Making steel (2)....the "Aristotle" furnace

I want to try making my own steel so, based on the specifications given by the Japanese swordsmith Sumihira, I built this oroshigane melting hearth furnace.

This simple vertical shaft furnace is used to melt scrap iron and steel, and in doing so, raise (or lower) the carbon content, hopefully to around 1.5% in my case. Make note that this furnace is for remelting scrap, NOT smelting iron from ore (maybe someday I'll give that a try too, but for now…). I'll give the particulars of this build in another post, mistakes and all, so those of you who want to give this a shot have something to go on. Everything I learn was originally shared on the net by someone else, so it's only fitting that I do the same. Successes and failures both.

For starters though……

After building my oroshigane furnace, I had some materials left over, so I quickly put together a smaller version, based on writings by Lee Sauder. A PDF of his original paper can be found on his website, along with some of his other writings. All are worth reading and it's thanks to his work that so many others are trying these archaic methods of steel production. He's the pro.

Lee Sauder smelting research

Aristotle furnace

Aristotle's steel

This “ Aristotle” remelting furnace is intended to be a quick and economical way to try making some steel and should be considered disposable. You might get 3-4 uses if you are careful but to try making it more robust rather defeats the purpose. You can slap one of these together and have it drying within an hour, a great afternoon project, for sure. Uses VERY little charcoal, one bag will last for multiple burns. If you've got clay in your yard, it'll cost nothing to make and it's super fun!

I've made three for these things now, but my success has been, ummm….not so good. Two aspects are important for this design to work. Clay and air. Last year, my friend Jeff and I tried building one of these but, living in Hawaii, we have no native clay here. What I did have was the clumping type of cat litter.

Clay

CAT LITTER WILL NOT WORK WELL AS A HIGH TEMPERATURE REFRACTORY!

Unscented clumping cat litter will reconstitute into a workable clay and is handy for lots of things, just not the extreme temperatures required to melt iron. At high heat, the clay starts to degenerate into a sandy powder. It shrinks a lot too, not what you want. If you have clay where you live, try that first ( it will likely work) but if you need to buy it, look for something with a high firing temperature, as close to a cone 10 as you can get. Lots of stuff will work though…..Just not cat litter, haha.

Air supply

Last year I used an old 12 volt air mattress inflator and it was fine. A hair dryer should be perfect for one of these small shaft furnaces and they are cheap and easy to find (if you can't borrow one ;-). A shop vac, set to blow, will be WAY too strong, but OK if you can throttle it down some.

Once your furnace is dry and up to temp, the steel making process only takes about 20 minutes. In my case, we were listening to the shriek of that inflator for 2 hours….WAY too long! We were melting down some ¼” rebar bundle wrap wire, no problem for this design, but something wasn't right. The iron bloom that formed in the furnace was stuck fast, so after smashing the stack to get the metal out, you could see that the area of the tuyere (air inlet) had slumped, greatly restricting the airflow. We did make a blob of low carbon iron, though not what I was shooting for. No pics, my bad.

This time, still traumatized from last years howling mattress inflator, I grabbed a small 50 cfm bathroom ventilator fan and gave that a shot. I mounted it in a very sophisticated, waterproof and mobile containment (ie: Walmart bucket w/lid).

I added a ball valve to the 2” pvc tubing so that I can adjust the airflow down, handy for slow preheats or for using in the real forge.

50 cfm works for a small charcoal forge, but a 100 cfm fan might be a better choice if you are buying something new. They aren't the perfect choice for a charcoal forge in general, but they work and are very quiet. If you are forging with mineral coal, don't waste your time with these, get a real blower.

For this “Aristotle” furnace, I used a mix of Home Depot fireclay, perlite (for insulation), shredded bark (for strength), and mortar mix to help things set up more quickly.

Despite what you might find on the internet, mortar/cement is a POOR choice for high temperature refractory. It's just not durable and when those hydrogen bonds reverse at high heat, it changes back into powder. It will work, somewhat, but there are better choices. Simple sand and fireclay seems to work better….20/20 hindsight.

I dry and preheat the still wet clay by burning some scrap wood, then start adding the guava charcoal that I made a couple of years back. You might remember my charcoal making ventures from before, and I'm finally getting a chance to use some of it. I really need to start making pine charcoal again, as this Guava burns slow. I'd prefer to have both on hand in the future.

At the center of the stack, you can see some of the ¼” mild steel stock that I am melting down.

Trying to melt down, that is.

Ellie melts down some old copper pennies and pokes the steel into the hot zone…..

….while Renee snuggles Nago the pig.

And in the ancient tradition of iron workers everywhere, I give offerings of ale and try to melt some bottlecaps. The stick of wire just sat there, laughing.

No love…..needs more air.

More in a bit…..