QuestionI have refined aprox. 20 ozt.of gold from scrap jewelry using the aqua regia method and precipitated with sodium bisulfate.Process was pretty strait thru no suprises but when I melted the pure gold in a silica style crucible with a propane/oxy torch and try to pour it into the graphite 1 oz ingot mold. It solidifies before it reaches all the edges of the mold. I have even tried melting the gold in the ingot mold but the surface tension of the metal seems to want to stay sort of balled up and not wet out to the corners of the mold. ANY HELP??????
Thanks in advance...
AnswerDavid, graphite can carry away a lot of heat quickly. While I can hold a charcoal block while melting metal in a dished out place in the block, with a graphite stirring rod used to stir molten metals the end of the rod very quickly becomes too hot to hold bare handed. Yes, it is all carbon but the structure is different.
I have not used graphite mold often, preferring smooth finished iron ingot molds. In your case, something needs to be hotter to allow the molten metal to flow out and not freeze so quickly. Try heating the mold just prior to the pour. Be sure your metal is hot enough to pour easily from the melting crucible. With a pinch of flux on the metal the appearance should be like a shiny almost rolling ball under the flame.
As for the surface tension causing the balling up effect, pulling the metal up at the edges, you will have to force the metal into the corners or be satisfied with the ingots done as you described. A flat face such as a smoothed charcoal jewelers block may be pressed onto the molten metal in the mold quickly and this will force the metal to the edges an flatten the top surface.
Pouring into a mold with two sides and a pour hole will come closer to getting what you might want. With some excess metal in the pour, the mold is filled and when cool the excess button of metal is trimmed from the ingot.
Best wishes. God Bless and Peace. Thomas.
