Text с: «methods of steel heat treatment»

Quenching is a heat treatment when metal at a high temperature is rapidly cooled by immersion in water or oil. Quenching makes steel harder and more brittle, with small grains structure.

Tempering is a heat treatment applied to steel and certain alloys. Hardened steel after quenching from a high temperature is too hard and brittle for many appli­cations and is also brittle. Tempering, that is re-heating to an intermediate temperature and cooling slowly, re­duces this hardness and brittleness. Tempering tempera­tures depend on the composition of the steel but are fre­quently between 100 and 650 °C. Higher temperatures usually give a softer, tougher product. The color of the oxide film produced on the surface of the heated metal often serves as the indicator of its temperature.

Annealing isa heat treatment in which a material at high temperature is cooled slowly. After cooling the metal again becomes malleable and ductile (capable of being bent many times without cracking).

All these methods of steel heat treatment are used to obtain steels with certain mechanical properties for cer­tain needs.

Vocabulary:

to immerse — погружать

to apply — применять

intermediate — промежуточный

oxide film — оксидная пленка

annealing — отжиг, отпуск

cracking — растрескивание

General understanding:

1. What can be done to obtain harder steel?

2. What makes steel more soft and tough?

3. What makes steel more malleable and ductile?

4. What can serve as the indicator of metal tempera­ture while heating it?

5. What temperature range is used for tempering?

6. What are the methods of steel heat treatment used for?

Exercise 1.6. Translate into English the following words and word combinations:

1. температура нормализации

2. мелкозернистая структура

3. быстрое охлаждение

4. закаленная сталь

5. состав стали

6. окисная пленка

7. индикатор температуры

8. медленное охлаждение

FAMOUS PEOPLE OF SCIENCE

Dmitry Ivanovich Mendeleyev

Dmitry Ivanovich Mendeleyev is a famous Russian chemist. He is best known for his development of the periodic table of the properties of the chemical elements. This table displays that elements' properties are changed periodically when they are arranged according to atomic weight.

Mendeleyev was born in 1834 in Tobolsk, Siberia. He studied chemistry at the University of St. Petersburg, and in 1859 he was sent to study at the University of Heidelberg. Mendeleyev returned to St. Petersburg and became Professor of Chemistry at the Technical Insti­tute in 1863. He became Professor of General Chemistry at the University of St. Petersburg in 1866. Mendeleyev was a well-known teacher, and, because there was no good textbook in chemistry at that time, he wrote the two-vol­ume «Principles of Chemistry» which became a classic textbook in chemistry.

In this book Mendeleyev tried to classify the elements according to their chemical properties. In 1869 he pub­lished his first version of his periodic table of elements. In 1871 he published an improved version of the peri­odic table, in which he left gaps for elements that were not known at that time. His table and theories were proved later when three predicted elements: gallium, germanium, and scandium were discovered.

Mendeleyev investigated the chemical theory of solu­tion. He found that the best proportion of alcohol and water in vodka is 40%. He also investigated the thermal expansion of liquids and the nature of petroleum.

In 1893 he became director of the Bureau of Weights and Measures in St. Petersburg and held this position until his death in 1907.

 

UNIT 2

METALWORKING

I. Text A: Metalworking processes: Rolling. Extrusion,

Text B: Drawing. Forging. Sheet metal forming,

Text C: Metalworking and Metal Properties.

II. Famous scientists. Mikhail Vasilyevich Lomonosov.

Text A: «METALWORKING PROCESSES»

Metals are important in industry because they can be easily deformed into useful shapes. A lot of metalworking processes have been developed for certain applica­tions. They can be divided into five broad groups:

Rolling,

Extrusion,

Drawing,

Forging,

Sheet-metal forming.

During the first four processes metal is subjected to large amounts of strain (deformation). But if deformation goes at a high temperature, the metal will recrystallize — that is, new strain-free grains will grow instead of deformed grains. For this reason metals are usually rolled, ex­truded, drawn, or forged above their recrystallization temperature. This is called hot working. Under these conditions there is no limit to the compressive plastic strain to which the metal can be subjected.

Other processes are performed below the recrystalli­zation temperature. These are called cold working. Cold working hardens metal and makes the part stronger. However, there is a limit to the strain before a cold part cracks.

Rolling

Rolling is the most common metalworking process. More than 90 percent of the aluminum, steel and copper produced is rolled at least once in the course of produc­tion. The most common rolled product is sheet. Rolling can be done either hot or cold. If the rolling is finished cold, the surface will be smoother and the product stronger.

Extrusion

Extrusion is pushing the billet to flow through the orifice of a die. Products may have either a simple or a complex cross section. Aluminum window frames are the examples of complex extrusions.

Tubes or other hollow parts can also be extruded. The initial piece is a thick-walled tube, and the extruded part is shaped between a die on the outside of the tube and a mandrel held on the inside.

In impact extrusion (also called back-extrusion) (штамповка выдавливанием), the workpiece is placed in the bottom of a hole and a loosely fitting ram is pushed against it. The ram forces the metal to flow back around it, with the gap between the ram and the die determin­ing the wall thickness. The example of this process is the manufacturing of aluminum beer cans.

Vocabulary:

useful — полезный

shape — форма, формировать

rolling — прокатка

extrusion — экструзия, выдавливание

drawing — волочение

forging — ковка

sheet — лист

to subject — подвергать

amount — количество

condition — состояние, условие

perform — выполнять, проводить

to harden — делаться твердым, упрочняться

at least — по крайней мере

common — общий

billet — заготовка, болванка

orifice — отверстие

die — штамп, пуансон, матрица, фильера, во­лочильная доска

cross section — поперечное сечение

window frame — рама окна

tube — труба

hollow — полый

initial — первоначальный, начальный

thick-walled — толстостенный

mandrel — оправка, сердечник

impact — удар

loosely — свободно, с зазором

fitting — зд. посадка

ram — пуансон, плунжер

force — сила

gap — промежуток, зазор

to determine — устанавливать, опреде­лять

General understanding:

1. Why are metals so important in industry?

2. What are the main metalworking processes?

3. Why are metals worked mostly hot?

4. What properties does cold working give to metals?

5. What is rolling? Where is it used?

6. What is extrusion? What shapes can be obtained after extrusion?

7. What are the types of extrusion?

Exercise 2.1. Find the following in the text:

1. могут легко деформироваться

2. нужные формы

3. подвергать большим деформациям

4. зерна свободные от деформации

5. температура перекристаллизации

6. пластическая деформация сжатия

7. самый обычный процесс обработки металла

8. самое обычное изделие проката

9. отверстие фильеры

10. первоначальный

11. сложное сечение

12. пустотелые детали

13. свободно входящий плунжер

14. зазор между плунжером (пуансоном) и штампом

15. толщина стенки

Exercise 2.2. Translate into English:

1. Способность металла перекристаллизовываться при высокой температуре используется при горячей

обработке.

2. Перекристаллизация — это рост новых, свобод­ных от деформации зерен.

3. Во время горячей обработки металл может под­вергаться очень большой пластической деформации сжатия.

4. Холодная обработка делает металл тверже и прочнее, но некоторые металлы имеют предел дефор­мации.

5. Листовой прокат может производиться горячим или холодным.

6. Поверхность холоднокатаного листа более глад­кая и он прочнее.

7. Поперечное сечение фильеры для экструзии мо­жет быть простым или сложным.

8. Алюминиевые и медные сплавы являются наи­лучшими для экструзии из-за их пластичности при деформации.

9. Алюминиевые банки, тюбики для зубной пасты являются примерами использования штамповки вы­давливанием.

10. Толщина стенки алюминиевой банки определя­ется зазором между пунсоном и штампом.

Text В: «DRAWING»

Drawing consists of pulling metal through a die. One type is wire drawing. The diameter reduction that can be achieved in one die is limited, but several dies in se­ries can be used to get the desired reduction.

Sheet metal forming

Sheet metal forming (штамповка листового металла) is widely used when parts of certain shape and size are needed. It includes forging, bending and shearing. One characteristic of sheet metal forming is that the thick­ness of the sheet changes little in processing. The metal is stretched just beyond its yield point (2 to 4 percent strain) in order to retain the new shape. Bending can be done by pressing between two dies. Shearing is a cutting operation similar to that used for cloth.

Each of these processes may be used alone, but often all three are used on one part. For example, to make the roof of an automobile from a flat sheet, the edges are gripped and the piece pulled in tension over a lower die. Next an upper die is pressed over the top, finishing the forming operation (штамповку), and finally the edges are sheared off to give the final dimensions.

Forging

Forging is the shaping of a piece of metal by pushing with open or closed dies. It is usually done hot in order to reduce the required force and increase the metal's plas­ticity.

Open-die forging is usually done by hammering a part between two flat faces. It is used to make parts that are too big to be formed in a closed die or in cases where only a few parts are to be made. The earliest forging machines lifted a large hammer that was then dropped on the workpiece, but now air or steam hammers are used, since they allow greater control over the force and the rate of forming. The part is shaped by moving or turning it be­tween blows.

Closed-die forging is the shaping of hot metal within the walls of two dies that come together to enclose the workpiece on all sides. The process starts with a rod or bar cut to the length needed to fill the die. Since large, complex shapes and large strains are involved, several dies may be used to go from the initial bar to the final shape. With closed dies, parts can be made to close toler­ances so that little finish machining is required.

Two closed-die forging operations are given special names. They are upsetting and coining. Coining takes its name from the final stage of forming metal coins, where the desired imprint is formed on a metal disk that is pressed in a closed die. Coining involves small strains and is done cold. Upsetting involves a flow of the metal back upon itself. An example of this process is the push­ing of a short length of a rod through a hole, clamping the rod, and then hitting the exposed length with a die to form the head of a nail or bolt.

Vocabulary:

to pull — тянуть

reduction — сокращение

to achieve — достигать

in series — серия, последовательно

beyond — выше, свыше

yield point — точка текучести металла

to retain — сохранять, удерживать

to bend — гнуть

shearing — обрезка, отрезание

edge — край

to grip — схватывать

lower die — нижний штамп

upper die — верхний штамп

forming operation — операция штампования

dimension — измерение, размеры

required — необходимый

increase — увеличение

open-die forging — ковка в открытом штампе (под­кладном)

hammering — ковка, колотить

within — внутри, в пределах

to enclose — заключать

rod — прут, стержень

bar — прут, брусок

involved — включенный

tolerance — допуск

upsetting — высадка, выдавливание

blow — удар

coining — чеканка

imprint — отпечаток

clamp — зажим

to hit — ударять

General understanding:

1. How can the reduction of diameter in wire drawing be achieved?

2. What is sheet metal forming and where it can be used?

3. What is close-die forging?

4. What is forging?

5. What are the types of forging?

6. What types of hammers are used now?

7. Where are coining and upsetting used?

8. What process is used in wire production?

9. Describe the process of making the roof of a car.

Exercise 2.3. Find the following word combina­tions in the text:

1. протягивание металла через фильеру

2. волочение проволоки

3. уменьшение диаметра

4. толщина листа

5. растягивать выше точки текучести

6. сохранить новую форму

7. края отрезаются

8. конечные размеры

9. уменьшить необходимое усилие

10. увеличить пластичность металла

11. воздушные или паровые молоты

12. сила и скорость штампования

13. внутри стенок двух штампов

14. отделочная обработка

15. малые допуски

Exercise 2.4. Translate into English:

1. При волочении проволоки диаметр отверстия во­лочильной доски каждый раз уменьшается.

2. Штамповка листового металла включает в себя ковку, изгиб и обрезку.

3. Небольшая деформация листа при растяжении помогает сохранить новую форму детали.

4. Изменение формы при штамповке производится путем сжатия между двумя штампами.

5. Края листа при штамповке отрезаются для по­лучения конечных размеров.

6. При проковке деталь должна быть горячей для уменьшения необходимых усилий и увеличения пла­стичности металла.

7. После ковки в закрытых штампах детали не тре­буют большой механической обработки.

8. При чеканке деформация металла невелика и отпечаток формируется на поверхности металла.

9. Высадка используется для изготовления головок гвоздей и болтов.