Miscellaneous Moulding Materials

Miscellaneous Moulding Materials

These are the moulding materials, besides those already described, that are used in foundry procedures. They include fire clay, clay wash, parting materials and core binders. Fire clay is a mineral product consisting essentially of hydrated aluminum silicate and it comes from the same source that sand does.

The purpose of using fire clay is that it offers a good bond when mixed with burnt sand, in the proportion of 1 ‘to 2 for coating the inside of cupolas and pouring ladles. Clay wash is a mixture of fire clay and water. It is used in the foundry where a strong bond Is required, and for repairing ladle linings with a fresh daubing mixture. Parting materials are parting sands or parting dusts which must contain no bond. A non-silica parting compound made from powdered phosphate rock is the material that is widely used as a parting dust. This is applied on the parting surface or joint of a mould from a dust bag to prevent the moulding sand from adhering to the moulding box or to the pattern. The following materials are suitable for binders: flour, resin, linseed oil, cereal products, dextrine, molasses, and numerous others, depending upon the type of castings, produced in the foundry. The primary purpose of binders is to influence the bonding properties of sand. Of all the binders, dextrin is perhaps the best. It increases air-setting strength, toughness, and collapsibility and prevents sand from drying rapidly.