Foundry work - types of electric furnaces?

[Just a Sparky]

Just trying to get a grasp on the differences and pros & cons between the various different types of furnaces which can be built for heating metal to a pourable state. The hypothetical end use here is for lost-PLA investment casting of project parts. Making handwheels, flywheels, Hirth joints (without spending all day on a shaper), custom low pressure pipe manifolds and other complex shapes in lieu of a 5-axis machining center. Materials involved would range from aluminum, copper and bronze to gray/ductile iron and maybe the odd stainless part.

Are carbon-arc furnaces only good for heating iron and steel? Does the carbon from the electrode alloy with the metal being heated or does it simply oxidize into CO2 in the heat of the arc? Carbon gouging rods can be had for relatively cheap and my welder has enough snort for this to be a very attractive option for me.

Are induction furnaces only good for heating ferrous metals with high electrical resistance? Pretty sure I know the answer to this one but I could be wrong.

Is it worth it to use a tungsten electrode in argon to avoid contaminating aluminum and bronze?

Has anyone here done/been around enough foundry work to answer these questions?

Thanks.

 

[plastikdreams]

We use electric vacuum melt furnaces at work, lots of non conductive stuff in these parts...mostly custom nickle based superalloys similar to Rene alloys and whatnot.

All I know is we are fed from 2 sub stations and the wires on the telephone poles are probably 1.500 diameter for each phase lol seriously they look to be the same size as all 3 wires on the drop for my home service.

 

[Just a Sparky]

After doing some more research and crunching the numbers, it's probably going to be a far smarter use of my time and money to just take a stroll over to the foundry on the other side of town. Supposedly they do rapid one-offs for a reasonable fee when provided with a workable pattern.

 

[fciron]

Induction heating is based on heat generated by induced electrical currents (more like eddies and turbulence, since there’s usually not a complete circuit) and works on all metals, not only magnetic ones.

 

[DDoug]

induction melting of glass - Google Search

 

[Joe Henderson]

I attended a shop tour at Chaparral Steel plant in Midlothian Tx. once. It was fascinating. They use big carbon electrodes and very high voltage with oxygen fed into the furnace to superheat the metal. They use some mega voltage. They produce a lot of stuff. Rebar, angle and the 4130 and other tool steel that's sent to LaSalle not far away. They finish the steel and tube it for sale. 12L14 is brought in on reels ( to LaSalle) because they get it from overseas up to 1 1/4" I think and it is peened and drawn, then finished and tubed. The salesman told me I could get their drops from the scrapyard in Dallas that picks up their bins but the jackasses wouldn't sell it to me.

 

[72bwhite]

Yup it’s the mold that is the expensive part of the process.
you would have to do a huge quantity on castings to justify
the price of an induction setup

 

[tdmidget]

I attended a shop tour at Chaparral Steel plant in Midlothian Tx. once. It was fascinating. They use big carbon electrodes and very high voltage with oxygen fed into the furnace to superheat the metal. They use some mega voltage. They produce a lot of stuff. Rebar, angle and the 4130 and other tool steel that's sent to LaSalle not far away. They finish the steel and tube it for sale. 12L14 is brought in on reels ( to LaSalle) because they get it from overseas up to 1 1/4" I think and it is peened and drawn, then finished and tubed. The salesman told me I could get their drops from the scrapyard in Dallas that picks up their bins but the jackasses wouldn't sell it to me.

Think you have it backwards. I spent 25 years in the scrap business. The mill right down the road had a fire, operator went to sleep and let the electrodes descend into the molten metal. Transformer overheated and burst, conductors melted. I went to bid on the scrap and the maintenance guy showed me around. I asked what voltage it took to make the arc. He said "480". I asked how do you get an arc like that with 480 volts? He said " that's not the problem, with 72000 amps, how do you stop it?".

 

[Joe Henderson]

It's been a long time since the tour. I can't say that the electrodes were lowered into the metal. I'm not sure that Chaparral ever had an event like that. Could have I suppose. I do know they use oxygen to super heat it. Their transformers are huge. Can't quote the voltage but the amperage sounds pretty substantial. I am not sure but I thought Chaparral Steel had a pretty much automated operation. It's a heck of an operation. Air products has a plant directly above chaparral and they take elements out of the atmosphere. They furnish Oxygen to the plant and sell nitrogen, hydrogen, Argon and such. It's right above the chipper that shreds compacted autos. Ever once in a while they'd chew up a gas tank (supposed to have been removed) and there would be a big explosion. The shredder is surrounded by fencing for that reason. Hard to get any good scrap metal around here. hard to get any metal around here. Have to go to Tyler Steel to get it. Dallas for tool steel.

 

[boslab]

Types I know, induction, arc, reverbatory, induction, big coil, reverbatory bloody big burner
Arc, carbon rod ( or telephone pole, strike arc, maintain.
Blast furnaces of course but they operate more like a reactor, and oxygen steel making 12” water cooled Lance, 5 holes and 70,000 m3 a minute oxy flow, at around Mach 2 +
Final cupola, drop bottom is usual
Mostly iron melting
Though ferroalloys sometimes use it a bit

 

[Joe Gwinn]

Some people have the biggest toys.

Electric Arc Furnace:​

They don't seem to be worried that the gondola might spill some incandescent iron.

I think that the immense 3-phase transformer is current-limiting, so while the open-circuit voltage may be ~480 Vac, the arc voltage will be more like 80 Vac. But those carbon electrodes really are like big telephone poles.

Added: "A mid-sized modern steelmaking furnace would have a transformer rated about 60,000,000 volt-amperes (60 MVA), with a secondary voltage between 400 and 900 volts and a secondary current in excess of 44,000 amperes." This from:

https://en.wikipedia.org/wiki/Electric_arc_furnace

 

[dalmatiangirl61]

Lots of small foundry videos on YT, think most are running propane or waste oil, but not sure if you can do steel/iron with those. Do you have access to coal, I know that can do iron/steel.

Edit: Quick look on YT shows some people melting iron with propane. Windy Hill has some good vids and appears to be more knowledgeable than some of the vid posters, not sure what he uses. A small foundry is on my to-do list, I'm thinking waste oil is the way to go, as it can be had for free. Electric would be nice, but not really cheap on several fronts.