31) Where is induction hardening applied ?
Induction hardening is done by using electricity. It is applied on wearing surface of crank shafts, cam shafts, axles etc.
32) Sometimes a thin brown and red oxide layer is formed on the surface of a copper part .How can it be removed ?
Pour few drops of hydrochloric acid on the copper part having oxide layer and wipe it with a cloth.
33) Differentiate between hardening and tempering ?
The main purpose of hardening is to resist wear and enable it to cut the other metals and reheating is not necessary. The main purpose of tempering is to reduce some of hardness and to increase the toughness. It consists of reheating after hardening to the temperature below the critical range.
34) What are the commonly found iron ores ?
Hematite, Magnetite, Limonite, Siderite and Iron pyrite are the main iron ores.
35) Differentiate between carbon steel and alloy steel ?
Carbon steel is the combination of iron and carbon. It is easily rusted and malleable. It can be easily machined and magnetic. Alloy steel is the combination of iron, carbon and other alloying elements. It is rust proof and harder and tougher. It is hard for machining and non magnetic.
36) Why is the soldering iron bit made of copper and not of steel ?
Because copper is good conductor of heat and quickly transfer its heat to the metal at the joint than the steel.
37) What do you mean by Brazing ?
Brazing is the process through which metal pieces are jointed by means of alloy of copper and zinc called spelter. The metal pieces to be joined should be heated instead of using a soldering iron bit. For this muffle as well as Smith’s furnaces are used. It provide much stronger joint as compared to soft soldering.
38) Why cast iron cannot be forged ?
Because it will break if heated and beaten by hammer.
39) What are the advantages of forging ?
- Metal can be forged to any shape.
- Metal can be forged in short time without wasting.
- The strength of steel as well as granular structure can be improved.
- The manufacturing cost is lesser than machining.
40) Which type of grains formed after hardening the steel ?
Hardened steel have contains fine grains.