5. Выдувка непластифицированного ПВХ используется при производстве прозрачных бутылок для напитков.
6. Полистирол легко вспенивается и используется для упаковки.
7. Полиэтилен — воскообразное вещество белого цвета с очень низкой плотностью и малой жесткостью.
The combinations of two or more different materials are called composite materials. They usually have unique mechanical and physical properties because they combine the best properties of different materials. For example, a fibre-glass reinforced plastic combines the high strength of thin glass fibres with the ductility and chemical resistance of plastic. Nowadays composites are being used for structures such as bridges, boat-building etc.
Composite materials usually consist of synthetic fibres within a matrix, a material that surrounds and is tightly bound to the fibres. The most widely used type of composite material is polymer matrix composites (PMCs). PMCs consist of fibres made of a ceramic material such as carbon or glass embedded in a plastic matrix. Usually the fibres make up about 60 per cent by volume. Composites with metal matrices or ceramic matrices are called metal matrix composites (MMCs) and ceramic matrix composites (CMCs), respectively.
Continuous-fibre composites are generally required for structural applications. The specific strength (strength-to-density ratio) and specific stiffness (elastic modulus-to-density ratio) of continuous carbon fibre PMCs, for example, can be better than metal alloys have. Composites can also have other attractive properties, such as high thermal or electrical conductivity and a low coefficient of thermal expansion.
Although composite materials have certain advantages over conventional materials, composites also have some disadvantages. For example, PMCs and other composite materials tend to be highly anisotropic — that is, their strength, stiffness, and other engineering properties are different depending on the orientation of the composite material. For example, if a PMC is fabricated so that all the fibres are lined up parallel to one another, then the PMC will be very stiff in the direction parallel to the fibres, but not stiff in the perpendicular direction. The designer who uses composite materials in structures subjected to multidirectional forces, must take these anisotropic properties into account. Also, forming strong connections between separate composite material components is difficult.
The advanced composites have high manufacturing costs. Fabricating composite materials is a complex process. However, new manufacturing techniques are developed. It will become possible to produce composite materials at higher volumes and at a lower cost than is now possible, accelerating the wider exploitation of these materials.
Vocabulary:
fibreglass — стекловолокно
fibre — волокно, нить
reinforced — упрочненный
expansion — расширение
matrix — матрица
ceramic — керамический
specific strength — удельная прочность
specific stiffness — удельная жесткость
anisotropic — анизотропный
General understanding:
1. What is called «composite materials»?
2. What are the best properties of fibre-glass?
3. What do composite material usually consist of?
4. What is used as matrix in composites?
5. What is used as filler or fibers in composites?
6. How are the composite materials with ceramic and metal matrices called?
7. What are the advantages of composites?
8. What are the disadvantages of composites?
9. Why anisotropic properties of composites should be taken into account?
Exercise 5.5. Find equivalents in the text:
1. композитные материалы
2. уникальные механические качества
3. полимерные матричные композиты
4. составлять 60% объема
5. углепластик
6. привлекательные качества
7. структура, подвергающаяся воздействию разнонаправленных сил
Exercise 5.6. Translate into Russian:
1. PMC is fabricated so that all the fibres are lined up parallel to one another.
2. Forming strong connections between separate composite material components is difficult.
3. Fabricating composite materials is a complex process.
4. Composite materials have certain advantages over conventional materials
5. Nowadays, composites are being used for structures such as bridges, boat-building etc.
6. Continuous-fibre composites are generally required for structural applications.
FAMOUS INVENTORS
Alfred Bernhard Nobel was a famous Swedish chemist and inventor. He was born in Stockholm in 1833. After receiving an education in St. Petersburg, Russia, and then in the United States, where he studied mechanical engineering, he returned to St. Petersburg to work with his father in Russia. They were developing mines, torpedoes, and other explosives.
In a family-owned factory in Heleneborg, Sweden, he developed a safe way to handle nitroglycerine, after a factory explosion in 1864 killed his younger brother and four other people. In 1867 Nobel achieved his goal: he produced what he called dynamite динамит. Не later produced one of the first smokeless powders (порох). At the time of his death he controlled factories for the manufacture of explosives (взрывчатое вещество) in many parts of the world. In his will he wanted that the major portion of his money left became a fund for yearly prizes in his name. The prizes were to be given for merits (заслуги) in physics, chemistry, medicine and physiology, literature, and world peace. A prize in economics has been awarded since 1969.
I. Text A: «Welding», Text В: «Other types of welding»
II. Famous People of Science and Technology: James Prescott Joule.
Welding is a process when metal parts are joined together by the application of heat, pressure, or a combination of both. The processes of welding can be divided into two main groups:
• pressure welding, when the weld is achieved by pressure and
• heat welding, when the weld is achieved by heat. Heat welding is the most common welding process used today.
Nowadays welding is used instead of bolting and riveting in the construction of many types of structures, including bridges, buildings, and ships. It is also a basic process in the manufacture of machinery and in the motor and aircraft industries. It is necessary almost in all productions where metals are used.
The welding process depends greatly on the properties of the metals, the purpose of their application and the available equipment. Welding processes are classified according to the sources of heat and pressure used.
The welding processes widely employed today include gas welding, arc welding, and resistance welding. Other joining processes are laser welding, and electron-beam welding.
Gas welding is a non-pressure process using heat from a gas flame. The flame is applied directly to the metal edges to be joined and simultaneously to a filler metal in the form of wire or rod, called the welding rod, which is melted to the joint. Gas welding has the advantage of using equipment that is portable and does not require an electric power source. The surfaces to be welded and the welding rod are coated with flux, a fusible material that shields the material from air, which would result in a defective weld.
Arc Welding
Arc-welding is the most important welding process for joining steels. It requires a continuous supply of either direct or alternating electrical current. This current is used to create an electric arc, which generates enough heat to melt metal and create a weld.
Arc welding has several advantages over other welding methods. Arc welding is faster because the concentration of heat is high. Also, fluxes are not necessary in certain methods of arc welding. The most widely used arc-welding processes are shielded metal arc, gas-tungsten arc, gas-metal arc, and submerged arc.
Shielded Metal Arc
In shielded metal-arc welding, a metallic electrode, which conducts electricity, is coated with flux and connected to a source of electric current. The metal to be welded is connected to the other end of the same source of current. An electric arc is formed by touching the tip of the electrode to the metal and then drawing it away. The intense heat of the arc melts both parts to be welded and the point of the metal electrode, which supplies filler metal for the weld. This process is used mainly for welding steels.
Vocabulary:
to join — соединять
pressure welding — сварка давлением
heat welding — сварка нагреванием
instead — вместо, взамен
bolting — скрепление болтами
riveting — клепка
basic — основной
to manufacture — изготовлять
to depend — зависеть от
purpose — цель
available — имеющийся в наличии
equipment — оборудование
source — источник
gas welding — газосварка
arc welding — электродуговая сварка
resistance welding — контактная сварка
laser welding — лазерная сварка
electron-beam welding — электронно-лучевая сварка
flame — пламя
edge — край
simultaneously — одновременно
filler — наполнитель
wire — проволока
rod — прут, стержень
to melt — плавить(ся)
joint — соединение, стык
advantage — преимущество
to require — требовать нуждаться
surface — поверхность
coated — покрытый
flux — флюс
fusible — плавкий
to shield — заслонять, защищать
touching — касание
tip — кончик
General understanding:
1. How can a process of welding be defined?
2. What are the two main groups of processes of welding?
3. How can we join metal parts together?
4. What is welding used for nowadays?
5. Where is welding necessary?
6. What do the welding processes of today include?
7. What are the principles of gas welding?
8. What kinds of welding can be used for joining steels?
9. What does arc welding require? 10. What is the difference between the arc welding and shielded-metal welding?
Exercise 6.1. Find the following words and word combinations in the text:
1. сварка давлением
2. тепловая сварка
3. болтовое (клепаное) соединение
4. процесс сварки
5. зависеть от свойств металлов
6. имеющееся оборудование
7. сварочный электрод
8. плавкий материал
9. дефектный сварной шов
10. непрерывная подача электрического тока
11. электрическая дуга
12. источник электрического тока
Non-consumable Electrode Arc welding
As a non-consumable electrodes tungsten or carbon electrodes can be used. In gas-tungsten arc welding a tungsten electrode is used in place of the metal electrode used in shielded metal-arc welding. A chemically inert gas, such as argon, helium, or carbon dioxide is used to shield the metal from oxidation. The heat from the arc formed between the electrode and the metal melts the edges of the metal. Metal for the weld may be added by placing a bare wire in the arc or the point of the weld. This process can be used with nearly all metals and produces a high-quality weld. However, the rate of welding is considerably slower than in other processes.
In gas-metal welding, a bare electrode is shielded from the air by surrounding it with argon or carbon dioxide gas and sometimes by coating the electrode with flux. The electrode is fed into the electric arc, and melts off in droplets that enter the liquid metal of the weld seam. Most metals can be joined by this process.
Submerged-arc welding is similar to gas-metal arc welding, but in this process no gas is used to shield the weld. Instead of that, the arc and tip of the wire are submerged beneath a layer of granular, fusible material that covers the weld seam. This process is also called electroslag welding. It is very efficient but can be used only with steels.
Resistance Welding
In resistance welding, heat is obtained from the resistance of metal to the flow of an electric current. Electrodes are clamped on each side of the parts to be welded, the parts are subjected to great pressure, and a heavy current is applied for a short period of time. The point where the two metals touch creates resistance to the flow of current. This resistance causes heat, which melts the metals and creates the weld. Resistance welding is widely employed in many fields of sheet metal or wire manufacturing and is often used for welds made by automatic or semi-automatic machines especially in automobile industry.
Vocabulary
gas-tungsten — сварка оплавлением вольфрамовым электродом в среде инертного газа
inert — инертный
edge — край
bare — голый
rate — зд. скорость
gas-metal arc — аргонодуговая сварка
considerably — значительно, гораздо
surrounding — окружающий
carbon dioxide — углекислый газ
droplet — капелька
liquid — жидкость, жидкий
beneath — под, ниже, внизу
layer — слой
weld seam — сварной шов
resistance — сопротивление
clamp — зажим, зажимать
sheet — лист
fusible — плавкий
granular — плавкий
semi-automatic — полуавтоматическая
to create — создавать
to submerge — погружать
General understanding:
1. What is the difference between the arc-welding and non-consumable electrode arc welding?
2. What are the disadvantages of the non-consumable electrode arc welding?
3. How is electrode protected from the air in gas-metal arc welding?
4. What is submerged arc welding?
5. What is the principle of resistance welding?
6. Where is semi-automatic welding employed?
Exercise 6.2. Translate into English:
1. вольфрамовый электрод
2. инертный газ
3. окисление
4. высококачественный сварочный шов
5. скорость сварки
6. аргон, гелий, углекислый газ
7. жидкий металл
8. слой плавкого материала в виде гранул
9. листовой металл
10. полувтоматические сварочные станки
Exercise 6.3. Translate into Russian:
1. In resistance welding, heat is obtained from the resistance of metal to the flow of an electric current.