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Small Heat Treat Forge


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Plan Fat50 Ammo Can : 11-3/4" x 6-3/4" x 8-1/4" inside dimensions. 8# 2300 degree Kaowool Ceramic fiber. 1 inch on the sides.  1 inch fire brick and 1 inch Kaowool for the shelf 2 inch Kaowool  on the top. Gives me a  chamber size 265 cubic inches My plan is one single 3/4 inch burner. I don't intend on welding with this forge. Is applying anything other then rigidizer necessary for my intended purpose? Any suggestions you might have would be appreciated.

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Yes. Rigidizer alone is not suitable for propane flame contact. Flame WILL penetrate the blanket and degrade it. A layer of hard refractory will prolong the liner's life considerably. Even a good kiln wash like Plistex will do the same. 

A single 3/4" burner is a lot of burner for that small volume, A single 1/2" burner might be enough to bring it to critical temp where a 3/4" will easily melt steel in it. 

If the fire brick is to stabilize temperature fluctuations covering it with another 2" of blanket eliminates that benefit. Otherwise I don't see a purpose for the brick. Add up what it does to forge volume. 1" blanket + 2 1/4" brick + 2" blanket = 5 1/4" X 9". Which ammo can dimension can you subtract  5 1/4" thickness from without filling the oven completely? 

Frosty The Lucky.

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1 inch blanket topped with 1 inch fire brick. 1 inch blanket on the side walls and 2 inches of blanket on the ceiling. Leaves roughly a 4 inch by 4 inch by 12 inch forge chamber. 265 cubic inch chamber area

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If you are only heat-treating, you will not need a 3/4" burner. A 1/2" NA burner with fine adjustment of the airflow can easily heat a much bigger volume than that.

I have built a few small HT forges using a burner based on a 1/2" Amal atmospheric injector. Intended as a cheap way to get good temperature control for a knifemaker on a budget. I used a 20" piece of 10" pipe, lined with 1" of blanket and with disks of 1" board for the ends, giving around 900 cu in. Everything got a wash of china clay in a solution of Sodium Silicate and water  because it was cheap, immobilized the surface fibres and the forge was not going to get hot enough to melt the Sodium Silicate (it melts at about 1100 degC-ish, around 2000 degF). 

It will hold HT temperatures to within a couple of degrees for plenty long enough to soak O1 and similar steels once it is adjusted. The adjustment is by the knurled portion which is threaded into the injector body and has a pipe thread the same size as the burner tube. This gives superfine adjustment of the mixture and therefore the temperature. The burner has a flame retention cup made from a short (1") length of 3/4" pipe welded flush with the end of the 1/2" pipe and a 3" length of 1" pipe slid on and welded to it.

Target temperature when the photo was taken was 800 degC (1472 degF). It was actually running at 801 degC (1474 degF).

I was trying to make a smaller version of the Don Fogg 55-gallon drum HT forge. It wouldn't work for me at all until I turned it over, putting the burner port at the top and the work/exhaust port at the bottom.

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