Induction Furnace Question



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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
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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.

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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
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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
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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, - - - - - - - - - - - - - - - - - - - - - - --+ Metalcasting and Games: http://webpages.charter.net/dawill/tmoranwms

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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.

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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 www.sanmartin.com

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sme wrote:

Having designed smps myself, this has to be the largest understatement I've heard in awhile.
Sounds like a pretty interesting project.
Steve Smith
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How about circulating propylene glycol instead of water, inside a copper tubing load coil? Nontoxic, basically nonconducting in case of a leak, and pretty cheap (Sierra antifreeze is about $7/gallon here in the US). It's a little viscous until it warms up, and doesn't have the heat capacity of water, but should be safer for you.
-- Regards, Carl Ijames carl.ijames at verizon.net
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I asked the Inductotherm people about that, they say don't use automotive type antifreeze, but you can add ethylene glycol to the water in very cold areas. Alan Black

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Auto antifreeze is ethylene glycol. Something doesn't add up! <g>
Harold
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Harold, Oh I know and agree, I bought the unit used and it seemed to have some scale so I asked about using coolant instead of water. They said not to use automotive coolant, I did not argue with the experts. This is my first induction melting unit, I've been bumming time on someone else's 100KW Pillar and am now forced to learn all about it. I had bought some IGBTs and was ready to build a microcontroller based unit but I needed something that I can get up and working in the short term. BTW what does <g> mean? Alan

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:)
See also <BG> (big grin) and E for evil, etc....
Tim
-- "I have misplaced my pants." - Homer Simpson | Electronics, - - - - - - - - - - - - - - - - - - - - - - --+ Metalcasting and Games: http://webpages.charter.net/dawill/tmoranwms
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    [ ... ]

    The same thing as ":-)". It is indicating that something was said with a smile (or a grin). The two symbols came from different groups. The ":-)" (smiley) originated with usenet newsgroups, while I believe that the "<g>" (grin) originated with bulletin board systems, perhaps at about the same time.
    Are there any bulletin board systems (the old kind, where everyone dials in to a central system) still in operation?
    Enjoy,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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The danger is not whether it is conductive or not; it is what happens when liquid hits molten steel!
Mark
P.S. Harold, we got my Inductotherm running a couple of months ago.

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That's real good news, Mark! Glad to hear it.
I recall you had a problem with blowing fuses (or tripping breakers) and were looking to try a soft start switch. Can you tell us how you resolved the problem?
Harold
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Hi Harold...
We finally wound up using 24 5000 watt dryer elements in series with the motor, which limited the starting current to 100 amps at 440 volts... the heaters radiate about 45,000 watts for about 30 seconds until the motor comes up to speed then go dark. They are then switched out of the circuit. Takes the chill out of the foundry right away! They are mounted overhead for safety... think of a SERIOUS infrared heater mounted to the ceiling...
There is a talented high school student named Trevor that is doing most of the hard work on this project. I am sure that he will be one of those people that we'll say "I knew him when..."
Mark

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Hi Harold...
We finally wound up using 24 5000 watt dryer elements in series with the motor, which limited the starting current to 100 amps at 440 volts... the heaters radiate about 45,000 watts for about 30 seconds until the motor comes up to speed then go dark. They are then switched out of the circuit. Takes the chill out of the foundry right away! They are mounted overhead for safety... think of a SERIOUS infrared heater mounted to the ceiling...
There is a talented high school student named Trevor that is doing most of the hard work on this project. I am sure that he will be one of those people that we'll say "I knew him when..."
Mark

when
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Boy, I'd love to hear their explanation for why auto antifreeze is no good but ethylene glycol is ok. The antifreeze has a lubricant for the water pump and an anticorrosion package but all that together is less than 1%, it's all compatible with copper tubing, steel, and cast iron, and the electrical conductivity is pretty low to avoid problems with dis-similar metals in the engine and radiator. I just thought the propylene glycol based antifreeze would be better here since it's nontoxic. I'm too lazy to look up the flash point but I don't think the glycols burn much unless there's another source of fuel to keep them going; even water hitting molten steel is going to be violent enough that I personally don't think the glycol would be worse, but I've never done the test ... :-).
-- Regards, Carl Ijames carl.ijames at verizon.net

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It has an open evap type cooling tower so possibly that is the reason. If it was a closed system with a heat exchanger it might be OK, just guessing. BTW I am in the US, central Calif Coast. Alan

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