Q: Induction heating?

I'm not an expert, but I have been around them and I have a 5 KW machine in my shop that is next on the list to get running. As long as electric current runs in the material (the work), it will get hot. The magnetic lines of force that cut through the work generate currents in the work, just like a wire in a generator's armature windings. These currents, in turn generate a magnetic field of their own, creating eddy currents, etc. which heat the work. There are lots of induction melting furnaces around, but, to the best of my knowledge, they are not cheap, if they are modern. However, when I went looking at used machinery dealers for small (under 20 KW) older style vaccuum tube induction HEATING units, I was able to find plenty of them in the $2000 to $10,000 range. Price depends on the amount of power you need. I think that if you find a used one, you should be able to seriously deal on it.

Pete Stanaitis

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steamer wrote:

any metal can be melted in an induction furnace if it is set up for it.. The power supply uses the coil of the furnace as part of the tuned circuit that induces currents into the metal that is being melted.. different metals will resonate at differnt frequencies and the circuit is tuned for max energy transfer to the metal.. it also changes the tuning as it melts.

Here is one induction furnace mfgr.

John

Yep, a 50 KW unit, motor generator type. Three generations of induction furnace power supplies yielded solid state devices, which are almost 100% efficient. The second generation, motor generator types, are only roughly half that level of efficiency, and the early models, spark gap with transformers, are down around 25% efficiency.

Induction melting and heating requires proper selection of frequency, depending on the desired effect. Large induction furnaces are capable of melting at line frequency, but as the size of the furnace decreases, the frequency must rise. Even non-conductive items can be heated by using extremely high frequencies. Some companies (Lepel) specialize in heating only, not melting.

Harold

Will work ok for any metal as they rely on induced current. There are problems for home use as they don't scale down very well.

1. As the size goes down the frequency has to go up for any efficiency (for the same reason that mains frequency transformers use a laminated iron core while a pc power supply at say 100KHz has to use a ferrite core). This means for a few KW you need frequencys of a few KHz
2. The power factor (crudely watts/VA) is terrible. This basically requires a big capacitor with either high voltage (10's of amps at 1000's of volts) or high current (100's of amps at 100's of volts). The capacitor has the full current flowing through it in the KHz range and these are not cheap.

That's not exactly true. The dental industry makes small units that melt only a half troy ounce for making dental castings. As you stated, they simply must be operated at higher frequencies, which they do.

Actually, for melting, they are equipped with a series of capacitors that are switchable while in use. Constant correction of power factor is necessary as the volume of molten metal continues to change. I understand the solid state variety works differently. I'm speaking of a motor generator type power supply.

Incidentally, my 50KW unit is powered by three phase 60 Hz, and requires a

190 amp supply to operate at rated output. Output of the generator is single phase 400 V @ 3,000 Hz. For a melting furnace that has a capacity of 100 pounds, this unit could easily have been used @ 10,000 Hz instead. That is likely the volume I'll choose to melt when I get it up and running. The furnace box is sized appropriately. They were available in both frequencies from Ajax Magnethermic. How they were intended to be used is what dictated the proper frequency for the consumer.

Harold

But then, that's capacitive heating. Like when you microwave your food! Others are still induction, only using a graphite or metallic (molybdenum or tungsten?) crucible.

Come to think of it... you ever get that thing running?

Tim

-- "That's for the courts to decide." - Homer Simpson Website @

Has this inspired madman made a show in this ng yet?

(Melting metals in a domestic microwave oven)

Jeff