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Text C: «metalworking and metal propeties»
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An important feature of hot working is that it provides the improvement of mechanical properties of metals. Hot-working (hot-rolling or hot-forging) eliminates porosity, directionality, and segregation that 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 elongated in the direction of flow. As a result, the toughness of the metal is greatly improved in this direction and weakened in directions transverse to the flow. Good forging makes the flow lines in the finished part 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 thinning and fracture during 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 exhibit greater strain hardening.
Fracture of the workpiece during forming can result from inner flaws in the metal. These flaws often consist of nonmetallic inclusions such as oxides or sulfides that are trapped in the metal during refining. Such inclusions can be avoided by proper manufacturing procedures.
The ability of different metals to undergo strain varies. The change of the shape after one forming operation is often limited by the tensile ductility of 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?
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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 при ковке 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.
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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 colored-glass factory. Most of his achievements, however, were unknown outside Russia.
UNIT3
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