Operating the Smelter

Previous: Constructing the smelter

Ore: we had access to some surplus magnetite powder (Fe3O4), so used that as ore. This is a high purity iron oxide, so we did not need to roast it or crush it. Due to the lack of silica in the ore, we added a little crushed glass to form slag.

Initially used a hand crank blower for airflow. Blower was connected to tuyere by a galvanized pipe T, with a screw cap on one end of T that could be removed to look into tuyere. Cranked near maximum blower speed (took a lot more energy to crank any faster). Partway through, blower started to fail, so switched to air from a small vacuum cleaner. As best I could estimate, airflow from vacuum was similar to the max airflow we got from the hand blower.

Used mix of hardwood and softwood charcoal (homemade). Used a large bowl to estimate 2 lb of charcoal and used this as standard measure. Marked a mug with a line for 1lb or ore and used this as standard measure.

DARC notes from similar smelter had a burn rate of 4lb charcoal/10 min. We were usually close to this, but often had a somewhat slower burn rate. This seems to have been okay.

 

Put a 1-2" layer of charcoal fines in bottom of furnace.
11: 55 am - Light a small fire using pine cones and scrap wood. Keep fire burning steadily, but not too hot.
12:45 pm - thinner parts of walls are warm, tap arch is hot
1:15 - start low airflow with blower, still burning wood
1:25 - fill furnace with charcoal.
1:35 - start adding more charcoal
1:42 - 2 lb charcoal burnt
1:45 - increase airflow to about 1 crank/2 sec
1:48 - start adding more charcoal
2:00 - 2lb burnt, increase airflow to 1.5 cranks/2 sec
2:02 - fill with charcoal
2:07 - 2lb burnt, keep adding, crank at 1 crank/1.2 sec (this is about the maximum reasonable crank, and it was often a bit slower than this)
2:10 - add ½ lb ore (adding ½ lb per each 4 lb charcoal)
2:17 - add ½ C crushed glass (clear)
2:35 - third ½ lb ore (missed recording one)
2:51 - add ½ C glass
2:53 - add 1 lb ore (adding 1lb ore per 4 lb charcoal)
3:08 - add 1 lb ore
3:25 - add 2 lb ore
3:35 - add 1 lb ore (2lb is a lot to add at once, now adding 1lb ore every 2 lb charcoal)
3:40 - add 1 lb ore (plug in tap arch pulled away from firebricks a bit, some hot gas escaping, but not much)
3:50 - add 1 lb ore
3: 55 - add more glass, piled sand in front of tap arch to block hole
4:00 - add 1 lb ore
4:05 - add 1 lb ore
4:13 - add 1 lb ore (after this, add 1lb ore twice per 2lb charcoal); number in [brackets] are minutes since last ore addition
4:20 - add 1 lb ore [7]
4:26 - add 1 lb ore [6]
4:33 - add 1 lb ore [7]
4:36 - add 1 lb ore [3]
4:42 - add 1 lb ore [6]
4:48 - add 1 lb ore [6]
4:53 - add 1 lb ore [5]
5:03 - add 1 lb ore, plus more glass [10]
5:09 - add 1 lb ore [6]
5:14 - add 1 lb ore [5]
5:20 - add 1 lb ore [6]
5:26 - add 1 lb ore [6]
5:31 - add 1 lb ore [5]
5:37 - add 1 lb ore [6]
5:43 - add 1 lb ore [6]
5:50 - add 1 lb ore [7]
5:53 - add 1 lb ore [3]
6:00 - add 1 lb ore [7]
6:05 - add 1 lb ore [5]
6:12 - add 1 lb ore [7]
6:17 - add 1 lb ore [5]
6:25 - add 1 lb ore [8]
6:31 - add 1 lb ore [6]
6:42 - add 1 lb ore [11] - may have missed recording one ore addition
6:49 - add 1 lb ore [7]
6:55 - add 1 lb ore [6]
7:00 - hand blower failing, switch to vacuum
7:06 - add 1 lb ore [11]
7:14 - add 1 lb ore [8]
7:20 - add 1 lb ore [6]
7:30 - add 1 lb ore (taped over holes in plastic bag around vacuum to increase airflow) [10]
7:34 - add 1 lb ore [4]
7:41 - add 1 lb ore [7]
7:48 - add 1 lb ore [7]
7:55 - add 1 lb ore [7]
8:02 - add 1 lb ore [7]
8:10 - add 1 lb ore [8]
8:20 - add 1 lb ore, stop adding ore, keep adding charcoal [10]
8:35 - final charcoal fill, let burn down
9:00 - nearly burned down to level of tuyere

Knock down furnace wall. When bottom part is removed, liquid slag runs out, leaving large bloom. Slag pool had nearly reached level of tuyere end, and firebrick were eroded up to 1" deep at top level of slag pool. (firebrick in picture below is upside down - slag pool had flat top and curved bottom). Details of Consolidating the Bloom.



We used 5 ½ sacks of charcoal (about 100 lb) and roughly 49 lb of iron ore.

Next: Consolidating the bloom

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