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) ( ), 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
shape ,
rolling
extrusion ,
drawing
forging
sheet
to subject
amount
condition ,
perform ,
to harden ,
at least
common
billet ,
orifice
die , , , ,
cross section
window frame
tube
hollow
initial ,
thick-walled
mandrel ,
impact
loosely ,
fitting .
ram ,
force
gap ,
to determine ,
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.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14. ()
15.
Exercise 2.2. Translate into English:
1.
.
2. , .
3. .
4. , .
|
|
|
5. .
6. .
7. .
8. - .
9. , .
10. .
Text : 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 ( ) 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 (), 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
reduction
to achieve
in series ,
beyond ,
yield point
to retain ,
to bend
shearing ,
edge
to grip
lower die
upper die
forming operation
dimension ,
required
increase
open-die forging ()
hammering ,
within ,
to enclose
rod ,
bar ,
|
|
|
involved
tolerance
upsetting ,
blow
coining
imprint
clamp
to hit
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.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Exercise 2.4. Translate into English:
1. .
2. , .
3. .
4. .
5. .
6. .
7. .
8. .
9. .
Text C: METALWORKING AND METAL PROPETIES
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 ,
|
|
|
to provide
improvement
property
eliminate ,
porosity
directional
to segregate
casting
elongated
to weaken ,
transverse
flow ,
finished
thinning
fracture
strain hardening
brass
beverage
can
to exhibit
inner
flaws ,
inclusion
trapped .
refining ,
to avoid
to undergo
tensile ductility
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.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Exercise 2.6. Translate into English:
1. .
2. .
3. .
4. .
5. .
6. .
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 colored-glass factory. Most of his achievements, however, were unknown outside Russia.
UNIT3
