Cast iron may be defined as “an alloy of iron and carbon containing more than 2% carbon”.
The minimum carbon content in a cast iron is about 2% while the practical maximum carbon content is about 4.3%. In addition to carbon, cast iron contains other elements such as silicon, sulphur, phosphorous and manganese. Cast iron is a pig iron remelted and thereby refined, together with definite amount of limestone, steel scrap and damaged castings ( foundry returns ), in a cupola or other form of remelting furnace, and poured into suitable moulds of required shape.
Classification of cast irons
- White cast iron.
- Malleable cast iron.
- Gray cast iron.
- Nodular cast iron.
- Mottled cast iron.
- Chilled cast iron.
- Alloy cast iron.
- Mechanite cast iron.
White cast iron.
- White cast iron is very hard and brittle.
- It is wear resistant and less ductile.
- Hardness varies from 400 to 600 B.H.N.
- It cannot be machined.
- Finishing to final size is done by grinding.
- Used for manufacturing wrought iron.
- For manufacturing those component parts which require a hard and abrasion resistant material.
- For producing malleable iron casting.
- For weaving plates, road roller surface, industry flooring, crushers, shot blasting nozzles.
- For pump lines, mill lines, ball for grinding ball mill.
- For dies and extrusion nozzles.
- Railway brake blocks.
Gray cast iron.
- Grey cast iron is brittle and may be broken if a heavy hammer is used.
- The ultimate tensile strength varies from 120N/mm^2 to 300N/mm^2.
- Hardness of grey cast iron varies from 150 to 240 B.H.N.
- Melting point is low.
- Good compressive strength.
- It is easily machinable.
- The graphite present, acts as a lubricant.
- Used in machine tool structure.
- Used in gas or water pipes for underground purposes.
- Used in frames for electric motors.
- Used in ingot moulds.
- Used in piston rings.
- Used in sanitary wares.
- Used in household appliances etc.
Nodular cast iron.
- It has very good casting properties as high fluidity and low melting point.
- It produces better machined surfaces.
- The tensile strength is 330N/mm^2.
- High strength and toughness.
- Good resistant to wears.
- It can be welded nicely.
- Used in paper industries machinery.
- Used in internal combustion engines.
- Used in power transmission equipment.
- Used in farm implements and tractors.
- Used in earth moving machinery.
- Used in valves and fitting.
- Used in pumps and compressors.
- Used in construction machinery.
Malleable cast iron.
- It is less brittle.
- Tensile strength of malleable cast iron is 180N/mm^2.
- Good wear resistant and vibration damping capacity.
- Hardness varies from 80 to 275 B.H.N.
- These cast irons show some ductility and toughness.
- Used in automobile parts.
- Used in sewing machine parts.
- Used in bicycle parts.
- Used in agricultural equipments.
- Used in electrical line hardware parts.
- Used in crank shaft.
- Used in power train parts.
Alloy cast iron.
Mottled cast iron.
- Mixture of the two states, grey cast iron and white cast iron.
- Strength and hardness varies according to the ratio of free carbon to combined carbon.
- Less tendency to rust than grey variety.
- Fluidity is good.
- Hard and brittle.
Mechanite cast iron.
- General engineering.
- Heat resisting.
- Wear resisting.
- Corrosion resisting.
- Nodular ‘S’ type.
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