Help with cold shuts while casting silver

Patrice Lemée

Patrice Lemée

Joined
Aug 13, 2002
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Once again seeking the help of the Jewelers on here and of course any one else with casting experience.

This is a small cross I cast in fine silver. I used Delftclay and it worked perfectly. Just need to do some cleanup.



My problem was with trying to cast wire for the pin that will be holding the cross. I used a steel mold especially design for that (sorry no pic) and the result as you can see is less than satisfactory. Forget the larger one, that was just runnout. As you can see I have two cold shuts (not sure if this is the right term). Is it maybe because I did not heat the mold enough or because there is no where for the air to go?



Any tips would be greatly appreciated.

Thanks
 
My casting experiences with silver years ago tells me both can case that problem. As well the silver itself must be at the right temperature or you could experience that same problem. Frank.
 
probably a combination of all three. Certainly you need someplace for the air to go.
 
Patrice Lemée;13152542 said:
Thanks Frank, I did not think about the temperature of the silver itself.
Click to expand...

I have never been a jewelry caster, but many years ago I was in the foundry business. I pored ductile, grey, and SS castings.
I always used black or green sands for my moldings and never steel. With all this being said, I'm sure they all work on the
same principles. Before you pour your product, your mold must be at a maintained temp so when pouring, the mold doesn't
take down the temp too fast. We always poured our product 50 degrees over to compensate for mold temps, air temps,
and slow pours (which always cooled product fast). I would watch those three factors and there shouldn't be any more
issues with air pockets in your castings.
Again, never worked with silver or jewelry, but I hope a little insight of mine would help.
Good Luck on your next melt !!!
 
I am familiar with centrifugal casting, not vacuum casting. With that said, an 'incomplete fill' can be caused by the metal not being hot enough, the mold not being hot enough or a physical obstruction (broken piece of invenstment blocking the 'sprue'. If you are using a centrifugal machine, a problem with the speed it spins may also cause an incomplete fill.

I am assuming that you are using clean metal (no solder or any other impurities) as this will have an effect on the flow of the metal.

And lastly, the casting God's may have been grumpy that day. I have done casting where I "knew" I had done everything correctly and the casting didn't come out properly. It happens, but don't asked me why...
 
Metal mold casting is quite a bit different than investment casting. The mold must be at the exact right temperature , the casting metal must be very clean, and the casting pressure is much higher ( either by centrifuge or other method).

On your project, the problems above are only part of the issue. Cast wire is inherently weak. It needs to be rolled to reduce the diameter and increase the hardness. I would just buy wire in the gauge desired. Order it as half-hard if you will be bending it before soldering, or hard if you will use it straight. After the parts are soldered and cleaned up, a hardening cycle in the oven at 575°F for an hour will make the pin nice and stiff.

With a wire ingot mold and a rolling mill you can make your own wire, but it is not worth it at less than industrial scale.
 
Thanks for all the info guys. I will keep them in mind for my next casting. After reading what you said, I am pretty sure that the main culprit was the mold being too cold.

I think that for this one I will have to go with stainless wire instead since Stacy said it will be too weak. Chuck, this will function as the tang pin and will also hold the cross. Not sure yet if I should put a cross on both sides of the handle or just the front side.
 
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