-Salt Tanks-
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These are the controls for my high & low temperature salt tanks. Salt tanks provide
accurate, oxygen free heating environments, eliminating variables and iron oxide, meaning that work
can be nearly finished before heat treating, and very predictably hardened, quenched & tempered. The digital
controllers receive input from thermocouples installed in thermocouple wells into the salt
tanks. They turn solenoid valves on and off as necessary, and have an algorithmical approach
to figuring out how the temperature responds. They're pretty amazing- I can simply dial in the
temperature I wish to heat at and off they go. And they can go off! You can read about the
pitfalls of all this convenience below.
I am using the Omron E5CN with the relay option to open and close the 12v solenoid valves. It will cruise the temperatures to within about 10 Degrees F. With the two valves on each line I can run the tanks manually, set a high burn and a low burn or simply fuel on and fuel off. |
 | These are my high & low
temp salt tanks for hardening, quenching and tempering blades. They are digitally controlled
and gas fired. The high temperature tank is comprised of a stainless
steel tube in order to resist the accelerated rusting which the salt produces. My salts are a 50 / 50 mix of sodium chloride and
calcium chloride- both cheap and effective. There are thermowells protruding into the tanks from
the bottom that hold 14" thermocouples. They measure the temperature
of the tanks and send that information to the digital temperature
controllers which open and close the 12v solenoid valves which in turn regulate the propane. The
propane is self-igniting at working temperatures in the high temperature tank. The low temperature
salt tank requires an electric ignition- I am using a
Carlin 41000,
which is a burner transformer for oil-burning heating systems. It turns on and off with the gas
solenoid.
Surrounding the stainless steel tube which holds the high temperature salt is a 14" diameter 3/8" thick pipe lined with Inswool and coated with an undercoat of Satanite and an overcoat of ITC-100. Satanite is a mortar refractory which is hard and stable; ITC-100 is a refractory meant for kiln walls which reflects heat very efficiently. The burners are based on Ron Reil's design. I had to use the 2" bell reducer and the Tweco Tip with an orifice of .035, and the Zoeller Flare to really get the burners up to temp. There are two so I can heat the top of the tank first, as the salts expand greatly when they melt and using the bottom burner exclusively would create a monster pipe-bomb. You can, should you so choose, drop a long tapered rod into the tank when you're done using it, and before the salts solidify. It will prevent blowouts on refiring by conducting heat and relieving pressure, so they say. The other exciting salt-tank risk results from introducing a blade with as little as a drop of water or oil on it. At 1500 F. degrees, one drop of water becomes three cubic feet of steam well nigh instantly, and your salt tank becomes a hot, molten salt-cannon. Neat! The exhaust port behind the tank is a 3" elbow that rises into the 4" stove pipe. The draft of the heating chamber gasses pulls additional air over the actual molten salts and effectively vents the fumes, which can otherwise rust damn near everything in your shop. The low temperature tank runs from 400 - 600F and can be used to quench as well as temper. It's so convenient, in fact, that I'm willing to risk the hygroscopic and self-oxidizing qualities the low temperature salts can exhibit... |