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Porosity


#1

Hi Dave: All those other things being true also, you might try something
which works for gravity casting and regarding spruing. This is done for
pieces much larger than jewelry, but principle the same. Your main sprue
(gate) has feeders from it which will fill your piece, diameter being at
least equal to your thickest part, gate is greater thickness than feeders.
Gate too is extended straight down beyond the model. Feeders come off
from the gate in the middle of the gate length. If your space is tight,
you can form the gate shaped like a “J” so that the gate wraps around
your model within the flask and the feeders would come off the J in
the middle. Theory being that by dropping your metal into gate first
leaves much of dross there and eliminating turbulence. Essentially metal
"fills" the piece rather than being forced into investment mold directly.
This method has gravity as impetus behind the metal rather than centrifugal
force, and used for casting bronze sculpture. But I have always used it
for spruing up my jewelry pieces with never a problem with porosity.
Hope that helps.

Susan

Susan: thanks for the tip. Are you using centrifiugal casting with this
method? I’ve heard of this before but it sounded like an oldfashioned
technique, guess thats wrong. Also are you casting silver this way or
gold? I’m assuming the sprue or gate that goes past the model should be as
thick also as the main sprue? This is something I think I’m going to try it
sounds very logical, thanks…Dave

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