Why is nobody dabbling with electric arc furnaces?

[strantor]

I've been "about to" get into metal casting for a few years now, and my level of interest is finally about to surpass my tendency to procrastinate.

I want to cast iron. I will start with aluminum as it seems an obligatory entry point into the craft but I don't want to invest in a technology that isn't suitable for casting iron because I know I'll outgrow it almost immediately.

Propane burners seem to be 80-90% of what everyone uses but as far as I can tell it's not the way to go for casting iron (possible but far from ideal). For that it seems you are better off with induction. But induction is expensive to buy or complicated to DIY.

What seems a lot less expensive and complicated is dumping a motherload of amps through a 10,000 degree arc into a crucible. But I can't find hardly any examples of anyone doing it at large-ish home/hobby scale. I find plenty of examples of the industrial scale 1.21 gigawatt smelting scene and I find plenty of shameless copies of this video by King of Random where he zapped a couple of ounces of metal between two carbon electrodes inside a tiny fire brick, but nothing in between. Why? Why is almost nobody pursuing this? It seems to me like the ideal way to melt metal. Electricity is way cheaper than propane, gets way hotter, melts way faster, and with much less rigmarole to set up the furnace and start melting. There must be some kind of fly in the ointment that I have not yet identified; what is it?

I did some tests today just using my TIG welder. Filled up a 2-1/4" socket and a sprocket bore with molten aluminum and it seems promising but I discovered that 3/32" tungsten electrodes just aren't going to cut it. I burned through 2 brand new electrodes in just a couple of minutes and also melted a TIG torch . I just ordered a length of 1/4" tungsten rod for further experimentation (and a new torch).










Obviously terrible result here but this is step 0 of what I'm sure will be journey.




This is the only thing I have found that is even close to what I am envisioning. (And it seems like a project that was never seen through to completion)

And this (which was inspired by above):

 

[Weldingrod1]

Some thoughts:
Bigger torch. been there, fried that, bought it... suddenly 1/4" Aluminum is weldable!

DC straight polarity will get 70% of the heat into the work.
You might try a carbon arc. I know for sure that the big Aluminum smelters use three phase Carbon arc for heating.
You will get into trouble with Aluminum alloy-ing with the Iron.
A graphite crucible could work, but two Carbon electrodes might work nicely. Ideally transferring via two arcs (including the work) rather than to the electrodes.

Might need a feedback system to keep the arc length right.

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[Shotgun]

"What seems a lot less expensive and complicated is dumping a motherload of amps"

As you quickly discovered, this is not less expensive or complicated. Controlling energy is hard. Controlling big energy is big hard. Collecting that energy from a home shops power supply and concentrating it to do your melt makes it even harder. Those companies that are using electricity to smelt have their own special connections to the power company.

 

[strantor]

DC straight polarity will get 70% of the heat into the work.

Yeah that's how I had it set up to start, but tried swapping it just S&G and burned up half an electrode in a manner of seconds. So I put it back.

You might try a carbon arc. I know for sure that the big Aluminum smelters use three phase Carbon arc for heating.

I am going to try it. I suspect tungsten will be better but it is definitely worth testing.

Might need a feedback system to keep the arc length right.

Yes I expect so. I was picturing something like a Cnc plasma Z-axis (or an actual CNC z-axis) with Torch Height Controller to sense the arc gap voltage and adjust electrode position.

Also maybe flooding the area with argon or other inert gas because I was getting loads of oxidation (I took the cup off the TIG torch and did not connect gas for my testing).

 

[Weldingrod1]

Yeah, you need to protect the Tungsten from air. The white stuff is probably Tungsten oxide.

BTW, Helium will increase the arc Voltage and thus the heating.

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[strantor]

"What seems a lot less expensive and complicated is dumping a motherload of amps"

As you quickly discovered, this is not less expensive or complicated.

if you're including the cost of roasted tungsten then yeah I'm upside down in this already. But I think scaling up the tungsten will scale down the cost (maybe I'm wrong, will see). As far as the energy cost goes, a 20lb propane tank refill is $25 and is about 4 gallons. There's 27kW of potential in a gallon of propane so 108kW for $25. If you burned that over 4.5 hours it works out to $5.55/kWh. 240V @ 100A for 4.5hrs is also 108kW but I only pay 15 cents per kWh for electric energy, so the propane costs 37X more than electricity (See edit below). On top of that, most of the propane goes into heating the furnace itself, the crucible, and the atmosphere around it, than into the metal. The electric energy can be directed straight into the metal so requires even less power.

Controlling energy is hard. Controlling big energy is big hard. Collecting that energy from a home shops power supply and concentrating it to do your melt makes it even harder.

Yeah controlling big power isn't so trivial and that's why big power induction is so expensive. I'm hoping big power arc furnace can be simpler since it doesn't require high frequency switching, just some variable transformer action. Maybe my 250A tig welder is actually all I need but I doubt it.

Those companies that are using electricity to smelt have their own special connections to the power company.

Yes I have read about that but I think you don't need that if you scale it down. People are melting crucibles of cast iron with 10Kw induction heaters and that's about 40A @ 240V. I don't see why a large-ish hobby scale arc furnace would need more than that.


EDIT: something felt off about that math and I just realized what it was. I was comparing 1 hour of run time on propane to 1kWh of electricity. Here is better math:
108kWh of propane energy: $25.00
108kWh of electric energy @ .15/kWh: $16.20
Propane costs 54% more than electricity.
But still considering that a propane furnace wastes a great deal of energy heating everything but the metal, that figure will probably be well over double what the math says.

 

[strantor]

Yeah, you need to protect the Tungsten from air. The white stuff is probably Tungsten oxide.

BTW, Helium will increase the arc Voltage and thus the heating.

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Tungsten oxide eh? Maybe that's what was causing my aluminum to blob up with a crusty exterior "shell" that seemed way too hard to melt to be aluminum. So gas is definitely needed. I'm almost out of argon so when I go for a refill I'll compare to the cost of helium. If it isn't unreasonably expensive I'll give it a shot. Thanks for the recommendation.

 

[Weldingrod1]

With a TIG torch on DC straight you put 70% of the electrical energy in the work and 30% in the torch. With AC its 50/50.
The energy goes where the electrons go. Just gotta remember the slippery little buggers are negative polarity. So, they flow from negative to positive.

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[SLK001]

Build and play with this for a while:



Ya got to love how this guy is looking into the crucible without any eye protection.

 

[benmychree]

Find a foundry that does cast iron at a reasonable cost, you will be money ahead compared to the direction you are headed in, not to mention the quality of the results.