Attetntion Jeff and Bruce... Both of you sound like you are very knowledgable
and I think I could learn alot from your tips.... Is there anyway of
contacting either of you? And where is it that you guys are from???? I am from
Pennsylvania near the Scranton area...I don't suppose either of you guys do
any casting seminars... Do you? THanks for your responses and keep em'
Marc WilliamsFrom: firstname.lastname@example.org on behalf of Jeffrey Everett
Sent: Tuesday, August 20, 1996 9:21 PM
Subject: Re: Casting
I'm now left to wonder at what flask temperature both of you are actually
I would estimate the center of the 1 1/2" x 2" flask is 900 degrees when
I cast. It could be a thousand, but I'm careful to differentiate between
heavy castings and thin castings. The metal alloy you use makes a large
difference as well. If you are using silicon additive alloys, you need
to superheat both the flask and the metal to avoid porosity. If you are
using the old standard yellow gold alloys you'll want to pour the metal
at the lowest flask and metal temperatures to avoid porosity. Annnnd,
the spruing is fairly critical. I say fairly because I've seen come
casters get great results using single sprues, where I would have use
two or three at least.
And are the castings porosity free? How about thin castings are
they coming out ok?
Yes, my casting are almost always prosity free. Porosity comes from
several causes. Improper spruing causes shrinkage porositiy, otherwise
known as hot-tear porosity. Tiny crevices, pits, hidden bubbles, and
holes in the wax leave tiny investment burs, flashing, fins and spikes
that break off when the metal flows in and generate sulphur dioxide gas
porosity. Bits of broken and loose investment from an unclean sprue base
and sprue as well as crud on the stirring rod contaminates the gold
possibly causing inclusions in the casting. Then, on top of all that,
you have cupric oxide porosity from burnt copper in the alloy, plus the
types of problems mentioned in the previous paragraph. But wait, there's
more! hee hee another time...
this all seems to risky since most my things are one of a
When I'm fast casting one of a kind pieces carved from hard wax, I use a
very thick investment slurry, and heat the oven more slowly, up to about
1300, then cool it to casting temperature, about a 4 hour process. I
have successfuly done very quick burnouts with carving wax, but when
I've put 4 or 6 or 20 hours into a wax, I don't take chances! I have a
friend that makes RTV molds of all his waxes before he casts them, a
good practice that I don't have time for.
have problems with porosity once in a while with a full 8 hour burnout. I
can't imagine there would be no porosity with a 2 hour or less cylcle...
problems. If you are using small flasks, the heat will penetrate within
about 20 or 30 minutes to the core of the flask and the wax carbon
should leave the flask as carbon monoxide. If you were burning out
photopolymer models, I could understand it, I use about a *minimum* 12
hour cycle with most of the time spent at 1350, otherwise I have unburnt
ash ruining the surface of the casting.
this is interesting...
Yes, isn't it? :)
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