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Bubbles on castings

To whom it might concern: I have been reading about some of you
having problems with bubbles. Maybe this will help. I learned
how to cast without any formal training, only trial and
error,{lots of error}. I mix my investment in a rubber bowl by
hand until smooth , like a pancake batter. ThenI place it under
a vacum bell and when the investment rises and then falls I vacum
it for 45 seconds. This will remove any air that was stirred into
the investment. Then it is poured into the flask and placed under
vacum again for an additional 2 minutes. Then it is allowed to
set. We do a burn out for about 4 hours slowly raising the temp.
to about 1400 deg. Then I gradually reduce the temp to approw.
800 deg. and cast in a Nycraft spin caster. This system is very
simple and works for me. It is very rare that we get any
bubbles, or a failed casting. My vacum pump came from W.W.
Granger and the bell jar from Rio Grande. Cost was about half of
the commercial made units and works just as good. Hope that
someone can use some of this info to develop their own system.
Good Casting, Fred e-mail @fredmary

Sometimes bubbles are inclusions in the wax. Your wax injector
may have condense water in the air supply and may spray minute
amounts of water in with the wax. Small air bubbles may be in
your wax and become invivible as the wax hardens. I recommend to
place all wax models on the rubber pad inside your vacuum bell
and pull a vacuum. It will pop any small under the surface bubble
and you can find and fix them. This is better than having them
pop inside the investment as it sets up.Place a fine metal
strainer over the intake hole. You don’t want to suck a wax into
your vacuum machine (g)

Have a platinum day
Jurgen J. Maerz
Manager of Technical Education