The sand used for sand molding is critical and determines the favorable or unfavorable out come of the casting, it controls the tolerances, surface finish and the repeatability while in production. The sand must exhibit the following characteristics:

Characters of sand casting:

FLOWABILITY: The ability to pack tightly around the pattern.

PLASTIC DEFORMATION: Have the ability to deform slightly with out cracking so that the pattern can be withdrawn.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 seam to escape from the mold during casing.
All of these requirements are dependent on the amount of active clay present and on the water content of the mixture.

SAND CASTING BENEFITS
Least expensive casting process
Casting can be up to several tons
Less expensive than machining shapes from bar stock
Can cast intricate shapes
Can be used with most pourable metals and alloys

From:http://www.ruyicasting.com/sand-casting.htm

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