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Old 07-19-2012, 02:17 PM   #1
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Smelting (or melting) Conundrum

Guys,
I've got a small, what appears to be, a clay crucible that I've melted about 15 grams of .925 in (started out as a mercury dime and two silver rings). I've used propane in the past but tried MAPP and it actually does better. Hotter, I think. Well, I purchased one of those graphite molds on e-Bay which has been milled for 1/4 and 1/2 oz. Thought it'd be neat to make a little "bar" rather than the button I was getting from the crucible. So, last night I place this sliver in the new graphite mold to melt it. Well, I must've held that MAPP flame on that silver for 5 solid minutes and, although it did seem to soften, it would never Melt. Melts in about 30 seconds in the clay crucible. Anything I should know? I realize a furnace would do it and so would acetylene, but I don't have that. (plus, I don't plan to get into doing this - I just happened to have the scrap silver and a torch and wanted to try it)
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Old 07-19-2012, 02:25 PM   #2
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Graphite (especially the better grades) is super thermally conductive. With the clay, you don't even have to heat the entire crucible, just the inside. When graphite gets into the picture, you're heating the entire thing to temperature - so it has more heat loss to the air. I use it in glass blowing as it doesn't stick to glass - but you use a small piece and in an insulated handle - the other end gets real hot real quick.

So, melt, then pour.
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Old 07-19-2012, 02:31 PM   #3
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Do you have access to any asbestos?
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Old 07-19-2012, 02:51 PM   #4
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Originally Posted by ancona View Post:
Do you have access to any asbestos?
Other than what's in my lungs from when I was a kid, no.
rblong2us and bushi like this.
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Old 07-19-2012, 02:55 PM   #5
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Originally Posted by DCFusor View Post:
So, melt, then pour.
Only problem is, that it's very difficult to hold the torch in one hand, keeping the flame on the silver, and pouring with the other. Also, gets real hot holding the crucible in my hand, so I have to use pliers.
No biggie. Glad I found out about the heat transfer, though.
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Old 07-19-2012, 03:04 PM   #6
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I've been known to support the crucible in something like coat hanger wire (or fat gage fence wire). Just twist it up with a loop that holds the thing, maybe add a wire to catch the tip edge so it doesn't fall out of the loop when poured. It then becomes easy to hold the thing - iron wire is a lousy heat conductor, just make it fairly long. Or make it short but give the pliers something to easily grab.
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Old 07-19-2012, 03:24 PM   #7
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Graphite is a heat sink. In other words, it soaks up the heat and diffuses it away from your silver.

The clay crucible acts more like an insulator, preventing the heat from leaving the silver.

When you pour the liquid silver into the graphite mold, the heat sink property of graphite speeds up the solidification of the silver.
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Old 07-19-2012, 05:51 PM   #8
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DCFusor, you got a PM
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