Induction heating?

Note: I am replicating this post on rec.crafts.metalworking.
I am in the process of cleaning up the place for a Badger Blacksmiths
meeting next Saturday. One of the other members (Don Hogenson) will do the
main demo, making a pair of tongs. But I, as host, am expected to do some
stuff, too. And I have plenty of things from which to choose:
Demo running a couple of generators from my Chinese wood chip Gasifier
---not much metal content, but might be interesting to some
Demo the use and making of blacksmith anvils from pieces of railroad rail
--- I will have one piece set up to cut the basic shapes w/torch
--- One set up on Mill to show truing the face
---One set up on a stand to show truing w/ angle grinder
---One set up on surface grinder to show finish grinding of face
---One set up on a stump to show that they really can work, as long as you
can keep it from moving
---Several pieces on a table to show/explain sizes/weights of rail
Show off trip hammer collection
But here's the question and intro to it:
Several years ago a guy (Keith Johnson) drove up the driveway and unloaded
a 5KW Westinghouse induction heater made in the 50's or 60's. He had been
at Bob Bergman's shop in central Wi to get an air hammer. Bob asked him to
deliver the induction heater to me to test/evaluate. It is about 4 feet
cubed. Tube type. It's mostly a 5KW radio station transmitter tuned to a
lower frequency, I think.
I have never fired it up. It takes about 50 amps of single phase 220 to
run it. And a water supply to cool the output coil. I think I will try to
get it going for the demo.
It came with only one output coil, but that one is about 4 inches long,
with an ID of about 2 inches, so I should be able to heat 1 inch bars pretty
well. -----IF it works at all. The manual tells me that there's about
10,000 volts running around inside, so I think I will keep one hand in my
Anyway, are any of you guys fooling around with induction heating? We had
some guys from Ameritherm up here 4 or 5 years ago demonstrating a 5KW solid
state unit that was about 1/20th the size of "my" machine, but it was about
$28K retail. Now the Chinese have a 5KW knock off of it for about $3K. A
friend of mine in AZ (Dan Jennings) bought one and it exceeded his (somewhat
low) expectations. Others (Roger Degner, for instance) have since gotten
them too.
So, what experiences do 'yall have with this method of heating things?
Pete Stanaitis
Reply to
Pete S
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As the engineer behind
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and this:
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maybe I can answer some questions.
5kW is "just adequate" for typical forging/blacksmithing activities. The main reason is that except for the specific workpiece the work coil and tuning were set up for, only a fraction of the available energy is coupled to the typical work. Those of you with ham radio experience will recognize this as the same phenomena as a mis-tuned final.
There are two major architectures in these small machines. Tuned RF and Royer. That tube type unit is almost surely a tuned RF unit. In this type of unit the work coil functions as half of a tank circuit, resonated with a capacitor. Very high current flows in the work coil which is usually water cooled. Coupling to the work piece is quite loose - that is, the work coil is usually much larger than the work piece.
The Royer type does not use an output tank and the current flow in the work coil is modest for a given power. It requires very tight coupling. That is, the coil should tightly conform to the work (though not touch it) to achieve maximum energy transfer.
The major operating difference between the two is what happens after the steel passes the Curie temperature (the temperature where it loses its magnetic properties). A resonant system struggles a bit below the Curie point but really lights up the metal afterward. "Struggle" is relative, of course. If 50kw is available to heat a half-inch rod, it will appear to snap to red heat :-)
The Royer is just the opposite. It yanks the steel to the Curie point and then greatly slows, again depending on the power available. A 500 watt Royer will heat a half inch rod to red heat in a few seconds but won't go any farther.
The problem comes when one tries to heat steel to white heat or higher to, for example, forge weld. Our old buddy Stefan-Boltzman (radiated power rises as the 4th power of absolute temperature) rears his ugly head. A piece that can be heated red hot with 500 watts will require many kW to be heated to near the melting point.
This guy, Jonathan
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who is an anesthesiologist by day and electronics hacker by night has built several 10kW units and sold one or two to knife makers. They seem to be quite happy.
He has also done levitation melting of steel, copper and aluminum with his unit. He has many youtube vids of this, posted under the moniker "imsmoother"
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I'll be happy to answer any questions if I can.
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Reply to
Neon John
Can I come to the demo? :) (actually I won't be able to get to your part of the country, but would love to see everything you have outlined above).
Reply to
Curt Welch
Sure, Curt. Come on up here. We have a spare bedroom.
Pete Stanaitis ---------------

Reply to
Pete S
Really cool stuff, John, thanks for that information. Prob'ly never use it directly, but I really enjoyed learning it anyway. No kidding. :)
Alvin in AZ
Reply to
Well, we didn't do the induction heating demo because the machine was doa upon turning on the cooling water. But we did do all the other stuff. Although OT, we got in a pretty nice demo of the woodgas generator running with a 3.9KW load. There's a video of that at:
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Pete Stanaitis ----------------
Reply to
Pete S

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