# Induction Furnace

Anyone ever try building a small induction furnace using a high frequency welding machine i.e. TIG welder?

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William, I'm no expert, but the high frequency energy in a tig welder is only a low power provider; just enough enegy to ionize the air in the gap between the electrode and the work. An induction furnace would take thousands of times more energy than the high frequency generator of the tig welder.
Think of the energy source for an induction heater or furnace as a Radio station's transmitter, running at frequencies usually well below the AM broadcast band, maybe as low as 1000 cycles per second.
William Robert wrote:

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As far as my understanding goes, an induction furnace is essentially an open ended transformer. The load (metal charge) is the secondary loop. The size of the charge affects the coupling. Larger loads couple easier than small loads.
There are 2 approaches to building furnaces to match the coupling of the load. You can either vary the frequency or capacitance to balance the applied load.
A small 10 lb furnace would need very high frequencies (couple of 1000Hz) to get enough coupling to melt the charge. A very large furnace (ie. 15 tons) could use line frequency - 60Hz to get the same result. The coupling also varies based on the temperature of the charge.
Most new induction furnaces use variable frequency to balance the load because of the availability of low cost, high power SCR's.
Short of going through the calculations to balance the load/inductive coupling/frequencies using a welder as a power source, I was wondering if anyone has gone down this garden path or am I wasting my time?
Cheers,

frequency
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William Robert wrote:

I recall seeing something about doing similar with an old microwave oven. Don't recall whether it was here or news:rec.crafts.metalworking .
Ted
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I don't know which method is more suicidal!

1000Hz) to

tons)
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William Robert wrote:

IIRC it was MIT that was using the microwave to melt small qty. metal samples. Could be wrong. No different than an induction furnace on the face of it. Just transferring energy with RF. Keeping the microwave from overloading it's own circuits was stated as a problem...but the metal was quite well contained by the time they had it wrapped in enough insulation to avoid losing all the heat from radiation. http://www.google.ca/search?num &hl=en&ie=ISO-8859-1&newwindow=1&safe=off&q=melting+metal+microwave&meta Cheers Trevor Jones
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William Robert wrote:

Or more conducive to angry relations with neighbours from causing RF interference on their domestic (or business) electronics!
You could be causing aggro to everything from phones, radio, tv, satellite reception etc, not to mention mains-borne interference getting into their house wiring. Then you're into their PC, their hifi - the lot!
Not a good road to go down.
Dave.
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Sounds like something for the anarchist's cookbook

interference on their domestic (or business) electronics!

reception etc, not to mention mains-borne interference getting into their house wiring. Then you're into their PC, their hifi - the lot!

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I have had some objects cast. The foundry that cast it for me used induction furnaces. They could melt one ton of stainless steel in 20 minutes.
I became interested and, with a bit of research, I built a small (very small) induction furnace that will heat a small nail red hot. It uses an 18kv neon sign transformer, spark gap, a large voltage capacitor and a coil of wire. The nail is inserted into the coil and in couple of seconds it is red hot. This is not very optimal. Solid state switching and frequency control would be the best. I have not continued with my experments.
I wonder if an induction rice cooker could be modified to serve as an induction forge ?
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I am actually debating on using a regular arc welder and a graphite crucible to melt a small charge of iron. Using a copper watercooled coil can become a pain, especially if it melts!

frequency
coil
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I do not think that the welder would work for the power supply of an induction furnace. Arc furnaces use water cooled copper electrodes; a DC arc welder or tig welder may work assuming it was capable of 100% duty cycle. There would need to be some mechanism to maintain the arc.
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induction heating starts with magnetic flux. The flux flexes the atomic state and heats the metal.
One wants high current concentrated into a small area - using a flux lens if possible or just a good tight design.
High voltage isn't needed. Remember the danger - but car batteries can deliver high currents. They can explode when rapid discharging takes place, and any ring on your finger or watch - that gets across the two wires -
THere are some really scary films on safety - melted rings/fingers dropping off....
Martin
--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer snipped-for-privacy@pacbell.net
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Copper coils and a few shunts work nicely.
I had a cool safety film showing what happens when molten metal and water come into contact. 1kg molten Al was dropped into a tank of water - kaboom, mini a-bomb!

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