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11. Communicative situations:

  1. Make a report on the topic “ What is the usage of FSW ”

  2. Speak with your friend about advantages and disadvantages of FSW

12. Retell the text. Text b plasma

Plasma welding. Plasma welding provides the highest effect when used for joining metals with a high thermal conductivity, such as copper, aluminium and other alloys. This method allows avoidance of preheating and performance of single-pass welding on a wide range of thickness of materials. Thus, the straight polarity plasma arc can weld copper up to 50 mm thick in a single pass without groove preparations. Plasma welding of aluminium and its alloys at a DCRP provides a high quality of welded structures up to 20 mm thick. Strength characteristics of the weld metal containing no tungsten inclusions and no oxide films are at a level of 95% of those of the base metal.

A range of the plasma welding machines has been developed. Machines operating at currents of 50, 100, 300, 500 and 800 A are available. The technology and optimal layout of the microplasma equipment have been devised for all types of welding of parts of thin-sheet metals (bellows, casings of instruments, magnetic cores, transformers and many others).

An important property of microplasma welding is a high degree of constriction of the arc and low sensitivity of sizes of the weld being formed (its width and depth) to variations in the arc length.

The use of this welding method instead of argon-arc welding leads to a substantial increase in productivity and quality of welding of thin metals (0.1 – 2.0 mm) and improves vendibility of products.

Modern electronics allows a contactless ignition of the arc, regulation of the current drop at the end of welding and fast precise setting of the process parameters.

Plasma surfacing. Surfacing can be used to make the most diverse items with the desirable surface properties, i.e. corrosion-, heat-, wear-resistant, antifriction, etc., as well as to repair worn-out pieces.

Plasma surfacing can be performed at a direct current of reverse or straight polarity, using wire or powder consumables.

Owing to minimum penetration of the base metal and its minimum dilution with the deposited metal, the process of plasma surfacing at a DCRP provides the preset properties of the metal even in the first of the deposited layers, as compared with the third or fourth layers in the case of arc surfacing. This leads to metal saving and raises labour productivity. Powder materials, such as Co-based alloys and Ni-based alloys, Fe-based powders, stainless steel and bronze wire can be used as the coating materials.

Plasma surfacing gains wide acceptance in manufacture and repair of valves of various-application internal combustion engines, rolling mill shafts and other parts.

Exercises

1. Remember the following words and word-combinations:

layout -устаткування;

bellows -ковальські міхи;

vendibility -здатність до продажу;

constriction -скорочення;

reverse polarity -протилежна полярність;

straight polarity -пряма полярність.

2. Read and translate the text.

3. Answer the following questions:

  1. What metals is plasma welding used for?

  2. What machines for plasma welding are available?

  3. What are the important properties of plasma welding?

  4. What does the modern electronics allow?

  5. What can surfacing be used for?

  6. What materials can be used as the coating ones?

  7. Where does plasma surfacing gain wide acceptance?

4. Are the following statements about the text true or false? Why?

  1. Plasma welding provides the highest effect when used for joining metals with low thermal conductivity.

  2. The straight polarity plasma arc can weld copper up to 100mm. thick in a single pass.

  3. Strength characteristics of the weld metal containing tungsten inclusions are very high.

  4. The important property of microplasma welding is low degree of constriction of the arc.

  5. Owing to the maximum penetration of the base metal and its maximum dilution with the deposited metal, the process of plasma surfacing provides the preset properties of the metal even in the first of the deposited layers.

  6. Plasma surfacing is not used in machine- building.

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