Exercise 4 Give the definitions to the following processes of solid-state welding. Discuss the possibilities of their usage
· coextrusion welding;
· cold welding;
· diffusion welding;
· friction welding;
· high frequency welding;
· hot pressure welding;
· induction welding;
· roll welding.
Exercise 5 Look through the text and find all Past Participles. Make up sentences of your own with them.
UNIT 9
SOLDERING
This method of joining metals consists of applying a metal of low melting temperature between the base metals. The parts to be joined are not brought to a plastic or fluid state — the molten metal merely holds the parts together by its slight diffusion into the base metals. Therefore, the strength of the soldered joint is determined by the strength of the weaker filler metal, and is by no means comparable to the strength of welded joints.
Soldering is divided into two classifications: hard and soft. Hard soldering employs filler metals which melt at comparatively high temperatures. Silver and copper-base alloys are metals that exhibit this characteristic. Soft soldering employs filler metals of low melting temperature, such as tin and lead alloys.
Soft soldering is used extensively in sheet-metal work for joining parts that are not exposed to the action of high temperatures and are not subjected to excessive loads and forces. Soft soldering also is employed in electrical work for joining wires and small parts.
BRAZING
This process is similar to that of hard soldering. It employs copper-base alloys as a filler metal, and the equipment for heating the base metals and melting the filler may be a furnace or a blowtorch. The filler metal in most cases is an alloy of copper and zinc which melts at temperatures below those of the base metals, although in the brazing of some of the aluminium alloys, the filler metal may be an aluminium of suitable character.
The joints must be cleaned and properly fitted before heat is applied. Oxides, scale, oil, grease, and dirt must be removed by chemical or mechanical means. Proper clearance between the base metals must be provided for access of the molten filler metal forming the bond.
Several methods are employed in brazing metals.
1. The base metals may be dipped into a vessel containing the brazing alloy in a molten state. The parts are assembled in a fixture before being dipped into the molten alloy.
2. Various torches may be employed for heating the joint. Filler metal is supplied to the joint as in gas welding.
3. Furnaces are used quite frequently, especially in batch brazing, where large numbers of parts are brazed simultaneously.
4. Electric brazing is conducted in a heat supplied by electric resistance of electric arc, or by induction. This method is appropriate for brazing small objects, where thin sheets of filler metal may be inserted at the joint.
Exercise 1 Comprehension questions:
1 What is soldering?
2 What classifications is soldering divided into?
3 What is hard soldering?
4 What is soft soldering?
5 What is brazing and how is it performed?
6 What methods are employed in brazing metals?
Exercise 2 Find the English equivalents from the texts to the following Ukrainian words and phrases:
Наплавний метал, листовий метал, сплав з мідною основою, паяльна лампа, збираються взажимному пристосуванні, групова пайка тугоплавким способом.
Exercise 3 Tell whether the following statements are true or false. Correct the false statements to make them true.
1 Soldering consists of applying a metal of high melting temperature between the base metal.
2 The strength of the soldered joints is comparable to the strength of welded joints.
3 Soft soldering is used extensively in sheet-metal work.
4 Brazing is similar to soft soldering.
5 The filler metal in brazing is an alloy of gold and silver which melts at low temperatures.
6 Electric brazing is appropriate for brazing small objects.