Principal Ingredients of Moulding Sands:

The principal ingredients of moulding sands are following:

(a) Silica sand grains,

(b) Clay (bond),

(c) Moisture, and

(d) Organic additives.

Silica Sand Grains

Silica sand grains impart chemical resistivity, refractoriness & permeability to the sand. They are specified according to their average shape and size. The finer grains would lead to more intimate contact and lower the permeability. But, fine grains tend to fortify the mould and lessen its tendency to be distorted. The shapes of the grain might vary from round to angular. The grains are categorized according to their shape as below :

a. Rounded Grains

b. Subangular Grains

c. Angular Grains

d. Compounded Grains

In practice, sand grains have mixed grain shapes. A sub-angular-to-rounded grain mixture would be the most excellent combination.