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[June 2000]
Alloy solves mould problem for pottery company
Denby Pottery Company (Denby, Derbys, England) has turned to a low-melting-point alloy to solve an awkward problem in mouldmaking.
Formulated by Mining & Chemical Products Ltd (Whitchurch, Hants, England) to melt at only 70oC, the bismuth-based alloy is used for casting inserts for ceramic-ware handles for master moulds.
It replaced conventional plaster, which could seldom be cast without cavitation and breakage of inserts, and took time to prepare.
Denby has found that the fusible alloy produces strong and dimensionally accurate inserts free of internal and external defects.
The pottery company casts the inserts individually in split moulds. Melted inexpensively on a small bench heater and poured by hand, the metal flows freely to ensure complete filling of the curved and narrow cavity.
After a few minutes cooling time, the mould is opened and the metal insert removed. Several inserts are made in this way for incorporation into the master mould from which the production mould is cast in silicone rubber.
The process is quicker and more reliable than casting in plaster, which can take up to 15 minutes to mix and is liable to lead to rejects.
MCP says that casting in alloy is not only a highly repeatable operation but the metal can also be recovered for re-use when the moulds are redundant. Moreover, in contrast to epoxy resin, one of the alternatives, it does not shrink on solidification. It is also easier to handle than wax and not subject to the blowholing that can impair wax inserts.
Pleased with the results in mouldmaking, Denby is said to be now considering extending the use of alloys to the rapid prototyping of new parts.
ENDS