Sam Thompson

Is this induction heating?

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Here's some more pics of the accessories that come with the unit...
And some coils i made... very easy to do...:P

Except... I'm still trying to figure out how to make one those flat coils that Grant has....:D

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I used 3 annealing units at work that are induction heaters, and I worked at a foundry that had an induction furnace.

Generally speaking big parts lower frequencies (HZ), smaller parts higher frequencies (up to MGHZ).

Fitting the coils as close to the part increases the coupling between the part, and the magnetic fields generated which makes it more efficient. The coils themselves can be insulated , so you don't make contact, since the magnetic fields are not affected by the insulation.

Lay a magnet in some grinding dust to see the magnetic fields. That is the zone that you want to stay in. It takes more power to project the fields out farther, so you can actually heat faster with less power, if your coil is closer to the part size. Coil spacing, diameter, etc. all play a part in coil efficiency. I went to an Ameritherm training session, and it was very informative about all phases of induction heating.

At the foundry it was fun watching 25 kilos of white hot chrome cobalt (3,250 degrees) floating , and spinning in the crucible then drop when the power was cut.

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That information is very helpful to me ...
I made a 7 turn coil and couldn't get the 2 1/8" to heat up much even after 20 minutes...
Then I made a 4 turn coil and voila... it worked...
is this what you are talking about in terms of lower and higher frequencies?... or is that something else...?

I've touched the steel to the coil on occasion without anything happening... but is there something I should be concerned about?

What kind of insulation is used on the coils?

I'm very fascinated and interested in coil design and your comments are very helpful....

Thanks

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The frequency is the power supply itself. Your unit is probably in the KHz range, that is the number of times per second that the polarity of the Positive/Negative reverse positions. The Pos. Neg. = North South poles in the magnetic field. What you are doing is taking the North South poles in the material itself and moving them at such a rate that it forms internal friction creating the heat in the part. It seemed odd to me that the copper we were annealing would heat because it is normally nonmagnetic, but it does.

Was the spacing of the coils the same on the 7, 4 turn units you made? They may have been canceling each other out to some degree.

With the units we had if a part touched the coil it would trip ,and shut the unit down. Any insulation that will take the radiant heat will work. Fiberglass, solid ceramic, Kaowool, etc..

We were annealing copper electrical connector ends that get crimped, as they were brittle after machining. The coils we had were different than yours since we could not pas the entire part through the coil, and it was automated. Think of a carousel with the parts on the outer edge. The coil was a U shape that straddled the parts. After heating they fell into a water bath. Some parts we were doing 2 a second continuously all day.

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Nobody has mentioned what appears to me like a great deal of oxidation on the work, since there is no neutral atmosphere around the piece such as would be found in a furnace or forge. I would think a small sheet metal box around the heater element with a relatively low positive pressure of CO2 or other shielding gas would greatly help with the scaling. Just put a normal welding flowmeter on a tank and keep the flow going while heating - could even tie in a solenoid to dump gas only when the unit is working.

The speed of heating is fabulous and even if there was no savings over propane, the ability to get small areas white hot for short bends or longer pieces to a consistent forging temp is worth the cost of the unit just to save time waiting between heats. I think a production shop would be hard-pressed to find something that worked better.

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You can heat anything that conducts electricity, nothing to do with magnetic. The coil induces a heavy current in the work and reverses the polarity 30,000 to 100,000 times per second. The machine "self-tunes" to the proper frequency. The coil is much like a transformer; increase the number of turns and you increase the voltage in the part but reduce the amperage. Amperage is the most important in heating.

Magnetic materials have totally different electrical characteristics below Curie (the non-magnetic temperature) than above. So any coil is a compromise when heating steel. The machine cannot generate the power needed to drive too many turns.

Coils may be insulated for convenience or to contain the heat. A ceramic tube prevents the escape of much radiant energy which is the source of much loss at high temperatures.

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What I wanted to say about nonmagnetic items was how they move around in the field, not the heating. Haven't had a lot of sleep lately. There were some copper parts that we had to contain as they went through through the coil to keep them from jumping out of the feed wheel.

As for the scaling, on our parts it was not any greater than heating them with a torch. The only problem I would see with a shielding gas is when the part is pulled out and exposed to the atmosphere it would oxidize. Really depends on how long it is at heat, and exposed.

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As for the scaling, on our parts it was not any greater than heating them with a torch. The only problem I would see with a shielding gas is when the part is pulled out and exposed to the atmosphere it would oxidize. Really depends on how long it is at heat, and exposed.


The photos posted by JDH appeared to show heavy scaling so that is what I based my comments on...and when you take the part out of the gas shield, it would oxidize no faster than a piece heated in a conventional gas or coal forge. It may be that the very rapid heating from induction would cause less scaling simply due to minimal exposure.

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Energy cost: Usually goes down by 50 - 90%! I used to use about $250. - $300. per month in propane, after switching to all induction, I saw my electric bill go up by about $25 - $35 per month. Now we probably have the cheapest electricity in the country @ 4 -5 cents per KWhour, but still.........

Scale is a function of time, temperature and atmosphere. Scaling is reduced for many reason. Quick heating minimizes scaling, also you don't need as high a heat because you can re-heat in just a few seconds. Yeah, I've thought about different schemes for heating in a neutral atmosphere.

While induction lends itself to production, it is really a dream for one off hand forging too. Pull up a stool at the anvil, have the induction coil on the opposite side of the anvil and just reach a few inches to heat your piece. Need some serious reduction? Heat it to a welding heat and it moves like butter. Re-heat in a few seconds. Many forging opportunities are lost just because of the need to "fire up" the forge. With the induction, flip a switch and you're ready to start forging. An induction forge and a fly press make the "urban blacksmith shop" possible. No smell, no noise, no blast of heat or noxious fumes.

Edited by nakedanvil

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O.K. Craig, pay attention now. I start with 3/16 tubing and bend it in a tight "hairpin". Notice I've hammered any kinks out - the tube does not have to be round. Then I anneal the bend by heating dull red and quenching in water, Clamp one leg in the vise and twist as shown. Put one leg straight down in the vise and start winding, be sure to anneal the first 2 inches or so to make the tight bend (note plier!). Then I wind it tight and go back over it with a screw-driver to open it up. START FROM THE OUTSIDE and work your way into the center. Might have to repeat 2-3 times. Make sure no coils touch.

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Note that I use a "trick" that is useful in forge work where you have two 90 degree bends right next to each other. Bent a 180 and then twist. Done that on many jobs. Look at picture #4. 90 degrees coming up and 90 degrees going right.

Edited by nakedanvil

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Thanks Grant....
Can I use 1/4?.... That's what I have been using for the coils... or is 3/16 the way to go... I think I need to get another adapter for that...:)

Very cool... been thinking on it all week... was going to try the torch bend method tonight and test tommorrow.... :D

Building an arm and spring guard for my 25lb Little Giant... :rolleyes:

You know me and safety... ;)

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No, you can't use 1/4! Kinks too easy. Craig, didn't I send you a coil with 3/16 soldered into 1/4? I just slip on some 1/4 stubs and soft solder the joint. I like good 'ol acid core leaded solder. I hate the "lead free" solders. They still carry it at ACE - "The hardware Place".

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Yup... as a matter of fact you did :D

Acid core leaded solder it is.... I'll see if I can duplicate your instructions.... and not take a month to do it...;)

Heck... I think I even have some 3/16 copper tubing lying under by bench...:P

Thanks Grant...

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Gosh, It's a Flemish coil! When I was learning to sail, the boat owner had a retentive problem with the appearance of the boat. All the rope on deck looked nice and tight like that when we left it.

Phil

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