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last night's shop time - Doug Ayen's Blacksmithing Blog [entries|archive|friends|userinfo]
Doug Ayen

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last night's shop time [Jul. 27th, 2011|01:33 pm]
Doug Ayen
The temperature dropped a bit, so I got some shop time in last night.



Didn't do much, just sanded down the handles on the chefsword, decided I didn't like the glue line on one scale so popped it off, cleaned it up, and reglued -- it should be set by tonight.

I decided I really didn't like the lack of carburization penetration on the blister steel. I hammered out a few of the thicker pieces to reduce the cross-section, and then put them back in the retorts with some more charcoal dust, bone charcoal, and graphite, and fired up the forge.

The retorts, which are capped iron pipes with weep holes so they don't explode, just barely fit in the gas forge, and as it turns out with both of them crammed in there, the forge starts to "backfire" even at a fairly high pressure (5psi -- I normally run it at 2 or 3 psi). As near as I can determine, the reduced volume of the forge creates backpressure on the venturi assembly, causing pre-ignition before the air/gas mixture leaves the assembly. This pre-ignition then heats up the assembly to above the ignition temperature of the propane/air mix, so the flame front moves further up the cast iron tube, which heats up higher up, etc. After running for a couple of hours, all three tubes were backfiring, which I considered dangerous enough to shut down for the evening. I'll see if I can move the retorts so that this doesn't happen, and if that doesn't work may try using one of the other furnaces I have in the shop.

Progress, in other words, or something.
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