"Scorsi" wrote in message
om...
"Ed Huntress" wrote in message
t...
"Scorsi" wrote in message
om...
Hello, I want to cast some fine pitch gears in a Silicone RTV mold. I
want to know what the toughest and/or strongest material is moldable
in silicone RTV that would also serve well to make well
detailed,resiliant and strong gears.

Probably some exotic graphite and A/B-cure epoxy.

If you want metal, spincasters have cast aluminum diecasting alloys in
silicone rubber. The rubber is a very hard, high-temperature version. It
doesn't last for many shots but it does work. It doesn't much resemble
the
common RTV type that's used for low-temperature casting.

Look up spincasting on the web.

Snip
Ed Huntress

Hi Ed, (and everyone else) thanks for the replies. I have talked to
some spincasting Gurus and it seems that the because of the huge
amount of pressure and heat that goes into making the rubber mold, the
spincasting process is a little hit and miss when it comes to casting
accurate gears. The rubber changes shape concentric to the middle of
the mold as it cools and pressure is released.

That's true about distortion. I didn't think you were considering
spincasting itself, but that you had some method for casting and you were
going to use silicone for the molds. I should have asked.


I was wondering whether it would be possible to cast Nylon or Delrin
in a Silicone Room Temp Vulcanizing mold?

I've never heard of it. They're both thermoplastics, and would have to be
pressure-molded in some way, such as by injection molding. I believe you'd
have the same distortion problem, in spades. Compression molding, transfer
molding, and injection molding of thermoplastics are done in metal molds.

Why silicone rubber? Refractory gypsum cements are handy. US Gypsum makes
one that's designed for casting aluminum or lower-melting-point metals. Then
you could cast zinc alloys, on a camp stove out of doors, if needs be.

If you want to use silicone rubber for a mold and you want a plastic gear, I
think you're stuck with the thermosets: epoxy, polyester, vinylester, and
polyurethane are the primary ones. I don't know if any of them would work
for you but polyurethane sounds like the most likely one to me.

Ed Huntress