The Cast Iron is obtained by re-melting Pig Iron with Coke and Limestone in Cupola Furnace.It is primarily an Alloy of Iron and Carbon.The Carbon contents in Cast Iron varies from 1.7 to 4.5 %.
It also contains small amounts of Silicon,Manganese,Phosphors and Sulphur.
The Carbon in a Cast Iron is present either of following forms,
01)Free Carbon or Graphite.
We can not use Cast Iron in those parts of Machines which are subjected to Shocks,due to its Property of Brittleness. Design of a machine must be very perfect for long life.
The Compressive Strength of Cast Iron is much greater than the Tensile Strength.Cast Iron has good Casting characteristics,high Compressive Strength,Wear Resistance,Excellent Machinability and Low in Cost.
These Properties made Cast Iron,a valuable Material for Engineering Purpose.
Following are the various types of Cast Iron,used in Engineering Field.
A)Grey Cast Iron.
B)White Cast Iron.
C)Mottled Cast Iron.
D)Malleable Cast Iron.
E)Alloy Cast Iron.
Effect of Impurities on Cast Iron.
As you know from above,that the Cast Iron contains small percentages of Silicon,Manganese,Phosphors and Sulphur.These may be treated as Impurities in the Cast Iron.The effect of these Impurities on the Cast Iron are as follows.
It makes Cast Iron Hard and Brittle.It should be kept well below 0.1% for Foundry Purpose.
It makes Cast Iron White and Hard.It is often kept below 0.75%.It helps to exert a controlling influence over the harmful effects of Sulphur.
It provides the Formation of Free Graphite which makes the Iron soft and easily machinable.It may be present in Cast Iron up to 4%.It also produces sound Casting,free from Blow Holes.
It aids Fusibility and Fluidity in Cast Iron,but induces Brittleness.It should not be more than 1%. When cheapness is essential in Light Engineering Casting,Phosphoric Irons are very much useful.
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