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HOME| Casting Comparison Matrix

RPM Rubber Plaster Mold

The Process: How RPM Castings Are Made

Molten metal is gravity fed into a permeable plaster mold consisting of two or more segments that had been formed in individual rubber molds, then dried and assembled. When the casting has cooled, the plaster mold is easily crumbled away.

1) A PATTERN, usually machined of aluminum and often consisting of several components in positive or negative form.


 2) A MASTER MOLD of tooling epoxy that has been cast against a pattern. The option of constructing the pattern in either positive or negative form offers time and cost savings and allows for inexpensive tool changes.

Most box type castings are tooled with a positive exterior pattern and a separate negative interior pattern.

The production gating system is a permanent part of the master tooling and is therefore accurately reproduced by the rubber mold for each production cycle.


 3) A RUBBER MOLD which is always positive and therefore has been cast either against a master mold or against a core pattern. The rubber mold, which is used repeatedly for making the plaster molds, can easily be duplicated for replacement or accelerated production.

Rubber permits easy ejection of plaster molds without draft in most instances. Absence of draft simplifies machining the pattern, minimizing tooling time and cost.


 4) The PLASTER used for the production molds is an extremely fine-grained material of low heat conductivity, enabling production of castings with smooth surfaces, accurate dimensions, thin section and uniform density.



HOMECasting Comparison Matrix