microwave gold smelter

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In the past I've played with melting metals in a microwave, eventually I'll modify one to make a full-blown furnace but haven't gotten there yet. My initial setup was to remove the turntable and line the inside of the microwave with refractory blanket. As Harold mentioned earlier in the thread, it's exactly like an induction furnace in concept but much higher frequency. Materials that will heat at this frequency are needed, such as impure silicon carbide, magnetite, MoSi2, etc. I used silicon carbide at first because it is cheap and works well. After a few minutes on high it will heat to a nice yellow-orange and will melt copper.

To build a furnace I plan to thicken the refractory lining leaving a chamber about 6" wide, in which I will place MoSi2 or SiC rods that will heat the entire furnace chamber. I will hook this up to a thermocouple & controller to set the temperature as desired.

Many lab-scale microwave furnaces are essentially this simple, and I'm surprised they aren't used for more things. Because the heating elements are not required to be mechanically durable as in resistance furnaces, they could be used at very high temperatures (i.e. >2000C) more easily than conventional furnaces. Also they can heat to these temperatures very quickly, if enough power is provided.

The main problem I see with melting metals is that the furnace has to be closed when operating, so it would be hard to watch what is happening and also hard to remove the crucible and pour the metal out.

Steve
 
I'm not an authority on microwave ovens, but one of the problems I'd expect you'd experience is overheating of the components. Induction furnaces are water cooled, including the heating coil. You wouldn't have that luxury with a microwave. It might be wise to increase its cooling ability via a large fan.

Please keep everyone advised. It will be interesting to see your results.

Harold
 
this is used in glass bead making

http://www.firemountaingems.com/details.asp?PN=H201083KT

this might work for gold also it appears to be just a round refractory box

Eric
 
Alright! Alright! I can see now I’m going to have to jump in here with my secret, secret, weapon i was saving for Flea Bay, but this is just to revolutionary, to super duper extraordinary, to ground breaking. Science said it couldn't be done. But from our labs in Liverpool comes a break through process. From the makers of such products as the famous T-9, Megan's mysteries, and the creator of the Platinumill comes this latest break through. Ladies and gentlemen if you will be so kind as to direct your attention to the Cat standing by the microwave with a box of hot pockets. That right ladies and gents. It's your first multipurpose Cooking sleeve slash black sand smelter slash fusion reactor slash use your imagination. All for the low low price of shipping and handling. That's right ! It's free! You only pay shipping cost. Advanced orders are being taken as we speak. Hurry now in time for the Christmas rush and we will include at no extra cost to you (beside shipping) our new Flux capacitor kit. That's right. I said Flux capacitor. Don't be the last on on the block to have your own Flux Capacitor. Operators are standing by...........

Now i'm just hungry. :cry:
 

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I don't know what that card board microwave food crisper thingy is ( Iam sure such things are pure science fiction) but if you have a flux capacitor I will trade a transwarp drive.
 
WELL MY THINGA MAJIGGY BEATS ALL OF YALL'S CONFOUNDULATED ELECTRONICAL THINGAMABOBBERS.(sticks tongue out at the unedumacated) :mrgreen:
 
You may want to check out this article. The home microwave referred to in the article was unmodified. These typically won’t survive this sort of use for very long. If you install a large fan and ductwork to the magnetron, it will live longer. You will also need a crucible made primarily from silicon carbide and insulation made from pure alumina. Zircar makes the best, but it’s expensive. If you wrap the insulation casket in aluminosilicate blanket, it will work much better (and faster).

http://www.industrialheating.com/Articles/Feature_Article/BNP_GUID_9-5-2006_A_10000000000000991975
 
The sellers of the microwave gold kiln will tell you that not just any 1200 watt microwave will work. The "inverter" type of microwave WILL NOT WORK. If you stop and think about it, a microwave oven is just funneling electrical energy into the cooking chamber. The firebricks which build the microwave gold oven act as an insulator. The energy goes in, heats the charge in the crucible, and the firebricks keep the energy (in the form of heat) inside of the kiln. If that energy leaked out, the inside of the microwave would self destruct.
 
bswartzwelder said:
The sellers of the microwave gold kiln will tell you that not just any 1200 watt microwave will work. The "inverter" type of microwave WILL NOT WORK. If you stop and think about it, a microwave oven is just funneling electrical energy into the cooking chamber. The firebricks which build the microwave gold oven act as an insulator. The energy goes in, heats the charge in the crucible, and the firebricks keep the energy (in the form of heat) inside of the kiln. If that energy leaked out, the inside of the microwave would self destruct.
Click to expand...

I am not so sure about the self destruct comment, but I do know that a Microwave works by passing high frequency microwaves through an object, exciting the molecules so that they oscillate/vibrate as such a high frequency/rate of speed that they rub up against their neighbors, creating friction which creates heat which in turn is what cooks food.

What totally baffles me is why anyone would spend the money, time, effort and energy on anything that doesn't do the job nearly as well as something that can be easily and simply made, costs much less, is proven to work time and again, has a low failure rate and you can do far more with it.

http://www.backyardmetalcasting.com/

http://www.backyardmetalcasting.com/hmkit.html

http://www.foundry101.com/search.htm

Scott
 
Tried it and it works I've used ceramic blanket as insulator and fused silica melting dish crucible. 700w kitchen microwave oven. 10g Ag melts in 8 min. Temperature inside oven never exceed 40c. ceramic wool was warm not HOT, crucible inside - white hot.
 
I think you'd have better luck with SiC carbide. I've been meaning to build one of these for so long. We already have a microwave ashing system that gets to 900 C. Basically an SiC plate that heats up.
 
etack said:
this is used in glass bead making

http://www.firemountaingems.com/details.asp?PN=H201083KT

this might work for gold also it appears to be just a round refractory box

Eric
Click to expand...

I got that exact kit and it works great for small glass fusing projects. It is just some kind of refractory material forming a round box with a pretty small hole in the top. The inside of the top section around the edges is coated with some black stuff that heats up from the microwaves and that transfers the heat to the glass. It also stays hot a long time so works to anneal the glass pieces but that wouldn't matter for melting PM's.

I did try putting a cupel with a piece of sterling silver in it but didn't leave it in long enough to melt it. It probably would but I felt eventually the coating would get too hot and be ruined or too much heat would be released into the microwave. The outside of the kiln gets hot enough to need gloves and the inside gets glowing hot.

I think it could work for melting gold or silver but not very large amounts and it would take a while to do. This particular kiln wouldn't be big enough to hold a crucible for a real assay or smelting but a larger model MIGHT.

There are probably better ways to smelt precious metals but this microwave idea probably does work. I have put small pieces of metal into my little microwave kiln with no sparking. I think the black coating (susceptor material) around the inside of the little kiln must keep the metal inside from sparking. Same thing if that susceptor material was mixed into the flux. I kind of wonder if the black sands (magnetite) from gold prospecting would work as the susceptor and possibly contain a bit of gold mixed in?

Brian
 
I like that Owl.

I've said before that it can be done it's good to see a proper video showing it from start to finish.

Jon
 

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