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 colour of the oxide film produced on the surface of the heated metal often serves as the indicator of its temperature.
Annealing is a 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.
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1. What is quenching?
2. What makes steel harder and more brittle?
3. What is tempering?
4. What temperature range is used for tempering?
5. What are the methods of steel heat treatment used for?
ВАРИАНТ 2
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STEEL
The most important metal in industry is iron and its alloy – steel. Steel is an alloy of iron and carbon. It is strong but corrodes easily through rusting, although stainless and other special steels resist corrosion. The amount of carbon in steel influences its properties considerably. Steels of low carbon content (mild steels) are quite ductile and are used in the manufacture of sheet iron, wire and pipes. Medium-carbon steels containing from 0.2 to 0.4 per cent carbon are tougher and stronger and are used as structural steels. Both mild and medium-carbon steels are suitable for forging and welding. High-carbon steels contain from 0.4 to 1.5 per cent carbon, are hard and brittle and are used in cutting tools, surgical instruments, razor blades and springs. Tool steel, also called silver steel, contains about 1 per cent carbon and is strengthened and toughened by quenching and tempering. The inclusion of other elements affects the properties of the steel. Manganese gives extra strength and toughness. Steel containing 4 per cent silicon is used for transformer cores or electromagnets because it has large grains acting like small magnets. The addition of chromium gives extra strength and corrosion resistance, so we can get rust-proof steels. Heating in the presence of carbon or nitrogen-rich materials is used to form a hard surface on steel (case-hardening). High-speed steels, which are extremely important in machine-tools, contain chromium and tungsten plus smaller amounts of vanadium, molybdenum and other metals.
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1. What is steel?
2. What are the main properties of steel?
3. What are the drawbacks of steel?
4. What kinds of steel do you know and where are they used?
5. What gives the addition of manganese, silicon and chromium to steel?
ВАРИАНТ 3
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METALS
Metals are materials most widely used in industry because of their properties. The study of the production and properties of metals is known as metallurgy. The separation between the atoms in metals is small, so most metals are dense. The atoms are arranged regularly and can slide over each other. That is why metals are malleable (can be deformed and bent without fracture) and ductile (can be drawn into wire). Metals vary greatly in their properties. For example, lead is soft and can be bent by hand, while iron can only be worked by hammering at red heat. The regular arrangement of atoms in metals gives them a crystalline structure. Irregular crystals are called grains. The properties of the metals depend on the size, shape, orientation, and composition of these grains. In general, a metal with small grains will be harder and stronger than one with coarse grains. Heat treatment controls the nature of the grains and their size in the metal. Small amounts of other metals (less than 1 per cent) are often added to a pure metal. This is called alloying and it changes the grain structure and properties of metals. All metals can be formed by drawing, rolling, hammering and extrusion, but some require hot-working. Metals are subject to metal fatigue and to creep (the slow increase in length under stress) causing deformation and failure. Both effects are taken into account by engineers when designing, for example, airplanes, gas-turbines, and pressure vessels for high-temperature chemical processes. Metals can be worked using machine-tools. The ways of working a metal depend on its properties. Many metals can be melted and cast in moulds, but special conditions are required for metals that react with air.
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1. What are metals and what do we call metallurgy?
2. Why are most metals dense?
3. Why are metals malleable?
4. What is malleability?
5. What are grains?
ВАРИАНТ 4
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НОТ WORKING OF STEEL
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.
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1. What process improves the mechanical properties of metals?
2. What new properties do hot-worked products have?
3. How are the flow lines in the forged metal oriented and how does it affect the strength of the forged part?
4. What are the best strain-hardening alloys?
5. Where can we use strain-hardening alloys?
ВАРИАНТ 5
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Drilling Machines
Drilling machines are very old machine tools employed for drilling holes of different sizes in metal or any other solid material. In addition to drilling holes, such operations as tapping, reaming, lapping, countersinking and counterboring may be performed on the drilling machines.
Drilling machines of different design are classified in various classes, the main of them are the following: upright or vertical spindle drilling machines; multiple-spindle drilling machines; radial spindle machines.
In all three types, the drill spindle rotates in a sleeve which does not rotate but is free to move axially to provide the not necessary feed for the drill.
In vertical spindle drilling machine the spindle is in a vertical position. The upright drilling machine has an upright column resting on a heavy base. The column equipped with a gearbox has a feed mechanism.
The feed mechanism represents a feed shaft with the necessary gearing by which the drill is cut into the work at a proper speed. The shaft and the gearing provide a mechanical feed and any adjustment of both the drilling head mounted on the top of the column and the table for drilling operations.
All adjustment for different classes of work is made by moving the table which is accomplished by turning the crank. The machine is also equipped with a ratchet lever for hand feeding the drill.
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1. What operations may be performed on drilling machines?
2. How are drilling machines classified?
3. Where does the drilling machine spindle rotate?
4. How is the spindle sleeve moved and what is provided by such a movement?
5. What structural feature gives the upright drilling machine its name?
Тексты по направлению
"Эксплуатация транспортно-технологических машин и комплексов", "Наземные транспортно-технологические средства"
ВАРИАНТ 1
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THE DIESEL ENGINE
In 1890s, Rudolf Diesel, a German, invented the engine that bears his name. As distinguished from gasoline engines diesels have no ignition system fed with electricity. The fuel is ignited simply by contact with very hot air in the cylinder. The operation performed is like this: when taken in the cylinder the air is highly compressed, the temperature rises so the heated fuel-air mixture burns. The higher the pressure, the higher is the temperature. Besides the compressed mixture produced more power than that uncompressed. Diesel engines power many of the used vehicles and other equipment. They are usually used in cases where engine weight is not a prime factor. Their advantage is that they are simple in design and use much heavier liquid fuels than gasoline engines. The cost of a heavier fuel is much less than that of a light one. Besides the fuel consumption of a diesel is much less than that of gasoline engines. Although applied for many purposes diesel engines have certain disadvantages. Their weight is more than that of a gasoline engine of the same power and it occupies much space. The disadvantages of diesels as passenger-car engines are slow performance, noise and smoke. All the companies investigating diesels are trying to reduce noise and smoke, but the problems are not yet entirely solved. Diesel engines clatter when started on a cold morning. And the warm-up period for all diesels seems too long to drivers accustomed to gasoline models.
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1. Who invented the diesel engine?
2. Do diesel engines have ignition system fed with electricity?
3. How is the fuel ignited in the diesel engine?
4. What is the operation performed?
5. What is the advantage of diesel engines?
ВАРИАНТ 2
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THE ENGINE
The word engine originally meant any ingenious device, and came from the Greek word ingenious, clever. Any kind of vehicle must be able to move. The ability to move demands power. A machine that produces mechanical power or energy is called an engine or a power plant. Engines present one of the most interesting groups of problems considered in the engineering field. One of the main problems is receiving the maximum possible power or thrust for minimum weight. The weight is included in the factor called the weight/power ratio, which may be defined as the weight in pounds per horse power output. Another important problem is that of fuel. Both in the past and today the designers work to lower specific fuel consumption. Specific fuel consumption is obtained by dividing the weight of the fuel burned per hour by the horse power developed. Another possible problem considered in any engine is its flexibility. Flexibility is the ability of the engine to run smoothly and perform properly at all speeds and through all variations of atmospheric conditions. One more important problem worked at by the designers is the engine reliability. The engine is to have a long life, with maximum of time between overhaul periods. In some cases the problem of balance is one of the main. Balance has several possible meanings but the principle factor is freedom from vibration. Besides any engine must be started easily and carry its full load in a few minutes. There are gasoline engines, diesel engines, gas turbines, steam engines, jet engines and rocket engines. Each of them has certain advantages and disadvantages over other forms of power plants.
2. Прочитайте текст снова и письменно ответьте на вопросы:
1. What did the word engine originally mean?
2. What is one of the main problems engines present?
3. What is flexibility of the engine?
4. Do the designers work at the engine reliability?
5. What engines do you know?
ВАРИАНТ 3
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THE ENGINE
Basically, the automobile consists of three parts: the power plant, or the engine, the chassis and the body. To these may be added the accessories: the heater, lights, radio, speedometer and other devices. The engine is the source of power that makes the wheels rotate and the car move. It includes electric, fuel, cooling and lubricating systems. It is usually called an internal combustion engine because gasoline is burned within its cylinders or combustion chambers. Most automobile engines have six or eight cylinders. The operating cycle of the four-stroke engine that takes place in the engine cylinder can be divided into four strokes. The upper limit of the piston movement is called the top dead centre. The lower limit of piston movement is called the bottom dead centre. A stroke is the piston movement from the top dead centre to the bottom dead centre, or from the bottom dead centre to the top dead centre. In other words, the piston completes a stroke each time it changes the direction of its motion. Where the entire cycle of events in the cylinder requires four strokes (two crankshaft revolutions), the engine is called a four-stroke cycle engine. The four strokes are: intake, compression, power and exhaust. Two-cycle engines have also been made, and in such engines the entire cycle of events is completed in two strokes or one revolution of the crankshaft. On the intake stroke the intake valve is opened. The mixture of air and vaporized gasoline is delivered into the cylinder through the inlet valve. On the compression stroke the inlet valve is closed so that the mixture can be compressed.
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1. What parts does the automobile consist of?
2. What is the engine?
3. How many cylinders do most automobile engines have?
4. How is the upper limit of the piston movement called?
5. How is the lower limit of piston movement called?
ВАРИАНТ 4
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