QuestionQUESTION: I have been trying to pore ingots using 99.9% silver granules into a graphite mold with the graphite spray. I have used a kiln to melt the silver and I've also used a propane/oxygen torch with borax. The problem I'm having is the silver doesn't pick up the mold inscriptions, in fact the side of the cooled silver that is next to the graphite mold looks like a moonscape. What if anything am I doing wrong?
ANSWER: Lex, be kind to the expert because without seeing it being done, I miss a lot of clues as to what might be going wrong.
Is there a lot of borax going into the mold with the silver? It would be unusual in a mold but I have seen that "moonscape" surface on the TOP of poured metal, not on a mold side or bottom. I have seen it apparently caused by the flux.
The most likely culprit is heat. Is the silver being poured with heat applied during the pour to maintain molten flow temperature? Is the crucible quite hot prior and during the pour? Graphite can pull heat away quite rapidly and a combination of silver not quite hot enough and a mold pulling out heat can cause a shrinkage surface.
Overheating will generally cause a messy looking metal in result though not so much with fine silver. Sterling can easily be overheated and cast or pour poorly.
If the mold is totally open on top is the silver surface tension causing and excessive rounding of the top surface? If so, a heated flat plate (graphite?) can be placed on the silver just as the pour is done, forcing the metal down and flat.
Try this once or twice: Take a small amount of the silver and pour onto the inscribed area and see how it cools. Watch it and you might gain more clues.
Both the gas/oxygen and kiln melting are fine but be sure the metal remains just as hot during the pour.
Lex, this should help but might not help all all! I am basing my suggestions on general situations. Best wishes with the pouring. God Bless and Peace.
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QUESTION: Thank you for your answer and yes the graphite mold is an open flat coin shaped mold. I tried pouring the unheated 99.9 fine silver granules directly onto the mold and set the whole thing in the kiln and ramped the kiln up to 1763 degrees Fahrenheit and held it till the silver started to move or "swirl". Then I let cool very slowly and still the moonscape.
The first time I did it with this method I quenched it quite quickly after it solidified and it had that rounding effect on the top and the moonscape on the bottom next to the graphite.
When I did it by heating with the torch I'm sure I didn't keep the silver hot enough during the pour but I can't keep the graphite hot enough using the torch, even when I heat the empty mold in the kiln and do a pour there doesn't seem to be a good solution unless you can see my mistake??
AnswerLex, you might be able to get the graphite to stay hotter by keeping it on a firebrick or similar surface which will retain heat, heat it in the kiln and take out just prior to the pour.
However it sounds like the silver is losing heat on the bottom and when the bottom starts to solidify the molten metal on the top pulls it and creates the surface you are seeing. This can happen in a casting mold when the metal in one area starts to cool and the other pulls metal away as it also starts to cool a split second later. This is shrinkage within the mold form due to contracting metal.
Otherwise, I would have to see it happen to know more. Best wishes in getting the overall hear right. God Bless and Peace. Thomas.
