Experimental Induction Furnace

The pending house move is forcing a radical disposal of lots of good
stuff, but here is something someone might like to 'take up the reins'
with. It's my prototye bench top Induction Furnace:
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Yet another sacrifice to the moving gods !!!!
AWEM
Reply to
Andrew Mawson
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Nice looking bit of kit Andrew ..your inventiveness at work. but would it not work better with insulation on the outside and an insulated lid and perhaps less land between the crusible and the coil. or was that a stage you never got to.
all the best.mark
Reply to
mark
Mark,
It is experimental - the crucible is sitting on a wooden bench !!!!
When the steel rod gets to a few hundreds of deg C the outside of the copper coils stay at 25 deg C - that's the beauty of induction - the energy is dissipated where you want it. The full sized version 15KVA version would have had a 12" diameter coil with central crucible, with the coil cast in refractory cement (there is a special one for this use) with water pumped through the coils for cooling.
It is also very good for pre-heating bearings and the like for slip fits - nice clean heat
AWEM
Reply to
Andrew Mawson
Does it have much of an effect on electrical/electronic stuff in the vicinity (tranny radios, pacemakers etc.)?
Regards, Tony
Reply to
Tony Jeffree
Tony,
Due to the small size, the prototype is running at about 30 Khz, so only just out of the audible range (up to perhaps 20Khz if you have young ears!) The full size would run at about 3 Khz as the mass is greater and the coil inductance greater. The controller sets the coil into resonance and you get a remarkably good sine wave across the tank coil, so relatively little in the way of harmonics at higher frequencies that would give the porential effects that you mention.
AWEM
Reply to
Andrew Mawson
Thats brilliant Andrew, I wish I had the skill to concieve and build stuff like this. I live in hope that one day a little switch in my brain will click and switch off the electronic dyslexia I suffer from.
I suppose you could even expand on the idea to include a home built induction hardening setup?
Peter
Reply to
Peter Neill
I've actually used it as it is to pop the chuck off a JT arbor - popped the chuck jaws down into the pot and heated it for a few minutes - as most of the heat was concentrated on the outer bits the arbor stayed relatively cool, and off it popped like magic
AWEM
Reply to
Andrew Mawson
Won't it burn thru the bench ?
-- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:-
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Reply to
John Stevenson
John,
The crucible stays remarkably cool - it is actually suspended perhaps 1/2" by the insulation, but it gets tepid when the charge is bally hot! As I said earier, the energy is being dissipated where you want it and not where you don't.
AWEM
Reply to
Andrew Mawson
Is the crucible conductive? I thought it was graphite from the photo. But the insulation looks a bit too thin for that.
Yikes
Any details about the special cement, supplier, cost etc?
Ta,
Reply to
Peter Fairbrother
photo. But
Peter,
This is the advice I've received:
Dear Andrew,
Suggest you look at Zircon Coil Plaster. Minimum package is 25kg bag
cost £47.90 plus VAT plus Delivery Charge.
This material has been used by Johnson Matthey refining at Royston as a
coil lining approx 1 inch thick. (used in melting of gold/silver)
adjacent to a clay graphite crucible.
Product data attached.
Yours Sincerely,
Graeme Lowndes
Sales Director.
Purimachos Limited
Waterloo Road
Bristol BS2 0PG.
Tel: 0117 9554361 Fax: 0117 9350844
Reply to
Andrew Mawson
Very interesting! Have I read right that you are switching the current on the secondary side (with the H-bridge)? And what was the voltage amperage you used and what the one planned?
Nick
Reply to
Nick Müller
secondary
Nick,
The tank coil is driven into oscillation by the 'H bridge' which is currently powered by the 24v 10A supply, however the final version was going to be off mains rectified using phase controlled thyristors so that the power level could be easily adjusted, so up to 415v peak (240 x root 3) - and my cable to the foundry is rated at 63 amps which limits the upper power level.
Suitable phase controlled thyristors and heat sinks are available to the purchaser by negotiation.
AWEM
Reply to
Andrew Mawson
Thanks. Now I got the picture. WOW ... 26kW. Really nice work!
I was just asking out of curiosity. And have another question (if you don't mind answering): Tuning the LC by the capacitors. Doesn't change the resonance frequency if there is something in the pot? I mean you are changing inductance. So did you have to tune the LC with every melt? But maybe, if the frequency is high enough, the iron in the pot doesn't change inductance because of all the _wanted_ losses in the "core". I'm not so familiar with this.
Nick
Reply to
Nick Müller
> > > >> >>It is experimental - the crucible is sitting on a wooden bench !!!! >> > Won't it burn thru the bench ? > > -- > Regards, > > John Stevenson > Nottingham, England. > > Visit the new Model Engineering adverts page at:- >
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's a sacrificial bench.
Reply to
Neil Ellwood
frequency
inductance.
doesn't
Nick,
Yes the resonant frequency changes not only with what you put in the pot, but also with temperature. I monitor the tank coil with an oscilloscope to check for a decent sine wave, and alter the frequency to 'chase the sinewave' as it alters. The current draw is also a good indicstor, hence the Avo in series with the DC source in the picture. NB AVO not part of the sale !!!
AWEM
Reply to
Andrew Mawson
Well he needs that amount of power for the castings for the 12" to 1' scale model of the Titanic he plans to build on his new estate...
Regards, Tony
Reply to
Tony Jeffree
...nah .... 26kW ..... that's SMALL FRY !
The commercial induction furnace that I've now got and will be installing at the new place is rated at 120kVA input 100 kVA output, but is limited to 87 kVA o/p due to the diesel generator I'll be powering it with.
If you see gliders in a few months circling near M25 J4 then they are probably over my heat plume !
AWEM
Reply to
Andrew Mawson
. I didn't want to ask wether you tune it with a scope. :-)
And you tune the frequency to reduce losses, right?
Very interesting. A have a book of the 50's about induction heating. They used tubes, as there were no transistors available. But I don't remember that they tuned to the resonance frequency.
Thanks for your explanations!
Nick
Reply to
Nick Müller
What volume (weight) of melt should it be capable of?
Regards, Tony
Reply to
Tony Jeffree

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