[TheForge] Microwaving Metals From the Virtual Junkyard

Mon Jan 5 21:33:01 2004

Hi Grover,

I used to be a radar tech (SPS-10 and BPS-15) many moons ago in the 
Navy and also worked on induction furnaces .  I did not want to get 
too technical about it in the last post (probably because I have 
forgotten what I used to know about magnetrons) but the fellow who 
did the first work that I know of using microwave ovens for melting 
tried graphite crucibles and found them to be too conductive. His 
working crucibles were mixtures of ferrite and magnetite with a 
graphite fireclay binder this provided a good impedance match to the 
radiated energy from the magnetron and got real hot. The biggest 
problem is getting rid of the radiant heat given off by the crucible 
so that the oven doesn't melt or catch fire.

Jim

>Microwave ovens work by generating power, and something absorbing the
>microwave power (for example food) and turning the "radiation" into heat.
>Water or food absorbs well, as it's resistive (essentially).  Metal is
>conductive.  Though it is possible to heat metal in a microwave, it is not
>very resistive, will likely offend the magnetron, make it snap and pop, and
>eventually the magnetron likely will die.  On the other hand, if there is a
>crucible is being used.  And something resistive is a component of the
>crucible (like graphite, a form or carbon, which makes a nice resistor to
>absorb the power), then the crucible would heat up, and then heat up the
>metal.  Still, watch it carefully and try not to offend the magnetron.  Any
>kind of arcing sound is a not so good thing<G>.
>
>I have found that if items are spaced up about 1-2 inches above the floor of
>an oven, then the oven is much happier in life.
>
>I repair microwave ovens at lunch for fun, and work with magnetrons (radar)
>as a part of my work. 
>
>Side note:  The way that ovens give you partial heating is by turning the
>magnetron on and off.  10 seconds on, 10 seconds off gives you half power.
>While it is possible to use a lamp dimmer to lower the power out of a
>magnetron, the filaments would also be lowered and it would suffer in the
>long run.  The on/off sequence is much easier to do<G>.
>
>Holler off line if you need details about magnetrons.
>
>-----Original Message-----
>From: [email protected] [mailto:[email protected]]
>On Behalf Of James Binnion
>Sent: Saturday, January 03, 2004 11:15 AM
>To: [email protected]
>Subject: Re: [TheForge] Microwaving Metals From the Virtual Junkyard
>
>
>If you are interested in working in very small amounts (under 10 oz
>of bronze) of metal it works. The first person to talk about this on
>the web is a sculptor from either Australia or New Zealand 5 or 6
>years ago he used a combination of refractory clay and a proprietary
>mixture of ferrite and magnetite to make crucibles that would absorb
>the microwave energy. He was melting bronze. In the past year Bill
>Roberts over on Artmetal list did some experiments with it and melted
>aluminum. There is no reason it will not work if you are willing to
>screw around with the development. Microwave radiation is not
>something to be careless with you can't see, smell, or taste it and
>by the time you feel it you are already burned. You can get very
>badly burned or even kill yourself  by being exposed to the microwave
>energy put out by a 1 kw oven magnetron. The amount of heat you are
>putting into the oven cavity can easily warp the box and break the
>seals letting the microwaves out so be careful.
>--
>Jim Binnion
>
>James Binnion Metal Arts
>Phone (360) 756-6550
>Toll Free (877) 408 7287
>Fax (360) 756-2160
>http://www.mokume-gane.com
>[email protected]
>Member of the Better Business Bureau
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-- 
Jim Binnion

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
http://www.mokume-gane.com
[email protected]
Member of the Better Business Bureau