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Electric Arc Furnace? Answered

I'm trying to make a furnace that can melt metal. 
I've done a lot of thinking on it, and I decided that I'm going to make an Electric arc furnace for a multitude of reasons.
I plan to use an arc welder as the power supply, with two carbon rods as the electrodes, creating an arc just above the crucible to melt the metal. I was wondering if anyone has done anything like this before? 
I plan to have the furnace body made out of firebrick and refractory cement. Would this pose any problems?
Also, how much strain does this put on a welder? Will it need to be shut off after a while due to overheating, or can it sustain it's own?
Finally, How much power does a typical arc welder use? (in terms of watts) 

Discussions

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lemonie
lemonie

8 years ago

I think that arc-furnaces operate at higher voltage than arc-welders.
You need variable height control on your electrodes and are probably best on a 30A mains supply min.

L

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tylervitale
tylervitale

Answer 8 years ago

I always thought the voltage didn't matter all that much: as long as you can produce a good hot arc you should be good, right?
I'm not talking about an arc furnace that passes electricity into the metal to be melted, I'm talking about having the arc be from electrode to electrode just above the metal.

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shomas
shomas

Reply 5 months ago

It is a bit nuanced.

Power over a period of time is energy. Obviously the point is to get a bunch of energy into the furnace far far far faster than the energy can dispate. A small furnace having a smaller surface area disapates less energy than a large furnace at the same temperature.

Power = voltage × amps
Amps = voltage / resistance.

Reguarding what voltage and amps: A good arc furnace will have very little resistance in the wires with most of the resistance in the space of the arc. That way the majority of the power is disipated in the arc. After sparcing the arc the air gets hot and conducts very well, so you might manually draw the arc further apart. Also angling the rods down under high currents cause magnetic fields in the arc that push the arc path further away and down to the metal, and you might arc to the metal. Too little resistance in the arc causes more power to be lost to heating your cables. A home arc furnace would be difficult to control if the voltage is too high, but needs to be high enough that you can pump significant amount of power into the furnace at amps that your cables can handle.

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steveastrouk
steveastrouk

Answer 8 years ago

Nah, even an arc has a voltage across it. The power IN the arc is still represented by I x V.

An arc furnace strikes the arc ON the metal to be melted, and is carefully adjusted so that the arc continues to strike on the metal.

Steve

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lemonie
lemonie

Answer 8 years ago

I would have said that (but I had to go to work), thanks.

L

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quader4
quader4

5 years ago

If you're interested in building an arc furnace, here's one the King of Random made:

1
steveastrouk
steveastrouk

8 years ago

A typical "domestic" buzzbox welder here is ~3kW. And most domestic welders ARE NOT continuously rated - they're usually <<50% duty at full output - 5 mins on, 5 mins off at a minimum. Not really ideal for a smelter. Melting metals takes a lot of power. Arc furnaces are used in steel making - look at things like the electro-slag process for example.

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tylervitale
tylervitale

Answer 8 years ago

well, maybe that could be ok for me...
I don't want to melt anything like tungsten or anything ridiculous like that. I just want to melt copper and aluminum, maybe steel or iron if I could. so with such a hot arc, I wouldn't need to have it on for that long.
Then again, you're definitely right about their power consumption.
I read somewhere about a guy who worked at a power plant, monitoring the meters and what not. He said that they had a large arc furnace nearby, and he could tell when the thing was switched on down at the station just from the sheer amount of power it drew!