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Calculating metal shrinkage in gold casting


#1

Hai,

How do calculate the metal shrinkage in jewelry gold casting?

Any method is available please share to me…

Thanks
ckanand


#2
How do calculate the metal shrinkage in jewelry gold casting? 
Any method is available please share to me.. 

It varies according to what type of metal, flask temperatures, metal
melting temperatures, investment type, etc.

The best method, assuming that you have reasonably controlled
casting methods, is to simply run actual tests. Take a wax model that
has been made a very precise measurement, such as a square plate, one
centimeter square and one millimeter thick, for example. Cast it as
you normally would. You can cast several, at different temperatures,
for each metal you cast. After casting, you can measure what the new
cast dimensions are, both along the length of the sides, but also the
thickness, and how it varies from the edges to the center of the
square. The resulting measurements can then be used to predict the
shrinkage of your castings, as the percentage shrinkage should be the
same, if temperatures and metal type are the same.

Another useful test is to make a precise metal model, say of a ring
band, a precise ring size, a precise width and thickness of the band.
Now make your usual type of rubber mold, and cast the wax models that
result, as above in various metals, using various temperature
combinations. This will give you actual differences from the original
metal model to the end reproduced castings, and it will also show you
the shrinkage from metal model to the waxes from a rubber mold, or
from the waxes to end castings. If you like, also finish and polish
those cast test rings, which then will give you total final
shrinkage from all causes, molding, injecting wax, casting, and
polishing losses between original model and final ring.

Peter Rowe


#3

I have used the formula of from the metal master through rubber mold
to wax to finished casting aprox. 6-8 % shrinkage is normal for
silver or gold or pewter. There are a lot of variables including the
type of rubber you use to make the mold with. The best way to be
sure is to measure. a test piece first.