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Casting quality - Centrifugal vs Vaccum


#1

Greetings to all my dear fellow Orchidians,

I am still in two minds whether Cebtrifugal casting result is
superior to vaccum assist casting or not.

When i see the Button of a Cenrifugally cast tree, it is concave in
appearance and that of Vaccum assist casting is of Convex in
appearance, does this indicates that centrifual castings are more
dence than vaccum assist castings?. and of better quality in grain
structure and other physical properties, please comment and share
your practical findings,so the differences are clear about the two
methods. Which method yeilds superior castings ( phisical and
chemical properties).

Thank you all in advance about your feed back and practical Insight.

May all be Peacful and Happy.

Umesh


#2

This is going to be similar to arguing politics or religion, you
will have advocates for both processes. And the right answer will
depend more on your situation than any other factor. There is
virtually no difference in density that is related to the casting
method. The button difference you see has to do with the centrifugal
force acting on the button while the vacuum cast one shows surface
tension acting on the button. Centrifugally casting is a little
tougher on the investment and you are more likely to break off pieces
in the process. But the bigest limitation on centrifuges is the
casting size. You are limited to smaller flasks and melts than can be
done with vacuum equipment. The only place where the centrifuge is a
standout winner is platinum casting where the speed of filling that
the centrifuge offers cannot be matched by the vacuum assist
machines.

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#3

I agree with James.

This is going to be similar to arguing politics or religion, you
will have advocates for both processes. 

I am sure there are people on the list that can compare the density
of centrifugally cast items vs vacuum cast items.

The shape of a sprue button is not a good way to compare the density
of a casting made with either method. The shape can be a reflection
of the mold and metal temperature.

I read someplace that a concave sprue button indicates the
temperature combination of metal and mold was slightly too cold. A
convex sprue indicates the metal and mold temperature was too hot.

Someone told me, when I first started vacuum casting, that my mold
temperature was too cold. I increased the temperature of the mold of
my next casting. The sprue button blew up like a balloon. I cut it in
half with my band saw. The thing looked like a sponge.

So much for the comments on sprue buttons. I will comments on some
of the merits of vacuum casting. Others who do centrifugal casting
can better list the advantages of centrifugal casting.

For me the most important feature of vacuum casting is the ability
to prevent fire scale when casting sterling silver. See “tips from
the jewelers bench” for the method of preventing fire scale. Vacuum
casting allows you to cast MUCH larger objects. You will be able to
control the temperature of the mold. The time between taking the mold
out of the oven and pouring will be less. You will need to use more
investment when centrifugal casting. The head space (amount of
investment above the project) must be greater. The force of the metal
hitting the end of the mold can cause the end to blow out. The rapid
input of the metal hitting parts of the mold in centrifugal casting
can break off thin sections of investment.

Just a comment about my own experience with centrifugal casting. I
had a lot of my jewelry cast by a shop using centrifugal casting. I
supplied the wax, they did the sprueing. Most all of the buckles and
larger pendants had stretch marks on the back side. I don’t gets
these when I vacuum cast.