Jump to content

Recommended Posts

Well, I tried my first bloomery run but got no iron for my troubles. I'm pretty sure I used too little charcoal, and I know the tuyere got partly plugged with slag at some point. What I did get was many pounds of some really dense material that I think is slag saturated with dissolved iron. It's dark greenish black and heavy like iron but grinds to a slightly shiny black surface, no silvery iron shininess in it at all. Other parts of the stuff look a lot like a bloom but aren't. Each part just shatters under the hammer no matter how hot I get it. It is somewhat magnetic so that must be where all the ore went.

 

I'm guessing I should use this in place of flux when I get the bloomery rebuilt and try another run. The stuff I produced stuck to the inside wall pretty well on the side above the air supply. I had to knock over the stack and bust out the bottom, hitting the stuff with a big iron bar from both ends to break it off where it stuck to the inside lining. Any tips or helpful feedback appreciated.

 

Here's more specifics. Materials were about 40 lbs of mill scale (thanks Wayne!), about 50 lbs charcoal. I started the heat with a blown wood fire inside, and when this burned down I filled up the rest of the way with charcoal.

 

The stack was cylindrical, about 14 inches ID and about 30 inches tall. It insulated well and didn't break down much with the heat although a couple fissures vented smoke by the end. I patched these with mud which fired to a nice brick red color. The air was supplied by a blower reducing into a 1 inch diameter hole about 7 inches above the bottom. It took about an hour to preheat, then about 6 hours more to run.

 

At the end of the run, I found the bottom inside (below the air inlet) was nearly empty, with a big shelf of the black stuff glowing bright orange, attached to the wall above the air inlet and extending more than half the diameter of the stack. No sign of the mill scale, which is why I'm thinking it must have dissolved into the slag. Not much charcoal left either by the time the last 6-8 inches of it burned down inside.

 

Backing up to the beginning, as the charcoal charge burned down, I started alternating charcoal/scale/flux charges, poking into the top foot or so with a pointy bar as needed so it would pack down. Each charge was about 3 lbs charcoal but I think I overshot and added more like close to twice that much scale, plus a small handful each of limestone powder and sandbox sand. Next run I'll go back to 1:1 charcoal/ore and will get a scale to weigh it.

 

Some of my charcoal was hardwood (oak/hickory) in big pieces, while about half was much smaller and mostly sweetgum. The smaller stuff was too small, and the air didn't get through it like I think it should have. The other stuff was too big. By the time it finally occurred to me to mix the two, I was 2/3 done.

 

I've got lots of ideas how to make the next run better, and with any luck even to produce some iron. But still, as a day playing with intense fire it was great fun. I've got the missing arm hair to prove it. :D

 

Michael Matthews

Link to post
Share on other sites

Just going off your verbal descriptions:

 

I'd encourage and reinforce the way that you're thinking about what happened. It doesn't matter what did happen, you're thinking about it and watching what's going on. Keen observation is the key.

 

The description of the slag is likely correct (magnetic, color, grinding, hammering on it, sticking to the side walls). So that means you got hot enough to melt the iron but not hot enough to keep the slag liquid. If the bloom is mostly slag, you might be adding too much sand/limestone. Mill scale should be mostly pure iron plus whatever alloy contaminants come from the original material. By all means recycle it. That's a great idea.

 

Too little charcoal. Your ratio is off. It should be more on the 1:5 proportion. There's no problem with mill scale. Lay in one pound of ore to at least five pounds of charcoal.

 

Stack height and diameter are fine. Patching air leaks is very much necessary to control the atmosphere. If you're venting it out somewhere, it's not heating on the inside.

 

The first couple times John and I did our smelts we didn't get what we hoped for, but learned a great deal anyway. Resist temptation to try to change all the variables at once. Be disciplined and only change one or two for each burn, otherwise you risk having a great bloom but not knowing what you did to get it, or vice versa.

 

Go for it.

Link to post
Share on other sites

Welcome to the wonderfull world of smelting :( Is'nt the learning curve wonderfull?

 

It gets like that. Sounds like you may have had too much sand, that or the ratio was off and/or the temps too high. The fuel/ore ratio is really important. You're right, use what you have for flux on the next run.

 

I've done a lot of runs experimenting with local ores and have had the same thing happen time and time again. Glad you tried your hand at it! It's hard at first, but when you look at a blade you've made from ore, it makes it all worth it.

Link to post
Share on other sites

MSTU,

 

Cool pics B)

 

It looks like one of the problems is that your tuyer is too big. Step the pipe down to 3/4", that will give your air flow more pressure, which means you will get better penetration into the furnace bore. You will always have a cool spot near the opposite edge, but it won't be as pronounced. I usually put the bulk of my ore where the cool spot is, as the hot area burns down, the ore gets a better chance to mix in and ends up staying longer in the furnace before it gets to the tuyer area.

 

Mike is right, change only one or two things at a time..

 

Not to detract from what he said, but there are guys that use the 1:1 fuel ratio charge for producing iron in a furnace like this. Use the 5:1 ratio for producing a high carbon bloom. I personally would shy away from that with the first attemps 'cause it is really easy to produce cast iron if you're not careful, but it's different strokes for different folks :)

 

I'm havng fun :D

 

Edit: for spelling :blink:

Edited by Jesse Frank
Link to post
Share on other sites

Jesse, Mike et al, here's some more thoughts...

 

With mstu's short stack, he should have no problem keeping things in the smelted iron to low carbon steel range. Time at temperature is the rule. His fire needs to be hot enough to melt the iron so it flows downward to collect in a bloom, not enough to keep the slag in liquid form and have a short enough drop to the bloom that the amount of time to collect carbon is low. If bloom accretion is sufficient, even if there is free carbon in the portion of the fire below the tuyere, it'll be too big to penetrate well. Then you could potentially run the fire long enough to get a heaping bloom (or at least until iron choked off the tuyere, not slag). The other tweak would be to point the tuyere downward to flow over the bloom and keep plenty of oxygen in the near-bloom vicinity to burn off any excess carbon and keep the slag liquid and flowing away from the tuyere.

Link to post
Share on other sites

Hey Mike,

 

The only reason I am still leery of cast iron is that I have accidentally made it in a furnace much smaller, with a shorter run time than MSTUs. You're right, time and/at temp is definitely key, which means that when I got the furnace too hot, it melted the iron, which means that it accumulated more than I wanted. Temp definitely has an effect, I don't have any charts off hand, but I know for example, that in a closed environment, to get a 1mm depth of approxamately 1% C, it will take about 4 hrs @ 1450f and 45 min at 1950f, which means that if you have a small bloom stuck just under the tuyer, where it might be 2400 or 2500 easily, carbon absorption can potentialy run rampant if there isn't something there to protect it. That could theoretically be an even bigger problem with a smaller furnace, since there will be less material at the hot spot to absorb carbon.

 

Maybe the dynamics of the larger furnaces you've been using are different, I dont know... That's just been my experience :unsure:

Link to post
Share on other sites

Thanks guys. Jesse, the tuyere is actually a 2 inch pipe to fit the blower, but what's not visible in the pictures is that it steps down to 1 inch or slightly smaller where it enters the wall. Probably I need some more mud, or duct tape, to get a better seal on the end where the blower connects to the pipe. This time I just set it next to it, and some air leaked out even though a lot went in. Also, I had the air intake on the blower choked down about halfway. Should I worry about too much air going in, or open it up more (presumably giving a higher temp inside)?

 

Here's another pic, sorry it's so tiny, I'm running out of attachment space:

P4030123.jpg

Edited by mstu
Link to post
Share on other sites

D'oh! :(

 

I'm sorry MSTU, when I mentioned the 15 degree angle, I forgot to mention that it is a downward angle <_<

 

What I would do is keep the setup you have, and on the 1" pipe, cover it with solid refractory, and taper the clay down to 3/4" and make sure it extends into the furnace for 2" or so. If you were able to save the furnace, add onto the top for another 10 to 12" or so and taper the bore to 12". It'll keep the furnace gasses in better, and help the ore mix in, too.

 

Adjust the air flow to what you need.. Ive been running over 2500f at the tuyer, I don't know how much, cause thats how high Guys' thermometer goes.. mine only goes up to 2000.

 

If you haven't yet, check out the rockbridge bloomery site, that's where ive gotten a whole heap of info. They really are the top of the game when it comes to these roman style furnaces B)

Link to post
Share on other sites

You should be able to rework the slag rather than just use it as a flux if it is iron rich. In WWI the italians reworked slag from Etruscan iron works from over 2000 years before !!

Link to post
Share on other sites
You should be able to rework the slag rather than just use it as a flux if it is iron rich. In WWI the italians reworked slag from Etruscan iron works from over 2000 years before !!

23397[/snapback]

 

 

How did they do it? I know that when the blast furnace started being used, they were recharging a lot of ancient flux, since they had figured out the whole calcium trick... I have a friend that was part of a dig over there on the beaches you're talking about, I'll see what he had come up with. Really cool stuff.. whole fields of hellenistic era slag, made in furnaces kind of like these... he was telling me how they ID'ed the charcoal for age and tree type, and those same trees grow on the hill overlooking the site today.... kind of mind boggling :)

 

I love this stuff :D

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...