Induction Furnace Question

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

--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.

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

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

Auto antifreeze is ethylene glycol. Something doesn't add up!

Harold

Oh dear me my oh no! Stainless is a very good resistor. We want the heat in the work, not the coil.

Tim

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

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Fair enough. Can I ask about the basic topology, namely, does it use resonance? Quasi-resonance? Is the heating current (reactive and otherwise) fully handled by the power devices (IGBTs I presume)? Is it a full wave setup?

Tim

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

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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

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

Uh huh. Thanks.

-- Jeff

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 mean? Alan

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.

:)

See also (big grin) and E for evil, etc....

Tim

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

- - - - - - - - - - - - - - - - - - - - - - --+ Metalcasting and Games:

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 "" (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.

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

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

automotive

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

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