Subject: Induction furnace questions.

From: [email-masked] (DOUG SPECK)
Date: 10 Jan 1994 08:12:20 GMT

I have some questions for this newsgroup's readers, and I hope the answers
will be of interest to all:

What exactly is an induction furnace?
What are its capabilities?
How does it work?
and, What power requirements would a home-use model have?

I am interested in forging in my basement, some knives ( up to swords, 
some day), and was thinking an electrical furnace would be safer indoors
than any flame-operated furnace, esp. in winter.

I am an Electrical Technologist, so I should be able to follow technical
explanations. ;)

thanks for your replies(in advance),
Doug Speck.

--
  [email-masked] - aka  T-Bear                                 

  Remember - The teddybear of today still carries the vestigial        
             claws of his ancestors...

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From: [email-masked] (Andy Dingley)
Date: Mon, 10 Jan 1994 22:01:57 +0000

> What exactly is an induction furnace?

It's a big coil connected to the AC mains. You put metal in the middle of it,
and the eddy currents generated melt the metal by resistive heating. It's
more efficient if you increase the frequency, but this puts the plant costs
up as you have to give up a simple direct drive for an AC->DC->AC convertor.

The advantage for metallurgical use is that it's a very pure form of heating;
no combustion required and if you want chemical purity it's easy to arrange
inert/reducing gas jackets around the melt. OTOH, it's an expensive way of
heating, the plant is expensive and it's not as efficient a consumer of
electricity as an arc furnace. For this reason, it's usually used for small
batch production of high quality metal alloys or accurate heat treatment of
finished parts (eg. springs/knife blades), rather than a general purpose
metal cooker.

Because it's low frequency, you don't have the RF interference problems that
you get with arc furnaces. Because it's inductive, you do have problems with
power factors. *You* don't have problems, but the power supply companies do -
if you try and run a big induction furnace they will want to know about it
and can charge you a great deal more for your electricity, as the cost of
coping with this disturbed power factor. A lot of commercial scale
installations have their own generating plant. for this reason.

I've built a small induction furnace (about ten years ago) as a lab project
for refining semiconductors. Not difficult at all, but then I was using
commercial parts on a not seriously limited budget. For efficiency, it ran at
around 600Hz (AFAIR) with a commercial thyristor drive and a coil made of
copper water pipe (water cooled). I think the max power was around 3kW, but
we only ran it at 1kW.

A DIY induction furnace is certainly practical, but I'm not sure I'd bother.
Too much construction effort and too high running costs. I'd look at propane
/ blown air as a source of high quality controllable heat for a moderate
price. Not too expensive to buy/build, more compact than a coke hearth & less
expensive to run than oxy-acetylene. You can certainly use it indoors,
provided you're sensible about hearths, fireproofing of walls/ceiling,
ventilation fans and gas leak detectors. Most fuel gases are heavier than air
and are a *real* hazard in basements - look in a boatyard for gas
alarms / auto-shutoff valves.

NB - Anything magnetic inside the coil's field (even outside the coil) will
generate heat. Be careful with construction materials !

BTW - What does oxy-acetylene cost in the US ? In the UK it's prohibitive for
low-use DIY purposes. The gas is affordable, but the bottle rentals are
extortionate.

   _                              Andy Dingley
 /  ) ' ,_  _,  /   _ ) _/_       Codesmiths of Newcastle
/_ / / / / (_) /_) (_)  /_        [email-masked]
          (_)                     +44 091 230 1695

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From: [email-masked] (James Foster x2912)
Date: Tue, 11 Jan 1994 17:46:10 GMT

|> BTW - What does oxy-acetylene cost in the US ? In the UK it's prohibitive for
|> low-use DIY purposes. The gas is affordable, but the bottle rentals are
|> extortionate.
|>
|>   _                              Andy Dingley
|>  /  ) ' ,_  _,  /   _ ) _/_       Codesmiths of Newcastle

Many supply shops sell tanks in addition to leasing them out.  This is
good for DIY use since it's nice to have the tanks always available, but
you (at least me) don't use that much gas.  Most shops that use a lot
of gas would lease since, as I understand it, the cost is not that great
as long as you don't keep the tanks over 30 days or so.  I think I paid
about $200 for my tanks (80 cf O2, 60 Ac I think) about 15 years
ago.  The cost has gone up quite a bit since then.

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From: [email-masked] (Rogers V. Collins)
Date: 12 Jan 1994 01:04:15 GMT

Lindsay Publications, inc 815-935-5353
P.O. Box 538
Bradley, Il 
sells books on metal working new and old. a lot of reprints on
old technology. I'm sure I've seen a book on induction furnaces
in their catalog.