Induction Furnace Question

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

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.

I'd be interested - what capacity?

On Wed, 2 Jun 2004 15:39:14 +0100, "sme" 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

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

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.

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.

Steve,

Add me to your 'interested' list - induction heating has been a 'must get round to it someday' back burner project for years. What are you using as the switching element and what is your upper power limit?

Andrew Mawson Bromley, Kent, UK

OH, WOW! This is starting to get very interesting! But, what do you use for a mold? Investment casting?

Jon

Hello Andrew .... A local chap I see.... I to live in Kent UK

Basically this is an off line high power smps (switch mode power supply).

Below is an overview of the process :- Low voltage oscillator that signals mosfet drivers that switches high power mosfets that alternates 400vdc into the primary which inducts into the secondary (low voltage high current) which alternates work coil (lower voltage higher current) that finally inducts eddie currents into the workpiece causing friction = heat

Some issues arise from ringing, frequency matching the workpiece, safe cooling of workcoil, making it safe for public use and finally making it look sexy. ;-)

Regards Steve.

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

Steve:

By all means, keep us informed! I and most of the other small-business jewelers I know would LOVE to have an induction melter, but commercial ones are way out of reach dollar-wise for most of us. I'd be very interested in a home-brew design, especially one for which someone else has already worked out the kinks!

Best regards,

Bob

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

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

Very exciting, could you please supply a schematic?

What kind of resonant capacitors do you use with the work coil?

Tim

-- "I have misplaced my pants." - Homer Simpson | Electronics,

Tim thank you for your reply...

At this time I would have to decline supplying you with a schematic or in this case it would be three or four schematics, Sorry. I am sure you can appreciate there has been a great deal of work put into this project to date. Ideally I would like to make this into a commercial viable product that the likes of you and I, hobbyist / jewellers could afford and feel that we are getting good value. I should stress at this stage that I am not out to make a fortune but rather it would be nice to make a living or a small cottage industry supplying this kit at a price we would all be willing to part with for such a device.

I initially posted here to try and gauge interest for the purpose to spur me on to refine the system I guess there's nothing like encouragement which so far the replies have given.

Saying this circumstances change and if they do I would be more than happy to supply a schematic to you.

Regards Steve.

Hi Steve By all means I am interested in learning all you want to teach about your induction furnace. I have written a couple of books for Lindsay Publications and there are disclaimers in the front of each book that do a very good job of covering the legal aspects of a project. This is not to say that someone will not try to sue you but It does make their chances of success very poor. Lindsay helped and guided me as I wrote both of my books because he believed there would be a market for them. I am sure he would be willing to consider your furnace because there is a real demand for it. Casting ferrous metals is hard and an induction furnace would be just the ticket. Please keep me on your list of people to keep informed, I am very interested. Rick

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

Quite interesting!, since its a new design I'm sure you are using IGBTs for the output circuit, since they have pretty much replaced the SCRs in induction power supplies. You mentioned you wanted to "keep the design a secret" but of course you can reveal what frequency and wattage you are planning to offer it at so we can all get an idea what applications it might be useful for. I have a Inductotherm VIP 60 in my shop, I replaced the banks of SCRs with a single high powered SCR for each side. This also allowed me to remove the dampening circuit on the output transformers, since inrush is not such a problem with the new ones. I did buy some IGBTs for a induction project. Since it was just for my own use. I would much rather buy one to get rid of that cooling tower. Tell us more! Alan Black