Friday, April 21, 2006

First Bloom to Bar (older post)

Since I have not added much this week - this is an older posting that may be of interest to the iron smelters or blacksmiths reading this. The original post was send to EARLY IRON back in January (!)
I did however work on a different bloom fragment yesterday.
At Early Iron 2, the smelter I was looking over ran in a weird sequence. Elisabeth and Toby from MIT had to leave before the sequence was really complete. Rather than not finish the smelt sequence, I took the thing over. The end result when the smelter was opened up was actually TWO blooms. The first was larger and more spongy, lower down. On top was what I remember Mike calling 'a cute little football'. This was an entirely separate bloom, about 7 1/2 lbs.

Anyway I took this one - which again is a size that just fits into my gas forge. (For me this is proving pretty important equipment wise!)
- Preheat about 45 minutes - to a dull orange. Rotated a couple of times.
- Put into the coal forge and up to a bright orange, again rotated and flipped. Did note the 'bubbling / oozing slag' that Lee mentioned. Maybe 10 minutes here?
- Cut in rough half.
- Stared to work one piece, compressing down. On the second heat, the piece fragmented in two. There was a fairly large cavity with slag in it about the centre - this is where the break occurred.
- Took what was now about a quarter of the original bloom (1 lb 3 oz) and worked it. I had my 'baby pan' scale on hand, so took weights of hot pieces at several points. Scaled photos too.

- Compressed that piece to a 'book' roughly 4 x 2 1/2 x 1/2. Cut and folded in half - welded.
I did this weld under my 50 lb air hammer. The first side fine, working middle to end. On the second side, one layer of the end pretty much fragmented to pieces.
I may have been working too hot (like a brilliant white).
I also suspect this part of the material had a much higher carbon content, judging from the appearance of the collected fragments and later observations.
- From here went back to hand working the piece, working more from the yellows back to orange. Although I typically would hit the piece three times then bounce it on to the floor. The hand work let me concentrate on the edges - the same diagonal facets that Lee describes.

At the end of all that, I had a piece roughly 2 1/2 x 2 3/4 x 1/2. This was forged out (again working at higher temperatures, never under orange) to a bar at 1 x 5 x 1/2" and 12.5 oz.

With the collected fragments (total 5 oz) the conversion of bloom to bar was:
Start - 24 oz
Bar - 12.5 oz
Fragments - 5 oz
Loss - 6.5 oz
(I make this bloom to bar at about 75% - compare with the P. Crow estimates)

I took the final bar and water quenched it from red. The end that was where the fragmentation happened turned that clean light gray to white look that you get when you water quench mild steel.

I cleaned one surface with the hand grinder and then flattened on the belt sander to 100 grit.
- At this process the sparks were the classic 'dull red balls'.
- The suspect end showed a brighter colour with some feather. (This did look like less than mild steel however).
- The polished surface shows as solid continuous metal.

A couple of general things:

- I had tongs on hand for sizes from three inches down to 1/2 inch - and used them all.
- I found at the first part of compacting the surface that the size changed so fast that even one tong would go from too big to too small in a single heat.
- I chased bouncing blooms across the floor at lot!
- Slag seemed to draw to the surface and splat off in hammering on every heat. Never any need to flux. Ended up with gloves on BOTH hands (I normally NEVER glove my hammer hand) there was a lot of goo flying around.

It occurred to me while writing this that a tool made of a loop of 3/4" on a stick would have helped keep the small irregular pieces on the anvil.

I echo everything that Lee says about consolidation right after pulling the bloom. My team has found we can not even get that initial temperature even using the smelter as a giant forge. We extract through the top of the smelter. This includes one step that we can add - compacting the bloom in place using a length of 4" log about four feet long (what the lads call a 'thumper'). This also helps by removing a lot of the loose 'mother' before we extract the bloom.

I've got two 16 plus blooms here as well. The only way I can think of getting them at anything like a workable temperature to split is to make a large pit forge like Mike made at Early Iron


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