Low temp salt options?

NickWheeler

NickWheeler

Joined
Dec 3, 1999
Messages
9,437
Hey Guys-

I was going to get a gas thermostat and build a pipe burner for my low temp salt (burner under a "pan").

But I'd like to keep it as simple as possible...so I went to Wal-Mart. They have a hot-plate burner for $15 (the type like those on a stove top), and I'm wondering if I can't just use a Brownell's heat-treat thermometer and that burner under a pan for the salt.

What do you guys out there have set-up?

Thanks :)
Nick
 
I dont see why that wouldnt work fine. I use a propane coleman cook stove with Brownells Nitre blueing salts and a Brownells thermometer. Once it gets to desired temp I simply adjust the flame. Why wouldnt an electric 2 burner work just as well?
 
I use a 1000 watt electric hot plate with an adjustable temperature control with a stainless pot, Brownells Nitre blue, and a thermometer. Once you get used to it and get the heat where you want it, it will maintain temperature for hours with only a couple of degrees of temperature shift.

I austemper all the time with a rig like this and have held temperature for over 20 hours. I like it 'cause it's cheap, small, and relatively safe as there are no open flames to worry about. You can expand the temperature control by using electric fry pan controllers and using the thermometer to calibrate the whole deal. I use a stainless tray for quenching blades into and a deeper, taller pot to heat color fittings and stuff.

Brian
 
Great post, Nick. I have been wodering about similar things. I was thinking the cast iron propane burners in Harbor Freight's catalog would be a cheap and accurate way to deal with low temp salts.

Is there a danger of "open flame" with low temp salts? Are they flammable?

Thanks,

John
 
Michael, We are heat-treating carbon steel blades in 1500 deg. salt (Barium Cloride) or sometimes called "liquid heat" and tempering in a low temp salt (Brownells Nitre Blue) There are real advantages like very little warpage, no scale, no overheating and grain growth, very clean and consistant results although a bit hard to understand for me. I like it better though. Paul Bos used to do blades this way before California EPA. The high heat salts are dangerous because of blow back if water comes in contact with it. Even a damp blade will cause molten salt to shoot in the air and land on your head!

Galloglas, I didnt think we could use a stainless tray with nitre-blue? I read the instructions and made a mild steel tray. Does stainless work? Thanks for the interesting input about the electric method. It should be easier to regulate. Why couldnt I just use an electric skillet or maybe one of those fry baby deep fryers? I wonder how hot they get?
 
For low temp salts I have never had a problem using stainless. I don't use a high temp. Salt rig as I don't have room but most of the guys I know who use high temp. salt use stainless tubes for containment.

The deep fryer concept for low temp. salt works if you modify the the temperature regulation circuit of the electic frypan...like displace the temperature sensor to make the fry pan run a little hotter than it is designed for. All of the fry pans I have come across only go to 550f which is plenty for austempering/martempering but most of the cool heat colors start at 550 and up. I *really* like the deep blue/purple you get at around 575f and the traditional blue comes at around near 600f.

Being an electronics tech by trade I have no problem adding resistors and stuff to the circuitry to get it to run a little hotter but caution others to be very careful about this kind of experimentation. Obviously the manufacturer of these devices never intended this kind of use and the user assumes all risk of fire or shock from "playing" with the circuitry.

The hot plate with a thermometer is simplicity itself and very safe if you keep combustibles away from the rig. Hot salt is a tremendous oxidizer and will drive a fire to uncontrollable very quickly. Never allow paper or wood or other things to burn up and accumulate in the salt as this will add carbon to the solution...and now you have salt peter and carbon in a pot which is two out of the three ingredients to gun powder. Add a rapid combustible like sulfer and it could go "boom".

Brian
 
Brian,
I have been thinking that I could get a stainless tube and weld a plate to seal the end. Then wrap the tube with the 'covered heater wire'(saw it somewhere, can't remember where). Insoluate with Kwool and add an outside cover. With a temp control unit I could have a low temp salt pot.
Does that sound reasonable? Is it something that an electrical dummy (but a cautious one) could do? How hot could it be made? That is would it be feasable for a high temp salt?
Lots of dumb questions, I know! Let me know where I'm going wrong.
Thanks lots, Lynn
 
Wow, thanks for all the replies! :)

I really like the simplicity of the hot-plate, but I'm wondering how long of a tank you can have with good results. I'm sure a small tank for small blade quenching and small part bluing would work great, but I'd really like to quench 52100 camp knives in the salt as well...this proposes 2 big problems: 1.) blade length proportionate to the tank length, and 2.) the temperature displacement that a blade with that much thermal mass is going to cause.

When I got my hoses made at the propane shop I checked out their camping stove tops. Those are basically a wrap around pipe burner, and would be really easy to make (or so I think).

I did notice Wal-Mart was SUPPOSED to have a double element hot plate. It has a 650 watt element and a 1000 watt element. I wonder how well this would work? I suppose for $25 it would be a pretty cheap experiment.

Thanks so much everybody :D
Nick
 
My old electric 2 burner hot plate got really hot and would have worked before the High burner got left on for a couple days and burnt out.

I have trouble telling how hot my hot salts are. The barium cloride burns the thermocouple up. I used a $40 ceramic tube an slid the thermocouple down into it and it worked but read under what actual temp was. ThenI leaned on it an it broke. I figure it read about 100 deg cooler. Is there a chemical proof probe? How are you guys judging temp in your hot salts? I need to maintain 1450-1500 deg for desired results.
 
Hey Bruce-

On Don Fogg's recomendation I bought a thermocouple from South Eastern Heaters, it's their Alloy 600 model. It's rated for volatile situations. Don said he really extends the life of the probe by crimping one end of a ss tube, creating a sleeve or "sheath" for the probe.

I'm hoping I can get up to Boeing Surplus and buy a piece of thin inconnel tube...that would last a VERY long time.

I'll try to get some pictures of my high temp salt rig Bruce, it's looking pretty decent. I made it so that it's totally self contained, so I can move it around the shop, and take it to hammer-ins and such.

John, I don't know about HF's cast iron units, I'll have to look into that. I know that their $16 weed-burner is a great example of venturi burner construction. My friend Tom Ferry heats his nitre salts with one of those burners set up underneath a Brownell's nitre salt pan.

Nick
 
Nick,

I just checked Brownell's site. Their tank is 40" long so should be good for all but the longest swords. A 52100 camp knife would be no problem.

As for thermal mass/heat conducting, etc., my understanding is that salts are a superior conductor and would bring just about anything down to an acceptable temperature rapidly and evenly. Again, the Brownell's tank, being 6"x6" by 40" is much like the long SS pipes into which many sword makers quench with no problems. Check out the 2 and 3 burner propane "stoves" at HF, they are reasonable priced, have a very simple/open design, and would provide adjustable and even heat over the length of a 40" tank.

Thanks for starting this Nick. You made me realize that I can get the salts, tank, and thermometer from Brownells for just over $100. High temp salts will have to wait till I move back to the Best Coast (I'm temporarily stuck on the Least Coast) this summer. BTW, is your high temp rig essentially a Don Fogg style forge with a SS tube inserted in the top?

John
 
Hi Lynn,

All of the guys that I know who are using hi temp salt pots use gas to heat it. I know of guys who have turned a heat treat oven on its back and put a stainless tube of salt into it for heating but had a lot of problems with getting burned out elements and stuff. Seems the salt (the high temp stuff) is a pretty fair conductor of electricity and this factor makes the use of electric ovens and high temp. salt kind of mutually exclusive. Kevin Cashen used electric heat for some time before going to gas fired salt rigs and will never go back as he had some severely bad luck with electricity and high temp salt. I’m not saying it can’t be done as I know it can be (I have done it) but high temp salt is a *very* scary thing if you are not extremely careful. Salt in the elements can get you shocked as well as burned so bad you can’t believe it. I really recommend making a propane fired, stainless tubed vertical high temp. rig. I really doubt that you will be able to get the temp. high enough with the scenareo that you are proposing and I feel that you are at risk for shock and/or fire hazard problems.

Nic, I have a stainless tray that is about 18” long X 6” wide and about 4” deep that I use for austempering/martempering of 5160, and O-1. It is heated to 475f to 550f by two 1000 watt hot plates and when set up will maintain temp. for up to 20 hours with very little temperature drift. When I quench a large blade the temp of this pot will go from about 500 to maybe 510 or 512 and then slowly settle back to 500 over about 10 or 15 minutes. This is no big deal when martempering as we only want to equalize the temperature at a point above the martensite start point of about 450f. But it can be a big deal when austempering as we like to keep the temp real close to the hold temp with as little variation as possible. A bigger quench tank is thermally more stable in that it has more mass and it will take more to raise or lower the temperature significantly.

I have not tried it but Brownells makes steel half tanks for chemical bluing that are fairly large. I’m certain that they could be heated with hot plates to 500+ and provide a more thermally stable and larger quench tank if that is what you need. This is a cheap option and I'm sure it would work well for marquenching/austempering blades.

Bruce, try www.omega.com for iconel thermocouples and controllers as they are the best for this kind of equipment and have some knowledgeable people to help you selest the right stuff.

Brian
 
Wow, this thread has generated a lot of information for me, thanks!!!

Yep John, my high temp rig is similar to Don's. I had never seen a digitally controlled salt furnace, so thank goodness for fellas like Don, Kevin Cashen and Mike Starling for all the info they put on their sites.

I can highly recommend the people at Omega. I spoke with an Engineering tech there (Frank) and he was very helpfull and easy-going. The only reason I opted to not order from them was because South Eastern Heaters sells a "Don Fogg special" which is the controller, thermocouple, and an R.C. suppressor.

I knew this set-up had been proven to work, so I went with it.

Thanks for the heads up on HF John :) I actually found one of their flyers after reading your earlier post and had found those stove tops. For $20 you can buy a two burner unit, that's cheap!

I didn't word my post above very well. What I was concerned with was how long of a tank I could get away with compared to the burner size. Meaning a single burner plate wouldn't heat a very long tank of salt. I'm sure a double burner would do very nicely just as Brian has reassured me (thanks Brian!)

So Brian, how thick is the metal that your quench tank/tray is made of? I have a piece of rectangular tubing that should work well with some caps welded on the ends and one side cut away. Thanks for your explanation, you nailed the answer to my question.

Thanks again everyone!!! :)
Nick
 
Wow Nick!
The crimped stainless steel tubing would work pretty darn good as a thermowell. Do you know what type thermocouple you guys are using? J? K? I am going to search for a good TC that is sealed or a thermowell that will hold up to a harsh corrosive environment. I will let folks know what I am able to come up with.

This is an excellent post!

C Wilkins
 
This is a great thread.

Nick, what does the entire "Don Fogg special" run pricewise? And are you using a venturi burner or forced air?

John
 
Originally posted by NickWheeler

So Brian, how thick is the metal that your quench tank/tray is made of? I have a piece of rectangular tubing that should work well with some caps welded on the ends and one side cut away. Thanks for your explanation, you nailed the answer to my question.

Thanks again everyone!!! :)
Nick
Click to expand...

The stainless tray I use is actually a tray like they would set out at a buffet table for silverware and stuff. So, it is rather thin walled. I mostly experiment with austempering small blades and send stuff larger than 6" or so out for heat treat when I can find guys who will cater to my madness and use my recipe for the blade. :D

When I finish the latest sword I am working on now it will be sold to provide some more sophisticated hi temp stuff (digital controlled oven) and a mill. But for the short term I am stuck with my *very* small shop and will have to send all blades longer than 18" out for heat treat...there just isn't room for bigger stuff.

But the stainless trays and deep pots have worked well for low temp. salt and I will probably continue to use a variation of them for as long as I continue to make sharp pointy things. I have never quenched blades in oil or water except as an experiment and austempering is my primary hardening method for small blades or swords.

Brian
 
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