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A prime feature of each of the recommended alloys is the
low temperature at which it can be poured: this combines with
low specific heat and latent heat of fusion to make it possible
to cast against many materials without causing undue thermal
expansion or distortion.
The viscosity and surface tension are also low, making for
accurate reproduction of the pattern. The volume changes,
both during and after solidification, are very small, ensuring
accurate, full size reproduction. Injection moulds cast in
MCP 137 have produced as many as 500 shots in prototyping
before wear became apparent; wear can be reduced by using
steel inserts at sensitive points.
It is possible to produce plastic components that are hollow,
and of a shape from which the core cannot be mechanically
drawn, such as tees and elbows; the alloy is simply melted
out when moulding is complete.
The process is ideal for prototype injection moulding, the
low temperature enabling the alloy to be cast against most
models including those made by stereolithography, laminated
object manufacture, fused deposition etc. Cast moulds can
be readily machined or etched to give special surface finishes,
useful in the automotive industry.
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