"Bruce W.1" wrote in message
news
I need to make some small parts. Ideally they would be made of steel.
And I'd really like to setup a home melting furnace, but my landlord
would not share my enthusiasm.

Low temperature metals are a possibility, like pewter, whitemetal, or
solder. However these aren't very strong.

I can do lost wax or RTV mold making. What's the toughest non-metal
material that I could pour into it?

The toughest thing I can think of is JB-Weld glue. It's just a little
too thick and doesn't flow very well. Epoxy is pretty weak. Then
there's urethane plastic...

Can anyone recommend a tough material for pouring into a gravity mold?

Thanks for your help.

First off, "tough" and "strong" are not the same thing. Among plastics,
Nylon is tough. Epoxy is strong.

JB Weld is a filled epoxy, and not a particularly strong one. Epoxy filled
with milled carbon fibers will be at least three times as strong, and many
times as tough. Epoxy filled with milled glass fibers also will be much
stronger and tougher than JB Weld.

However, epoxy filled with milled fibers does not pour well. When it's
molded, it's injected under pressure. There are very short carbon fibers and
glass fibers that will pour, and their strength potentially could be almost
as great. But, when you get enough of the fiber into the mix to make a
really strong composite, it's too thick to pour. You're limited to a lower
percentage of fibers than the ideal, and considerably less strength.

Your application, holding antenna parts together, sounds like it needs
strength rather than toughness. You can get 5,000 psi or so with filled
epoxy. Zinc casting alloys can be six or eight times higher than that. The
Zamak 27 mentioned by Tim has 55,000 psi yield and 61,000 psi ultimate
tensile strength, but it creeps over time, and you have to get it up over
800 deg. F or so to melt it.

Solder may be 5,000 psi or so, en-masse. I don't know about the low-temp
alloys, which are bismuth-based. Look up Cerro Metal Products Co. They
probably have specs for Cerrobend and so on, online.

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.

But are you sure you have to mold these parts? Is it something you're doing
in volume? If not, wrapping fiberglass tape, soaked in laminating epoxy
(WEST System is one good brand) will be much stronger than any plastic part
you can mold, of any plastic you can buy. Pound-for-pound, it will be
stronger than most metals. It will just have to be thicker for a given
strength.

--
Ed Huntress