"John Campbell" wrote in message
...
steamer wrote:

--Hey, anyone out there got an induction melting furnace? I'm
suddenly wondering if these are any good for melting aluminum, brass,
etc;
i.e. do they depend on the material being melted having a magnetic field
to grab, or will nonferrous stuff melt just as well?


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.

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.

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.

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