Методичка по английскому языку для ИТС (пр. С.С.Иванов)

When much work of the same general character and size is to be handled, a permanent oven may be constructed of the fire brick, leaving a large opening through the top and also through one side. Charcoal may be used in this form of oven as with the temporary arrangement, or the heat may be secured from any form of burner or torch giving a large volume of flame. In any method employing flame to do the heating, the work itself must be protected from the direct blast of the fire. Baffles of brick or metal should be placed between the mouth of the torch and the nearest surface of the work so that the flame will be deflected to either side and around the piece being heated.

The heat should be applied to bring the point of welding to the highest temperature desired. The heat should gradually shade off from this point to the other parts of the piece. In the case of cast iron and steel the temperature at the point to be welded should be great enough to produce a dull red heat. This will make the whole operation much easier, because there will be no surrounding cool metal to reduce the temperature of the molten material from the welding rod below the point at which it will join the work. From this red heat the mass of metal should grow cooler as the distance from the weld becomes greater, so that no great strain is placed upon any one part. With work of a very irregular shape it is always best to heat entire piece so that the strains will be so evenly distributed that they can cause no distortion or breakage under any conditions.

The melting point of the work which is being preheated should be kept in mind and care exercised not to approach it too closely. Special care is necessary with aluminum in this respect, because of its low melting temperature and the sudden weakening and flowing without warning. Workmen have carelessly overheated aluminum castings and, upon uncovering the piece to make the weld, have been astonished to find that it had disappeared. Six hundred degrees is about the safe limit for this metal. It is possible to gauge the exact temperature of the work with a pyrometer, but when this instrument cannot be procured, it might be well to secure a number of temperature cones from a chemical or laboratory supply house. These cones are made from material that will soften at a certain heat and in form they are long and pointed. Placed in position on the part being heated, the point may be watched, and when it bends over it is sure that the metal itself has reached a temperature considerably in excess of the temperature at which that particular cone was designed to soften.

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I) проводимость металла; 2) деформация; 3) металлы сжимаются; 4) сохранять неизменное положение; 5) под напряжением; 6) сила сжатия; 7) чугун; 8) угольная подушка; 9) форсунка; 10) огнеупорный кирпич; 11) печь для обжига; 12) равномерно; 13) раскалить докрасна; 14) расплавленный металл; 15) иметь неправильную форму.

Переведите на РЯ следующие слова и словосочетания из текста:

1) to put heat into metal; 2) preliminary heating; 3) the heat applied at the weld; 4) a loose wall; 5) temporary arrangement; 6) a baffle of brick; 7) to deflect; 8) the heat should gradually shade off; 9) wasteful procedure; 10) aluminum casting; 11) to gauge the temperature; 12) to be in excess of the temperature; 13) to distribute evenly; 14) to procure some material; 15) to expand.

Подберите синонимы к следующим словам и выражениям:

adjoining, evenly, preliminary heating, to deform, to obtain, to provide the desired increase, methods are applied.

Укажите «ложныхдрузей» переводчика:

напряжение, неправильный; contract, original.

Вставьтенужноеслово.

1. Preheating avoids the danger of ... through expansion. 2. The total amount of heat necessary to put into metal is increased by the ... of the metal. 3. All the metals used in welding ... as they cool. 4. While cooling the added metal will ...

under the strain. 5. The workpiece may be preheated in special . . . 6 . The temperature of the parts heated should be ... raised to avoid cracking. 7. The oven for preheating may be temporary or ... . 8. In the process of preheating the workpiece must be protected from the of fire. 9. The heat should gradually from the highest temperature desired. 10. The strains should be evenly ... to avoid distortion or breakage.

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Unit 7. ELECTRIC ARC WELDING

This method bears no relation to the resistance welding, except that the source of heat is the same in both cases. Arc welding makes use of the flame produced by the voltaic arc in practically the same way that oxy-acetylene welding uses the flame from the gases.

If the ends of two pieces of carbon, through which a current of electricity is flowing while they are in contact, are separated from each other quite slowly, a brilliant arc of flame which consists mainly of carbon vapor is formed between them. The carbons are consumed by combination with the oxygen in the air and through being turned to a gas under the intense heat. The most intense action takes place at the center of the carbon which carries the positive current and this is the point of greatest heat. The temperature at this point in the arc is greater than can be produced by any other means under human control.

An arc may be formed between pieces of metal, called electrodes, in the same way as between carbon. The metallic arc is called a flaming arc and as the metal of the electrode bums with the heat, it gives the flame a color characteristic of the material being used. The metallic arc may be drawn out to a much greater length than one formed between carbon electrodes.

Arc welding is carried out by drawing a piece of carbon which is of negative polarity away from the pieces of metal to be welded while the metal is made positive in polarity. The negative wire is fastened to the carbon electrode and the work is laid on a table made of cast or wrought iron to which the positive wire is made fast. The direction of the flame is then from the metal being welded to the carbon and the work is thus prevented from being saturated with carbon, which would prove very detrimental to its strength. A secondary advantage is found in the fact that the greatest heat is at the metal being welded because of its being the positive electrode.

The carbon electrode is usually made from one quarter to one and a half inches in diameter and from six to twelve inches in length. The length of the arc may be anywhere from one inch to four inches, depending on the size of the work being handled.

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While the parts are carefully insulated to avoid danger of shock, it is necessary for the operator to wear rubber gloves as a further protection, and to wear some form of hood over the head to shield him against the extreme heat liberated. This hood may be made from metal, although some material that does not conduct electricity is to be preferred. The work is watched through pieces of glass formed with one sheet, which is either blue or green, placed over another which is red. Screens of glass are sometimes used without the head protector. Some protection for the eyes is absolutely necessary because of the intense white light.

It is seldom necessary to preheat the work as with the gas processes, because the heat is localized at the point of welding and the action is so rapid that the expansion is not so great. The necessity of preheating, however, depends entirely on the material, form and size of the work being handled. The same advice applies to arc welding as to the gas flame method but in a lesser degree. Filling rods are used in the same way as with any other flame process.

In a great many places the use of the arc cuts the cost of welding to a very small fraction of what it would be by any other method, so that the importance of this method may be well understood.

Any two metals which are brought to the melting temperature and applied to each other will adhere so that they are no more apt to break at the weld than at any other point outside of the weld. It is the property of all metals to stick together under these conditions. The electric arc is used in this connection merely as a heating agent. This is its only function in the process.

It has advantages in its ease of application and the cheapness with which heat can be liberated at any given point by its use. There is nothing in connection with arc welding that the above principles will not answer; that is, that metals at the melting point will weld and that the electric arc will furnish the heat to bring them to this point. As to the first question, what metals can be welded, all metals can be welded. The difficulties which are encountered are as follows: In the case of brass or zinc, the metals will be covered with a coat of zinc oxide before they reach a welding heat. This zinc oxide makes it impossible for two clean surfaces to come together and some method has to be used for eliminating this possibility and allowing the two surfaces to join without the possibility of the oxide intervening. The same is true of aluminium, in which the oxide, alumina, will be formed, and with several other alloys comprising elements of different melting points.

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Переведите на РЯ следующие слова и словосочетания из текста:

1) carbon vapor; 2) metallic arc; 3) flaming arc; 4) wrought iron; 5) detrimental to the strength; 6) head protector; 7) to adhere; 8) to bring to a temperature; 9) heating agent; 10) to liberate heat.

Найдите в тексте синонимы к следующим словам и словосочетаниям:

1) to protect; 2) harmful; 3) to stick together; 4) to gasify; 5) to fill completely with; 6) to separate from conducting bodies; 7) very bright light;8) to be concentrated at a point; 9) to stick to; 10) to get rid of, to remove.

Вставьте предлоги.

1. The carbons turn to a gas ... the intense heat. 2. There are few means ...

human control to provide such intense heat. 3. The metal of the electrode burns

... the heat. 4. During arc welding the work is laid ... a table made of cast or wrought iron. 5. The operator should wear some form of good ... his head. 6. The work should be watched ... pieces of coloured glass ... .7. Some protection

... the eyes is absolutely necessary. 8. The heat is localized ... the point of welding. 9. The necessity of preheating depends ... some factors. 10. This is true

... aluminum and some alloys.

SUPPLEMENTARY TEXTS

Holding work in a chuck

Short parts, are usually held in a chuck. This method of holding work is of great importance since it is widely used with lathes. A chuck is a rotating vice which may be attached to the nose of the lathe spindle. There are three important varieties of lathe chucks, su.chas independent Jaw chucks, concentric or self-centering chucks or contracting chucks.

An independent four-jaw chuck belongs to the group of simple chucks. The chuck has four jaws, carried in a radial slots in the chuck body. Each Jaw of the chuck can be adjusted independently by means of its own screw. It offers the possibility to fasten works of both cylindrical and non-cylindrical shape in such chucks. The body of the chuck is provided with ascrewed hole to fit the spindle nose of the lathe.

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The concentric chuck usually has three jaws which can be moved in and out together by means of a chuck key, which is inserted into the opening of one of the three bevel gears, meshed with a large bevel gear. A multiturn spiral groove is cut on the flat reverse side of the large bevel gear. The bottom projections of the jaws are inserted into the separate turns of the groove. When one of the bevol gears is turned by means of, the chuck key its motion is transmitted to the large bevel gear. The rotation of that large bevel gear causes simultaneous and uniform motion of all the three jaws along the slots of the chuck by means of the spiral groove. When the gear with the spiral groove is rotated in that or another direction the jaws are either approached to or removed from the centre thus clamping or unclamping the work. The concentric or self -centering chuck is very convenient in operation as all its jaws are moved simultaneously. Consequently a work of cylindrical shape is clamped exactly along the spindle axis. This centering is done automatically, therefore such chucks are called "self-centering".

For finishing the external diameter of work which is already bored axially a mandrel is used. A mandrel is a bar with centre holes at each end. The mandrel is mounted between centres and enables the outside of a workpiece to be turned concentric with the inside and in general such work would have the hole finished first and the outside finished on a mandrel subsequently. The advantage of mounting work on a mandr el is that of being able to reverse the work on the centres so that the whole of the work exterior can be operated on by cutting tools.

Holding work in a vice

Vices are attachments which are mainly used for holding workpieces in machine and fitting shops. It should be noticed that a vice may also be used as an attachment for holding workpieces on a metal-cutting lathe.

Depending on the character of operation performed bench vices or parallel vices may be applied. Bench vices are made from forged steel and are of rugged construction. If their construction were not rugged, they could not be used when heavy-duty operations such as cutting, rivetting, etc. are performed. A bench vice consists of two jaws: the movable jaw and the solid jaw. At the end of the solid jaw there is a lug for securing the vice to a bench. The extension rod of the jaw is built in a wooden pillow. A workpiece being

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clamped between the jaws, they are moved together by means of a squarethreaded screw. By unscrewing the screw the jaws are moved apart by a spring riveted to the solid jaw. In parallel vices the jaws move parallel to each other. It should be pointed out that parallel vices in their turn are subdivided into swivel vices and plain vices. The jaws of all the vices are mode of accurately ground tool stool. They may be moved together or apart by means of a handle. A swivel vice, being the most convenient vice in operation, consists of a vice base, a solid jaw and a movable jaw. The motion of the movable jaw is provided by the rotation of a screw inserted into a fixed nut. When the screw is rotated by means of a handle the former will screw in and move the movable jaw to the workpiece to be clamped. The vice base is mounted on a swivel plate being connected with the latter by a spindle. A bolt is inserted into a T-groove. By turning a handle the bolt may be loosened and the vice may be turned in a desired direction. The swivel vice may be turned through any angle as the bаsе of the vice in held to the table with a swivel plate.

Plain vices differ entirely from swivel vices in the absence of the swivel plate, the vice base being bolted directly to a bench. The vice of such a type is made from grey iron, steel hardened plates with a nut being screwed to its jaws. The plain vices is used for light milling operations. Parallel vices are convenient for clamping workpieces, but as their jaws are of little strength they are non-suitable for heavy-duty operations. Universal vice may be used for general tool-room work. It can be swivelled up to 90° in the vertical plane and up to 36O0 in the horizontal plane.

Lathe operations

To machine a piece of work on centre в, each end of the work has to be countersunk. This is accomplished with a combined drill and countersink. When mounting the work between the centres care must be taken to see that the centres are in good condition. The dead centre in the tailstock will be the first to show wear caused by friction that is why it should be well lubricated.

The work is held firmly but not too tightly on the live and dead centres. Too great a pressure of the dead centre against the work will make the centre and work heat up so as to cause wear from friction.

As a general rule the tool holder must be placed in the tool post at approximately 90° with the centre line or a little in the direction of the dead

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centre when feeding toward the headstock. The point of the cutting tool should be on the centre line between the dead centre and the live centre.

The following operations may be performed on the lathes straight (cylindrical) turning, taper turning (by using the compound tool rest or taper attachment), facing (cutting at right angles to the axis of the work), either straight or taper boring and external or internal thread cutting. A thread may be cut with a tap, die or with a threading tool (cutter).

For producing short tapers the compound rest is generally swiveled to the required angle and cutting tool is fed by hand. The taper attachment may be used to produce internal and external tapers, the tool being fed automatically. In producing tapers the point of the tool must be on the centre line of the work.

The taper attachment of the lathe should be used in cutting pipe thread, the compound rest is set over towards the right on saddle at the proper angle. The feed of the carriage is toward the headstock. In cutting the left-hand thread the compound rest is moved towards the left on the saddle and the feed of the Carriage is toward the tailstock.

When facing the thickness of a piece to a size which is held in close limits the compound rest may be swiveled at an angle of 30° from the face of the work and the tool fed in with the compound feed screw. The tool is fed in along the hypotenuse of a triangle. From a theorem in geometry (which states that in a right triangle the side opposite 30° angle is equal to onehalf the hypotenuse) it can be seen that the thickness of the work is reduced one-half thousandth for every thousandth the tool is advanced with the compound feed screw.

While cutting cast iron a deep cut should be made because cast iron has a very hard scale on the outside and in cutting this cast iron tool has to be forced under this scale or the cutting edge of the tool will be broken.

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