Cast iron is an alloy of iron and carbon. It is obtained by re-melting pig iron with coke, limestone and steel scrap in a furnace known as ‘‘cupola”. The carbon percentage varies from 1.7 to 4.5 %. It also contains small amount of silicon, manganese, phosphorus and sulphur.
Production of Cast Iron
Cast irons are normally produced by melting Pig iron in cupola furnace with coke, lime stone and other fluxes. The limestone and fluxes aid in separating the impurities from the pig iron. The limestone also acts as an agent to carry off the oxides and ash from the fuel. Cupola is fired with coke to produce high temperatures required for melting pig iron and scrap.
Properties of Cast Iron.
(a) It is brittle.
(b) It is very weak in tension, so it cannot be used for making bolts and machine parts which are liable to tension.
(c) It is having good casting characteristics.
(d) It has high compressive strength and high wear resistance.
(e) It is having excellent machinability.
(f) Its tensile strength is 100 to 200 MPa. (Mega Pascal)
(h) Its compressive strength is 400 to 1000 MPa.
(i) Its shear strength is 120 MPa.
(j) Density of cast iron is – 6.8 to 7.8 gm/cm3.
(k) Melting point of cast iron is 1150 to 1200°C.
Types of Cast Iron Cast Iron may be classified as follows:
(a) Grey Cast Iron
(b) White Cast Iron
(c) Mottled Cast Iron
(d) Nodular Cast Iron
(e) Malleable Cast Iron