Experiment 32: The Arc Furnace!

For a while, I've had the idea of building an arc furnace.  When I saw The King of Random's video on building one using microwave parts, I knew it was time to act.  Together, a friend and I successfully built an electric arc furnace.

This project has been fairly difficult and expensive, to be honest.  At first, we got the wrong type of 8AWG wire (it was car audio wire instead of "normal" 8AWG stranded copper wire).  It had very thick insulation and so I couldn't get as many turns into the transformer as the TKOR used.  Thus, the furnace didn't really work.  After that, we got some of the right wire and wound the transformers.  This was an extremely difficult and unpleasant step.  We could only fit 15 turns (rather than 18), and even at that, it was an awful experience putting the coil into the transformer.  Fifteen turns seems to work fine, though.

After that was done, I had trouble getting lantern batteries for carbon electrodes.  Though I will refrain from using foul language, I can only say that the recycling center I tried to get old lantern batteries from was uncooperative.  My friend finally got some from a recycling center near him.  We found that when extracting carbon rods from batteries, it is much easier if they are new.  The manganese dioxide in old batteries becomes hard as a rock, making it difficult to get the rods out safely.

Another friend graciously gave me some alumina firebricks, which were easy to carve into the furnace.  Rather than cutting two furnaces out of the brick like TKOR did, We cut the brick in half and cut the 2" hole in the middle of one half, effectively making a furnace with thicker walls.  We used the other half as the lid.  The idea was that once one part wears out, the roles can be switched.  Another 2" hole can be cut in the lid to use as a furnace, and the bottom of the old furnace can be used as the new lid.

Having assembled all the arc furnace parts, we tested it on first zinc, then aluminum, then copper, and finally iron.  The zinc melted but it also burned.  This is typical of zinc.  The aluminum melted nicely... too nicely.  As I poured it into my aluminum muffin tin, it promptly melted right out onto the patio.  I suppose I should have used steel to contain the brightly glowing aluminum.

In the video below, I used the furnace to melt copper scrap.  This worked quite well.  I found that the time it takes to melt the metal is longer than what TKOR says in his video (this is probably because I used larger amounts).  When molten, the copper had an amazingly shiny glowing orange surface.  It looked absolutely terrific.  I used my foundry sand and a new, shorter casting flask to cast a neat little Cu tile for my element collection.  After some cleaning up, it turned out very well.

Regrettably, after the copper melt, the furnace broke in half!  There was only one crack, but it ran down the full furnace height, making it unsafe for use.  I quickly turned the lid into a furnace and then used the broken furnace as the new lid.  Once the swap was complete, I melted some iron/steel.  It took about six minutes, and I should have gone longer, but the vice grip electrode holders were becoming too hot to hold, even with fireproof gloves.  I tried to pour the molten iron into my Fe tile mold, but as I picked up the furnace, the radiant heat promptly burned me through the fireproof leather gloves!  I only managed to get a tiny bit of iron into the mold, but I undoubtedly cast iron!  For me, it was quite an achievement, given that I have only cast aluminum and copper until now.  The rest of the iron froze in the furnace, so I will have to remelt it to get it out.

I am quite pleased with the results (Cu tile, achievement of casting iron), except for the broken furnace and the failed iron pour.  I learned a few good lessons from the experience:
  • Cast in they daylight - the extreme light difference between the glowing iron and the evening darkness made it hard to see what I was doing when casting the iron.
  • Friends are always helpful in building complicated projects
  • Make some sort of handle for the electrode holders and the furnace - the heat that these parts radiate when casting iron is too much to safely handle, even with gloves
  • Don't try to scrape leftover metal out of the furnace.  This could have been the reason the furnace broke (or it could have been thermal shock).
Though it was difficult at times, I have enjoyed this project immensely.  There are few things as satisfying as casting glowing orange streams of molten iron.  :)