Упражнения

Упр.1. Найдите в тексте английские эквиваленты следующих слово и словосочетаний:

1.Выявить утечку тока; 2. подключить последовательно; 3. станина агрегата; 4. заземление в стабилизаторе; 5. частое \ неоднократное перегорание предохранителей; 6. в качестве профилактической меры; 7. о неполадке такого рода свидетельствует…, 8. отказ (агрегата); 9. проволока 30 калибра; 10. без перегрузки.

Упр.2. Переведите следующие слова и словосочетания:

1.Close the switch; 2. insulator; 3. connect the wire to a terminal block; 4. carefully tracing the primary circuit; 5. this must be a clean connection; 6. a binding post of the regulator; 7. the remedy for a short circuit; 8. to draw an open circuit; with no stock in the welder dies; 10. without giving a moment’s trouble.

Unit 33. 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 burns 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.

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 aluminum, in which the oxide, alumina, will be formed, and with several other alloys comprising elements of different melting points.

VOCABULARY

To bear no relation to…- не иметь отношения к…

Voltaic arc – вольтова дуга

Carbon vapor – пары углерода

To be consumed - расходоваться

With the heat – под действием тепла

Carbon arc – угольная дуга

Carbon electrode – угольный электрод

To make fast – закрепить. подвести

To saturate - насыщать

Detrimental – вредный, вредоносный

To adhere – слипаться, соединяться

To puddle the weld – зд. заливать шов

Gauge – зд.калибр

Casting - отливка

Rolling - прокат

To insulate - изолировать

Screen - экран

Head protector – защитный головной уборr

To conduct electricity – проводить электричество