology
Devices or ideas that improve the lives of humans.
Students and Parents
Technology Education is project-based-learning, that is done individually or in groups. It is hands-on, involves a lot of problem solving, and creativity. We use a lot of math and science concepts, and most classes projects end with friendly competitions, and are a lot fun.
Technology education provides students with experiences that encourage them to question what they do not understand, to promote exploration and problem solving, to foster limitless growth through life-long learning and, most of all, to motivate and inspire youngsters to achieve their maximum potential.
STEM is taught at Weber
Science, Technology, Engineering and Mathematics
1. Electrification
2. Automobile
3. Airplane
4. Water Supply and Distribution
5. Electronics
6. Radio and Television
7. Agricultural Mechanization
8. Computers
9. Telephone
10. Air Conditioning and Refrigeration
11. Highways
12. Spacecraft
13. Internet
14. Imaging
15. Household Appliances
16. Health Technologies
17. Petroleum and Petrochemical Technologies
18. Laser and Fiber Optics
19. Nuclear Technologies
20. High-performance Materials
“All experts start as beginners!”
-Elbert Hubbard (1856 - 1915)
“Any sufficiently advanced technology is indistinguishable from magic.”
-Arthur C. Clarke (1917 - )
-Putt's Law
S.T.E.M. is taught at Weber Middle School.
Science, Technology, Engineering and Math
What is STEM?
NYS STEM Ed. Collaborative working definition of "STEM Education:"
STEM Education refers to utilizing the NYS MST (Math Science and Technology) Standards in the teaching and learning of the Science, Technology Education, Engineering and Math (STEM) disciplines, in an innovative, integrated, collaborative, and applied fashion to a level of challenge sufficient for college and/or career readiness. (Developed in part from the National STEM Initiative)
What Kinds of MATH Terms Are Taught
· Divide
· Height· Triple Beam Balance Scale· Ruler· Multiply· Width· Round Up / Down· Graph Paper· Strength-to-Weight Ratio· Decimal· Calculator· Horizontal· Measure· Fraction· Common Denominator· Vertical· Inches· Right Angle· Equilateral· Diagonal· Feet· Degrees· Symmetry· Counting· Customary· Acute Angle· Truss· Pounds (lbs.)· Metric· Obtuse Angle· Trapezoid· Grams· Centimeters· Perpendicular· 3-Dimensional· Convert· Millimeters· Parallel· 2-Dimensional· Aerodynamics· 1/16 of an inch· Increment· Limitations & Constraints· Orthographic· ¼ of an inch· Span· Comparison· Friction· 1/8 of an inch· Whole Number· Greatest vs. Least· Light vs. Heavy· Wheelbase· Specifications· Weight & MassMinimum vs. Maximum· Length· Exact & Specific· Odd vs. Even· Thrust· Distance· Patterns· Drag · Gravity· Reduce· Improper Fraction· Lift vs. Downforce· Trajectory· Cylinder· Streamline· Coefficient· Cube· Sphere· Cone
You are living in a unique age. You live in a world the produces new information and knowledge at such a rapid rate that no one individual can hope to know everything. In order to be a productive member of a rapidly moving and highly technical society, you must become technically literate. You must be aware of the importance of technology in our society, what technology is, and how technology works in the production process, as well as comprehend basic concepts in technology education.
. Develop Human Potential
Appreciate Learning About Technology
Explore and Experience Technology
Study the Impact of Technology on Society
Integrate Other Disciplines with Technology
Develop Problem Solving Skills Related To
Technology Education
Utilize and Evaluate Appropriate Resources in
. Integrate Technology and Careers by Awareness,
and Exploration
A. Develop Human Potential
1. Enhance student's positive self-image
2. Manage the learning environment
3. Develop appropriate social skills
4. Develop student technical skills
5. Enhance student thinking
6. Augment communication skills
7. Encourage and develop student leadership skills
8. Utilize and expand team work skills
B. Appreciate Learning About Technology
1. Realize the importance of technological literacy
2. Realize the connection between technology and society
3. Realize the importance of understanding how things work.
4. Become an informed decision maker regarding technology.
C. Explore and Experience Technology
1. Identify and utilize current content for technology education.
2. Experience the intellectual process of a technologist by: analyzing, constructing, designing, modeling, computing, etc.
3. Experience the safe use of tools, equipment, material and processes associated with current and future technologies.
4. Asses and evaluate the use and impacts of technology in society
5. Perceive and experience changes as it relates to technology
6. Understand and apply the process of innovation/invention
D. Study the Impact of Technology on Society
1. Identify technology's impact on society
2. Research the impacts of technology on society
3. Debate the impacts of technology on society
4. Discuss possible outcomes and tradeoffs
E. Integrate Other Disciplines with Technology Education
1. Network and develop cooperative interaction with other disciplines
2. Share, exchange, and evaluate human and physical resources with other disciplines
3. Develop and conduct multidisciplinary education activities
4. Apply knowledge and skills acquired from all disciplines
F. Develop Problem Solving Skills Related To Technology Education
1. Develop critical thinking skills related to technology education.
2. Develop creative abilities to solve problems
3. Research and develop ideas related to problem solving
4. Apply systematic approaches to solve problems
G. Utilize and Evaluate Appropriate Resources in Technology
1. Identify resources of Technology
2. Select the resources needed and determine their impacts
3. Determine the availability of resources
4. apply the resources 5. Analyze the effects of the of the resources
H. Integrate Technology and Careers by Awareness, Application, and Exploration
1. Create awareness of career opportunities
2. Develop positive work ethics
3. Assess student career interests and abilities
4. Provide direction for career opportunities
5. Reinforce basic skills(i.e., math, science, communication skills.
6. Develop employability competencies(i.e., responsibility, cooperation, flexibility, dependability, etc.)
Goals of Technology - http://wickone.myweb.uga.edu/Research/process.htm
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In the early 1900s furs were often made without a closure. That is where the fur clip comes in. If a fur simply wrapped around your shoulders you could use this clip to hold it together in the front. This is a stunning triangle shaped clip with blue and white rhinestones. There are some prongs on the back of the clip to keep it secure for wearing. You could easily wear this with a scarf or on a hat as long as you are mindful of the prongs in the back.
Measurements: 1.5 x 1.5 inches
Vintage 1930s Rhinestone Triangle Fur Clip
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Housing Rights in Northern Ireland
Housing Rights publishes housingadviceNI, a resource that aims to provide reliable independent housing advice and information to the public in Northern Ireland. The website is funded by the Northern Ireland Housing Executive.
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4th Grade
What's Happening in Fourth Grade Tech?
September - Digital Citizenship
Distant Learning
Fourth graders met the Netsmartz Kids who helped them learn how to be safe online. They learned the UYN rules (Use Your Netsmartz).
Image result for netsmartz kids"
1. I will tell a trusted adult if anything makes me feel sad, scared, or confused. 2. I will ask my trusted adult before sharing information like my name, address, and phone number. 3. I won’t meet face-to-face with anyone from the internet. 4. I will always use good netiquette and not be rude or mean online.
September - Password Protect
Fourth graders learned how to come up with a memorable phrase and how to then create a PW using that phrase. They used first letters of each word and then added a familiar number to that phrase. Familiar numbers included their homeroom number, lunch number or how many students in a class they take.
Image result for password safety"
October - Introduction to Coding
One of the skills fourth grade needs to start coding on code.org is how to determine the direction Angry Bird needs to go to capture The Pig. We used paper grids to program a block pattern. Students used directional arrows to guide their partner on how to recreate a block pattern. Next students will use block based coding to solve puzzles on code.org.
Image result for code .org angry bird"
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Computer-Based Instruction: How a Web-Based Course Facilitates English Grammar Instruction
Author: Mohammed Abdulmalik Ali
Keywords: Computer-Assisted Language Learning (CALL), Computer Aided Instruction (CAI), English Language Instruction, Teaching English Grammar, E-Learning
This study aimed to investigate the effects of Computer-Assisted Language Learning (CALL) as compared to Teacher-Driven Instruction (TDI) on the achievement of EFL undergraduates in Saudi Arabia. The instructional material dealt with modal English language verbs. This research was carried out on a sample size of 68 EFL undergraduates divided into two equal groups namely: experimental (CALL) group and control (TDI) group. The control group was taught with the regular prescribed textbook while the experimental group was given a unique Web-Based instructional material based on Hot Potatoes as a language learning software. Two tests were conducted, pre-test and post-test with both groups at two intervals. The pre-test was undertaken immediately at the end of the instructional period, and a delayed post-test three weeks after the instructional period. Findings revealed that the performance of the experimental; (CALL) group was significantly better than that of the control (TDI) group on both post-tests, however, the performance of both groups on the immediate post-test and delayed post-test had shown a considerable improvement.
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| 0.998309 |
Modelling agricultural policy: Second BESTMAP annual General Assembly
Between 2 and 4 November 2021, BESTMAP held its second annual General Assembly (GA) meeting in a virtual environment. Led by the Project Coordinator Guy Ziv and Project Manager Jodi Gunning of University of Leeds, UK, the event was attended by representatives from all of the BESTMAP-partnering organisations.
Divided in three days, the agenda of the GA meeting followed through the BESTMAP story so far, discussions and setting the plan for the end game of the project. Each of the BESTMAP teams presented their progress so far and achieved goals in terms of producing project-derived results. Also, it has been discussed how the project overcame the past and present challenges such as the current COVID-19 situation.
The BESTMAP consortium discussed how to ensure the sustainability of project outcomes and secure the legacy of BESTMAP after the end of the project. During the meeting, the attending members had the opportunity to drive ideas to a ‘parking lot’, designed to help identify the most pressuring topics. The ideas collected there, were used to form break-out groups on the last day of the GA and resolve key aspects of the BESTMAP activities.
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The narrative approach in public events, accompanied by the stimulus of artistic expression, allows the audience to discover connections in the interpretation of reality, opening up surprising new knowledge scenarios. If thoughtfully designed and based on appropriate content, these formats are excellent strategies for fully engaging a non-expert audience.
The artistic performances are carefully integrated into the narrative, delivering an unconventional voice for the scientific story. Once integrated into the format and its contents, artists, scientists, and the general public become involved in defining a common narrative and, ultimately, a new multicultural language.
Space, Time, Gravity
A journey to discover the universe and its many messengers - gravitational waves, light, cosmic rays, and neutrinos - that physicists detect in order to investigate its structure
Cosmic Tale
One of INFN’s most successful shows, a dialogue between physicists accompanied by music, literature, and animated drawings, which traces the entire evolution of the universe, leading the audience to explore the very frontiers of our knowledge
What I Don’t Know
A highly experimental show that interweaves science and street art, guiding the audience to the discovery of some of the most fascinating mysteries of contemporary research such as dark matter, dark energy, and antimatter, in a unique event in which scientific speakers and artistic performances alternate.
Discovery Machines
On the occasion of the 2016 study weeks dedicated to a large new particle accelerator, a conference show dedicated to physics, its challenges, and the extraordinary machines built by scientists to unravel the infinitely small.
Lights and Waves Rhapsody
In an alternation of words and music, a three-act narration of the most extraordinary discovery in physics of the last 100 years: the first detection of gravitational waves emitted by the collision of black holes and the fusion of neutron stars
Music Imagines the Body
A concert-story on the theme of the body and the technologies we use to describe and explore it, going as far as how the mysteries of the human brain are investigated
A Taste of the Universe
A universe-themed cooking show, an unusual plot that offers the opportunity to taste culinary interpretations inspired by physics and joke about the similarities between scientists and chefs – two professions that have to do with creativity and research, even if in different ways.
“Fisiche”, Feminine Plural
Prompted by the irony of Serena Dandini, three outstanding scientists go over some of the most fascinating ideas about the nature of our universe
Einstein Was Right
A dialogue between leading researchers on the occasion of a momentous announcement: the detection in 2016 of the first gravitational waves, which opened up extraordinary new perspectives on the universe.
Cosmic Digressions
The universe and its exploration as a meeting point between basic research and space missions, in an original dialogue accompanied by music and literature
On Art and Science
A journey in search of common languages between art and science, in a dialogue between music and literature with the art historian Philippe Daverio.
Dante and the modern science
A show that traces that thin thread that links Dante’s poetry to modern science
The JackaL and the Presidents
An irreverent dialogue about the universe and extraterrestrial life between the comic group The JackaL and the presidents of INFN and the Italian Space Agency (ASI)
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How Much Foundation Movement Is Too Much?Individuals who ask “How much foundation movement is too much” will receive a variety of answers depending on who they ask. The answer will depend on the respondent’s vested interests and opinions about the appropriate performance standards, building codes, legal precedents, and market expectations. It is not at all uncommon for two engineers looking at the same data, to reach different conclusions. As one would expect, an engineer testifying for a plaintiff will see a situation differently than an engineer testifying for a defendant. The seller of a home will tend to minimize the importance of movement while a buyer will zero in on the issue. In part, varying opinions are the result of the fact that the standards published by the Post Tensioning Institute and the American Society of Civil Engineers are not strictly numerical and do allow an engineer to exercise some subjective judgment.
Slab-on-ground foundations are built of steel-reinforced concrete. Over time, design criteria have changed to incorporate the experiences of the engineering and building communities. In general, older slabs (those from the 1950s, 1960s, and 1970s) tend to be thinner and have less reinforcing steel than newer slabs. As a result, expectations for an existing slab should take into account the age, and hence the standards that applied at the time of construction.
Foundation slabs are not perfectly rigid or perfectly stationary. Per the Post Tensioning Institute, “Slab-on-ground foundations are not designed to control soil movement. Rather, they respond to soil movement. They are not infinitely stiff or immovable, therefore they will experience out-of-plane curvature (also known as deflection or bending) and planar tilt.”
Soil movements are caused by:
1. The shrinking of expansive soils as they dry.
2. The swelling of expansive soils as they absorb water.
3. The compaction and settlement of fill dirt.
4. Soil slips on hillsides.
As slabs move, the structures that they support also move. How and of what materials a home was built affect to a significant degree how much foundation movement is acceptable. The more rigid and brittle the materials used to build a house are, the more rapidly damage will appear. Hard plaster walls are more brittle than sheetrock, brick veneer is more brittle than wood siding, ceramic tile floors are more brittle than wood floors. The age of a home is also important. Owners are typically less tolerant of movement in homes that are less than ten years old. Purchasers will often pay a premium for older historic homes fully expecting that floors will be out of level and knowing that the doors and window will not be square.
Over the last thirty years, various bodies have had a hand in determining standards for acceptable foundation movement. Some of the bodies are:
1. The American Society of Civil Engineers
2. The Post Tensioning Institute
3. The American Concrete Institute
4. The committees that prepare the various building codes
5. The marketplace
6. And the courts.
As of 2021, the two numerical standards that are most widely used are 1% for tilt and L/360 for deflection. A tilt of 1% is one where foundation slopes exceed a rise or fall of one inch in a span of 100 inches. 100 inches is eight feet four inches (8’4”). Deflection is harder to describe and calculate. Deflection measures how far the surface of a slab lies from a hypothetical surface. For those that are interested in reading the published standards, the document published by the PTI is the Guide for Performance Evaluation of Slab-on-Ground Foundations PTI DC10.8-18, and the document published by the ASCE is Guidelines for the Evaluation and Repair of Residential Foundations.
Individuals can perceive slopes but often have a hard time feeling or seeing curvature. Based on 30 years of experience by the staff at Advanced Foundation Repair, we believe that most people will not notice a slope that is less than a rise or fall of one inch over twenty feet. Most people will definitely notice a slope that exceeds a rise or fall of one inch over a distance of ten feet. For the average person, what is significant is based on what they can perceive.
Unfortunately, aside from situations where specific warranty standards apply, there are no written standards. If foundation movement is causing damage that a homeowner finds unacceptable, and foundation repairs can eliminate or reduce the problem, then repairs are appropriate when an informed homeowner decides to purchase repair services.
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Jurassic reptiles were forced to adapt to sea level rise
Ancient sea level rise disrupted the diversity of marine ecosystems during the Jurassic period. Photo by Nikolay Zverkov
Sept. 5 (UPI) — New analyses of fossil teeth have offered scientists new insights into the impacts of sea level rise on Jurassic food chains.
Sea levels rose considerably over the course of the Jurassic period, the 56 million years between the Triassic and Cretaceous periods. As revealed by the fossil record, some species thrived, while others were pushed to the margins.
To better understand the dynamics of this upheaval, scientists studied the shapes and sizes of teeth found among Jurassic strata along the coasts of England.
All of the teeth were sourced from marine sediments representing an 18-million-year period when sea levels fluctuated dramatically. The owners of the ancient teeth belonged to a diverse food chain called the Jurassic Sub-Boreal Seaway.
The analysis suggests the Jurassic Sub-Boreal Seaway resembled food chains found in the modern ocean, with apex predators like plesiosaurs and crocodiles co-existing with smaller species. The chain’s diversity was made possible by a plethora of resources and species specialization.
The diversity didn’t last, however. As the new research showed, rising sea levels reduced the numbers of shallow water species that used thin, piercing teeth to catch fish. Larger species, on the other hand, flourished.
Bigger marine reptiles, boasting stronger jaws and broader teeth, may have also benefited from shifts in ocean chemistry and temperature, researchers suggest.
Scientists shared their analysis this week in the journal Nature Ecology and Evolution.
“Studying the evolution of these animals was a real — and rare — treat, and has offered a simple yet powerful explanation for why some species declined as others prospered,” Davide Foffa, geoscientist at the University of Edinburgh, said in a news release.
The findings could help scientists better anticipate how rising sea levels will affect food chains and ecosystems in the modern ocean.
“Teeth are humble fossils, but they reveal a grand story of how sea reptiles evolved over millions of years as their environments changed,” Steve Brusatte said. “Changes in these Jurassic reptiles parallel changes in dolphins and other marine species that are occurring today as sea-levels rise, which speaks to how important fossils are for understanding our modern world.”
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Her skin but a carpet for others to stompHer heart but a slinky, a toy or a topHer soul is not seenHer cries go unheardHer feelings are said, but they don’t speak a word.Her skin it now boilsHer heart simply poundsHer soul it is shatteredHer cries are pronounced.Her feelings are hurt as she crumbles insideHerContinue reading “FINDING HERSELF”
Winding Road
Eclipsed by the full-grown trees, highlighted by the sunset shades in the sky, stood the start of her past. Layered bricks that formed her character; the creator of the creature that carries the baggage. The swing still shrieks in the shadows, as the weeping willow dances in the neighbouring meadow. Her footsteps creep to theContinue reading “Winding Road”
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IELTS Vocabulary – Academic Word List (94)
Revise’ comes from a combination of two latin words: ‘re’ meaning ‘again’ and ‘visere’ meaning ‘to see.’ The common usage today means ‘to look at something again.’
Students revise their notes before an exam. Lecturers revise their course content every year. Books are published in revised editions.
random event, randomly assigned
reinforce the numbers, reinforce the strength
restoration services, restorative dentistry
revision sheet, revision week, revision of
scheduled event, schedule for, schedule of, unscheduled stop
Academic Word List 94
Vocabulary for IELTS – Academic Word List 94
1. The plane was several hours late because it made an ______________ stop in Bolivia due to engine trouble. (schedule, revise)
2. Albert ______________ his study plans after he realized he had done so well in the exams and could enter medicine with his marks. (revise, schedule)
3. Her dental bill was expensive because she had to have some _______________ work done. (restore, random)
4. Students were _______________ assigned to groups. (random, reinforce)
5. The staff at the Help Centre were busy all day with calls for assistance after the fires. They had to call for ______________ to take over after they had worked 12 hours straight. (restore, reinforce)
Answers (in the wrong order)
5. reinforcement/reinforcements 3. restorative 2. revised 1. unscheduled 4. randomly
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Pre-Writing Activities
One challenge for many writers, be they beginners or seasoned professionals, is how to get started. Reflect on your own experiences with writing – have you ever had trouble organizing your ideas? Many writers find prewriting activities useful. Prewriting is important because writing is a process that helps you learn, not just an exercise in which you set down on paper the things you already know. Prewriting can help you figure out what you know, what you still need to know, and how various pieces of your argument fit together. Read this lecture introducing two common prewriting techniques and complete the practice exercises.
Pre-Writing Activities
Many students say that the hardest thing about writing is getting started. They look at a blank piece of paper or a blank computer screen and cannot think of a thing to say. Pre-writing activities are a great way to come up with ideas to write about. They can help you dig deeper into the topics, think about an idea in a new way, and organize your thoughts so that you can create a well‐written paragraph.
There are many different pre-writing activities you can use, and no one method is better than another. Use whichever method you prefer. Try each one out until you find a method that works well for you. Here we will discuss just two prewriting strategies you can use: freewriting and idea wheels.
A. Freewriting is a method in which you write out everything you know about the topic, even things that might seem unimportant. The key to freewriting is to write without stopping. Keep writing even when you think you are stuck and don't have anything else to say about the topic. It is okay to let your mind wander to ideas that are only somewhat related to the topic. This can help lead you to ideas you had forgotten, or help you to see the relationships between ideas.
When practicing the freewriting technique, first write down all of the facts you know about the topic. Then ask, how do I feel about this topic? Where have I heard about it before? What would my friends and relatives think about this topic? It is helpful to create a list of questions you have about the topic. The answers to these questions may provide more material you can use in your paragraph.
Practice I: Freewriting
Write without stopping for five minutes on one of the following topics:
1. Dogs make great pets.
2. Children should be given chores to do.
3. Explain which holiday is your favorite.
When you are done, look at what you have written. Did you write more or less than you expected? Was it hard writing for five full minutes? Do you have enough information to turn into a full paragraph?
B. An Idea Wheel, sometimes called clustering, is another pre-writing strategy. It is like freewriting, except that instead of writing out a list of ideas, you draw them into a wheel to help you see the connections between the ideas. Imagine the topic is at the center of the wheel. In a circle around it are blank bubbles to write ideas in. Each bubble has a line connecting it to the topic, making the diagram look like a wheel with spokes. For example, if the topic is "elephants", the wheel would start with the topic in the center:
Then, spokes are added to connect the center with surrounding bubbles for new ideas:
The next step is to fill in the smaller bubbles with things you know about elephants. For example, you could write that they are mammals, are very large, live in herds, and are vegetarians. Other bubbles might contain information about where they live or how humans interact with them.
You can see how some of these ideas overlap. The bubbles about where they live in the wild and where they live in captivity are closely related. You could draw a line between those two bubbles to show the connection of those two ideas. You can also see that there is way more information here than you could use in a single paragraph! There is enough here for several paragraphs or even a short essay. If you only have to write one paragraph, then you could pick just one bubble and focus on that. Instead of elephants in general, your main idea sentence could be "Humans encounter elephants in captivity". Each of the items in that bubble can now become a major or minor supporting sentence.
Practice II: Idea Wheel
On a separate piece of paper, construct an idea wheel for one of the two topics you did not use for Practice I. Spend between 5 and 10 minutes on your wheel, making sure that the topic is the center. When you are done, look back at what you wrote. Did you write more or less than you expected? Was it difficult to work for the full five minutes? Do you have enough information to edit that into a paragraph?
Practice III: Moving from Pre-Writing to Writing
Now we are going to take a completed pre-writing exercise and turn it into a paragraph. You are going to fill in the chart below to help you construct your paragraph, which should include a main idea and major and minor details. You may use either of the two pre-writing exercises that you have already completed. You do not need to write out full sentences in the chart, but be sure to include enough information so that it is clear how you are going to develop the chart into a paragraph. Once the chart is filled out, create a paragraph by rewriting each piece of information as a complete sentence. This will give you a finished paragraph of five to seven sentences.
NOTE: Do not just write "I will give an example". You need to provide a few words about what that example will be.
• Unacceptable: "I will give an example of why spanking is bad"
• Acceptable: "Young children don't know why they are being spanked"
Main Idea:
Support #1 (indicate if this is a major or minor detail):
Support #2 (indicate if this is a major or minor detail):
Support #3 (indicate if this is a major or minor detail):
Support #4 (indicate if this is a major or minor detail):
Support #5 (indicate if this is a major or minor detail):
Support #6 (indicate if this is a major or minor detail):
Source: Washington State Board for Community and Technical Colleges,
Last modified: Friday, January 8, 2021, 12:42 PM
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To form a standing wave, two coherent waves must travel in opposite direction. But is it it necessary for them to have the same amplitude and no phase angle difference?
• 3
$\begingroup$ You can check it yourself. Just write down two waves with different amplitude/phase and add them $\endgroup$ Apr 1 '16 at 18:37
• $\begingroup$ One can plot is it as well, www.desmos.com $\endgroup$
– Kashmiri
Jan 30 '21 at 17:11
The fact that they are coherent means they have a constant phase difference. And from a constant phase difference it follows that their interference pattern will be stationary.
However, unless they have the same amplitude, the nodes of the "standing wave" will not be completely zero. Instead, you can think of the larger one as the sum of two waves. If we call the wave traveling to the right A, and the one traveling to the left B, then we can write $A=A_1 + A_2$ where $A_1$ has the same amplitude as $B$. Then $A_1$ and $B$ will form a standing wave pattern, and superposed on that pattern is the wave $A_2$. When $A=A_1$, $A_2=0$ and you have a perfect standing wave.
• $\begingroup$ How can I help clear that confusion for you? $\endgroup$
– Floris
Apr 2 '16 at 12:48
• $\begingroup$ First of all thank you a lot, but i still i have some confusion:-a) Suppose they are not coherent and they have a phase difference, then will a standing wave be formed. B) You mentioned that they won't form perfect standing waves if their amplitudes are not same , so basically standing waves is possible even if their amplitudes are not same.Again, thank you a lot. $\endgroup$ Apr 2 '16 at 12:57
• $\begingroup$ Well if waves travel in opposite directions their phase difference depends on the point where you measure it. As long as they have the same frequency there will be a stationary point where their phase difference is zero $\endgroup$
– Floris
Apr 2 '16 at 13:01
• $\begingroup$ As for the second point - if they are not of the same amplitude they will not form a "perfect" standing wave (with a zero node) but a "partial" one. In RF engineering partial reflection (of signal into an antenna for example) is very important and it is measured by looking at the "standing wave ratio" - the ratio of amplitudes at the antinode vs the node. This is one when there is no reflection and infinite for perfect reflection (equal amplitude in both directions) $\endgroup$
– Floris
Apr 2 '16 at 13:05
• $\begingroup$ So basically, to form a standing wave , two waves must have the same frequency and they must be travelling in opposite direction? $\endgroup$ Apr 2 '16 at 13:06
Your Answer
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Much of our understanding of Earth’s climate history is based on interpretation of geochemical variability within the CaCO3 tests and skeletons of marine organisms. Geochemical climate proxies are typically cast in terms of equilibrium thermodynamics, but there are important differences between the compositions of carbonates accreted by living organisms and predictions for carbonate minerals in equilibrium with seawater. These differences are commonly attributed to ‘vital effects’ thought to be caused by biological modification of the calcifying environment and of crystalgrowth kinetics. If this were true, then biologically modified crystal chemistry may be unpredictable or challenging to model mathematically,...
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Paperback - £55.00
Publication date:
05 June 2003
Length of book:
218 pages
ISBN-13: 9780761826002
China Reconstructs includes ten articles that investigate the reconstruction of modern China and provide different dimensions to the vibrant and multifaceted history of the country. The book discusses how prominent individuals, political parties, and ordinary people alike looked for ways to "reconstruct China" in a period of great political upheavals.
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Reciprocal sum of vectors
This post is a slight modification of section 2.0 “The Parallel Sum of Vectors” from W. N. Anderson & G. E. Trapp (1987) “The harmonic and geometric mean of vectors”, Linear and Multilinear Algebra, 22:2, 199-210.
We will consider vectors in a real N dimensional inner product space, although some of the results given herein apply equally well to the complex case.
We use a, b, . . . to represent vectors. The inner product of a and b is written ⟨a, b⟩ and the norm of a vector a is given by ||a|| = ⟨a, a1/2.
Given vectors a and b, their arithmetic mean is defined by (a + b)/2. To define the harmonic mean we require an involution which is described next.
If a is a non-zero vector, define a′ (to represent the reciprocal of a) by
a′ = a/||a||² = (1/||a||)(a/||a||) = â/||a||.
First notice that for a non-zero scalar k,
(ka) = ka / ||ka||² = a / k||a||² = a′/k.
Next we see that a″ = (a′)′ = (a/||a||²) = ||a||²a′ = a and therefore is an involution. A direct computation shows that ||a||−1 = ||a′||. The following Lemma is used below.
LEMMA 1 Given vectors a and b if a + b0, then a′ + b′ ≠ 0.
Proof Suppose a′ + b′ = 0. Then a/||a||² + b/||b||² = 0. Since a′ = −b′, we have ||a′|| = ||b′|| or ||a|| = ||b||, which implies a + b = 0. ¤
The involution considered above may be viewed as the “inverse” of a vector, and since Anderson and Duffin used the inverse of a matrix to define the parallel [reciprocal] sum of matrices, we define the reciprocal [parallel] sum of vectors a and b as follows: a reciprocally added to b, denoted by ab, is given by
ab = (a′ + b′).
From Lemma 1, we see that the definition is appropriate when a + b0. In the case that a = 0 or b = 0, we define ab = 0.
The following theorem summarizes some basic properties of the vector operation parallel addition; the proof consists of direct calculations and is omitted.
THEOREM 2 Given vectors a and b with a + b0, then
(i) ab = ba, [commutative]
(ii) aa = a/2, [non-reflexive]
(iii) (ka) ⊞ (kb) = k(ab). [distributive]
A deeper result is that the reciprocal sum of vectors is an associative operation.
THEOREM 3 Given vectors a, b, and c, if a ⊞ (bc) and (ab) ⊞ c are both defined, then they are equal. And they both equal (a′ + b′ + c′).
THEOREM 5 Given vectors a and b with a + b0, the reciprocal sum ab may be written as follows:
ab = (a||b||² + b||a||²) / (||a + b||²).
… The triangle inequality implies that
||ab|| ≥ ||a|| ||b|| / (||a|| + ||b||),
and since km = km/(k + m) for scalars k and m, we have shown the following result.
COROLLARY 6 ||ab|| = ||a|| ||b|| / ||a + b||, and ||ab|| ≥ ||a|| ⊞ ||b||.
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Rules Of Composition – Weight Balance
Rules Of Composition - Weight Balance
Rules Of Composition – Weight Balance
As keen photographers, we are always looking for the best compositions and balance in our photography. These are important photography rules for composing your images well and creating something visually stunning.
Weight or balance are the terms given to compositional elements within your scene, and the visual impact they have. Some objects will have a stronger presence compared to other elements in the frame. As a photographer, it is down to you to include them or cut them out. This will depend on the effect they have on your overall composition.
There are many ways we can do this, both visually and conceptually. Light and dark areas are simple yet effective ways to create a balance. Just like other areas of photography, breaking the rule can also work well. But learn them first, so you can bend the ideas successfully.
Symmetrical Weight Balance
A symmetrical weight balance is also known as a ‘formal balance’. This is the most obvious way to compose your images. Unlike the rule of thirds, you arrange your most important element directly in the centre of the frame.
Most images with a symmetrical weight balance will be in the horizontal format. This just makes it is easier to show the symmetrical elements. They don’t need to be exact and perfect. They just need a similar feel in weight and presence, allowing them to appear balanced.
Asymmetrical Weight Balance
Asymmetrical weight or balance is often referred to as ‘informal balance’. This can be tricky to achieve since you immediately want to put things right in the middle. By following the ‘rules of thirds’, you will find it is easier to compose your image in this manner. It can give a harmonious feel to the image.
This composition has the capacity to draw the viewer in for longer. This is because it often feels more interesting than a subject smack bang in the middle of the frame. If you feel that the scene is unbalanced, place one or more secondary subjects in the remaining space. The image above could benefit from a bird or plane in the negative space.
Size Weight Balance
You will find that size is one of the best ways to show a balanced composition. Size for us humans is relative. Bigger things tend to be closer to us, and smaller things are often farther away. Manipulating this idea can help you to create some very interesting images.
It goes without saying, bigger objects hold more weight than smaller items. Because of this, they will attract the viewer’s attention more. It would be beneficial to you and your photography to make your main subject the biggest object. You can do this with your perspective and cutting down the distance between you and your main subject.
Colour And Saturation Weight Balance
Bold bright colours stand out more than saturated ones. A burst of colour against a plain, monotone background will grab the viewer’s attention more. This allows you to set up the image, forcing the attention on one or two objects.
Colours can complement each other. So having either comparative colours or contrasting colours can help to make an image more interesting. Having similar colours next to each other can help make a fluid transition from one item to another. This will keep the viewer engaged for longer.
Tone And Contrast Weight Balance
Tone and contrast play a huge part in the photographic process. Darker objects hold more weight than lighter ones, so you can use this for the benefit of your photography. Shadows and dark objects can also be distracting from the main theme. If so, just reframe and shoot again if necessary.
Tone and contrast are especially powerful in black and white photography, as the colour is not an issue. Areas of high contrast draw your eye. Try and capture dark objects on a light background or vice versa. It would be better to have some detail in the negative spaces to help engage the viewer.
Texture Weight Balance
Patterns and textures are interesting to humans as we seek them out and focus on them. They are a visual phenomenon, and become strong, natural points of interest. Strong textures can help support an image by balancing an off-centre subject. Yet, textured backgrounds can detract the viewer’s attention from the main focal point.
This is a compositional tool that can help in other compositions. For example, the below image denotes a conceptual weight balance, as the idea in the image could be seen as nature vs. man-made. The shape and form of both the foreground and background play off each other.
Focal Weight Balance
The focus is just one way we can force and push the viewer’s attention to an area or subject within our frame. Items in focus will hold more visual weight than those areas out of focus. The depth of field or differential focus is a powerful tool in removing unwanted areas of a scene.
The best thing is that the out of focus areas still give us a texture that is interesting. They may even be repetitions of what is in focus, and it allows the viewer’s eyes to move on once they found the focused object.
Light And Dark Weight Balance
Light and dark are very powerful tools in photography. Every image is a mixture of lights and darks, either whites and blacks, or highlights and shadows. A darker image can help to create a moody atmosphere, whereas a lighter one has the potential to have a softer, more innocent feel.
The darker areas draw the viewer’s eyes to the lighter ones. You can use this technique for natural framing, for example. You can even mix it with a more conceptual idea, such as light and dark meaning good and evil.
People/Animals Weight Balance
Including people or animals can work very well in balancing a composition. They are very noticeable subjects for us. We know how big a human or an elephant should be. So when they are placed in the image, it gives a sense of scale and helps our interest stay in the frame.
They also give us a sense of place and time, due to their mise en scène. You can tell that the below image is a humorous one, taken by a street photographer, possibly in Paris in the 1940s, for example. Photographing people has the potential to create something interesting. By using the background, you can help the foreground more attractive.
Lead Room Weight Balance
‘Lead room’ or ‘nose room’ is a concept in photography where you allow space in front of the photographed subject’s gaze. This allows the viewer to see that the person is looking somewhere, and not just at the end of the frame.
We expect to see a little in front of the person, otherwise, it can cause tension, which doesn’t make for a well composed or balanced image. If you feel that the image is unbalanced, include the object the person is looking towards or at.
Conceptual Weight Balance
A conceptual idea to compose from can be very powerful. Juxtapositioning these concepts can create a story or interest through the contrast of their ideas. For example, this below image shows the seperation of the rich and poor neighbourhoods. We can see the size of their houses, how much space they have and even the differences in the landscape.
Similarly, the conceptual ideas behind composition can go from obvious to thought-provoking. In the image below, we see some steps, and a boy at the bottom, looking at the first step. This represents a challenge that needs to be overcome with purpose, effort and courage. They work well as the two contrasting ideas balance off one another.
originally posted on by Craig Hull
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Social Cooling
I coined the term “social cooling” to help a wider audience understand the long-term negative side-effects of living in a data driven society. The issue is that digital systems greatly amplify social pressure, which could lead to more conformity.
In the media
Reddit, MetafilterThe Guardian, Observer. A video item was made for ABC News.
In 2020 it suddenly became the 37th most discussed post on Hackernews with over 1000 comments. And a little later it caused another big discussion.
Talks and workshops
I have given countless talks on the subject. These presentations have typically energized audiences, with many questions and heataed debates afterwards. After a moment of shock that things have already gotten this bad, people are always very positive about learning more about this issue, and how we can engage it.
An video of my talk on Social Cooling for the 34C3 conference can be found here.
A related project is
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MSc thesis project proposal
Heart rate extraction from speech signals
The heart rate signal is a crucial physiological marker often used to identify multiple conditions and diseases such as chronic stress, depression, heart failure, and arrhythmias. Apart from its high diagnostic power, the heart rate signal is relatively easy to record using smart watches or electrode-based systems that measure the electrocardiogram (ECG). However, one still relies on the good use of such systems. For instance, the electrodes must be correctly attached or the watch needs to be completely fixed to the wrist so that movement artefacts do not influence the recordings. As a consequence, these systems are often limited to either subjects who willing use them (e.g. as gadgets) or who have sufficient motoric and cognitive skills to use them regularly. With this in mind, the extraction of heart rate information from signals like speech is of paramount importance. Reasons for this include the fact that speech is an easier to record signal, which can be acquired under (often) general conditions.
In this project, students will first record speech and ECG signals simultaneously using available hardware. The speech signals will need to be processed and different algorithms will need to be designed and tested in order to extract heart rate information from them. This information will be validated against the heart rate signal extracted from the ECG signals. Different conditions can be tested, for instance, when subjects only produce certain sounds, or when they are in different rooms (e.g., dead room vs. any classroom).
• Matlab
• Courses on Signals & Systems and on Machine learning
dr. Carolina Varon
Circuits and Systems Group
Department of Microelectronics
Last modified: 2020-03-13
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Planets of Other Stars III
Getting There Quickly
When Einstein linked space, time and gravity the way to Warp space-time was implicit in his equations. Very quickly the first "wormhole" solution was found to his equations, and the Einstein-Rosen Bridge was born.
But researchers in the 1950s and 60s quickly showed that the wormhole solutions were unstable, collapsing quicker than even light. At roughly the same time new solutions were found and the "Black Hole" was born. Some "Black Hole" solutions seemed to form stable wormholes within their mysterious "event horizons" - a ring of infinitely dense mass would rip a flaw into space-time, linking Universes or far-flung parts of one universe.
By the late 1970s such Kerr-Newman Black Hole wormholes were shown to be unstable. Accelerated mightily by the ring singularity surrounding the wormhole any mass falling in would send out space-time distortions, gravity waves, that would close the wormhole before it could be accessed. Once again another bridge across space-time was closed.
However several general relativists, led by Kip Thorne and inspired by Carl Sagan, sought out new wormhole solutions in the 1980s that could be traversed by masses, even masses as frail as humans. By threading the throats of their wormholes with "exotic matter" they found that links across space - and maybe time - could be maintained. A diverse bestiary of wormhole solutions were discovered - cubes, pyramids, discs and so forth. Some claimed that these could be used to build time machines, while others claimed that Nature abhors time travel and actively destroyed any path that might thread back on itself through time.
The question most people ask now that wormholes are respectable objects of research is how and when... which presently can't be answered. The energies required are daunting, but we don't yet know everything there is to know about gravity and space-time to truly say for sure. But before I boldly go there let's explore another issue... nullifying the effects of acceleration, which is related to the above in surprising ways.
What is Inertia?
Matter resists motion. Or rather, it resists any changes in its motion, any accelerations. To change an object's motion takes force and the expenditure of energy over the distance that the change in motion occurs. What is the source of this resistance? Newton and Galileo accepted inertia as an unexplained fact, but the development of electromagnetic and quantum theory has perhaps led to a deeper insight. What if inertia is caused by space itself resisting the change in the fields of the mass involved? Every particle of normal matter has fields other than gravity - electromagnetic and nuclear forces. Space itself is filled with virtual fields thanks to the
Heisenberg Uncertainty relations - there is no such thing as "empty space" in a quantum field. So as a particle is accelerated its fields interact with the virtual fields of space to create a reaction force, inertia. This theory of inertia has been developed extensively by several physicists, notably Bernard Haisch. Could inertia then be controlled? As yet no one knows how, but let's look at the forces that hold the Universe together.
Forces and Fields
table 1 - forces of Nature
Force Range (metres) Force Particle Relative Strength Mass (GeV)
Colour/Strong Nuclear 10^-19 gluon 40 ~0
Weak Nuclear 10^-14 W+, W-, Z 10^-3 ~86, 97
Electromagnetic Infinite photon 1 ~0
Gravity Infinite graviton 10^-39 ~0
Higgs (field) Universal Higgs boson n/a ?170 - ?220
A major puzzle in physics is the relationship of the various forces and fields in Nature. Currently four forces are known, with a possible "mass-creating" field associated with them (see table 1.) In the 1920s Klein unified electromagnetism and gravity by hypothesising a fourth spatial dimension through which particles vibrated - this created the known properties of the electromagnetic field. This fourth dimension was incredibly small - far smaller than an atom - but by moving in that dimension particles created the electromagnetic field. Because the other forces were unknown in the 1920s physics soon superseded Klein's theory. But in the 1970s and 1980s interest was revived in the ability of tiny other dimensions to unify the forces of nature. Until this time fundamental particles had been described in quantum mechanics as POINT particles, since physically extended particle models could not reproduce known physics. However such a model collapses into? mathematical absurdity as the scale is reduced to the PLANCK LENGTH - the scale at which space-time itself is unstable due to quantum fluctuations.
A possible solution was found in SUPERSTRING THEORY which proposes that fundamental particles aren't points, but are in fact tiny one-dimensional "strings". The "Super" part of "Superstring" refers to the mathematical structure used to describe the forces which the strings generate as they vibrate in the curled-up higher spatial dimensions. To reproduce known particles and forces the number of dimensions is constrained to ten - 3 large (maybe infinite), 1 time (maybe infinite), and 7 curled up. Because the higher dimensions are curled up in a specific way, forming a Calabi-Yau manifold - the vibrations of the strings that compose ultimate particles are constrained to specific "harmonies" of vibration. In a sense particles are the "notes" that can be played in space-time. But in recent years the size of the curled up dimensions have been questioned.
At first physicists assumed the tiny dimensions were curled up at the Planck Scale - about 10^-35 metres - and so superstring energies were at the fantasic energy level of 10^19 GeV - ten million trillion times the mass of a proton (proton mass ~ 1 GeV, a convenient measure of energy, since mass and energy are equivalent.) This energy scale is far beyond the 1,000 or so GeV that particle accelerators can energise particles to, and this led many to think superstrings would be forever beyond direct testing experimentally. However some began studying mathematically what would happen if the dimensions were of different sizes. To their surprise the dimensions for the weak, electromagnetic and colour forces could be MUCH larger - at 10^-19 metres, which reduces the energy scale of their Unification from an incredible 10^16 GeV, to within about 10,000 GeV. This is just beyond current accelerator energies - we could be on the verge of unifying three of the Universe's forces. But what about gravity?
At first it seemed that gravity could be generated by dimensions as large as a millimetre, and still not be noticed by current experimental systems!
However the interiors of stars can be explored indirectly by their self-destruction in supernova explosions. These occur when a very massive star fuses its core into iron. Stars exist in a dynamic balance between compression by gravity and the energy of fusing particles in their cores. An iron core is a catastrophe since iron takes more energy to create than it releases in nuclear fusion. When enough iron is produced the core is forced by the weight of the outer layers of the star into catastrophic collapse. The outer core collapses onto the inner core which sends a shock-wave outwards through the rest of the star. Immense amounts of gravitational energy is converted into fused particles heavier than iron, and a multitude of neutrinos - by-products of weak-force nuclear reactions involved in creating elements and neutrons. The explosion in 1987 of a nearby supernova allowed physicists to refine their models of supernova explosions, and by this severely constrain the kinds of graviton<->particle interactions that could draw-off energy from neutrino production and creation of heavy elements. Thus, researchers conclude, the gravitational vibrations of strings occur on a scale much smaller than a millimetre, though no one yet knows how small.
So what does this mean for interstellar travel?
Unlimited Power?
Earlier I asked: Are there any power sources better than fusion energy?
Perhaps GUT energy - GUT stands for Grand Unification Theory, which describes the hypothetical unification of three of the natural forces.If we could push some seed-matter to GUT conditions we might be able to tap into the raw power of Creation itself, restarting the Big Bang in minature. In its very earliest phases the Universe is believed to have undergone a time of exponential expansion powered by matter-energy created by a GUT "phase transition". If the GUT energy scale is about 10^16 GeV, then it might forever remain beyond our abilities. But if the unification scale is much larger - say 10^-19 metres - then its achievement might be just around the corner.
With GUT energy, propellant - any old matter will do - could be pushed very close to lightspeed without the need for immense amounts of fuel for generating power for an accelerator system. Imagine if propellant could be accelerated to 0.995 c, then its relativistic "mass" is ten times its rest mass, so it is effectively ten times more propellant...
Imagine starships with GUT reactors - they launch with partially filled tanks in the Inner Solar System, then fly out to the Oort Cloud and latch onto a "small" comet. With the immense power of a GUT reactor they can then accelerate up to as close to lightspeed as desired. But is there anyway that we might accelerate to such speeds faster without suffering the effects of high acceleration?
Space Drives?
A "space drive" is an old science fiction idea which uses the analogy of free-fall to describe a propulsion system with high acceleration but without crushing "gee forces". Inertia hasn't been neutralised, just by-passed or "damped" [aka Star Trek...] When an object falls freely no "gee forces" are felt even at immense acceleration - with one caveat. When the gravitational source is large the rate at which gravity changes as you fall is minimal. But neutron stars and black holes have very "steep" gravitational fields that change rapidly. In such a situation the change in acceleration is felt as tidal forces, and these can be intense near very dense objects. Otherwise no forces are perceived while falling.
Hence a "space drive" could be described as "falling free" towards a "travelling" gravitational source. Or it could also involve using space itself as your propulsion system, so all the particles within the ship are accelerated evenly? How could this be achieved? Yoshiro Minami speculates that a very intense electromagnetic field could "pinch" space, and on release accelerate a space vehicle. However the magnetic fields involved are incredibly intense - 90 billion Tesla. A Tesla field creates a one newton force between magnetic fields separated by a metre - the Earth's field is much weaker, and not even neutron stars achieve the field intensity Minami's drive requires.
Minami suggests that other fields in space could be manipulated - perhaps the Higgs field, which creates the mass that each particle has. Hence by "pinching space" via the Higgs field very high accelerations without gee forces could be produced. With GUT Unification perhaps occurring at lower energies than expected then perhaps manipulating the Higgs field won't be as difficult also?
Faster than Light?
If space can be "pinched" then can it be "warped"? Potentially this is the ultimate way to the stars using physics far beyond what we know about in any detail. In 1994 Miguel Alcubierre published a study of a "warped" space-time structure that travels faster-than-light, and yet obeys Einstein's "laws". How is this possible?
Einstein's theories of Relativity, Special and General, are based on two basic premises - that all physical systems are equivalent, and that all observe the speed of light to be the same. How does this work out in practice? Simplistically, physical systems - like spaceships and human bodies - are chiefly based on the electromagnetic forces of their constituent particles. The speed of disturbances in the electromagnetic field, such as pulses of light, are not based on any other factor than a physical ratio between the magnetic and electric components of the field. From our own experiences these don't change whether we are moving or not, falling freely or standing on the Earth - or else life would be very different. Hence what relativity means is that at a local level the fundamental relationships between particles, their forces, don't change regardless of what they are doing collectively. Since the forces are the "framework" that make up the particles this makes sense. Travelling "faster-than-light" would require a NEW framework...
But what applies to particles does not apply to space-time. Wrap a sphere of "normal space-time" containing a ship in a bubble of distorted space-time, then faster-than-light can be achieved. The "warp bubble" requires some unusual effects - in the direction of travel space must be collapsing into the bubble, and it must be expanding behind the bubble. This is somewhat like what space-time was doing in the early stages of the Big Bang, which might mean that it is achieveable by GUT technology. Or maybe not?
Several researchers have estimated that to create a two hundred metre wide warp-bubble would take about 6.2 x 10^62 kilograms of negative energy times the c-factor it is travelling at - a figure that dwarfs the known Universe by about a factor of 10 billion! And it's negative energy, which no one knows how to create in any quantity for any great length of time. Alternatively the bubble could be shrunk - the energy needed is related to the area of the bubble - to microscopic size. It would then be a pinched "throat" to a mini-Universe containing a ship, but no one yet knows if this is possible, and physically reasonable sizes for the bubble [~10^-19 metres] would still take twice the mass of Jupiter in negative energy.
Chris van den Broeck, who developed the micro-sized warp field suggests there are still great difficulties with his system, but for sub-light the warp has real potential - I suspect it is another possible space-drive, since within the bubble no acceleration effects are experienced. A starship could accelerate to arbitarily close to light-speed within an arbitary time.
Planets of Other Stars I
Planets of Other Stars II: Getting There
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1. Capable of being (or designed to be) injected.
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