Mini Arc Furnace Melts Its Way Into Our Hearts

[Grant Thompson], aka “The King of Random,” threw caution to the wind when it came to his latest awesome project – a mini electric arc furnace (EAF) (YouTube link). [Grant] uses a refractory brick as a furnace and crucible for the molten metal.  He wears eye protection and a respiratory mask as he cuts up the brick – a good idea, since you don’t want to inhale any of that dust. The electrode grips are made with things you can find at a hardware store, including copper wire and coupling, and 2 pairs of vice-grip style pliers. The copper wire is stripped and attached to the metal handle of the pliers using hose clamps. The pliers are now functional electrode grips- just put a carbon rod in each grip and hold them close to each other…but not without protection! [Grant] harvested the carbon rods  from the cells of 6V lantern batteries – dead batteries work just as well for this. It’s also a better bet to do this outdoors with decent ventilation and away from anything flammable. [Grant] realized that the rods from the batteries have a wax-like coating on them that takes about 30 seconds to burn off in spectacular flames the first time they make electrical contact. However, you can purchase carbon rods by themselves if you want to avoid ripping open batteries and possibly setting yourself on fire. The mini EAF runs on a welding power supply [Grant] made from microwave oven transformers  (YouTube link).

When it’s time to melt some metal, the scrap metal is placed into a bowl drilled into the brick. Using the electrode grips, the carbon rods are placed into the brick’s pre-drilled holes. It only takes ten seconds to melt pure zinc – do NOT do this with galvanized steel or brass castings, as zinc oxide is very hazardous to your health.

In the videos featured below, [Grant] shows a variety of metals are no match for his mini EAF. He even manages to melt rocks from his backyard! It goes without saying that an EAF (video link) can be very dangerous. When you’re dealing with high voltage, plasma, white-hot molten metal, and toxic fumes, you better know what you’re doing (or have a great life insurance policy). [Grant] has a penchant for showcasing projects that can make an OSHA inspector cringe,  but you have to admire his gumption!

42 thoughts on “Mini Arc Furnace Melts Its Way Into Our Hearts

          1. Some time ago (perhaps 20yrs) I saw such a construction as the start up for a carousel at some entertainment park. A plastic vat (cut open 20-30l canister) filled with water, a movable steel frame with 3 steel blades (probably isolated) with cables connected to it and a wooden handle. To give power to the motor the operator pushed the handle down and sunk the blades into the water. This contraption was probably connected to the starpoint of the induction motor and allowed a slow start.

  1. While I’ve understood the principals for a long time, to see someone actually make a damn arc furnace I could use in my kitchen (if I’m crazy enough) and make it work, mind fucking blown. This, scaled up, with large carbon electrodes from msc- just made my scrap reclamation pile for home machining WAAAY more fun :) This is the kind of thing I love Hackaday for!

    1. Looks much funnier than the household equipment… You work on a foundry? What do you guys smelt?
      I remember seeing some stuff on these industrial arc furnaces during some inorganic processing classes…. can`t remember exactly but I think it was a class on galvanoplasty or something.

        1. There are multiple configurations for EAFs, this one uses 3 18in diameter carbon electrodes with 3-phase being pumped through each one at around 40kA. That will change depending on the a number of factors such as power quality, material, material layout, etc.

    2. Having had the chance to visit Accelor Mittal in Luxemburg EAFs will always have a deep respect from me. Seeing it in video is one thing. Standing dozens of yards from one of these in real life, in an environment that looks completely out of this world due to all the brown dust covering EVERYTHING, and then feeling the meters thick concrete floor shaking and rocking as tons of steel are getting melted with massive bangs and zaps is an unforgettable experience.
      The sheer violence involved is just unimaginable.

    3. I love my arc furnace. 150T supplied with a 34.5KV/1200v (depending on the tap) 88MVA arc transformer. That translates to a maximum of 55,000 amps. The wet charge explosions are spectacular!

    1. Pretty much any place that supplies construction material…. and around here they go for like 2-3$ each….
      Also, if you drop by an apartment block construction site they probably can supply you with a couple broken bricks for free as they frequently break during transport and almost all multi-store building use these bricks as a way to keep flames from spreading between the apartmens

    2. Nope, not construction supply. All they usually sell is hard fireplace brick. Not sure the firewall bricks are the same. Ask for their rated temperature.
      I’d suggest going to a Ceramic/pottery supply store. Maybe some art supply stores if they sell kilns. But $6 bricks are pretty cheap. Expect to pay more.

      1. While small construction supply stores seem to only sell these hard fireplace bricks (which way too good heat conductors if you`re operating at the temps of this arc furnace), most big-ish stores around here sell low density blocks for these anti-flame walls, and they`re alumino-silicate bricks rated for some damn high temperatures…. Maybe it`s because there are a few companies producing these bricks around, but I expected things to be the same everywhere.

  2. I made an arc furnace after school one day when I was 14, at our apartment. The plans were in a book I checked out from our school library.

    I cut the carbon electrodes from standard (non alkaline) D-cell batteries. An electrode from a welding shop would be much easier (who has carbon D cell batteries?). The wires were crimped to the electrodes using old curtain rod or battery casing. A hose clamp would work well. Power was 110v a/c from an extension cord. Current was moderated using a glass bowl of salt water. A lead sinker held each wire end submerged in the water (hmm, I guess I did get that bowl from the kitchen. Is lead toxic?). The water will be heated to the boiling point during furnace operation. Holes were drilled in a small flower pot for the electrodes.

    To operate furnace, strike an arc. Do not look at blinding light. Do not touch bare metal or both sides of circuit. Avoid contact with boiling salt water O’death while system is energized. Have a good excuse ready for when parents inquire about flickering house lights.

    I was also able to weld with this setup, replacing one electrode with a ground clip (ok, it was a paperclip).

    I built the arc furnace a few times. I guess I had to keep going back. It was one of the coolest, most dangerous DIY projects I ever built. I was very much in awe of it. That it was so incredibly hot, so dangerous and so easy to build. I was only shocked once, while welding (from hand to hand, and I lived). A later version filled the flower pot with plaster to create a more concentrated and compact chamber.

    Surprisingly, I never demonstrated it for my friends. I remember thinking that it was too dangerous and I would get blamed for any accident.

    1. I just got that book out of the library a couple of days ago. It’s called “Build-It-Yourself Science Laboratory.” It’s been reissued by Make. I was reading it going, “yeah, I’ve got carbon rods … I can do that!” The salt-water rheostat instructions gave me full-on chills. Awesome. Idiot/Savant-class brainwave.

      1. It probably goes without saying I was home alone when I first built this.
        The salt water is a great hack if you ever need improvised current limiting. My play time was always limited by the boiling water. I always wanted to build a larger reservoir, but again, there was an element of fear. The heat from the arc just grows, the water boils, the extension cord leads get hot and the insulation starts to get soft.. and it seems like something has to give.
        If the vessel holding the salt water ever broke then the electrocution risk could be (even more) substantial.
        At one point I bought a lamp dimmer thinking I could use it in place of the salt water. It fried the first time I tried to strike an arc.
        I’d love to build this with some kids and demonstrate it, but I pale at the thought of them trying to reproduce it alone.

        1. Ah, I was actually wondering about a lamp dimmer. Makes sense that it wouldn’t be able to handle that kind of current. The MOT route is starting to look positively sane. Which is probably a bad thing…

  3. I’ll second the warning about the hazards of zinc oxide fumes. Got a wicked case of zinc shakes while melting down two kilos of brass casings in crucible with a coal fired forge. Thought the updraft from the fire would carry the fumes into the pull-down hood. I was wrong.

      1. There is a very bad typing error in the write up. It should be edited to prevent unnessesary misunderstandings.

        The video mentions the melting STEEL not zinc. Zinc oxide fume (smoke) is indeed something to avoid breating. Zinc oxide in vaseline (petroleum jelly) is waterproof sunscreen and pretty inert.

        They are not inherently more so, the zinc in the alloy can be easily volatilised at the arc furnace temperatures. Any zinc electroplate or hot dip galvanised coating will also evaporate at the melting temperature of the base metal. Zinc and its alloys are safe-ish to melt with controlled temperature and/or atmosphere furnaces, galvanised steel melting will always result in zinc oxide fume if there is oxygen or air available.

      2. It is not! When you melt zinc you get zinc oxide dust/fumes. You need good protection.
        But I just think about the reason for this danger. Zinc is an essential element for humans. And zinc oxide is an ingredient to several medical and cosmetic preparations (sun screen, wound cream,…). Is it a specific problem with inhalation, a toxicity to the lungs, or is it a systemic overdose of zinc?

  4. Making really cool stuff out of metal, to me, always meant casting. I could cast parts I could never machine
    with my small equipment, but I thought, it would cost a fortune to have even one thing cast.

    This furnace proves it’s possible. I know raw graphite isn’t crazy expensive in blocks, and it’s easy as hell to
    machine. I could finally make that iridium watch case now, machine a rough graphite mold quick for a shaped
    crucible, throw it into one of these bricks, and melt just enough iridium I can afford to a ring with lugs- that I can
    machine away with minimal effort.

    Iridium and exotic element casting should now be possible for me thanks to this project- this thing makes things
    that were before, quite frankly near impossible now very possible! Can’t wait to make one and melt iridium…

    Anyone know if you could melt alumina and chromium into a sapphire boule with this setup? I need a crystal
    furnace too but don’t have 100k or something like that laying around..

    1. I`m pretty sure alumina and chromium = ruby…. ain`t sapphires alumina and titanium or something?
      Either way, I think you`d have problems with contamination as Jehu said…. maybe it`d be worth trying a Mo or tungsten electrode, though tungsten family metals also oxidizes so maybe you`d need to do it in an argon atmosphere…. aaand things just got a bit to fancy again lol

    2. Arc furnaces aren’t generally used for casting in the applications that you’re referring to. Those are usually reverberatory furnaces or the like. The carbon from the elctrodes would contaminate the melt

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