A number of foundry materials are used in the castings to give protection to the mold and the surface of the nucleus against the action of the molten metal, and help to produce a smooth and clean skin on castings.
Bituminous coal dust is one of the carbon b – Ing involved in greensiding materials. When the molten metal comes into contact with the surfaces of mould containing coal dust, a gaseous envelope is formed that is resistant to the fusion of sand to the metal. A product of tar is also formed which has an effect of binder near the face of the mold. Its use improves the finish of casting, increases resistance to both dry and green and also reduces the expansion.
For the purposes of deciding if a particular requirement of this standard is met, the final value, observed or calculated, expressing the result of a test or analysis must be rounded in the number of significant places withheld in accordance with the SI: Z – 1960 *. the rounded value should be the same as the value specified in this standard.