1. Chilled Casting. The mould used for chilled casting is either of a metal having high melting point or the mould may be given a lining of such a metal. This results in rapid conduction of heat from the surface of the casting with the result that the casting will have harder outer surface and softer inner core, Chilled castings are very useful in making railway carriage wheels.
2. Centrifugal Casting. The casting produced by pouring the metal in speedily rotating mould is called centrifugal casting. The crystallization of the molten metal takes place from the farthest end unlike the normal casting where the crystallization takes place from sides which are exposed to cooling. Therefore, centrifugal castings are uniform and strong. Even thin castings symmetrical about the axis of a cylinder can be obtained from this method of casting.
3. Malleable Cast Iron. It can be obtained by annealing the castings. The cast product is packed in an oxidizing material such as iron ore or in an inert material such as ground fire-clay. The pack is put into an oven and is heated to a temperature of about 870oC. It is kept at that temperature for about two days and is then allowed to cool at the rate of 5 to 10 degrees per hour. Iron ore acting as an oxidizing agent reacts with carbon and carbon dioxide escapes. The annealed cast product is free from carbon. If the cast product is packed in an inert material, slow cooling will separate out the temper carbon. Malleable cast irons are used for complicated structures.
4. Inoculated Cast Iron. The molten pig iron before casting is inoculated with soluble silicon compounds like calcium silicide. The silicon added in this way has got a better effect. Pearlitic cast iron having microstructure of small flakes of graphite set in pearlite is formed in this way.
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