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View Full Version : High temp salt tanks.Need help



son of liberty
12-10-2010, 06:09 PM
Ok I have a few questions for toughs of you using these. Im looking at building one but cant decide if I want to go with gas or electric heat. My plan is that if I go with gas ill build it much like a round forge on end with a PID controlled gas valve, pretty much the same if I go with electric only ill line it with soft brick and run the coil around the inside. As it stands now gas is winning but I just don't have enough experience to make a wise decision as to effectiveness.

Quench will be the same as always , oil tank with a manual burner to bring the heat up. From what I have been reading the greatest benefits of salt tanks are not in the low temp and if I can get away with using just one tank I would like that.


Any help would be appreciated greatly

son of liberty
12-10-2010, 06:32 PM
As Normal I read more and get a bit scared, I think what im going to do is build it with gas but try it without salts for a bit until I feel brave enough to put salts in it. If I use a Thermocouple and a PID inside the pipe I should be able to hold and regulate a consistent temperature. Anyone got anything to add?

EdCaffreyMS
12-10-2010, 09:29 PM
My opinion is that gas (propane) is the way to go for salt tanks. Electric can work, but in my experience electric heated salt tanks take MUCH longer to heat up, and have much wider swings in temp that gas with everything else being the same. One of the most important things to realize about salt tanks is that the smaller you can keep the actual salt vessel, the more accurate the temps and the less "swing" you will experience. For example, my salt vessel is 2" ID X 20" long (deep)...I built the tank taking into consideration the largest blades I planned to us it on. What your dealing with when the salts are in there liquid state is thermal mass. The larger that thermal mass is, the more likley you will experience wider swings in temp from the set point.
I think it's very important that you place a steel rod in the tank while the salts are in their liquid state, and allow the salts to cool down with the rod in place. This rod will transmit heat the next time you "fire up" the salt tank, making the area directly around the rod melt before the rest of the salts. Since salts expand greatly when heated, it will be a "pressure release". Without something of that nature there is a good chance that if your burner is at the bottom of the tank (which I believe is the best method), the salts at the bottom of the tank will melt, expand, and create a "mortar". I have actually seen two shops where this occurred. Thankfully nobody was injured, but in both cases the roof of the shops had to be patched/repaired.
If you've not seen it yet, I have a page on my website with salt tank information. (http://www.caffreyknives.net/bsteel.htm)

By taking the time to think things through, and keeping a respect for them, salts tanks can be a valuable addition to your shop.

Kevin R. Cashen
12-11-2010, 09:33 AM
Thank you Ed for taking the time in include the paragraph on safety with this equipment, now I don't have to spend as much time on it. I will no longer dispense advice about salt baths if the receiver is not entirely willing to put up with the safety lecture as well. No other piece of equipment has had people scaring me with their approaches like salt baths. That is not to say that you have displayed anything less than the appropriate caution Mr. Liberty, but too often I have had people tell me they are done building their salt baths and now want to know what they are and how they run:what!: This is like saying they just finished their nuclear reactor and want to know if they should dump in the uranium or plutonium that they managed to buy!

Be certain to obtain the appropriate salts, and go gas. I have several pages of horror stories about electric with high temp salts, but if they don't' scare people enough I simply pull out my list of how much hurt the electric route can continuously put on your wallet and that is usually does it. Gas is faster, more accurate, cheaper to run, easier to build, and far more durable, but it does add an extra "kaboom" factor the equation, so please be safe study up and know exactly what you are building and why. I say why because salts are not for everybody, nor are they necessary to make knives but there are certain luxuries they can provide, if those benefits outweigh the hassles and hazards then salts can be handy, otherwise a good oven is by far the most common approach.

son of liberty
12-11-2010, 10:14 AM
I have seen some pictures of the mistakes some have made and it out right scares me. I would like to think I have the sense enough to give them the respect they deserve but I have also been guilty of a bone head mistake from time to time and im sure not above doing it again.

At this point I think ill build the assembly but use it without salts as sort of a temperature controlled forge with the vessel that would hold the salt instead, just being a tube to put the blade in and hang while it heats. should provide an even heat through the tube and when I feel that its time I can replace the vessel and fill it with salt.

EdCaffreyMS
12-11-2010, 10:37 AM
If your going to do that, and I am envisioning it correctly (vertical orientation, with the open end of the "tank" facing upward) there are couple of things to remember/consider. The open end of the pipe will be facing up. Heat ALWAYS travels in an upward direction, and your method of heat transfer is air rather than a liquid (the melted salts). Next, if you place the blade into the tank with the tip facing down (which is what most would do), you have a number of factors working against you.....air is poor conductor of heat compared to liquid, the open end being up will allow the heat to escape much more rapidly than if it were in a horizontal position (such as placing "pipe" horizontally in a forge), and the the ricasso/tang area will have more mass....but that will be towards the open end of the tank, which means it will heat up slower than the rest of the blade, and since there is much more heat escaping the open end of the tank, I suspect you will see 1/2 of the blade (middle to tip) getting to temp much quicker than the ricasso/tang area. In short, without the liquid salts in the tank, I think you will see very uneven heating. I can understand your trepidation about the salts, but I don't think that an empty tank is going to perform like you're anticipating. If your not going to use actual salts, I believe it would be simpler, and more effective to place a pipe horizontally through your forge and go that route....I believe it will yield better results, with much less cost/effort than a "salt tank" setup with no salts in the tank.

son of liberty
12-11-2010, 10:51 AM
What about temperature regulation, should I eye ball it or should I put the PID in the forge and use it when im heat treating placing the thermocouple in the pipe? I was hoping to really be able to get some soak times on the steel with a bit of consistency.



Man thanks guy you are a great help!

EdCaffreyMS
12-11-2010, 02:25 PM
You're not going to get very good temp regulation with an empty tank...that's a simple fact of air being a poor conductor of heat. The fact that the end of the tank will be open, and that is generally where people insert the thermocouple, will magnify the issue.

I understand what your trying to do, but IF the tank does not contain liquid, there is going to be a HUGE different in the accuracy and how well the whole system works. Like I said before, I think you would be better off by placing a pipe through your forge, and using it in the same manner.

son of liberty
12-11-2010, 05:28 PM
Thanks man, I greatly appreciate the help and will fallow your advice.

son of liberty
02-14-2011, 08:40 PM
Quick question, what salts are you using in your high temp tank and what salts in your low temp tank?

son of liberty
02-15-2011, 01:15 PM
Another question, Is it better to use schedule 80 pipe with a welded seam, or 40 that is seamless?