Федеральное агентство по образованию
Волжский политехнический институт (филиал)
Волгоградского государственного технического университета
Кафедра иностранных языков
Семестровая работа
по английскому языку.
Перевод технического текста с английского языка на русский язык.
«METAL-CUTTING MACHINES. HYDROELECTRIC POWER-STATION. EARLY HISTORY OF ELECTRICITY»
10000 знаков.
Выполнил:
Студент гр. ВТС-231
Мусаелян Э.А.
Проверил:
Доцент
Крячко В.Б.
Волжский 2009
METAL-CUTTING MACHINESLATHES
A lathe is known to be essentially a machine tool for producing and finishing surfaces of work pieces. The machine is designed to hold and revolve work around an axis of rotation so that it may be subjected to the action of a cutting tool moving in a horizontal plane through the axis of the work. When the cutting tool moves in a longitudinal direction or parallel to the axis, the operation is known as "turning"; when it moves in a transverse direction, it is known as "facing". In addition to turning and boring, which the machine is primarily designed for, many other operations, such as drilling, threading, tapping, and, by employing special adapters grinding and milling, may be performed on a lathe.
Lathes used in shop practice are known to be of different designs and sizes. These lathes fall into various types, either according to their characteristic constructional features, or according to the work for which they are designed. The size of a lathe is determined by the diameter and length of work that may be swung between centers. Lathes of comparatively small size, which may be mounted on a bench, are termed bench lathes, and are intended for small work of considerable accuracy; lathes provided with tools held in a revolvable turret are called "turret lathes": lathes in which work pieces to be treated are held in a chuck are known as "chucking lathes"; lathes in which most of operations are performed automatically are named "automatic lathes".
Besides there are also many special-purpose lathes such as crankshaft lathes and wheel lathes for turning crankshafts or engine driving wheels respectively; screw-cutting lathes for threading screws, etc. The engine lathe used for metal-turning operations is fitted with a power-actuated carriage and cross-slide for clamping and holding the cutting tool. In engine lathes the cutting tools are generally guided by the machine tool itself, in other words, they are operated mechanically, while in some lathes the cutting tools are guided by hand. The engine lathe consists essentially of the following basic parts: the bed, the headstock, the tailstock, the feed mechanism, and the carriage.
The bed is a rigid casting with two longitudinal walls firmly connected by cross ribs integral with the casting. The bed serves as a base to support and align the rest of the machine. The upper surface of the bed is provided with parallel V-type and flat ways or guides for accurate aligning of the sliding parts of the lathe—the carriage and the tail-stock. The headstock is located and firmly bolted to the left-hand side of the bed and carries a pair of bearings in which the spindle-rotates. Many modern lathes have a motor built into the headstock-with the spindle serving as the motor shaft. The spindle ,-being one of the most important-parts of a lathe, is a steel hollow shaft with a taper bore for the insertion of the live or running centre on which the piece to be turned is placed. The other end of the work is" supported by the non-rotating dead or cup centre. The nose of the spin-die is accurately threaded for chucks to be screwed on it. The chucks, in turn, hold and revolve work pieces together with the spindle. The head- stock also incorporates the change gearbox driven by a set of speed-change levers. The change gearbox lathe at different speeds required work pieces of various diameters.
The tailstock located at the right-hand side of the bed, is a casting carrying a non-rotating sleeve, which together with the nut can be advanced or retracted by means of the tailstock revolving screw operated by the hand wheel. The tailstock may be moved anywhere along the lathe bed and can be clamped in place at any point. On changing the position, the tailstock slides along the two inner bed ways one of which named flat way is of rectangular cross-section and the other one is of V — section. The tailstock sleeve mounts a hollow spindle with a standard taper bore for holding the lathe centers or tapered tool shanks. The dead centre fits in a Morse taper hole in the sleeve and may be removed by retracting the sleeve, thereby bringing the end of the tailstock screw against the rear of the centre and forcing it out. The tailstock spindle has a large area bearing in both the front and rear of the tailstock. To facilitate measurement of the spindle travel the tailstock spindle is graduated.
The feed mechanism for both longitudinal and cross feeds of the engine lathe is simple and easy to operate. It comprises a cone of gears, an intermediate shaft and a set of sliding gears. The fine change shifter slides on a splined shaft and carries a tumbler gear which is dropped into engagement with a gear on the cone corresponding to the thread or feed selected on the index plate above it.
Movement of the carriage and the cross-slide can be reversed either by reversing the feed mechanism with the reverse handle or by shifting the single lever located on the carriage apron. Suitable speed ratios between the spindle and the feed mechanism are provided by a change gearbox. The carriage is a unit intended for mounting the tool, and capable of sliding along the two outer V-type ways, on which it is supported, in a direction parallel to the spindle axis.
For turning and facing operations the carriage is driven from the headstock spindle by gearing or belting through a feed shaft. For thread cutting, where a definite amount of carriage movement is required for every spindle rotation, a lead screw, geared to the spindle, is used for the motion of the carriage. The carriage is made up of two principal parts, one of which carries the saddle, which slides upon the bed and on which the cross-slide and the tool rest are mounted. The other part, termed the apron, represents the front wall of the carriage. It provides a support for the operating hand-wheel and control levers, as well as carries the mechanism for engaging the feed mechanism of the lathe to drive the carriage. The cross-slide mounted on the carriage can move at right angles to the spindle axis. It is operated by the cross-slide screw which turns in a nut fixed to the carriage.
On the top of the saddle there is the compound rest for mounting the tool post. The compound rest is similar to the cross-slide, except that it can be swung around at an angle. It has a circular base graduated in degrees, so that it may be set at any angle, and may be used for cutting bevels, tapered work and similar jobs. The compound rest is actuated by a screw which rotates in a nut fixed to the saddle. The tool post intended for holding the tool fits in a tee slot in the compound rest, and the toolholder is adjusted, and clamped by the tool post screw. Engine lathes are fitted with a multiple disc clutch and brake. The powerful multiple disc clutches when disengaged automatically engages the plate brake.
There are three important methods of holding and rotating work in engine lathes, which may be referred to as turning between centers, chuck work, and faceplate work. In turning between centers, the work is supported by the 60° conical points of the live and dead centers. It turns together with the live centre on the dead centre. In chuck or faceplate work, the work to be machined is held in a chuck or a faceplate.
HYDROELECTRIC POWER-STATION
Water power was used to drive machinery long before Polzunov and James Watt harnessed steam to meet man's needs for useful power.
Modern hydroelectric power-stations use water power to turn the machines which generate electricity. The water power may be obtained from small dams in rivers or from enormous sources of water power like those to be found in the USSR. However, most of our electricity, that is about 86 per cent, still comes from steam power-stations.
In some other countries, such as Norway, Sweden, and Switzerland, more electric energy is produced from water power than from steam. They have been developing large hydroelectric power-stations for the past forty years, or so, because they lack a sufficient fuel supply. The tendency, nowadays, even for countries that have large coal resources are to utilize their water power in order to conserve their resources of coal. As a matter of fact, almost one half of the total electric supply of the world comes from water power.
The locality of a hydroelectric power plant depends on natural conditions. The hydroelectric power plant may be located either at the dam or at a considerable distance below. That depends on the desirability of using the head supply at the dam itself or the desirability of getting a greater head. In the latter case, water is conducted through pipes or open channels to a point farther downstream where the natural conditions make a greater head possible.
The design of machines for using water power greatly depends on the nature of the available water supply. In some cases great quantities of water can be taken from a large river with only a few feet head. In other cases, instead of a few feet, we may have a head of several thousands of feet. In general, power may be developed from water by action of its pressure, of its velocity, or by a combination of both.
A hydraulic turbine and a generator are the main equipment in a hydroelectric power-station. Hydraulic turbines are the key machines converting the energy of flowing water into mechanical energy. Such turbines have the following principal parts: a runner composed of radial blades mounted on a rotating shaft and a steel casing which houses the runner. There are two types of water turbines, namely, the reaction turbine and the impulse turbine. The reaction turbine is the one for low heads and a small flow. Modified forms of the above turbine are used for medium heads up to 500-600 ft, the shaft being horizontal for the larger heads. High heads, above 500 ft, employ the impulse type turbine. It is the reaction turbine that is most used in the USSR.
Speaking of hydraulic turbines, it is interesting to point out that in recent years there has been a great increase in size, capacity, and output of Soviet turbines.
Hydropower engineering is developing mainly by constructing high capacity stations integrated into river systems known as cascades. Such cascades are already in. operation on the Dnepr, the Volga and the Angora.
EARLY HISTORY OF ELECTRICITY
Let us now turn our attention to the early facts, that is to say, let us see how it all started.
History shows us that at least 2,500 years ago, or so, the Greeks were already familiar with the strange force (as it seemed to them) which is known today as electricity. Generally speaking, three phenomena made up all of man's knowledge of electrical effects. The first phenomenon under consideration was the familiar lightning flash —a dangerous power, as it seemed to him, which could both kill people and burn or destroy their houses. The second manifestation of electricity he was more or less familiar with was the following: he sometimes found in the earth a strange yellow stone which looked like glass. On being rubbed, that strange yellow stone, that is to say amber, obtained the ability of attracting light objects of a small size. The third phenomenon was connected with the so-called electric fish which possessed the property of giving more or less strong electric shocks which could be obtained by a person coming into contact with the electric fish.
Nobody knew that the above phenomena were due to electricity. People could neither understand their observations nor find any practical applications for them.
As a matter of fact, all of man's knowledge in the field of electricity has been obtained during the last 370 years, or so. Needless to say, it took a long time before scientists learned how to make use of electricity. In effect, most of the electrically operated devices, such as the electric lamp, the refrigerator, the tram, the lift, the radio, and so on, are less than one hundred years old. In spite of their having been employed for such a short period of time, they play a most important part in man's everyday life all over the world. In fact, we cannot do without them at present.
So far, we have not named the scientists who contributed ' to the scientific research on electricity as centuries passed. However, famous names are connected with its history and among them we find that of Phales, the Greek philosopher. As early as about 600 В. С (that is, before our era) he discovered that when amber was rubbed, it attracted and held minute light objects. However, he could not know that amber was charged with electricity owing to the process of rubbing. Then Gilbert, the English physicist, began the first systematic scientific research on electrical phenomena. He discovered that various other substances possessed the property similar to that of amber or, in other words, they generated electricity when they were rubbed. He gave the name "electricity" to the phenomenon he was studying. He got this word from the Greek "electrum" meaning "amber".
Many learned men of Europe began to use the new word "electricity" in their conversation as they were engaged in research of their own. Scientists of Russia, France and Italy made their contribution as well as the Englishmen and the Germans.
МЕХАНИЗМЫ ДЛЯ РЕЗКИ МЕТАЛЛА ТОКАРНЫЕ СТАНКИ
Токарный станок, как известно, является по существу станком для того, чтобы преобразовывать и обрабатывать поверхности заготовок. Механизм разработан для того, чтобы держать и вращать заготовку вокруг оси вращения так, чтобы заготовка могла быть подвергнута действию режущего инструмента, двигающегося в горизонтальном направлении через ось работы. Когда шаги режущего инструмента располагаются в продольном направлении или параллельно оси, то действие известно как "обработка"; когда инструмент перемещается в поперечном направлении, действие известно как "соединение". В дополнение к обработке и соединению, для которых механизм, прежде всего, предназначен, есть много других действий, типа бурения, нарезка резьбы, выявление, и, также применяются специальные измельчения, которые могут быть выполнены на токарном станке.
Токарные станки, используемые в практике вычислительного центра, как известно, являются различные видов и размеров. Эти токарные станки подразделяют на различные типы, согласно их характерным конструктивным особенностям, или согласно работе, для которой они предназначены. Размер токарного станка определен диаметром и длиной работы, которую можно расположить между центрами. Токарные станки сравнительно небольших размеров, который могут быть установлены на месте размещения самого элемента, называют местными токарными станками, и предназначены для маленькой работы высокой точности; токарные станки, в которых заготовки поддерживаются в Чаке, известны как "чаковые токарные станки"; токарные станки, в которых большинство действий выполнено автоматически, называют "автоматическими токарными станками".
Кроме того, есть также много токарных станков специального назначения типа токарных станков коленчатого вала и колесных токарных станков, для того, чтобы повернуть коленчатые валы или двигатель, вращая сами колеса соответственно; винтовые режущие токарные станки для того, чтобы пронизывать винты, и т.д. Машинный токарный станок, используемый для поворачивания металла, оснащен приводимым в действие энергией вагоном и взаимным держателем для того, чтобы зажимать и держать режущий инструмент. В машинных токарных станках режущие инструменты вообще движутся непосредственно со станком, другими словами, они используются механически, в то время как в некоторых токарных станках режущие инструменты управляются вручную. Машинный токарный станок состоит по существу из следующих основных частей: ложи, главной части, хвостовой части, механизма подачи, и вагона.