Saturday, April 21, 2018

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.

Aristotle furnace

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.



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…..

Friday, April 20, 2018

Oroshigane......making steel (1)

The weather gods have shown pity on us and granted a brief window of dry weather, just enough time for me to gutter the new roof…..and explore a new rabbit hole. With the drainage under  control, it's time for me to shift gears a bit and take on something that I've been wanting to try for years; making steel.

Why would anyone want to make their own steel when so many excellent carbon steel alloys are widely available? Is homemade steel better in some way then what is already out there? In a word….


So then, why put time and effort into  working with such a ridiculously crude and outdated a material? After all, this is essentially a backdoor production method that hasn't seen the light of day in nearly 300 years. I could go on about the mystical alchemy inherent in the transformation of iron to steel, the connection to ironworkers ages past etc, and while that is certainly true, the short answer is that it's just plain cool. Come on now….who wouldn't want to make their own steel?

In the Japanese swordsmithing tradition, the blacksmith can select a variety of different steels and re-melt them into a more easily worked form. This blacksmith made steel is called Oroshigane, and while I am not especially interested in making swords, I AM interested in their steel. Broken blades that shatter during the quench, old cast iron teapots, even the steely crumbles that accumulate in the bottom of the forge, all of this can be combined and blended to create a steel with the specific qualities desired. Call it extreme up-cycling.

It's all about the carbon

Steel, at its heart, is a simple compound of elemental iron and carbon. The amount of carbon added to the iron is very small, but it's impact can be huge. Take iron and add only 0.2-0.3% of carbon and the result is mild steel, the most common structural steel in use. Kitchen appliances, “wrought iron” furniture, the list goes on and on, but most of what we see on a daily basis is made of iron that has been made tougher by a miniscule addition of carbon. Add 0.4-0.6% carbon and you start getting a steel that can be made harder and therefore suitable for more extreme duties. Car axles and shafts, hammer heads, nails, lawnmower blades, wrenches….generally medium carbon steel.

The sweet spot for carbon steel, at least for cutting edges, is around 0.8-1% carbon. Knife steel, Western woodworking plane blades and chisels, old car springs and such fall into this group. Steel with more than 1% is more of a rare animal, but Japanese woodworking tools (planes and chisels) generally use this very high carbon steel, likewise taps and dies, and some metal working files.

At the higher end of the carbon steel spectrum, steel with carbon in excess of 0.8% makes the material more difficult to work. Forging is physically harder as the material just doesn't like to move, even at a high forging temperature. Forge welding becomes more difficult too, particularly when joining wrought iron to steel as my favorite tools do. Without delving into the metallurgy, any carbon in excess of 0.8% has the potential to cause trouble, unless the smith really knows what they are doing.

Add 1.2%-2%% carbon and steel turns into a tricksy thing, and can exhibit a range of traits not normally associated with traditional carbon steel; superplasticity, extreme toughness, impact resistance and high elasticity…...all the while maintaining a very high degree of hardness. Again, this assumes that the blacksmith is highly skilled. Some of the tool steels used in laminated kanna blades use this UHCS (Ultra high carbon steel is the term) for the cutting edge, laminated to antique wrought iron.

A carbon content upwards of 2% is termed cast iron, and while cast iron is a wonderful thing for pots and pans or engine parts, it's of no direct use in hand forging. As the carbon content of iron rises, the melting temperature falls (a trait that will come into play shortly), so having a very high carbon content allows iron to more easily become fully molten, then be poured into a mold….cast into a usefully shaped component.

So, why all all of this blather about carbon content? At, or near melting temperature, iron is able to either take on (or lose) carbon, and that's what the oroshigane melting furnace is for.

This small shaft furnace heats the iron to a partially molten state as it descends towards the bottom of the column. Wood charcoal acts as both the fuel source and adds the carbon component, all brought to a furious heat by an air source that increases the rate of combustion. The concept is a simple one but, as they say, God is in the details. Shaft volume, air volume and pressure, carbon content of the starting materials, even the size and type of charcoal is important.

Of most importance perhaps, is the height above the floor where the air blast enters the column. The temperature of the furnace is highest proximal to the air inlet, so if your furnace floor is at a level with the air inlet (Tuyere is the term), the molten metal will be getting the full force of the air blast. This will actually burn out carbon, so if you are trying to lower the carbon content of cast iron to a more forgeable level, that's where you want to be. If your aim is to raise the carbon content to make some cutlery steel, you want the iron to be able to fall through the heat zone and collect underneath the air inlet, where it sits and absorbs more carbon, eventually resulting in...cast iron.

I'm just getting going with this, both the steel making and the long winded particulars. If you are truly interested in this field of inquiry, there are a few places to go, materials to read. Here's the shortlist …...

Jesus Hernandez wrote up his experiences forging a blade out of steel made in a so-called “Aristotle” furnace. The swordsmith’s oroshigane furnace I made is nearly identical to this, and it was in reading this forum thread that I first became really interested in making my own steel.

This thread is a perfect example of how information is disappearing daily from the web. If you find something of interest, document it well, because the original information might be gone before you know it. To view this post in its entirety with all of the important images, you need to go Wayback……the Wayback machine will take you there. Donate if you can.

A new way to make steel

Bladesmiths forum is one of my favorite resources for edgy inspiration. They have a whole topic section devoted to smelting ore and making steel, tons of information here….

Daniel Cauble has had some laudable success in making his own oroshigane, really inspiring work, beautiful steel.

But my main source? The Japanese swordsmith Sumihira gifted us with actual particulars and details of how he raises and lowers carbon content in his work. It is from his writings that I got the measurements for my little furnace. Gold!

The forging process, beginning with making the oroshigane (Google translates oroshigane as “wholesaling”, but you can figure it out….mostly).

Lowering the carbon content of cast iron = sageba = ”lowering place”

It's a start. More to come….

Wednesday, April 4, 2018

Sucker Hole or not......get the roof up quick!

Finding good, used building supplies here on the Big Island is a real trick. Yes, there is a Craigslist here, but after repeatedly seeing ads offering water soaked offcuts and the type of items that you'd normally be pulling out of the dumpster, all at next-to-new prices….you get burned out after a while. I guess it's a natural result of needing to have everylastthing shipped in at great expense that makes people think that this stuff is made out of gold, but every now and then you find some deals.

One of the metal roofing companies not far down the road has occasional scratch and dent items, and if your stars are all in alignment, they might actually have something at the exact time you have need. Don't count on it. Steel roof at $2/linear foot doesn't last long, so when you see it, grab it. All of it. I did, about six months back, in anticipation of getting a real roof over our heads, and that time is now. One slight problem; the rain just won't give me a break.

A Sucker Hole, for those of you who aren't familiar with the term, is a break in the cloud cover that makes you think that it could turn into a decent day…...then as soon as you get started on something good, the clouds return, usually with a vengeance. Hahahahahaha…..SUCKER!

The Ace Hardware store here sells two different colors of large tarp; grey/brown and white. Both tarps are made by the same company, but the white tarps have proven VASTLY superior in both finish and durability. Despite the grey/brown tarp having a moderately reflective grey surface to minimize heat gain, the white colored tarps stay markedly cooler, like 30% cooler, so says my IR temperature gun. Go figure….in any event, relying on ANY tarp to keep you and yours dry is something all done on faith. We've been lucky, to say the least, but crossing your fingers for over a year in a climate as rainy as this one will test anyone's faith.

Now if only it would stay sunny for a few days…..

An actual bedroom, lucky kid.

I've been sitting on that decent sized pile of metal roof for months, and now that I've finally framed in Ellie's new addition, it's time to put it to use. The rain stopped, it's time to go for it!

And, the gods being fickle (at best!).....the clouds came back. In force.

Ahhhhh Hubris, you've gotten me again.

Actually, I got everything buttoned up, just in the nick of time, but only minutes away from a serious deluge. And only a couple of leaks, haha. It beats the tarp though. Next thing to do is gutters. At least now that it's raining again, I can get back to work on my fuigo.

It never ends, this building stuff.