Demonstrating the Aristotle Furnace

Yesterday I undertook a demonstration / hands on session at the monthly meeting of the Ontario Artist Blacksmith Association. I had been part of the team that researched the working system for a small re-melting furnace (Smeltfest 2009). This is a simple to build small furnace, economical and fast to run. It will convert almost any iron based material (scrap, alloy, carbon content) into a small puck of bloomery like material with a mid to high carbon content. This allows someone to experience the unique textures of bloomery iron - without the effort and expense of a full sized iron smelt.

After an overview and demonstration of the process, I invited individual participants to run a furnace cycle and produce their own puck of metal. Seven individuals took part - with excellent results every time! The blade smiths gathered where particularly interested, as the application to their work was obvious.

Observing the furnace, near the end of a cycle.
Both these fellows would take turns making their own 'puck'.

I had prepared a short handout to distribute. As travel, timing (and luck) would have it, I was not able to get photocopies made in time for the demonstration. The handout is duplicated below. It will also be available as a PDF download. (Links will be placed on my regular blog, my iron smelting web site, and the OABA web site.)

The Aristotle Re-Melting Furnace

A simple way to make bloomery type carbon alloys

This furnace is based on the writings in Aristotle's "Meterologica' and later Ole Evenstad's descriptions in the 1780's.
The original concept belongs to Skip Williams, who then introduced a prototype to the Early Iron group a Lee Sauder's Smeltfest event in 2008. At Smeltfest 2009, our team concentrated specifically on the working dynamics of the Aristotle Furnace, with over 30 individual test firings.

The furnace is build like a miniature short shaft smelter. A standard 2 litre plastic pop bottle makes a good internal form. The ideal material for the walls is a 50 / 50 mixture of dry shredded horse manure mixed with powdered potter's clay.
A standard carpenter's pencil, or a piece of 3/8 rod is used to make the blast hole.
Critical measurements are :
1) the angle of the blast hole - at 20 to 25 degrees down from horizontal
2) the depth of the furnace floor below the blast hole - at 5 - 7 cm
3) height above the blast hole - at about 20 cm

A single firing consumes about 2 kg (standard galvanized pail) of charcoal over 25 - 30 minutes. The fuel should be broken to 2.5 cm or smaller, with dust screened out.

Temperature is determined by consumption rate, in turn modified by volume of the air blast. Ideal consumption is roughly 200 gms every 4 - 5 minutes (determined by timing a standard measure - a standard coffee holds about 200 gm)

The raw material can be almost any iron source. At first it is suggested that short lengths of standard 3/8 - 1/2 mild steel bars be used. Cut this into roughly 15 - 20 cm lengths, a total of 600 - 800 per firing.

Each bar is placed roughly 1/3 the distance back from the blast hole side, deep enough into the charcoal that the pieces hold it upright in place. The pieces are then allowed to descend as the charcoal level drops. Keeping the furnace full of charcoal, new bars are added as the previous ones drop below the upper surface. The last bar is covered with a last addition of charcoal, then the surface level is allowed to drop, burning the remaining fuel.

At this point a pointed hook can be inserted underneath the 'puck' of collected bloomery steel. It is a good idea to scrape out any slag that has gathered in the bottom of the furnace, then the whole can be re-filled with fuel for an additional process.

The result is a mid to high carbon metal, with the physical texture characteristics of bloomery iron. The created 'puck' typically weighs about 500 - 600 gms (65 - 75% yield). Once consolidated, this enough material to make two 4 - 6 inch long tanged knife blades.


Descriptions and further reading on the Web:

"Teeny-tiny Bloomery"
by Skip Williams

"A different way to make steel"
by Jesus Hernadez (on 'Don Fogg's Knife Forum')

Aristotle's Steel
by Lee Sauder (PDF download)

"Steelmaking in a tiny open furnace"
Donald Wagner (This is a photo essay from the same event that Lee's article above was based on.)

Part of the OAC Crafts Projects Grant

You Can't Always Get...

...what you WANT
(But if you try some times...)

(This posting an echo from Bloom to Bar)

This is a look at what happened yesterday in the forge.
If you check back to yesterday's posting. You will see that the concept I had come up with was to take one of the smaller, more compact looking blooms and layer it up on to a carbon steel core. The intent was to preserve the ragged edge into the finished object.


The bloom I chose for this was the one from Smelt 14 - at Dan Nickel's 'Folly at the Forge' event. (Black Rock Forge - Traverse City MI, February 2006. The story of that smelt is an interesting tale of endurance, it was 20 bellow F when we started!) The piece was a fragment at 485 gm off a much larger bloom. As we had forged down the full bloom to bars at the event, I knew the material was a 'nice workable iron' (from my notes).

As it was about fist size to start, it easily fit inside my two burner propane forge to pre-heat. This allowed me to bring the core up to temperature more slowly. Also allowed this process to take place while I was getting my main coal forge set up and started. All the actual forge work was done in the hotter coal fire.
(Note that I have altered this image in an attempt to get it closer to the actual colours you would have seen. The camera 'sees' down into the infra-red differently than the human eye does. The actual colour would have been a 'bright orange'.)
This is the end result of the initial flattening stage. I worked the raw bloom starting at a welding heat. I took two heats working with the hand hammer, concentrating mainly on the flatter of the rectangular sides. Then I took several heats on the air hammer, again starting with welding each time. The action there was primarily to draw the rectangle down to a wide and thin flat bar.
Here you can see the results after being cooled and cut into two fairly equal pieces. The loss from bloom to this stage (as you can see) was down to 394 gms

Thats a total loss of 91 gm, or about 20%.
The metal at this point still had some fissures in it, especially along one edge. If I was really trying to make a solid working bar, I would have collapsed the bloom into a square cross section, allowing me to work all four of the edge surfaces (instead of just concentrating on two). I would have undertook at least one more weld series. My estimate is that the total loss would have been closer to 25 %


The two bloom iron plates were roughly 1 3/4 inch wide x 3 3/4 long x 1/4 thick. I took a piece of standard 1045 middle carbon spring steel (new leaf spring) and placed it as a core. A working handle was MIG welded to the spring. I then tack welded the three pieces together at the far end. You can see that the central cut end of the bloom plates was placed at the far end.
(I normally wire together my starting layers. Also I like to weld from the far end back towards my body. Just habits!)
At this point there was a total of 643 gms of material, the stack was roughly 3/4 inch thick.You can see that the spring was a bit wider, at 1 3/4 inch. I left the plates all even on the 'cleaner' edge of the bloom pieces. (Remember a ragged effect was my initial goal.)


The finished result.
This billet is roughly 8 inches long (with the more or less pointed end) x 1 3/4 at the base x 3/8 thick. I have given it a fast surface clean on the high speed sander. Although there are certain to be some flaw lines, generally the surfaces are welded fairly tight.

Although this billet will certainly work up into a potentially quite nice blade, it is not quite 'what I need'.

Back to the pile for another attempt...

Metal Stocks & Sizes Guide

Located in Owen Sound Ontario, Krueger Custom Steel may not be convenient for many reading this.
I have been purchasing from Krueger pretty much since they started business in 1994.

What has set them apart in my experience has been the acceptional level of service they have provided.
- They 'talk blacksmith' - understanding the (now old) British Gauge system as one good example
- Extremely reasonable 'local' delivery policy (less than the gas cost!)
- Good stock of standard sizes kept on hand
- Availability of specialized materials on order, usually within a week.
- Ability to provide cost quotes / order specifics via e-mail (so written down!)

At the Wareham Forge, my normal practice is to order in bulk, usually once a year for all my standard sizes. I am thus purchasing the smaller hot rolled, structural and pipe materials in multiple hundreds of feet. It is true that I might be able to get my order a wee bit cheaper at those volume levels from one of the larger industrial suppliers. Once delivery costs are added from major centres, that price advantage disappears.
Most importantly for me, the extremely high level of personal service I have always received from Krueger completely overweighs any slight cost savings.

What will be quite handy to the general member of OABA is a brand new feature available on their web site.
They have placed a complete metal stock guide available as a downloaded PDF. This kind of guide is invaluable for telling you just what sizes and materials are easily available. It includes 'weight per foot', which is handy for figuring out just what that wild idea of yours is going to total up at. (I've been caught by that one a couple of times!)

The Steel Guide PDF is available at : http://users.sitewaves.com/index.cfm?page=803&r=13615
Just hit the 'View Steel Book Catalogue' button at the top of the page

Krueger Custom Steel
1610 20th Street East
P.O. Box 187
Owen Sound , Ontario
Canada , N4K 5P3

Phone: 519-371-7930
TollFree: 1-888-244-4187
Fax: 519-371-7852
Email bkrueger@bmts.com
WWW.Kruegersteel.ca

All the Myriad PIECES...

(An echo from today's posting on 'Bloom to Bar')


Now that the layout table is not needed for the assembly of the hydraulic press (being modified specifically for this project), it was time to empty the milk crates full of blooms:

Click to *greatly* enlarge
Yesterday's work in the shop consisted of sorting all the pieces into historical order. Each piece was then photographed and weighed. There are over 60 individual pieces, ranging from full sized blooms (the largest at over 7 KG), down to small fragments. With luck even the small pieces can be welded as part of stacks towards creating layered steel billets.

I also spent a good hour attempting to work out some kind of useful method of measuring the volumes via water displacement. This in aid of determining the density of each bloom. This may not be critical towards artistic use of the individual blooms. However, keeping my archaeological slant in mind, once compaction and forging into working bars starts, the original density information will be lost. Better to record seemingly useless information - than work past it had find out later the data was significant.

Although I really have made a serious attempt to keep each bloom labelled, what I found was that the process of shifting around sharp edged metallic blooms had shredded bags and obscured labels. There are a number of pieces that obviously have been mis-labelled, a few (some of the largest!) with no labels at all. At least one distinctive bloom is missing from the pile.

I am attempting to keep notes relating the specific process used to create an individual bloom / bloom fragment to the compaction to bar process. Most specifically as it relates to individual carbon content and general ease of forging.