On Sun, 13 Mar 2005 22:26:30 -0500, "Ed Huntress"
wrote:


All of these materials can be molded in plaster, and all but the Zamak can
be molded in silicone; even the Zamak is good for a few shots in a
high-temperature, high-rigidity industrial molding silicone compound. They
even use it for a few shots of molded aluminum. Watch out molding
polyurethane in silicone. If my memory isn't failing me, they're
incompatible.

Incompatible with tin-cure RTV. Platinum-cure RTV is OK.

http://www.tekcast.com/ is about spincasting, but they have a range
of supplies and materials including Zamak and castable urethanes.

Another source of plastic casting materials is
http://www.burmanfoam.com/estore/ProductSearch.asp They're
primarily into special effects for movies.

More yet at http://www.eagerplastics.com/cast.htm and
http://www.polytek.com/ Polytek's print catalog is almost a "how
to" manual.

"White metal" (which Zamak is) has gotten a bad rep in consumer
products because product designers used an absolute minimum of
material to keep cost down. It's actually pretty good stuff. See
http://www.fishercast.com/products/diecasting/zinc.aspx for some notes
on its properties, and favorable comparison to aluminum, magnesium
and plastics. A couple of these alloys have higher tensile strength
than aluminum and considerably higher yield strength and shear
strength.

Scrapyard test for zinc alloy: get some copper sulfate at a garden
store and dissolve some in water. A drop of that on Zamak will turn
dark, while aluminum won't change color.

You can sand-cast "white metal' and of course you can use the lost-wax
process aka investment casting.