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The new forge

2012-06-20 , ,

I built a forge out of a scavenged refrigerant canister. It works! Here’s my first effort, a 1/2” steel bar drawn, scrolled, and twisted.

The construction of the shell was simple. First, I holed the empty canister with a large punch and filled it with water (the MSDS read that the old contents were non-flammable, but better safe than sorry), then cut the opening with an angle grinder fitted with a cutting wheel and trimmed the cut with aviation shears and snips. Next, I brazed on two pieces of bed frame angle iron and two flat sections to make legs. The burner support is a hand drilled and tapped 4” x 2 1/2” threaded pipe nipple held to the forge body with a pair of thin collar nuts. If I do this again, I’ll need a better method as the grinder is sloppy on curves and the shears barely make it through the steel. A drill press would also have made for easier going on the burner support, I improvised a U-shaped wooden jig and clamped the whole thing in the vise.

The lining was applied in layers. I lined the shell with 1” 8# Inswool 2400dF refractory blanket. I wanted it to fill in so I used the exterior circumference (c=Π*d, see how that middle school geometry is useful?) plus a half inch over and the full, untapered length of the cylinder for my measurements. The ceramic blanket was easy to cut and I misted it with water to keep the dust down but I misjudged how hard it was to work with it in a tight space. I had planned to roll it up, slip it in, and let it unroll and expand but I had to cut it into three pieces to get it to fit without crushing. I cut a tapered hole for the burner flare and later I stuffed some scrap into the collar around the mounted burner to seal it. The second layer is roughly 1 1/2” of Kast-o-lite 3000dF castable refractory applied in two layers. I mixed up six pounds of it a little thinner than indicated and applied it by hand to the wetted ceramic blanket, let it dry a few days, fired the forge for a few minutes then followed the next day with another six pounds. I paid attention to making a cone for the burner. After letting the refractory cure for a few days, I fired the forge to full heat and let it cool overnight. The last layer is a thin coat of Plistix 900F, a refractory service coating that is good to 3400dF and supposedly improves the efficiency of the forge due to reflecting IR. I mixed roughly a pound of it to a thin consistency and dabbed it on with an old paint brush. It went on like a chalky, slightly gritty, thin white paint.

The insulation works fairly well. After forty-five minutes the exterior of the forge is uncomfortably warm but not painfully hot. The burner holder gets just less than searing hot where it enters the shell and the pipe collar does not show discoloring yet.

Forge in operation and tuned. Nice blue flame.

The dragon’s breath and a look into the hot forge

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