Hi there. I think the answer to your problem may be dependent on a few different things. I built my salt pot based on Ed Caffrey's design and the info he has on his website. It includes a vent on the lid along with a gas rated solenoid. Personally, I wouldn't want to do it without the solenoid. I also have valves that I can shut so I have some more control over the situation. I also ended up using the potassium chloride. And yes, if you look at the data sheet, it begins solidifying a little over 1400 F, but it has a much higher working temp, too. All trade-offs, I suppose.

In specific regard to the salts not cooling faster.... I don't know what your setup is, exactly, so please only take what I'm saying with a grain of salt. These things can be dangerous if not approached carefully, built safely, and used appropriately. I'm assuming you have the salts in a stainless tube in the middle of a vertical forge? What's the diameter of the tube, wall thickness, and the distance from the outer edge of the tube to interior of the forge? All these things matter and will effect what you're experiencing. Imagine the same burner in these two situations: 2" I.D. tube with 1/8" wall thickness, and the edge of it being 2" from the interior edge of the forge. Second, a 2" I.D. tube with 3/8" wall thickness, and the outer edge being 9" from the interior of the forge.

That same flame will heat the contents of those tubes in very different ways. And after the burner turns off, the temp of the contents will do some very different things. So, your design and the materials used (if its at all of the design I'm describing) will help determine how quickly the salts heat up and cool down. For instance, I have a friend who ended up with a stainless tube something like 3/4" thick wall (lucky dog....). That tube may take longer to transfer the heat to his salts, but the thick walled tube helps hold that heat and he has very little temp fluctuation when his target temp is set. You'll pretty well always have some degree of temp swing because even though the burner shuts off, there's all that heat in there and everything's on the way up, as that tube has heat left that it's transferring to the salts. It will continue up some before topping out and then falling. Then, when the burner comes back on, it'll keep falling until the burner has built up enough heat inside for the tube to gain more temp that then gets transferred to the salts and it all starts over again. The nice thing with a thermocouple and solenoid is everything can be programmed in and the gas shuts off then back on and you bounce between those known temps (above and below target). I hope that all makes some sense....

You mentioned turning the burner on and getting a boom and not wanting to have the lid blow off. Again, I don't know what your design looks like, but I'd take a look at how your forge is designed. If you end up with too much propane in the forge before it finally lights...then "exciting" times could be ahead... But if the interior of the forge is hot and there's no gas (shut off), I'm not sure why it would be worse waiting longer for the temp to fall before turning the gas back on? It should reignite right away because of the hot forge interior and not get that boom?

I hope things work out for you with this. There are some really really smart people on here with a lot of experience with salt pots. Hopefully some will come give there two cents. Hit them up and be sure you have everything figured out well. These can be SO good for helping with proper austenizing temps, even heating, no oxidation, etc. But, they certainly require due caution. Sorry for all the safety "stuff"-you may likely be doing great already, but just in case someone reads this that doesn't get understand...

Jeremy

Hi Jesse!

Jeremy laid it all pretty well. Based on what I read in your post, it frightens me that you don't have some type of "control" on the salt tank. You mentioned getting distracted....that can spell serious trouble. I highly encourage you to set up a PID temp controller with a thermocouple. The way it is, you're taking too many chances with something that could seriously injure or kill you!

The major factor in heat up and cool down rates with salt tanks is all about the thermal mass. That mass being the tank itself, and the salts it contains. Its a lot like heating a large chunk of steel in the forge..... the mass determines how long it takes to heat to a given point, and also how quickly it will cool down. Applying that thinking to a salt tank... the bigger the mass of salt and tank..... the more likely you are to have "undershoot" and "overshoot" of desired temps. With that in mind, I always recommend that you build the tank with a ID of the widest blade(s) you generally do. Personally, the tank I use is 2"ID, 316 SS, 5/16" wall X 16" long.

If you apply a blown burner, the "cold" air coming in when the flame is off will cool the salts down quicker....but it will also usually cause the temp to fall far below where you want it. Then, once the burner is ignited again, its going to likely overshoot. SOMETIME you can anticipate the "lag", but its always a guessing game, and always requires YOU FULL, UNDIVIDED ATTENTION.

For about $100 you can get a PID, thermocouple, and a gas valve. It stil won't be "perfect", but if you're wise about how you setup the PID to turn the flame on and off, you can usually keep the temp within 10-20 degrees on the up side, and 25-50 degrees on the downside. And when you have those moments of distraction, you're risk of something seriously bad happening is dramatically reduced.

Jeremy, Thank you for that extensive trouble shooting. Im not at home to measure just now but i know it's a2 inch I.D 316 stainless tube but only 3/16 wall. 18 inch long set in a12 inch diameter vertical forge with 2 inch ceramic wool. I'll have to go check what the dimension of the exhaust port is.

Ed, I'm embarrassed to say that i have had the pid and solenoid and a stack of thermo couples for going on six months now, just workings away from home then only getting a couple hours a weekend to "play" in my shop as my wife would say, i always tend towards working on another blade instead of doing things i maybe should. As far as the getting distracted, i should qualify that. I'm not turning it on and going to watch a movie or anything, I'm pretty diligent cuzi obviously don't want to ruin all my hard workor burn the shop down, the worst thing so far has been over heating the tank by 100 degrees out so. But i do hear where your coming from and i think i will make the assembly of this a priority. I'm just on lunch now and trying to write this ad quick as can on my phone, I'm gonna come back to this after work on my computer and see if I've missed anything. Thank you guys for the speedy and informative responses. Becoming a forum member is paying off already.

hi again.

so Ed would you suggest that 3/16 is a little too light of wall thickness for 2 inch by 18? I am currently using a one inch t-rex venturi to heat it up, is that maybe too much i wonder as well? it seems like i have to crank the psi down to a trickle and almost close the choke to keep the salt near the temp i want, and i thought about it all day at work that that could be contributing to the frightening re firings. Not enough air flow to push the fuel and so it just settles in slowly?? am i way off base with that? the only functioning of these ive seen is nick wheelers on his youtube vids and when his kicks on it sounds like its going more full bore that mine. also i apologize if my "going to watch a movie" comment came off as defensive or snarky. i re read the thread when i got home and it rubbed me wrong. I do want you to know that i dont approach this method lightly and i take every precaution in ppe and fire suppresion. I fully respect the destructive power inherent in contained volatile molten substances, and I appreciate any and all the help I can get.

Jesse Bartram

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