Q. Describe the terms "Solids zone", "Mushy Zone" and "Liquid Zone" used in solidification of casting and explain directional solidification in casting.

Ans. Solidification of casting :  After molten metal is poured into a mould a series of events takes place during the solidification of the casting and its cooling to ambient temperature. These events greatly influence the size, shape, uniformity and chemical composition of the grain formed throughout the castings which in turn influence its overall properties. The main factors affecting these events are :

(i)       The type of metal.

(ii)      The thermal properties of both metal and the mold.

(iii)    The shape of the mold.

(iv)    The geometric relationship between volume and surface area of the casting.