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Hi, after several years of thinking about it I finally had a go at oroshigane, using the Aristotle forge method laid out by Skip Williams. I have so far made 5 runs, with at best marginal results. I'm going to summarize each, and hopefully someone can point me in the right direction.

 

First run, tuyere the diameter of a pencil, 45deg about 3 inches above floor. Was doing this run mostly from memory having read the post by Jesus, but anyway it took almost an hour and a half to melt the 600 or so grams of mild steel. No bloom, lots of slag. Clearly I wasn't getting hot enough.

 

Second run, I made more charcoal, paying better attention to quality and size. Again a long run to melt 600g and got a very small slaggy bloom w/ lots of un-melted bits sticking out. Was happy to have gotten something though.

 

Third run, very similar to the second. In the end I decided I was getting way to much slag and not running at a high enough temperature.

 

For the fourth and fifth runs, I changed the furnace over to one made of mortar mix, with hopes of less slag. I further refined the charcoal to try to get it to a more consistant 1cm size. and I increased the size of the tuyere.

For these two runs I actually got blooms, although my run times were still quite a bit longer than the 10-20 minutes quoted in the original thread by Jesus, but I didn't seem to have excessive slag this time.

The next day I tried forging them and to my surprise they held together and welded up nicely. The problem then was upon hardening and trying to break them they didn't harden.

Now I'm not terribly good at reading a spark test, but I thought there were parts of the bloom that had high carbon so I was surprised when I couldn't harden them. I've tried twice now, the second time bringing them up to bright orange, so I'm guessing I took mild steel and made wrought iron instead of steel.

 

Any ideas on what I'm doing wrong would be greatly appreciated. I'm guessing maybe the bloom spent too much time in the bottom of the furnace and was de-oxidized but I would love to hear other thoughts on it.

Thanks, Justin

 

p.s. the blower was a 112cfm from blacksmiths depot.

Edited by justin carnecchia
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Justin:

 

First - there are a couple of guides to the Aristotle method, done up individually by those of us involved in the original 'Smeltfest' research group that worked up Skip Williams' concept furnace.

My guide is posted at : http://www.warehamforge.ca/ironsmelting/Aristotle-HO.pdf

On my blog at : http://warehamforgeblog.blogspot.ca/2012/03/demonstrating-aristotle-furnace.html

 

One description you left out - How high was your furnace?

 

You say you followed Skips original description. Did you use the shredded horse manure with clay (possible sand) mix?

 

Normally what should happen is that your first use burns in the furnace to some stable shape internally. It is not unusual to get a lot more slag your first cycle. It should stabilize after that firing.

 

As you indicate - charcoal can be surprisingly important in the small scale of the Aristotle. You do indicate that you adjusted for correct (walnut) size the second time around. Did you screen out the dust / fines ? (Nothing larger than pea sized ideally)

What brand of charcoal / type? A lot of us have experienced problems with cheaper brands (Cowboy brand especially, but there is one brand made of tropical cut and slash stuff that is also inconsistent.)

 

The big one - air flow / burn times.

It may be that using a blacksmtih type blower (that is a crank blower you mention?) may pose a problem. You need not only *volume* but also a certain *pressure*. My own experience is that crank blowers may produce volume, but they often have little force to the air flow - and given the small size of the normal inlet tyuere to an Aristotle - the air kind of 'bounces off' the tyuere.

You need to watch the *rate* of consumption. Burn rate should be roughly 200 gms / 4 - 5 minutes. For those metrically challenged, that is roughly a standard coffee can measure.

 

Remember that the internal layout (the distance of the base level below the tuyere entry point) is largely what will control carbon absorbed by the growing 'puck'.

Each individual furnace is a bit different (and a brand new furnace always gives different results until it stabilizes inside). Once you can effectively get the source bars to effectively melt and re-deposit into a mass, you can expect to tweek that base level to start modifying carbon.

 

You must remember that any working with bloomery type materials (either full iron smelting or hearth modification) is more an art than a science!

If you are expecting a single 'cook book' method - you are certainly not going to get the single use method to specific product situation that many blade makers have been expecting...

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Having only done this method once under the watchful guidance of Jesus Hernandez, I suspect the blower is the issue. I have that same blower and it is not suitable for pressure applications. It's just a squirrel cage in a fancy housing, not worth half the price. A small shop vac with a router speed control is much better. It won't be loud, as it will work at no more than 20% speed.

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If you added metal, and it melted, but all you got was slag, then i would assume the metal oxidized, keep it further from the tuyere. Like both have said, you need an air supply with pressure, an old vacuum cleaner works great, or a good bellows. Keep after it, it's never an exact thing, some runs are better than others.

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Thanks for your feedback.

Darrell, the furnace is about 10inches high, maybe 12" with the tuyere entering about 4" above the floor. First furnace was made with clay and straw. Second was made with mortar mix and straw (hard to find stuff like fire clay here). Charcoal was made from ponderosa pine, I'm guessing that I need to further refine the size. Blower was the aforementioned 112cfm Blacksmith's Depot blower, also a possible problem though my burn rate was right around what your describing.

 

Alan, thanks. I too am wondering if that is part of the problem. I have an old shop vac, I'll give that a try.

 

Anyway I've got a 10lb sample of "pure" iron coming from Hoegannes so I'm exited to give this another try. I've been wanting to play around with some no-manganese steel for a few years now, keeping my fingers crossed I can get this to work.

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Hi Justin,

 

Welcome to the world of melting metal to make metal :)

Like most have said, it is likely your air supply. In the stand up Aristotle design, your air flow is probably the biggest factor in success.

 

The big problem I have found with the Aristotle design is, you have little control over the amount of carbon you get. With practice, you can get better, but IMHO it is very difficult at best.

A few years ago Lee Sauder turned me onto the Evenstad papers, for then on I found a much more reliable way.

Hearth-refining.

Here are my Picasa pages. there are a half dozen or more pages about shallow heath-refining. It basically makes the same product as the Aristotle, with 10x the control.


https://picasaweb.google.com/106800196895572422821

 

There are some pics of Zeb's design in this one as well.
https://picasaweb.google.com/106800196895572422821/FBHearthRefining

Have big fun, keep at it. It does take some practice.

 

Mark

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Hi Mark thanks for the info and links to the pics. Could you give me an idea on the inside dimensions of the hearth furnace and how big/high up/angle of the tuyere? Also what about it gives it better control?

Maybe a better question would be what are the factors that influence carbon content?

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Hi Justin, All that info is likely in my Picasa posts.

 

Here are the Evenstad papers. http://donwagner.dk/REHD/REHD.html

My hearth is about 12 in. round, and about 6 in deep. I use fire brick to make it smaller as needed. My tuyere comes in flat. I use old air mattress blowers for air.

The depth from the tuyere to the floor is what sets the carbon content. As you will read in the link above. It can be use to decarb cast iron. hc steel, and to carburize plain iron.
It cleans most of the slag from bloom iron, and wrought, and can make some very pretty material.
It may even remove P & S, and other nasties from bloom and wrought. One of the reasons it was used in period.

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Thanks again Mark, you have been very helpful. -Justin

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So Mark, reading the paper you linked and looking at your images, am I to understand correctly that a depth under tuyere of ~1 inch yields clean iron, and a depth under tuyere of ~2 inches yields steel? Does that match your experience?

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I usually go for about 1.5---2x that amount. I found that 1 in. didn't give you much room for the melt to grow.

 

Plus, with the power of my air, I wanted to get the steel out of the flow.

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I still need to build my Evenstad hearth. Now that I have some clay I just might very soon! Of course copious amount of pics and vid will follow.

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Justin:

 

you also said :

"First run, tuyere the diameter of a pencil, 45deg about 3 inches above floor"

 

The Smeltfest team initially ran Aristotle furnaces for over a week - something like 5 -6 different builds, over 35 individual firings.

As with the full sized iron smelting furnaces, the 'magic number' for the tuyere down angle is * 22.5 *.

You can get good results from 15 to 25 down - but you should stay in that range.

 

Your 45 degrees is so steep that you would be placing the air blast right on top of the developing metal 'puck' - and slag is all you would likely be your result. You would have most likely just cut up any developing metal deposit.

 

Did you see those bright 'burning iron' sparks at the top of your furnace? (Bad sign!)

 

Those who try to warp this process via using higher temperature refractories are putting too much work / expense / (theory) into the build. The intent her is a fast, easy to build furnace - which should be considered 'semi disposable'. With the small size, my own experience is that you are far more likely just to break the thing when extracting the metal puck - than suffer significant erosion to the furnace walls. Some erosion *is* to be expected (remember what I said about 'virgin' furnaces.

Simple potter's clay, or cobb mixes (chopped organics) work extremely well. Cheap and easy.

 

You mention a furnace at 10 - 12 inches tall - but with the tuyere point set at 4 inches above the base. That gives you only a reaction column of perhaps as little as 6 inches. Just barely enough. Especially when combined with the next factor...

 

You mention using pine as your charcoal.

The Aristotle system was developed and tested for hardwood charcoal. And also for charcoal sized at walnut to pea sized pieces (as I mentioned).

Different types of charcoal can act quite differently in any smelting related furnace. With the Aristotle, the miniature size means any margins for error are also quite small. Softwoods are going to burn faster - and collapse the working column quicker. You would certainly have to make some modifications to the entire working system to account for this.

 

As Mark has suggested - each working system varies from a theoretical base template. Each variation from the exact details given in any description means also a potential variation in the results.

If you copied *all* the method exactly, then you *might* get expected results as given. Do remember that these smelting and hearth based furnaces are only recently 're-discovered' - there is still a large amount of objective experimentation required to realistically understand and control all the variables involved. (Compare this with learning to forge weld - only at least an order of magnitude more complex!)

 

I have personally run / observed the Aristotle system run over at least 20 + different furnace builds - and maybe 75 + individual firings. (bet Mark has done a big pile of these as well).

Every time you build a new furnace - there is almost always other variables that need to be adjusted before you get some desired result.

 

If you wanted to consider any of the smelting processes 'science' - it would certainly be 'rocket science'.

The *process* has to be considered as big an objective as the physical *product*.

Otherwise you might as well just purchase modern alloy from your steel supplier...

 

Enjoy the experience!

 

Darrell

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Thanks Mark, I have read that one. Sounds like with the Aristotle it is pretty hit or miss as to the carbon content. I rehardened the two bars I previously forged out and was finally able to break them. Showed a mix of steel and iron with multiple burst sparks on the steel areas. I would have prefered a bit more steel to iron, but they should be usable. If nothing else I'll use them for fittings.

Also I changed up the air supply, shortening the pipe from the blower to the furnace and enlarging the tuyere slightly. With those modifications I think the furnace is now operating correctly, as the time for melting 600g of iron went from an hour to 15min. I haven't had a chance to forge out the bloom yet but from outward appearances it seems more solid and the spark test looks to be high carbon (though I'm still not real adept at interperting the sparks).

I'm interested in trying out the hearth furnace, but it sounds like it is limited to producing around .7% carbon content and I'm wanting more in the1% range. I have also considered building a Japanese sword forge, but for now I'll give the Aristotle a little more time.

Thanks for everyone's advice, -Justin

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Well, finally got enough steel to get busy making a knife. Started with three of the denser blooms I got, and they all drew out into bars nicely (though the slag did a number on my forge's lining). After welding them up I drew them out and cut into four, repeat, you all know the drill. Just as I was approaching five hundred layers or so I was giving the billet a squeeze on edge and got two big bubbles in the outer layer on each side. Kind of a bummer to blow it this far in with a stupid welding mistake... I've never had much luck closing this type of seperation so at this point I'm not expecting much from the billet. I will finish welding it up though, as my main goal is to see how this type of steel works with hamons for me. So I will proceed from an experimental point of view and at least get the feel of heat treating it.

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Thanks Jesus, I will try that next time. When I cut the billet I cut through the bubbles in hopes of driving them out. It's been about a year since I've done any pattern welding, ultimately I should have have welded up a billet of factory steel for practice before committing to the oroshigane.

Anyway, I did a couple more welds and on first inspection everything seems solid. Not seeing any bad welds on the edges or on the flats. So I'm keeping my fingers crossed but I think I have enough left to make a knife.

On a side note has anyone else had issues with slag eating their forge lining? If I keep at this I think I'm either going to have to build a charcoal forge, or use a castable refractory for re-lining my current forge. Oh well no big deal, I have to say I'm having the most fun I've had since I first started forging knives. Can't wait till the weekend to finish forging this one.

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Yes, bloom slag will kill your forge very fast. Not only does it eat kwool, and most other refract. it leaves a big slaggy mess, that makes it near impossible to gain good heat.

 

You have to protect your forge.

 

I make 3500 castable floors, and just chuck them when they die. Plus, I try to do the first few compactions of bloom in the charcoal forge, that just has a clay/sand floor.

Then it just becomes the very high temps, and flux, you need to worry about. It's all very messy and destructive.

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  • 2 weeks later...

So I managed to get the billet up to around a thousand layers with no major flaws visible. I would have liked to have gone higher but was running out of material. Anyway, forged it out into tanto shape, and last night I hardened it. I was pleased to not hear any pings, and on closer inspection it appears to have survived the ordeal. The blade took a fair bit of sori, so I assumed it hardened and I quickly got it into the oven for an hour at 400deg.

Once it was cool enough to handle I took it to the grinder and knocked off the clay and scale, gave it a couple passes and then looked to see if the hamon did what I wanted. I've been trying to get a convincing choji hamon for several years, and that is what finally lead me to try making my own steel. Anyway the strange thing is I didn't see a hamon? Typically when using w-2 or 1075 the hamon is clearly visible fresh off the grinder at 50grit.

I gave it a few more passes at 50 and then took it to 200grit, thinking I'd be able to see it now... Well I think I see it? Very faint though. Is this typical?

I have thought of re-hardening it, but I have a very low success rate at that (0%), and given the time I have into this project I couldn't handle having it crack. So I'm going to go ahead and finish it, keeping my fingers crossed that the hamon's there just waiting to be brought out. Just wondering if any of you with experience doing Japanese style blades with oroshigane and bloom steel have had similar experiences.

Thanks for everyone's advice, it has been very helpful. Hopefully by next weekend I'll have some pics of a finished blade. -Justin

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Coaxing a hamon out of this type of steel is not easy as each blade is different from the next given the variations in steel composition and heat treat and how those two interact with each other. Polish the blade beyond 2000 grit then etch and see what you get. You may need to experiment with your abrasives at the end to see the hamon.

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Thanks Jesus, I have it to about 320g as of now and I think there is a hamon. It is already clear that my methods for W-2 will not do the trick. It will be an interesting project at any rate.

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So I etched and when first taking it out of the vinegar it appeared that I had a very nice hamon. Unfortunately when I cleaned off the oxides it wasn't there. I did one more etch before noticing a hamon right around the tip and just a touch around the ha machi. Oh well, I got a very nice ustori though.

A little bummed out, but this is after all a learning experience. The blade was a little wide to start so I will grind down the edge and have another go at it.

I have to say I'm a little surprised, talk about shallow hardening. I was hotter than I do for w-2 and quenched in water, I guess hotter next time? Thinner edge? On the plus side, the little bit of hamon I did get was very bright, so I'm confident that I should be able to see it from the start.

Hopefully the blade will survive a second attempt, and I will have some pics soon.

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I am a bit confused about your previous comments. You said that you saw a hamon right after etching. It is so, then the hamon is there and you just need to figure out how to make it show but on your second sentence after another etch you could not see it. Which is it?

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