Английский. Учебное пособие для аудиторной и самостоятельной работы студентов III курсов ммф йошкарОла пгту 2013 удк 811. 111 (07)
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Задание IV
Задание V
1. The internal resistance offered by a part to an externally applied force is called … a) stress b) load c) impact 2. The toughness of the material decreases when it is … a) rolled b) measured c) heated 3. When a part is subjected to a constant stress at high temperature for a long period of time, it will undergo … a) fatigue b) creep c) fracture 2. Определите, какие из данных утверждений истинны, а какие ложны: 1. Steel is less elastic than rubber. 2. Copper and zinc are widely used ductile materials. 3. Toughness is desirable in parts subjected to shock and impact loads. 4. Steel is more easily machined than brass. 5. Creep is considered in designing shafts and gears. 6. Hardness embraces many other properties such as deformation and machinability. 3. Ответьте на вопросы к тексту: 1. How can the properties of metals be grouped? 2. What are the mechanical properties of metals associated with? 3. What is elasticity? 4. What are the commonly used malleable materials? 5. How is resilience measured? Задание VI 1. Выполните письменный перевод текста. 2. Выполните устный пересказ текста, используя необходимые фразы. Unit 7 Задание I
Commercial, attack, dielectric, medical, polymerization, chloride, thermoplastic, container 2. Прочитайте следующий текст: PLASTICS Plastics are large and varied group of materials consisting of combinations of carbon and oxygen, hydrogen, nitrogen, and other organic and inorganic elements. While solid in its finished state, a plastic is at some stage in its manufacture, liquid and capable of being formed into various shapes. Forming is usually done through the application either singly or together, of heat and pressure. There are over 40 different families of plastics in commercial use today, and each may have dozens of subtypes and variations. A successful design in plastics is always a compromise among highest performance, attractive appearance, efficient production, and lowest cost. Achieving the best compromise requires satisfying the mechanical requirements of the part, utilizing the most economical resin or compound that will perform satisfactorily, and choosing a manufacturing process compatible with the part design and material choice. Most people have now outgrown the impression that plastics are low cost substitute materials. Those that still view plastics as cheap and unreliable have not kept up with developments in polymer technology for the past ten years. Many plastics did indeed evolve as replacements for natural products such as rubber, ivory or wood, which became unavailable or on short supply. But the new materials did not necessarily replace the older ones permanently nor made them obsolete. In many cases, they met an increased demand that could not be met by the natural product alone. Today’s engineering resins and compounds serve in the most demanding environments. Their toughness, lightness, strength, and corrosion resistance have won many significant applications for these materials in transportation, industrial and consumer products. The engineering plastics are now challenging the domains traditionally held by metals: truly load bearing, structural parts. Types of Plastics Plastics are non-metallic, synthetic, carbon-based materials. They can be molded, shaped, or extruded into flexible sheets, films, or fibers. Plastics are synthetic polymers. Polymers consist of long-chain molecules made of large numbers of identical small molecules (monomers). The chemical nature of a plastic is defined by the monomer (repeating unit) that makes up the chain of the polymer. Most plastics are synthesized from organic chemicals or from natural gas or coal. Plastics are lightweight compared to metals and are good electrical insulators. The best insulators now are epoxy resins and teflon. Plastics can be classified into several broad types. Thermoplastics soften on heating, and then harden again when cooled. Thermoplastics molecules are also coiled and because of this they are flexible and easily stretched. Typical example of thermoplastics is polystyrene. Polystyrene resins are characterized by high resistance to chemical and mechanical stresses at low temperatures and by very low absorption of water. These properties make the polystyrenes especially suitable for radio-frequency insulation and for parts used at low temperatures in refrigerators and in airplanes. PET (polythene terephthalate) is a transparent thermoplastic used for soft-drinks bottles. Thermoplastics are also viscoelastic, that is, they flow (creep) under stress. Examples are polythene, polystyrene and PVC. PVC is a thermoplastic polymer made from vinyl chloride, a colourless solid with outstanding resistance to water, alcohols, and concentrated acids and alkalis. It is obtainable as granules, solutions, lattices, and pastes. When compounded with plasticizers, it yields a flexible material more durable than rubber. It is widely used for cable and wire insulation, in chemical plants, and in the manufacture of protective garments. Blow moulding of unplasticized PVC produces clear, tough bottles, which do not affect the flavour of their contents. PVC is also used for production of tubes or pipes. Polystyrene is a thermoplastic produced by the polymerization of styrene. The electrical insulating properties of polystyrene are outstandingly good and it is relatively unaffected by water. Typical applications include light fixtures, toys, bottles, lenses, capacitor dielectrics, medical syringes, and light-duty industrial components. Extruded sheets of polystyrene are widely used for packaging, envelope windows, and photographic film. Its resistance to impact can be improved by the addition of rubber modifiers. Polystyrene can be readily foamed; the resulting foamed polystyrene is used extensively for packaging. Polythene is a plastic made from ethane. It is one of the most widely used important thermoplastic polymers. Polythene is a white waxy solid with very low density, reasonable strength and toughness, but low stiffness. It is easily moulded and has a wide range of uses in containers, packaging, pipes, coatings, and insulation. Thermosetting plastics (thermosets) do not soften when heated, and with strong heating they decompose. In most thermosets final cross-linking, which fixes the molecules, takes place after the plastic has already been formed. Thermosetting plastics have a higher density than thermoplastics. They are less flexible, more difficult to stretch, and are less subjected to creep. Examples of thermosetting plastics include epoxy resins, most polyesters, and phenolic polymers such as phenol-formaldehyde resin. Epoxy resin is a thermoset plastic containing epoxy groups. Epoxy resin hardens when it is mixed with solidifier and plasticizer. Plasticizers make a polymer more flexible. Epoxy resins have outstanding adhesion, toughness, and resistance to attack from chemicals. They form strong bonds and have excellent electrical insulation properties. Large, complex, void-free castings can be made from them. They are also used as adhesives, and in composites for boat building and sports equipment. Elastomers are similar to thermoplastics but have sufficient cross-linking between molecules to prevent stretching and creep. 3. Запомните необходимый минимум профессиональной лексики:
Задание II 1. Определите по формальным признакам, какой частью речи являются следующие слова, и переведите их: Commercial, attractive, appearance, impression, replacement, permanently, absorption, frequency, sufficient, obtainable, protective, outstandingly 2. Определите значение суффиксов и префиксов в следующих словах и переводите их: Subtype, inorganic, outgrow, unreliable, unavailable, lightness, solidifier, colourless, insulator, unaffected Задание III
2. Подберите эквиваленты к словосочетаниям, обозначенным цифрами:
3. Подберите подходящую пару к словам, обозначенным цифрами. Полученные словосочетания переведите.
4. Заполните пропуски предложенными словами: Polythene, polystyrene, performance, thermoplastic, absorption, resistance
Задание IV
Задание V
1. Plastics consist of carbon and other organic elements. 2. Plastics are low cost materials and are less reliable than metals. 3. Polystyrene has high resistance to chemical and mechanical stresses at low temperatures.
Задание VI 1. Выполните письменный перевод текста. 2. Выполните устный пересказ текста, используя необходимые фразы. Unit 8 Задание I
Erosion, ultrasound, electrode, stationary, rotation, modern, automatic, regulation, miniature, abrasive
MACHINE TOOLS Machine tools are used to shape metals and other materials. The material to be shaped is called the workpiece. Most machine tools are now electrically driven. Machine tools with electrical drive are faster and more accurate than hand tools: they were an important element in the development of mass-production processes, as they allowed individual parts to be made in large numbers so as to be interchangeable. All machine tools have facilities for holding both the workpiece and the tool, and for accurately controlling the movement of the cutting tool relative to the workpiece. Most machining operations generate large amounts of heat, and use cooling fluids (usually a mixture of water and oils) for cooling and lubrication. Machine tools usually work materials mechanically but other machining methods have been developed lately. They include chemical machining, spark erosion to machine very hard materials to any shape by means of a continuous high-voltage spark (discharge) between an electrode and a workpiece. Other machining methods include drilling using ultrasound, and cutting by means of a laser beam. Numerical controls of machine-tools and flexible manufacturing systems have made it possible for complete systems of machine-tools to be used flexibly for the manufacture of a range of products. Lathe Lathe is still the most important machine tool. It produces parts of circular cross-section by turning the workpiece on its axis and cutting its surface with a sharp stationary tool. The tool may be moved sideways to produce a cylindrical part and moved towards the workpiece to control the depth of cut. Nowadays all lathes are power-driven by electric motors. That allows continuous rotation of the workpiece at a variety of speeds. The modern lathe is driven by means of a headstock supporting a hollow spindle on accurate bearings and carrying either a chuck or a faceplate, to which the workpiece is clamped. The movement of the tool, both along the lathe bed and at right angle to it, can be accurately controlled, so enabling a part to be machined to close tolerances. Modern lathes are often under numerical control. The various complicated machine-tools now used by engineers are designed to do the same jobs as the hammer, the chisel and the file, but very much more quickly and efficiently, and with much wider range of application. The vastly increased production of modern times would never have been possible without these machines to take the place of hand work, nor could the hand-worker ever produce the precision now needed. The machine tools which have replaced the chisel and file and which shape the metal by removing parts of it are shapers, planers, milling machines, drilling and boring machines, grinders and lathes and those which have replaced the hammer and which press the metal into the required shape are steam hammers, forging and pressing machines and sheet metal work tools. Milling Machine In a milling machine the cutter is a circular device with a series of cutting edges on its circumference. The workpiece is held on a table that controls the feed against the cutter. The table has three possible movements: longitudinal, horizontal, and vertical; in some cases it can also rotate. Milling machines are the most versatile of all machine tools. Flat or contoured surfaces may be machined with excellent finish and accuracy. Angles, slots, gear teeth and cuts can be made by using various shapes of cutters. Drilling and Boring Machines To drill a hole usually hole-making machine tools are used. They can drill a hole according to some specification, they can enlarge it, or they can cut threads for a screw or to create an accurate size or a smooth finish of a hole. Drilling machines are different in size and function, from portable drills to radial drilling machines, multispindle units, automatic production machines, and deep-hole-drilling machines. Boring is a process that enlarges holes previously drilled, usually with a rotating single-point cutter held on a boring bar and fed against a stationary workpiece. Shapers and Planers The shaper is used mainly to produce different flat surfaces. The tool slides against the stationary workpiece and cuts on one stroke, returns to its starting position, and then cuts on the next stroke after a slight lateral displacement. In general, the shaper can make any surface having straight-line elements. It uses only one cutting-tool and is relatively slow, because the return stroke is idle. That is why the shaper is seldom found on a mass production line. It is, however, valuable for tool production and for workshop where flexibility is important and relative slowness is unimportant. The planer is the largest of the reciprocating machine tools. It differs from the shaper, which moves a tool past a fixed workpiece because the planer moves the workpiece to expose a new section to the tool. Like the shaper, the planer is intended to produce vertical, horizontal, or diagonal cuts. It is also possible to mount several tools at one time in any or all tool holders of a planer to execute multiple simultaneous cuts. Grinders Grinders remove metal by a rotating abrasive wheel. The wheel is composed of many small grains of abrasive, bonded together, with each grain acting as a miniature cutting tool. The process gives very smooth and accurate finishes. Only a small amount of material is removed at each pass of the wheel, so grinding machines require fine wheel regulation. The pressure of the wheel against the workpiece is usually very light, so that grinding can be carried out on fragile materials that cannot be machined by other conventional devices. |