Tuesday, June 05, 2007

Iron Smelt Course Results...

This is just a fast overview of the Introduction to Iron Smelting course held at the Wareham Forge over June 1 - 3, 2007.

The participants for this program were Colin Paddon of Grassie ON, and Stephen Midkiff of Elmira PA.

On Friday evening there was a quick run through of the basic process to be undertaken with the construction of an Econo Norse style furnace. We finished this up just as we were loosing our working light. The evening was completed with a discussion of the background theory of iron smelting and an examination of alternate ores and smelter constructions.

Saturday was a long working day. For this smelt, commercial hematite blasting grit was used as the ore. Charcoal had been purchased pre-sized and screened. After finishing smelter set up (tuyere and base) the usual split wood pre-heat was started. Students then prepared a small amount of rock ore and standard charcoal to size to learn those processes.

Working in roughly 30 degree C heat, the furnace was run through the normal sequence of pre-heat, raising to operating temperature and charging with ore. The furnace preformed extremely well, maintaining an even average burn rate of 4 lbs charcoal each 8 minutes (ranged from 7 to 9 per bucket). An even ore charge rate of 3 1/2 lbs per bucket / 8 minutes was smoothly established. In total 49 lbs of the hematite ore was charged. The lack of slag available from this pure iron oxide was balanced nicely by the slight inflow of the sand / ash packing that results from the loose brick construction of the Econo Norse smelter. The smelter ran very consistantly, with only a single slag tap being required, late in the sequence, to keep the tuyere clear.

The burn down phase was started at roughly 3 1/2 hours, with a 2 lb shock charge added. A first attempt at extraction was made via the tap arch and removal of the front plinth block. Little liquid slag was observed, and the bottom of the slag bowl was firm and completely filled the smelter interior. Although several strikes were made on to the top of the bloom / slag bowl, it was not possible to free the mass from the smelter. The sheet metal containment was then cut with the intent to disassemble the smelter from the top down. Unexpectedly, the whole loose brick structure collapsed, freeing the large mass of slag encased bloom. In a mad scramble, the mass was grabbed and moved over on to the wood stump. Surprisingly little loose 'mother' was hammered off. The resulting bloom proved quite dense and well compacted. A cut was started to section the bloom into two pieces, but by the time it had been worked down half way we were all pretty much exhausted and too much heat had been lost.

Racing the bloom back to the workshop, a couple of alternative cutting methods were tried on the still dull red mass. In the end a cutting torch was used to finish off the last 1/3 at the bottom of the cut. When the pieces were put on the scale, the finished bloom weighed in at a remarkable 28 lbs! This result is a 60% return from the ore, certainly the highest yield I personally have seen to date. Judging from the sparks produced with a hand grinder, the carbon content would appear to be in the middle range (like a spring steel).

(this is one of the cut half pieces)
Stephen was able to spend the following day in the forge compacting his half of the bloom. His starting mass was roughly 8 inches long by 4 thick and 4 wide at a total of 14 lbs. This block just barely fit into my gas forge to allow an even pre-heat to a middle orange. The piece was then placed in the coal forge to finish bringing it up to a low yellow working temperature. Again the small air hammer on hand (only 50 lbs) could just manage to choke in that 4 inch size. Although it was extremely slow going, over several hours Stephen was able to compact the starting bloom down to reasonably solid starting bar.

I am extremely pleased with the results produced by Colin and Stephen. This despite the quite punishing working temperatures on smelt day. Although they did have my guidance, the two of them undertook all of the work involved in the smelt. Afterwards I did warn them that good luck was certainly a factor for such an extremely successful first smelt!

(after the conversion to a rough bar - finished weight 11 lbs)

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

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