Jeff Urban wrote:

Just mentioning, a company called Ohio Crankshaft was a pioneer in
this a long time ago. Induction heating was used for hardening, mainly
case hardening steel. It was called the TOCCO process.

In the old days the flux wasn't all that well controlled and there was
plenty of power. The olman told me that the machine pulled 700 amps a
700 volts. This brought cranks and cams up to quenching temperature in
seconds, maybe sooner. After all 49 Kw can do that. About the flux,
when they said get everything metal out of your pockets they meant it.
One guy had a lighter on him working with the machine and got burned
really badly.

Some minor info available here : http://papers.sae.org/370166/

There is not a whole lot of info on it available on the net searching
directly for TOCCO. But then as good as it is, they screwed up a whole
lot of Chevy camshafts about 25 years ago or so. ALOT of them. I got a
buddy who actually knows how to work on those things, but there are
only so many. There doesn't need to be that many. At 49 Kw I'm sure
the process goes pretty fast. That was kinda the idea.

Anyone want to buy an induction cooktop ? I got one stashed somewhere,
just because I figured it could be dangerous.

To build the box that feeds the coils should not be all that
difficult. It does not use microwave frequencies, it's just RF. Some
switched mode power supplies run higher frequencies these days.

J
Well, most of them operate in the 30k..80k hz range, I guess that is a
good pick for the eddy current generations.

I just wonder how they actually did it years ago, as far as getting
that much power at that frequency ?

You can use a thyristor approach which was used for power supplies
once, it also can be used to for an induction heater.

Years ago getting the electronics for switching style of heater would
of made it impractical in many cases however, I guess if you have the
room to put such equipment then you're all set.

At work, we have one area that uses a induction heater to bond a
special wire together in a ceramic mold. The coil is actually a split
that needs to be assembled around the point where these two items come
together. The block is non-conductive but contains the conductive coil
tubing. When the block gets put back together, these tubing's get
electrically connected to each other and they have O-rings in there too.

That unit is a 10kW unit using a 60 hz square wave driving a series
resonant tank, the coil being the induction coil. There is no inverter
in there per say, but due to the high Q, ringing of the tank is used to
produce a 60 hz pulse of ~ 50 kHz of ringing on the coil. It works very
well and is semi portable.

Jamie