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Casting Fine Silver


#1

Greetings All,

Any suggestions on casting fine silver?

All the pieces have a flaw at the sprue area, a small hole or groove.
Pieces are about 5 pennyweight each and were cast 10 at a time.

Thanks,
Bill in Vista


#2

As I get castings made in S/S for my setting class, I do notice
defects at times…check the rubber mold right at the sprue area…is
the sprue in the wax stage properly joined to the shank? the
thickness may not be adequate in the wax stage too, …check if too
much powder in the release stage in the mold. is the sprue really
full of wax to the shank Gerry!


#3
    All the pieces have a flaw at the sprue area, a small hole or
groove. Pieces are about 5 pennyweight each and were cast 10 at a
time. 

Have you checked your waxes for air bubbles? I had a similar problem
with sterling, only on one certain wax design. Turned out that the
sprues were getting bubbles in them during the wax injection.
Adjusting the wax pot temp and pressure solved the problem. I hope
yours is as simple to fix!

–Kathy Johnson
Feathered Gems Pet Motif Jewelry
http://www.featheredgems.com


#4

Hi Bill, Make sure the sprue is larger than the piece you are casting
and sprued at the thickest part of the piece. Next, you need to cast
with the flask temp significantly higher than your regular sterling
casting. Next, use a crucible dedicated for fine silver casting. Flux
the crucible only (not the metal) with Boraxo. Super heat the
crucible before adding the fine silver. Use ONLY fresh fine silver
grain. Add more button weight than you normally do. Super heat the
silver, THEN get the flask. I find centrifugal works better. What do
you Vac people say? John, J.A.Henkel Co., Inc., Moldmaking Casting
Finishing, Producing Solutions For Jewelry Artists.


#5

Sprue placement and thickness is very critical in pure metal
casting. Casting pure metals is different than alloys. The main
reason is that there is no solidification range in pure metals, they
transition instantly from liquid to solid. This means that as a
casting cools it cannot draw molten metal from the sprues to fill in
the shrinkage that occurs upon cooling like it can in an alloy where
there is a range of temperature where the alloy is in a semi liquid
state . This often results in large shrinkage porosity that is found
near the sprue connection. The way to avoid or reduce this is to
make the sprues thicker than the section of the item where they
attach. Also make sure you are attaching the sprue to the heaviest
area of the design. Ideally you want the thinnest sections farthest
away from the pouring cup/button and the section of the casting to
get progressively thicker as it gets closer to the pouring cup. This
way the casting solidifies from the outside of the flask inward with
the pouring cup/button being the last section to solidify. – Jim
Binnion

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160


@James_Binnion
Member of the Better Business Bureau


#6

There is no thing that can’t be filled by centrifugal casting.
However, the larger/heavier the piece to be cast, vacuum casting is
preferred.

Chris


#7

Hi Bill,

Metal solidifies first wherever it is thin and then draws from
wherever it is thick as it cools. Sterling and 14K are forgiving
with respect to this rule, but fine silver will not let you slide.
Unless you provide enough feed for the thick parts, that
solidification will cause the juncture (from thick to thin) to look
like a wet sponge, or it will look like just the surface of the metal
has ripped open. Is that what it looks like?

As a rule of thumb, when you think you’ve over-sprued it, that might
be enough. You can try using a larger center sprue, also, that might
help. We use the lowest flask temperature possible (just above
getting no-fills) and the lowest metal temperature possible. We do
use larger buttons. Reusing clean fine silver doesn’t seem to
present a problem.

Give yourself a break, though, if you are having trouble casting
fine silver. It is a difficult metal.

Dana Carlson