First let me say it's great that we now have a forum for smelters! This is something I always wanted to try but never got it going, so here is my chance to get educated in this and maybe gather what I need to give it a try.

Well, it all started with the quest for the perfect temper line, or hamon if you will. I made one or two tantos from 1095, W1 and 5160 and though 1095 gave the best looks it's pretty far from what the japanese smiths get from tamahagane.

Then once I went to Rodrigo Sfreddo's shop and we tryed to make some steel from iron wire. We used his old coal forge (or is it charcoal? I am always confused - I mean the burned wood stuff) with small coal (charcoal) and once it was really hot we started to pour iron wire cut in 1cm pieces.

We got a pretty decent piece of metal with lots of slag and lots of voids. The spark test showed it was pretty high on carbon but a few days latter when he started forging, folding and welding it (in order to bring it down to a proper carbon content) and acctualy forging it into a knife, it presented some boubles on the welds - something that would happen with regular factory steels.

He did forge one knife from it (even though there were serious weld problems) just to see how it would behave with clay during HT and the result was a nice edge and a VERY WILD hamon, much easier to control and design and with lots of activity.

So in order to make this more efficient and acctualy set up a consistent production I cam up with a furnace plan I would ask you guys to take a look at:

http://img279.imageshack.us/img279/2513/smeltingxe4.jpg

Please excuse the poor MS Paint skills.

What I think that might help is the bowl feature on the bottom that might help keeping the metal all together (a problem we found was that the metal tends to accumulate on the blower pipe if the bottom of the furnace is even with the pipe) and the extra temperature provided by the propane that we didn't use on our previous attempts.

Also, I plan to add some glass and sand to help.

Questions:

1) do you have any thoughts on the furnace design?
2) do you recomend any other things I should put in there with the coal (charcoal?) and the iron?
3) what's the best way to prevent voids?

Thank you very much!

Based on the many other designs I've looked over, you may want to put a slight downward slope of 10 to 15 degrees on the air pipes into the chamber. You may also want to put their entry point a bit higher off the bottom to give the iron a bit more room to form together below them. This is based on smelting designs I've seen, while it sounds like what you're doing is more of a remelting, sometimes called by the French term "grappage". You can preheat the chamber with a propane burner before adding charcoal, then switch over to air once the charcoal is in and burning well. The charcoal lumps should be of a consistent size. The air source should have at least some pressure behind it, which usually seems to mean a centrifugal or 'squirrel cage' blower rather than a fan-type blower. The height of the stack influences how much carbon the iron will take up, higher stacks allow more time at temperature for carbon to come in.

Anyway, that's what I've learned (or think I've learned) from several years of reading about this and three attempts at smelting (one partially successful). I look forward to any advice the more experienced may have to offer.

Michael

Thanks a lot Michael, you have valuable knowledge, very much apreciated.

Your tips brought more questions though...

The air source should have at least some pressure behind it, which usually seems to mean a centrifugal or 'squirrel cage' blower rather than a fan-type blower.

What's a 'squirrel cage' blower and how does it look like?

The height of the stack influences how much carbon the iron will take up, higher stacks allow more time at temperature for carbon to come in.


Then I figure I have to calculate, somehow, the inner chamber volume and height in order to try to predict how much carbon I want to add to the iron. Is there a way to calculate that? Even an estimation?

Here's a 400cfm forge blower that would be great for a smelting setup:

blower (http://www.blacksmithsdepot.com/Templates/cart_templates/cart-detail.php?theLocation=/Resources/Products/Forges_and_Parts/blowers/400_CFM_Blower)

This is about the size of one I have seen used to run a medium-sized kodai furnace by Mike Blue and Randal Graham. You really need the pressure behind the air to keep the tuyeres from clogging.

I don't have a clue about the height/volume equation.:( Generally speaking I suspect a one-man operation uses about a 10"-12" (25-30cm) bore. The furnace I saw earlier had a four-foot (130cm) tall stack atop the firebox and yielded a bloom with about .9% carbon.

That was starting with iron ore, though, I do not know what would happen if you used scrap steel it the grappage method. Wood charcoal is always the fuel of choice.:flame:

Thank you Alan, now I understand the "squirel cage" setup... it would sound like a "hamster wheel" setup for us in Brazil :D

Anyway... I beed to find a good blower, that's gonna put me on hold for a while on this project but I will eventualy find something. Now that you mentioned preventing clogging, I see that was one of the problems we had in our first experience. We had to stick a thik steel wire every once in a while to open that thing.

Now if we get .9% carbon (aprox.) from 130cm tall furnace I might be looking into something between that and 150cm. Sounds reasonable to me. Let's see if any of the gous have any more info on carbon content X furnace size for us to improve our guestimantions :D

Thanks a lot Alan!

The following link is to a short video of a smelt by Mr. Graham and Dr. Blue as mentioned above. I was not at this event, but it's similar to the two I have attended. Pay attention to the size of the furnace and especially the color and amount of flame at the top of the stack.

http://home.mchsi.com/~feralchild1/TunnelMillMovie.wmv

While it would appear this furnace is about 190cm tall, the base is on a steel platform that raises the floor of the hearth about 35cm off the ground. The tuyeres come in about 15cm above the floor of the furnace, angled downward. They are tapered from 2.5cm to about 1.5cm at the mouth.


There is another forum where folks talk about this stuff, at risk of offending Brent: :yield:

http://forums.dfoggknives.com/index.php?showforum=25

I'm not promoting anyone, just sharing information.:smokin

Cool.. that gives me some more ideas... maybe I can build a smaller setup but proportional and give it a try. I still need more blower power though.

My plan is to make a narrower tube, but tall enough to make the iron travel a good deal through the charcoal. I am also looking for a furnace I can use over and over again, so I think I might use a two section tube plus lid and bottom that can be detached, so I can take verything apart and out back together.

By the way, how tall is Mr. Graham? If the furnace is 190cm tall he might be over 210cm tall!!!

Randal is about 190cm himself, but he was standing on a platform beside the furnace. ;)

Don't go too tall or too narrow, or you'll get cast iron instead of steel. :eek: There's not a lot of difference between a blast furnace and a cupola furnace except bore, height, and raw material. The idea with a tatara/bloomery furnace is to keep iron ore in contact with Carbon monoxide at elevated temperatures, thus reducing the iron oxides to pure iron with some carbon. A blast furnace does this faster and at higher heat, adding more carbon and producing cast iron direct from ore. A cupola does this with bits of cast iron in the charge and is even faster and hotter. Solid cast iron and charcoal/coke goes in the top, molten cast iron comes out the bottom.

What you are talking about doing is sort of a cross between these things; putting solid steel bits and charcoal in the top and getting a mass of steel bloom from the bottom. You will have to watch time and temperature more closely, as you don't want the steel to take up too much carbon or become fully liquid. All I can say is experiment and tell us what happens! :101