Method of preparing resin coated foundry sand using unsaturated polyester

A method of preparing a resin coated sand for forming molds and cores for use in sand mold casting processes, the method comprising the steps of:

• mixing a major amount of a heated foundry sand with a minor amount of an unsaturated polyester, which is solid at room temperature, such that said unsaturated polyester liquefies and adheres to the particles of said sand, said unsaturated polyester having at least three ethylene double bonds per 1000 g of said unsaturated polyester;
• adding a solution of a polymerization initiator for said unsaturated polyester in an organic solvent, absent any cross-linking agent, to the mixture of said sand and said unsaturated polyester while the temperature of said mixture is such that said unsaturated polyester remains in liquid state but hardly cures even in the presence of said polymerization initiator, said organic solvent being selected such that said organic solvent and said unsaturated polyester have no mutual solubility;
• stirring the resultant mixture thereby mixing said solution in the absence of a cross-linking agent, with said unsaturated polyester and causing said organic solvent to evaporate;
• and
• lowering the temperature of said resultant mixture with continued stirring until solidification of said unsaturated polyester adhering to the particles of said sand.