Q. Describe the type of Facing and Backing sand?
Facing sand. This sand is used directly next to the surface of the pattern and comes into contact with the molten metal when the mould is poured. As a result, it is subjected to the severest conditions and must possess, therefore, high strength and refractoriness. This sand also provides a smoother casting surface and should be of fine texture. It is made of silica sand and clay, and some additives without the addition of used sand. The layer of facing sand in a mould usually ranges from 25-50mm.
Backing Sand. This is the sand which is used to back up the facing sand and to fill the whole volume of the flask. Old, repeatedly used moulding sand is mainly employed for this purpose.