On Apr 8, 2:56*pm, Jamie
t wrote:
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
In 70;s Doug Schatz (then, of Applied Materials in Sunnyvale, CA)
designed and built the Pachydyne series of Induction Furnaces for sale
to companies like Bethlehem Steel. They were simple inverters: AC
mains to DC, then DC to AC, 50kHz at over 150kW. All done using 3-
phase H configuration SCR switches. Doug knew everything about how to
turn on, and how NOT to turn on, an SCR. The SCR's were those 'hockey
puck' packages that rattled if you shook them, so you'd clamp them
into the heat sink to collapse the glass package and make contact to
the SCR substrates. The wiring was 3/8 inch copper tubing with water
running through the tubes for cooling. It only took 7 turns of tubing
around a carbon graphite sink full of zinc chunks to melt the zinc
down into liquid in less than 20 minutes. You could walk up to the
liquid, stir it, add stuff, whatever. I was told that action was
impossible using a gas fired caldron. The induction furnaces were
used in controlled atmosphere to make esoteric alloys. His solid
state inverter were 85-90% efficiency and intended to replace vacuum
tube systems that were about 10% efficient! Imagine your electric
bill!
During development, there were lots of dramatic failures! Like when
no one thought about the fact that a metal washer is a shorted
transformer turn, so when they were first operating the system, the
washers got hot, burnt through bolts and mounting hardware, thus
supporting members and electronics started falling down - showers of
sparks and fire! Or, trying to debug operation, when all the unit
would do is go ZAP and burn out all 12 SCR's, which cost $100ea and
took all day to replace. From that to the final version, where the
design was so robust you could walk up to the tank with its loops of
copper pipes (wires) and drag a shorting rod over pipes, producing an
impressive shower of sparks and an accompanying crack as breakers and
shut down went off - but afterwards all you had to do was reset and
turn back on and you were up and running again.