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THE SAND PROCESS

HOW IT WORKS The Sand Casting ( Green Sand ) molding process utilizes a cope ( top half ) and drag ( bottom half ) flask set-up. The mold consists of sand, ( usually silica ), clay and water. When the water is added it develops the bonding characteristics of the clay, which binds the sand grains together. When applying pressure to the mold material it can be compacted around a pattern, which is either made of metal or wood, to produce a mold having sufficient rigidity to enable metal to be poured into it to produce a casting. The process also uses coring to create cavities inside the casting. After the casting is poured and has cooled the core is removed.

The material costs for the process are low and the sand casting process is exceptionally flexible. A number of metals can be used for castings in sizes from ounces to many thousand pounds. The mold material is reclaimable, with between 90 and 95% of the sand being recycled, although new sand and additions are required to make up for the discarded loss. These features, combined with the relative ease of mold production, have ensured that the green sand molding process has remained as the principal method by which castings are produced.

THE SAND
The sand used for green sand molding is critical and determines the favorable or unfavorable outcome of the casting. It controls the tolerances, surface finish and the repeatability while in production. Remembering that the tolerances on sand castings are usually wider than the other casting methods. The sand must exhibit the following characteristics:

FLOWABILITY: The ability to pack tightly around the pattern. PLASTIC DEFORMATION: Have the ability to deform slightly without cracking so that the pattern can be withdrawn.

GREEN STRENGTH: Have the ability to support its own weight when stripped from the pattern, and also withstand pressure of molten metal when the mold is cast. PERMEABILITY: This allows the gases and steam to escape from the