Q. What do you mean by Moulding materials?
Various types of materials are used in the foundries for the manufacture of casting moulds and cores. These materials are divided in to two groups: basic and auxiliary. Basic moldings materials include : Silica sands, which forms the various base and the various binders. The at is auxiliary group includes various additives which impart desired properties to the moulding and core sands.
The essential constituents of moulding sand are:
• It is cheap, plentiful and easily available.
• It is characterized by a high softening temperature and thermal stability, which is highly refractory.
• Easily moulded, reusable and capable of giving good details.Silica sand forms the bulk of moulding sand.
Binder may be present in natural sand or added to silica sand separately. In combination with water, it is the bonding agent in green sand. Although moist particles do adhere to one another slightly, but coating with moist clay, the strength of the mixed sand is increased three folds. Clay imparts cohesiveness and plasticity to the moulding sand in the moist state and increases its strength with sufficient plasticity, the sand is said to be "tempered".
Additives impart to the moulding sand special properties (strength, thermal stability, permeability, refractoriness, thermal expansion etc.)