Induction Furnace Question

Dear Group,
I am posting this message in an attempt to gauge interest for a project I have been working on. I have been a hobbyist of metalworking for some time and currently posses a
lathe and CNC milling machine which I enjoy the use of very much. I have also cast metal using traditional foundry methods (gas / charcoal) and this is what seeded my interest for this project.
I have designed an induction furnace which is currently in it's testing stage. Initially this furnace was not going to see light of day out side of my own workshop but while demonstrating it to a friend he showed a great deal of interest and mentioned that many like minded hobbyists may be interested in such a device.
So I guess I am posting this to gauge interest from the group and seek advice to what value both from usage and monetary you would put on it.
I would like to apologise in advance if members of this group see this post as a form of spam. Please be assured that this is not my intention. I agree it would be nice to make a little cash out of ones hobby and give up the office job ;-)
Regards, Steve.
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wrote:

Greetings Steve, By all means you should post any info you can. There has been much interest in induction furnaces expressed in this group. Cheers, Eric
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Eric, thanks for the encouragement.
Currently the system can heat 20mm tool steel to yellow / white in about six seconds. I am currently working on the cooling aspect using a closed loop water supply that flows around the work coil. The system is running at approx. a third of full power so melting of steel should be achievable. Additional testing and fine tuning of variable frequency is also in the process. All circuitry is solid state and is currently cooled by standard PC fans which will eventually make the unit very compact and transportable.
The circuit boards where designed using Eagle PCB then cut on a CNC Denford Starmill (1988) that I was lucky to find going for a song. Incidentally I managed to convert this mill to run on Linux EMC patched into its original L297 / L298 stepper drivers. The original control circuit could only hold approx 32kb of info so this is now bypassed.
This has been a part time project with many trips to the library and countless hours rambling the web for as much info on induction as possible. Hopefully soon it will all payoff.... ;-)
Regards Steve.

a
own
in
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I'd be interested - what capacity?

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BoDiddly thanks for your interest,
I think it would not be unreasonable to say that stock of around 30-40mm dia could be worked. This could be placed in a small removable crucible of which the work coil surrounds Eddie currents will then be induced into the workpiece which acts as a primary single coil (high amps) this causes friction that heats the piece and eventually melts it.
This setup would be ideal for working on smallish pieces using centrifugal lost wax casting. In fact one of the reasons I got interested in induction stemmed from my interest in micro gas turbines and the wish to cast inconnel turbine blades. But I am still a little way from this, but moving in the right direction I hope ;-)
Regards Steve

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sme wrote:

OH, WOW! This is starting to get very interesting! But, what do you use for a mold? Investment casting?
Jon
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Ok Jon this is a short summary of the process as I understand it ...Most of this information comes from a very good (excellent) book on this topic called "Centrifugal or Lost Wax Jewellery Casting" by Murray Bovin.
A shape can be designed using a cad package such as rhino etc etc This can then be converted to Gcode which can then be processed by Linux EMC which drives the CNC mill.
Carving wax is mounted and the mill set in motion once completed your desired part should be replicated in the wax.
This wax part is hung inside a flask(a tube) to be eventually surrounded by investment.
Investment is composed of cristobalite, gypsum, silicas and modifying agents. cristobalite is a volcanic mineral. It is now made by heating silicas to 2680C - 3040C.
One problem with investment is air bubble's the solution is to vacuum them out by placing the investment inside a bell jar.
The slurry (investment) can then be slowly pored into the flask containing the wax part once this process is complete burnout can take place. Burnout removes the wax leaving the impression in the solid dried investment.
This can then be placed in the centrifugal casting machine ready to receive the molten metal.
Once the metal is in place a pin is pulled sending the clockwork centrifugal arm rotating which forces the molten metal into the investment. Once cooled the investment can be removed hopefully leaving the finished part intact.
Note : you could skip the steps of designing and cutting the wax part if you have a piece to copy by taking an impression of it in rubber then poring molten wax into the rubber mould. This would give you your lost wax part. Alternatively you could carve the wax by hand as many Jewellers do or at least they used to.
Hope this helps Jon forgive me for any unclear rambling ;-)
Regards Steve

dia
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sme wrote:

OK, I am familiar with the investment casting concept, You didn't have to go to such great detail for this, I was just wondering what casting technique you were going to use. It seems like an exotic thing to be casing in Inconel!
Thanks,
Jon
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wrote: That's great Steve. It sounds like this would be a great setup for case hardening and tempering home made tools. I have a tig welder and could use the argon to shield the part during heating and so avoid tool wraps, flux, etc.. Eric

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Eric it would be a nice clean table top solution no stoking of coals or use of gas would not even have to venture outside the workshop.... great for those winter months :-)
One thing that does concern me is safety. If I was to sell this (cottage industry style) I could not guarantee the safe usage or negligence from the user and in the days of ambulance chasing litigation lawyers I could end up loosing the shirt on my back or worse so I guess this would need a great deal of thought. Not sure how this lies as yet!
Regards Steve.

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wrote:

Well Steve, just don't sell it. Give away the plans along with a disclaimer that says this is fir info only, not for building, and if you are stupid enough to build it and burn down the house then tough beans. But there are all kinds of publications available for sale with instructions to build various lethal devices so sell it if you want. Eric
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Have you tried using copper tubing for your coil? I believe this is the standard type of set up for commercial units, though they probably are not using plumbing tube, but for a low power unit it may be usable.
sme wrote:

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James P Crombie
Slemon Park, PEI
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Machineman, thanks for you reply. I was looking as 5mm copper tube bent into a coil. Water could then be fed through this as a cooling agent. Problem really lies with safety aspects as water in close proximately with high voltage circuitry .......
Regards Steve.

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    --Seems to me you'd be better off making the cooling coil out of stainless tube, lest you risk a burn-thru of the copper, which melts at a much lower temp, yes? Better safe than sorry and all that... Heat transfer sucks big time with stainless compared to copper tho.
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Nope! Commercial induction furnaces use copper coils, which are water cooled. Burn-thru is no problem as long as you don't expose the coils to the melt, and make sure you have water circulating. The typical induction furnace has a pressure switch that shuts down the furnace if you lose water pressure.
Harold
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Oh dear me my oh no! Stainless is a very good resistor. We want the heat in the work, not the coil. <G>
Tim
-- "I have misplaced my pants." - Homer Simpson | Electronics, - - - - - - - - - - - - - - - - - - - - - - --+ Metalcasting and Games: http://webpages.charter.net/dawill/tmoranwms
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Yep. The coil should have low resistance. It's not a heating element, it's a winding in a transformer of sorts.
Harold
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*Cooling* coil?
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heat
In a sense, yes. Because it lives in such a hot environment (the actual melting portion of the furnace), it must be cooled. The coil is generally buried in refractory, so it doesn't see the direct heat of melting, although it is very close to it.
Harold
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Uh huh. Thanks.
-- Jeff
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