Nutless wonder

The way I misunderstand it, eddy currents inductively induced in the target dissipate power because of resistance.

Very nifty.

--Winston

Would it also activate getter (assuming you can get hold of caesium or whatever it is) in a valve/tube , should anyone try and make any ? eg

en Francais

Induction heating has been around a lot longer than modern semiconductor devices - ideal for case hardening steel shafts.

[snip]

As it happens, there is an instructable posted a few days ago that describes how to build your own induction heater. It is not totally trivial, but seems quite doable:

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RoRo

Take a look at some induction heaters in action in action. Watch the wrap.

Mikek

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 :

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

Uh... that's 490kW -- nearly half a megawatt.

ah, just enough to keep you warm in the winter, on the other side of the building that is :)

Jamie

Well, at least you know your nuts won't get cold.

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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.

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I don't know if I'm going to try to build one of these things. I should probably stick to repairing Grundig radios. What do you think Winston? Lenny

(...)

I would start small.

Instead of 150 KW, how about 180 W? :)

You could get into plenty of trouble with that, for not much money.

--Winston

klem kedidelhopper wrote in news: snipped-for-privacy@fw28g2000vbb.googlegroups.com:

Grundig???? switch to Philips......

Interesting:

We have in our inventory a whole case of hockey puck SCR's rated for 1000 Volts at 2500 amps. We really are getting to the point where there may not be any use for them. I think I may suggest to Ebay them or what ever.

We no longer have the few huge motors that required those in drives that require a separate feed from the switch gear just to operate them.

We have only one 1800 HP motor left operating.

Jamie

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Thanks for posting the site for the demo Winston. I got intrigued with this thing after we replaced the leaf springs in my wife's car. The nuts were all naturally good sized and all were frozen. The one near the plastic gas tank couldn't be heated with the torch and had to be cut with a Sawzall. It was a very awkward procedure. A few days later I saw the ad for this induction tool, (about 1000.00) with coils, etc. Seeing the paper clip heated is interesting but it sure isn't a 5/8 shackle nut. It really puts into perspective the power required to do this sort of thing. Lenny

(...)

You will see many YouTube and internet articles about induction heating.

There is this Extremely Nifty chip called the IRS2153.

Add two NMOSFETS and a few ancillary components and you get the basis of a very competent mini induction heater.

Please keep us in the loop!

--Winston