Sunday, May 06, 2012

'Production Smelt' - RESULTS

I would refer you back to yesterday's post for the details of the set up for this smelt.

Furnace in use
The first thing is don't do this alone.
You *can* run a successful smelt as a lone individual. It is however a massive amount of work.
- I spent a half day clearing out an old furnace and preparing the area and laying the base.
- Then a fairly long day preparing, mixing clay and building the furnace.
(Roasting ore was done separately, but the two batches there could have been undertaken during the work sessions above).
- Another half day gathering up the roasted ore, setting the tuyere and running a slow drying fire. I broke up 3/4 of the ore at the same time.

Smelt day, I broke charcoal while the first stages of pre-heat (with wood) was taking place.
I started that day at 8 am gathering tools and getting them out and arranging the work site.
The pre-heat was extended to allow time to break that charcoal (64 kg worth / 8 bags).
The main smelt sequence itself ran over 7 1/2 hours, from first charcoal fill to start of the extraction. In the end I decided to use all of the 'Jamestown Brown' ore that I had roasted and crushed. The total ore added was just under 42 kg. The total charcoal consumed was 55 kg (7.5 full 8kg bags, before breaking). I had a real hard time getting this bloom free. I ended up having to break way 2/3 of the slag mass by chiselling it off in small pieces. I really have no clear concept of how long this took, but working down inside the hot furnace was absolutely exhausting. My guess is that I was at it at least a half hour.

The total smelting session took 13 hours!

Slag mass, the furnace just opened.
So by the time I pulled the bloom free, the bloom had cooled considerably. I did try to work over the surface with a 5 lb hand sledge. This did knock some of the clinging slag 'mother' free, but really was not effective in compacting the metal itself. I tried a fast weight measurement, but frankly I think the reading was not all that accurate. (What I recorded was 12.27 kg). Frankly, this is a much larger bloom than I normally make.

Hot bloom mass - after hand hammering
I rushed the bloom back from the rear yard into the workshop. I had started my two burner gas forge before I started the extraction, but there was no way the mass would fit. Although the bloom was closer to a red heat at this point, I quickly started the hydraulic press. I made a partial compaction, but it was obvious that the bloom was far too cold, and several larger pieces broke free. I swapped in the cutting head and made a cut from both sides, most the way through. At this point I might have been able to get the individual 'half' sections into the gas forge, but frankly, I was way past too beat to work.

Main bloom, cold and after sectioning
This morning, I was able to pull the scored bloom off the floor, and sweep with a magnet to recover any fragments.
The main bloom itself now weighs a quite respectable 8.83 kg.
I recovered another 1.46 kg of fragments. Two pieces are a good size (at 501 and 324 gms) and look solid enough that I should be able to work them down to smaller bars.
The overall yield (using the 10.3 kg total recovered) comes to roughly 24 %.

The furnace itself, despite all the pounding and prodding, was found to be in remarkably great shape the next morning. There is one very small crack right near the top edge, but otherwise the shaft is in perfect shape.
The copper tuyere might have melted just a tiny bit. I'll have to measure it to be sure. The wall around the tuyere did errode a slight amount, but it does not look more than a centimetre or two.
After a small amount of cleaning up, I'm certain it will be quickly ready for another use (Thanks Lee!)

(very) Tired but happy
(but let's get more of the gang here *next* time I decide to try this...)

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

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