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QUESTION:There are well informed folks here that hopefully may help me with my
interest in induction heating. I have read about the use of a ring type
inductor surrounding a crucible to melt iron or any metal. These accounts
usually end before the results are published (unfortunately, not a good
sign) or I have not been able to completely follow a successful system.
Anyone know of some text or accounts of such a system?
ANSWER: It's not common for folks to have induction furnaces at home, mostly because
of cost and power requirements. If you intend to make a melt of any
substantial size, they can get out of hand quickly. I have a 50 KW Ajax
Magnethermic motor generator type induction furnace, which, in the way of
evolution, is a second generation induction melting system. They run at
about 50% efficiency, and one of this size is capable of melting up to 200
pounds of steel or iron. A smaller furnace size (100 lbs, for example)
would melt at twice the speed. The most desirable, the third generation,
are solid state and extremely efficient, running almost 100%, but the cost
puts them out of reach for most hobbyists.
The motor generator types are affordable with considerable luck. Mark, one
of the subscribers to RCM, had extremely good fortune in obtaining his unit
(30 KW Inductotherm, as I recall) for precious little money. The only
draw back to the second generation machines (motor generator types) is that
they are very bulky. My 50KW unit power supply weighs 3 tons and requires
a 400 amp 3 phase service to run.
If you are interested in doing very small work, there are induction units
made for the dental industry that will melt and cast as little as a half
ounce of metal. Still, price makes them beyond reach for hobby use unless
you've won the lottery recently. It is important to know the volume you
wish to melt, for size of furnace influences frequency. As the size
increases, frequency drops. Very large furnaces (hundreds of tons) can run
at line frequency. While mine is a 3000 Hz machine, I would have been
somewhat better off to have it be a 10,000 Hz machine, which was also made
in the same size. By running slightly higher frequency, smaller items can
be melted initially. Once you have a molten heel, it makes little
difference. Starting with chips, for example, is likely impossible for
me. At this point I have no idea, I've not run my furnace yet.
I suggest you contact one of the induction furnace manufacturers and obtain
some literature on furnaces to get an idea of their capabilities and
requirements. Then keep an eye open for a deal. One sold recently on
government auction for what could be considered a give away price, though
still not cheap. It was worth well over $100,000 new and had been used
very little. I suggest you ignore units made by Lepel if you intend to
melt. Their specialty is heating, not melting, so the frequencies available
tend to be too high. You'll learn more about that if you get some
literature and also do some research on induction melting.
The melting coil of which you speak is not so simple. While you do have a
coil to do the melting, it is contained within a furnace box built of proper
refractory and tilting mechanism so you can pour from the furnace to a
ladle. The furnace is heavy and bulky, just as the power supply is, and
is water cooled, just as the power supply is. You must deal with
considerable water, water that should be at room temperature to prevent
condensation on the components. Water consumption can be high, but is
reused in conjunction with a cooling system, it is generally not run to
waste.
I am not trying to discourage you where induction melting is concerned,
just trying to have you understand some of the conditions about which you
must come to terms. Induction melting is not for the timid, nor the poor.
It is the finest way to melt, however. It is rare to find cupolas in
operation today, having been replaced pretty much totally by induction
melting, which puts out virtually no fumes because there are no products of
combustion, at least at the furnace. The power company may have a different
view of that statement. EPA isn't real fond of a cupola running without
some means of controlling the crud that they emit.
Sorry I couldn't provide more information for you, but without specific
questions, I could rave on all day and never hit on that which you may care
to know.
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