Page 135 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

Machine base, tables, slideways are made of cast iron because it is dimensionally stable after a period of aging.

Because of its graphite content, cast iron provides an excellent bearing and sliding surface.
The melting point is lower than that of steel and as grey cast iron possesses good fluidity, intricate casting can
be made.

Grey cast iron is widely used for machine tools because of its ability to reduce vibration and minimize tool chatter.
Grey cast iron, when not alloyed, is quite brittle and has relatively low tensile strength. Due to this reason it is not
used for making components subjected to high stress or impact loads.
Grey cast iron is often alloyed with nickel, chromium, vanadium or copper to make it tough.

Grey cast iron is weldable but the base metal needs preheating.
White cast iron
This is very hard and is very difficult to machine, and for this reason, it is used in components which should be
abrasion-resistant.
White cast iron is produced by lowering the silicon content and by rapid cooling. When cooled in this manner, it
is called chilled cast iron.

White cast iron cannot be welded.
Malleable cast iron
Malleable cast iron has increased ductility, tensile strength and toughness when compared with grey cast iron.
Malleable cast iron is produced from white cast iron by a prolonged heat-treatment process lasting for about 30
hours.
Nodular cast iron
This is very similar to malleable cast iron. But this is produced without any heat treatment. Nodular cast iron is
also known as:
Nodular Iron - Ductile Iron - Spheroidal Graphite Iron
This has good machinability, castability, resistance to wear, low melting point and hardness.
Mealleable and nodular castings are used for machine parts where there is a higher tensile stress and moderate
impact loading. These castings are less expensive and are an alternative to steel castings.
Wrought Iron (Manufacturing process) (Fig 1)
Wrought iron is the purest form of iron. The analysis of Wrought iron shows as much as 99.9% of iron. (Fig 1)
When heated, wrought iron does not melt, but only becomes pasty and in this form it can be forged to any shape.

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CITS : WCS - Electrical - Exercise 11