Text С: «METALWORKING AND METAL PROPETIES»



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Text С: «METALWORKING AND METAL PROPETIES»



An important feature of hot working is that it pro­videsthe improvementof mechanical propertiesof met­als. Hot-working (hot-rolling or hot-forging) eliminates porosity, directionality,and segregationthat are usu­ally present in metals. Hot-worked products have better ductility and toughness than the unworked casting. Dur­ing the forging of a bar, the grains of the metal become greatly elongatedin the direction of flow. As a result, the toughness of the metal is greatly improved in this direction and weakenedin directions transverseto the flow.Good forging makes the flow lines in the finishedpart oriented so as to lie in the direction of maximum stress when the part is placed in service.

The ability of a metal to resist thinningand fractureduring cold-working operations plays an important role in alloy selection. In operations that involve stretching, the best alloys are those which grow stronger with strain (are strain hardening)— for example, the copper-zinc alloy, brass,used for cartridges and the aluminum-mag­nesium alloys in beverage cans,which exhibitgreater strain hardening.

Fracture of the workpiece during forming can result from inner flawsin the metal. These flaws often con­sist of nonmetallic inclusionssuch as oxides or sulf ides that are trappedin the metal during refining. Such in­clusionscan be avoidedby proper manufacturing pro­cedures.

The ability of different metals to undergostrain var­ies. The change of the shape after one forming operation is often limited by the tensile ductilityof the metal. Met­als such as copper and aluminum are more ductile in such operations than other metals.

Vocabulary

feature— черта, особенность

to provide— обеспечивать

improvement — улучшение

property— свойство

eliminate— ликвидировать, исключать

porosity— пористость

directional— направленный

to segregate— разделять

casting— отливка

elongated— удлиненный

to weaken— ослабевать, ослаблять

transverse— поперечный

flow— течение, поток

finished— отделанный

thinning — утончение

fracture— разрушение

strain hardening — деформационное упрочнение

brass— латунь

beverage— напиток

can— консервная банка

to exhibit— проявлять

inner— внутренний

flaws— недостатки, дефекты кристалличес­кой решетки

inclusion— включение

trapped— зд. Заключенный

refining— очищать, очистка

to avoid— избегать

to undergo— подвергаться

tensile ductility — пластичность при растяжении

General understanding:

1. What process improves the mechanical properties of metals?

2. What new properties have hot-worked products?

3. How does the forging of a bar affect the grains of the metal? What is the result of this?

4. How are the flow lines in the forged metal oriented and how does it affect the strength of the forged part?

5. What are the best strain-hardening alloys? Where can we use them?

6. What are the inner flaws in the metal?

7. Can a metal fracture because of the inner flaw?

8. What limits the change of the shape during forming operations?

Exercise 2.5. Find the following in the text:

1. важная особенность горячей обработки

2. улучшение механических свойств металла

3. необработанная отливка

4. направление максимального напряжения

5. способность сопротивляться утончению и разру­шению

6. проявлять большее деформационное упрочнение

7. разрушение детали при штамповке

8. внутренние дефекты в металле

9. неметаллические включения

10.способность металлов подвергаться деформации

11.ограничивается пластичностью металла при ра­стяжении

Exercise 2.6. Translate into English:

1. Горячая обработка металла улучшает его меха­нические свойства и устраняет пористость и внутрен­ние дефекты.

2. Удлинение зерен в направлении текучести приковке значительно улучшает прочность металла в этом направлении и уменьшает его прочность в поперечном.

3. Хорошая проковка ориентирует линии текучес­ти в направлении максимального напряжения.

4. Деформационное упрочнение металла при холод­ной обработке очень важно для получения металлов с улучшенными свойствами.

5. Внутренние дефекты металла — это неметалли­ческие включения типа окислов или сульфидов.

6. Изменение формы при штамповании металли­ческих деталей ограничивается пластичностью метал­ла при растяжении.

FAMOUS SCIENTISTS

Mikhail Vasilyevich Lomonosov was a famous Rus­sian writer, chemist, and astronomer who made a lot in literature and science.

Lomonosov was born on November 19, 1711, in Denisovka (now Lomonosov), near Archangelsk, and studied at the University of the Imperial Academy of Sciences in St. Petersburg. After studying in Germany at the Universities of Marburg and Freiberg, Lomonosov returned to St. Petersburg in 1745 to teach chemistry and built a teaching and research laboratory there four years later.

Lomonosov is often called the founder of Russian sci­ence. He was an innovator in many fields. As a scientist he rejected the phlogiston theory of matter commonly accepted at the time and he anticipated the kinetic theory of gases. He regarded heat as a form of motion, suggested the wave theory of light, and stated the idea of conserva­tion of matter. Lomonosov was the first person to record the freezing of mercury and to observe the atmosphere of Venus during a solar transit.

Interested in the development of Russian education, Lomonosov helped to found Moscow State University in 1755, and in the same year wrote a grammar that re­formed the Russian literary language by combining Old Church Slavonic with modern language. In 1760 he pub­lished the first history of Russia. He also revived the art of Russian mosaic and built a mosaic and coloured-glass factory. Most of his achievements, however, were un­known outside Russia. He died in St. Petersburg on April 15, 1765.


UNIT3

 



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