FOUNDRY SAND COATED WITH UNSATURATED POLYESTER AND ITS APPLICATION TO MOULDS AND CORES

摘要

A resin coated sand for use in sand mould casting processes, for example aluminium alloy casting process, comprises a foundry sand coated with a binder of which the principal material is a crystalline unsaturated polyester which is an untacky solid at room temperature, optionally together with the addition of a cross-linking agent. To cure the binder during the formation of sand moulds and cores for use in sand mould casting processes the binder contains from 0.1 to 5 parts by weight, per 100 parts by weight of crystalline unsaturated polyester, of a mixed radical polymerization catalyst comprising a first organic peroxide having a half-life of 10 hours at a temperature not lower than 130 DEG C, e.g. cumene hydroperoxide, and a second organic peroxide having a half- life of 10 hours at a temperature lower than 130 DEG C but not lower than 100 DEG C, e.g. dicumyl peroxide, the first peroxide forming from 10 to 90% by weight of the total weight of first and second peroxides. The resin coated sand is prepared by first coating the particles of the foundry sand with the binder, excluding the catalysts, by a hot-melt process and adding the catalysts after reducing the sand temperature to a suitable level.