Controls

The controls for these gas fired salt pots are pretty simple. Gas is brought from the supply through a hand valve to a low pressure regulator and to a solenoid valve and on to a regulator for the high pressure side for the high temperature pot. In the case of the low temperature pot, the regulated high pressure and low pressure lines go to different burners as explained in the previous section.

Electronic Temperature Controller

Electronic temperature controllers are now widely available. There are a range of capabilities and output types. We very much like the ones with PID control as they tend to move faster toward the desired temperature with less initial overshoot. We also like the controllers that have relays at the outputs that can switch 110V. Makes the wiring easier. Do make sure that you get a controller with adequate range for the high temperature pot. A three digit controller is not enough!

If you are patient, eBay has been a good source of controllers over the last two years. We bought two Omron PID controllers with all the bells and whistles for $140. Both were new and came up running just fine. Search for "Omron" or "temperature controller."

If you don't have the time to scounge around for the part and pieces ... they're all available from MSC.

When you lay out your controls it is wise to remember that these things are most often used when there is some reason to get at them quickly. Mike Alexander's experience in operating manufacturing units shows in this clean and useful presentation. (Sorry about the pic ... I'll replace it with a better one.)

Using the Pots

We do mostly carbon steel and damascus, but have now done rather a few ATS-34 knives as well. Mike Alexander's pattern is as follows:

1) 15 minutes at 1950F in the high temp pot.

2) Immediately into the low pot at 400F for 15 minutes.

3) 8 hours in liquid nitrogen

4) Two draws at 400F for 1 hour each. Yields 61 Rockwell C hardness, and is supposed to be more stain resistant and tougher than an air quench and draw at 900F. This a little softer than D. Holder's blades (last 4 we had done were RC 62.1, 62.3, 61.4, and 62.3). However, knives hardened with Mike's technique are the tough that we see in blades treated by Paul Bos.

So far, users have not had any complaints with them. I asked one of my customers how he'd fared sharpening the knife ... he said he hadn't needed to. So I asked (rather suprizedly) "Haven't been using it? He responded: "Yup, field dressed five deer with it this year ... don't need to sharpen it though." (I was much relieved!)

No Scaling or Warping

We've seen no scaling or warping of blades hardened in the salt pots. Some practical pointers though:

1) Blades must be DRY when they are placed in the high temperature pot. Introduction of any moisture into a 1500F to 2000F environment gets very exciting!

2) Blades MUST be oil free when placed in the high temperature pot. Any carbon bearing material is instantly flashed off and it leaves tracks for later on ... seems to burn away a layer of surface steel.

3) Believe it or not, you have to agitate the blade upon placement in the cold pot to assure rapid enough cooling. Our first attempts at doing simple carbon steels were not successful because the rate of temperature drop was not high enough.

4) Blades can be taken to quite a high polish before they are heat treated, and clean back to that same polish in a jiffy.

Last Warning

Before you take on this for yourself, remember that D. Holder only charges $5 a blade to do a nice job. If you REALLY have to do it yourself ... do NOT construct these things on the "completely cheap." Use good materials for the containment vessel, good controls, and layout of the controls. Molten salts (from 350F to 2100F) are amazingly vile and dangerous materials. The introduction of water into a hot pot results in instantaneous vaporization and a resulting steam explosion that projects molten salt where ever it wants to go!

Molten salt does TERRIBLE damage to people.

Overheating of low temperature salts can cause oxidixer explosions!

Salt pots must be used will all due care and caution. As we CANNOT control the manufacture or use of this design, you're on your own and we CANNOT accept ANY liability whatever!