Tips & Techniques - Low-Temp Salt Pots

The design criteria for a low temp pot are:

(1) something that can take temperatures of 600F without problems;
(2) something that can accommodate an electric hot-water heating element; and
(3) something with a decent volume and a large enough diameter to control foaming while still being long enough to handle your longest blades.

Less critical but desirable characteristics are robustness and/or corrosion resistance, repairability, and electrical safety (hmmm...maybe the last one ought to be moved up in priority a bit)

My low temp pot consists of an old steel SCUBA tank - but fire extinguisher bottles can also be used.  I originally used a 4" diameter pipe but found that the salt will foam and run over the edge. By going to a larger diameter (~8"), that problem vanished.  Another advantage of the SCUBA tank is that the heating element threads into the value seat.

At the top of the tank, I fabricated a steel box (1/4" plate) to handle boil-overs. While this turned out not to be needed for that purpose, it does allow the use of cross-bars (see the notches in the edge) that extend over the tank and let me hang blades on wires. The top also has a handle (with a rotating piece of pipe as the grip - more on this below).

The tank is bolted (not welded) to a heavy base made of a chunk of I-beam (8" tall x ~12" long) with a hole blown in the web. It also has a handle attached.

You can see from the photo to the right how the element is wired (very carefully). Salt and electricity is not a good mix, so use a copper washer and high-temp RTV gasket materials to get a good seal. Also expect to replace the element from time to time. On of the reasons I bolted the tank in place was to make getting a wrench on the element a whole lot easier. I also used underground cable and made sure that there was a positive ground from the three-prong plug to the base of the unit.

Surrounding the tank is a layer of fiberglass insulation (the pink stuff) held in place be a sleeve of thin roofing metal and a couple of radiator clamps.

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I use Nitre Blue Bluing Salts (Cat # 082-090-020) from Brownell's. The salts have a temp range which nicely handles what I need but they are extremely corrosive and hydroscopic - leave some out in Florida, and in a few minutes you have a pool of corrosion.

Auxiliary equipment is shown to the right and explained in the description of the heat-treat in the page you just left.