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Old 06-08-2012, 12:11 PM   #1
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Home Smelting

Anyone here ever melt their own silver at home? Cast your own bars and the like?
I saw a video using a propane torch, (or butane-basic plumbing torch) and this guy placed some silver pieces in a crucible with some borax and melted it. He then polished it up and made an interesting little ingot.
Looked pretty neat. I cast my own lead bullets and think I could probably adapt to silver (I realize you need about 800 degrees C, so it's much, much hotter), but the principle seems to be the same.
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Old 06-08-2012, 12:44 PM   #2
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Only in tiny amounts, to make activation samples for my fusion reactor. I found propane/forced air a little anemic, so I switched to mapp gas/oxygen, and that rocks for this. Since I do it in my upstairs lab (right next to the bullet casting rig!), I found a surplus "oxygen generator" sold as medical gear to avoid having to lift tanks up the stairs - it works a charm and is good for my glass and quartz blowing too.

You have to find a friend in the junk biz to get one, they're not supposed to be sold to mere humans, medical use only stuff...regulations, sigh.

Made my own little torch for this. It uses a wire welder tip for the flame head - they just happen to be just right for a small, very hot flame. I used a couple of small needle valves right up near the torch head, so I have very little volume of mixed gas and oxidizer in the system - this is important for safety, you can get quite the bang otherwise.

Gold would make great bullets, BTW - nice high density, higher than lead, and higher melt point and strength mean you could get higher velocity without deforming the sucker. "The man with the golden gun" got it wrong - it's the bullets you want. Just soft enough to take the rifling...should be sweet.

But I'm not rich enough to have tried that, even with a high probability of getting the bullet back to re-melt.


Sure would freak out a forensics guy if used in a crime, that'd be a real head-scratcher for them, eh?
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Old 06-08-2012, 12:56 PM   #3
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Yeah, he'd extract the bullet and place it in his pocket. Just think if it were a .375 H&H.
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Old 06-09-2012, 09:46 AM   #4
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Originally Posted by Mark View Post:
Yeah, he'd extract the bullet and place it in his pocket. Just think if it were a .375 H&H.
I couldn't really justify the oxy torch in my home and I wanted to work with Au as well, so I started building a little induction furnace. Not many parts involved for a simple rig but you need to feed it quite a bit of power (like 1-3kW, either line-driven from mains or from series car batteries) and while it can work directly on metal samples it works best with a small graphite crucible for PMs or high-conductivity metals.

If you are handy with a soldering iron, search for these terms: 'ZVS' 'Mazilli oscillator' 'induction heater'. There are alternatives with some reliability advantages but this type of driver is by far the cheapest & simplest to build.

While a rig like this is ok for small quantities e.g. refining small amounts of scrap - for anything bigger than 1oz at a time you'd better stick with oxy or use a dedicated furnace.

I've seen some 'microwave furnace' products floating around which are essentially a kind of hollow firebrick, where you put the metal (or whatever) sample inside and shove it in the microwave. The firebrick provides thermal and electrical insulation while the microwaves generate strong currents in the sample. I think these are intended for glasswork (I don't remember the details for that particular stunt) but some people have used them for smelting too.

I think an oxy torch is the preferred weapon of choice though, if you have the workspace for it...
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Old 06-11-2012, 08:42 AM   #5
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For my middling HF high power needs, I use a chip from IRF that will drive a full H bridge of power fets running up to 600v on the rails. I've not tried it as an induction heater driver, but use that to drive primaries of multi KW high voltage supplies, and it's "robust". The trick with an induction heater is the few turns of coil are very low impedance, and you generally need to resonate that with a big high quality capacitor to get the impedance up to where you can drive the thing. The huge circulating currents will destroy a lower quality capacitor, and most people find they have to make the coil out of tubing so they can run cooling water through it.

http://www.coultersmithing.com/forum...0f126bd4285151

Shows the driver board I designed. It handles the issues of dead time (making sure one fet is off before the other is turned on) and so on very nicely, and you can see it's about as simple as it gets.
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Old 06-14-2012, 06:36 AM   #6
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Thanks DCF, that does look like a powerful bit of kit for induction heating! And could be the basis of a great smelting oven.

Yeah - the capacitors are tricky. A friend of mine uses Celem caps for his induction heater but they are extremely expensive. I just scraped together a decent number of cheap pulse types and paralleled them on a thick foil rail and it worked ok - cheap'n'cheerful!
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