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Casting porosity _ Major Boyce

Major Boyce:

I use perforated flasks in my casting shop. They are somewhat
expensive but do not require such things as wax web or drinking
straws. When I used to use a centrifugal setup I used the
drinking straws on the inner edge of the flask. I would stick
them in just as the plaster was starting to set up. Perforated
flasks are the best for vacuum casting, however I can imagine
that regular flasks will work with the wax web or straws.

I thought about building my own melting furnace but chose to buy
one instead. I purchased one from a company in California, USA.
Pyramid Products Co. They produce and sell several sizes of
melting furnaces.

Home Shop Machinist magazine has published a series of books
based on their magazine. “Projects” book Four details a gas
powered metal melting furnace.

To date I have no means other than “by gosh and by golly” to
determine the temperature of the molten metal. I pretty much look
at the quality of the castings and try to determine if everything
was done correctly. In a perfect world I suppose we would all
have immersion pyrometers or some such device. I have never used
one but can imagine it would be nice to eliminate some of the
guess work.

Building a vacuum chamber is a pretty basic welding job. I did
machine the top plate to guarantee proper sealing to the flask. I
use a high temperature gasket available for perforated flasks
that has held up for many years. Like I said previously I plumbed
in a 1" line to the chamber to insure a quick evacuation of air.
1" is probably overkill, but with a large vacuum pump I wouldn’t
go less than 1/2" at the least.

Hope this helps and don’t hesitate to ask any other questions.
If I can’t answer them I am sure someone on this list can do so.
I am amazed at the diversity of knowledge available here.

Kenneth Gastineau