Sunday, March 20, 2011

SMELTFEST 11 - initial doings

As some of my closer readers know, I'm away right now at Lee Sauder's shop in Lexington Virginia for the annual gathering of the North American Early Iron Underground. Here's a fast report...

One of several projects and investigations under way is the construction of an African styled passive draw furnace under the direction of Jake Keen*. (Jake seen in the image above.) It is a slag pit furnace, with a long trench off one quadrant, intended to drag out the eventual slag block. The core of the furnace is framed with saplings, we are using sections cut from an old water heater to frame the openings where the clay tuyeres will be inserted. Believe it or not, there are even MORE rocks in the 'soil' here at Geminal Ironworks than the ground in Wareham.

The construction of the furnace is clay cobb, mixed with chopped local plants (a wild variant of broom straw). Jake is inserting a layer of straw between the frame and the applied clay mix. This is to allow the clay to shrink without cracking (we hope) as it dries. My job at this point was applying a further 4 inch layer of clay like soil, another line of straw, then revetting with stone and back filling with earth. This is to support and keep the bottom 18 inches or slow from slumping.

This is the construction of the furnace as it was completed. You can see the dome of the furnace proper extending to the shaft. To speed construction, we have constructed a stainless steel pipe as chimney. A natural draft furnace needs a certain minimum height to create the air flow dynamic. (Our combined brains are a bit fuzzy on the details here, best guess is at least 6 feet of height is required.) Not seen in this image is a sliding hatch cut in that allows for feeding ore and charcoal at the bottom edge of the pipe. In Africa, likely some kind of scaffold would be used (??) to add new material.

This is a type of furnace that Jake, Lee and Mike McCarthy had seen as ruins in their recent trip to Africa. As partially buried furnaces, the lower construction is a matter of some guess work here. Of course the upper shafts were all erroded off, so the exact working height is unknown as well. Our stainless pipe extends at least 10 feet up, working on the theory that taller is better here.

Today Jake will start a gentle fire in the lower pit, attempting to slowly heat and dry the massive clay walls with out excessive cracking. Also for today will be making all the clay tuyeres. The plan is to start with four tubes for each of the four arches framed by the metal pipe.

* This is the famous ' Are you ... JAKE KEEN?! '

More to come...

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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