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Vacuum casting issues


#1

Hi Orchid Community,

My name is Max Goodman, I run the jewelry program at a community art
studio called 3rd Ward in Brooklyn, NY. Currently, we run a lost wax
casting class. We cast using a Vigor brand vacuum chamber from the
1940s that belongs to a coworker. When we first got the vacuum in the
shop we ran a test cast by pouring manganese bronze into our flasks
at 900 degrees farenheit. Our test cast was successful, and following
that we have had mixed success. Lately, we’ve had an extremely low
success rate, though as far as I can tell nothing has changed. Our
vacuum has a knob that points either towards the investment table or
the casting chamber, but it seems to add suction to both regardless
of where the knob is pointing, and it doesn’t release until we turn
the motor off, even if the knob is positioned on the release setting.
Though the guage reads at its maximum setting while casting (30 psi)
it seems to me that the metal is not being vacuumed properly into the
moulds, and this is what is causing our failed casts. We have tried a
number of metals, including sterling silver and a new
lower-melting-temperature bronze that is designed for pour casting,
and raising the temperature on the flasks in the kiln, nothing seems
to make a difference, so I’m turning to you Orchid Community. Here
are my questions:

  1. Do you know of a place where I can get a vacuum repaired,
    preferably near New York City?

  2. Can you think of any human errors I might be making that I have
    not thought of?

  3. Do you know any tricks for successful vacuum casting?

I await your knowledgeable answers, and thanks in advance for your
thoughts and help!

Sincerely,

Max Goodman
www.3rdward.com


#2

Did you check that it had enough oil in the machine? That can cause
issues…


#3

Max,

It sure sounds like a flask blew out, investment or metal sucked into
at least the 3 position valve. Start by taking it apart going from
the flask side. Investment a chore to clean out, metal and lots of
drilling etc (not fun and I should know :slight_smile: Ya might need to replace
parts but it is not the end of the world or machine.

It is not 30 PSI but rather 30" of mercury column. In case you have
to take it to a HVAC type repair place know the right words. (yellow
pages, call first and your problem might be amusing enough with a
gift of coffee and donuts)

Given the season folks tend to be generous unless mad assed over
worked.

jeffD
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand


#4

Hi Max, I had an old swest vauum casting machine that I was having
the same issues with. I was having fits with low success rates also,
mainly using sterling. Difference is I was at 7500 feet, where your
close to sea level. I went to a centrifigual caster and have been so
much happier. My success rates are now at about 99%. That’s just an
option…hope that helps.

Tom


#5

Dear Max, Sounds to me like the selector switch has gone out on your
casting table. Contact me directly at [dabillie at bellsouth dot net]
I will give you the info on getting your casting table back up and
running again. I used to run the casting program at a local community
collage here in western north carolina.

Hope I can Help
Sincerely,
David Alberts


#6

The previous posters mentioned the first two ideas I was going to
suggest.

Here’s another one that got me the first few times.

I read about a trick to use a wet paper towel between the rubber pad
on the vacuum table and the metal flask. The idea is that it would
keep me from having to buy new rubber mats every few castings because
the flask wouldn’t burn into the rubber that way.

That part works great, by the way. But the first few times I did it
I forgot to tear a hole in the paper towel so the vacuum unit had an
unobstructed path to the flask.