Chapter III machine parts

1. Welding

Welding is a process which provides a non-detachable joining of two like metal pieces¹ by heating them till melting condition or fusion without or with mechanical pressure. Fusion of two metal pieces may be brought about² by different types of welding, such as hammer welding, thermit welding, electric welding and gas welding.

Hammer welding is a process in which two metal pieces are joined and fused together by force from a hand or power hammer after having heated these pieces in a blacksmith's forge until they reached their plastic stage.

Thermit welding is a process consisting of a chemical reaction obtained by igniting finely divided aluminium and iron oxide. This type of welding is used in repairing rails, frames, etc.

Electric resistance welding is a process consisting of heating metals to be welded to their plastic temperature and then applying mechanical pressure for achieving a non-detachable joining of the metals.

Resistance welding processes form a group consisting of many types of welding. Selection of each type of welding depends on the kind and size of metals to be welded. Resistance welding embraces such processes as spot welding, butt welding, electric arc welding, etc.

Spot welding is a process in which two metals are held between electrodes passing a heavy current through the metals to be welded. The electrodes having been forced together by pressure join the surfaces of the metals in a spot, the size of which is about the same as that of the tip of the electrode. This kind of welding is suitable for welding parts of airplanes, refrigerators and automobiles.

In butt welding the parts to be welded are pressed together while heat is generated by passing a heavy current through the area of the joint. Butt welding may be applied for welding pipes, tubing, rods, etc.

Fig. 32. Electric Arc Welding:

1 - carbon electrode; 2 - additive;3 - plate; 4 - weld

Electric arc welding is a process in which surfaces to be joined are fused together by the heat of an electric arc. The electric arc was invented in 1802 by the famous Russian scientist V. V. Petrov, who demonstrated the possibility of utilizing its heat for fusing metals. Fig. 32 shows the process of electric arc welding. By bringing the work and the electrode together as conductors, an electric circuit is

established. When the conductors are separated, an electric arc is created in which the electrical energy is converted into heat, its temperature being as high as 7000°F³. An additive is placed into the flame of the electrical arc. An additive is a metal which is externally applied to the place of welding and melted to form a weld together with the material of the work. The electric arc melts both the edges of the parts to be melted and the additive used. The electrode having been removed from the place of welding, the molten metal cools, solidifies and forms a weld, joining the parts of the work.

In autogenous (gas) welding the source of heat is the gas flame obtained from a gas which is often acetylene. Acetylene mixed with oxygen in a torch when ignited gives a steady flame. The welding torch consists essentially of a gas mixing chamber and is designed in two types: the low-pressure injector type and the equal-pressure type. In the injector-type torch the acetylene is delivered at very low pressure and the oxygen enters the torch at high pressure and velocity expanding in the mixing chamber. Then the acetylene is drawn by suction created in the mixing chamber in a constant ratio to the oxygen. Autogenous welding is carried out in different ways and methods. According to the movement of the torch, welding may be divided into rightward welding and leftward welding. In rightward welding the torch moves ahead of the additive, and in leftward welding the additive moves in front of the torch. In practice rightward welding is mostly used. Gas welding may be used for cutting metals and repairing agricultural machines and implements.

¹. two like metal pieces - два однородных куска металла

². fusion of two metal pieces may be brought about - сплавление двух кусков металла может быть произведено (выполнено)

³. 7000°F=7000 degrees according to Fahrenheit ['fa:renhait] - 7000 градусов по Фаренгейту

Exercises

I. Use the following words and phrases in sentences of your own:

electrode, to weld, fusion, non-detachable joining, electric resistance welding, to ignite, iron oxide, arc welding, spot welding, torch, velocity, autogenous welding, to generate, current

II. Answer the following questions:

1. What is welding and what is it used for? 2. What types of welding do you know? 3. What is the source of heat for arc welding? 4. What is the source of heat for gas welding? 5. What gas is used in autogenous welding? 6. What methods of autogenous welding do you know? 7. What is spot welding? 8. What is butt welding used for? 9. What is hammer welding? 10. What does the selection of a given type of welding depend on? 11. What processes does resistance welding embrace?

III. Supply synonyms for the following words:

burner, to fuse, various, to get, to convert, ahead of, to utilize

IV. Underline the suffixes in the following words and state what part of speech they belong to:

detachable, fusion, mechanical, pressure, obtained, finely, resistance, molten, rightward, agricultural, implement, suitable, possibility

V. Give derivatives from the following words and translate them into Russian:

to obtain, chemistry, final, to achieve, to conduct, electrical, external, press, wide

VI. Change the following sentences using the subordinate clauses instead of participle and gerundial constructions and translate the following sentences into Russian:

Example: 1. Having fused two metal pieces we obtained a weld.

When we have fused two metal pieces we obtained a weld.

2. We heard of their having applied a new kind of additive to obtain firm joining.

We heard that they have applied a new kind of additive to obtain firm joining.

1. After having heated two metal pieces in a blacksmith's forge they reached their plastic stage. 2. Having heated the additive to its melting temperature it began to diffuse into the metals to be joined. 3. We heard of their having applied termite welding to provide a non-detachable joining of two like metal pieces. 4. The engineer informed them of the hammer welding of two metal pieces having been completed. 5. We know of Petrov's having invented the electric arc. 6. Having been asked to join these rods by butt welding, I had to prepare my instruments for this work. 7. Having found a new method of welding, we were able to join machine parts better and faster.

VII. Give English equivalents of the following words:

сварка встык, контактная сварка, термитная сварка, сплавлять, шов, соединение, выбор, электрод, ток, площадь, присадочный материал, зажигать, ремонтировать, газосмешивающая камера, затвердевать, остывать, скорость , пламя

VIII. Giving answers to the following questions describe the process of electric arc melding shown in Fig. 32:

1. What process is shown in Fig. 32? 2. How can an electric circuit be established in electric arc welding? 3. When is an electric arc created? 4. Where is the electrical energy converted into heat? 5. What is an additive? 6. Where is an additive to be placed? 7. What is melted by the electric arc? 8. When does the molten metal cool, solidify and form a weld, joining the parts of the work?