Tabletop kiln for small salt pot?

[the possum]

Hey there, guys. I could use your input on something.

I have wanted to set up a small salt pot for heat treating, for a long time. The primary reason I want to go this route, is because I make miniature knives. Tips get needle sharp so it's very easy to overheat them with a torch. Decarb and scale are a real concern, since even polishing it off can change the fit of parts (like the lock of a folder, for example). I can't start with hardened steel since I do nearly all the shaping with a hacksaw and files, and tiny drills.

Basically, I want to have better control of the process with tiny pieces, and from reading about this stuff for like 10 years, I still think salt sounds like it would give the best results.

I was looking for some crucibles on Amazon for melting silver, and came across this:
https://www.amazon.com/Tabletop-Fur...&ie=UTF8&qid=1496944348&sr=1-30&keywords=kiln

The gears in my mind started churnin'. I haven't researched these in depth yet, and there's a bunch of other types and models, but I like the small size, and the idea of being able to punch in a precise temperature and hold it. Plus, the cost is reasonable & I wouldn't have to build something or spend hours on research to make sure I was doing so safely- I could happily spend the shop time on other stuff.

I believe this one uses electric coils for heat (not induction), and I'm aware of the risks burning it out if molten salt spills down inside. It comes with a graphite crucible though. Can graphite safely hold molten salt? Or would it break down? If graphite's a no-go, do you see any reason I couldn't just put a stainless flask in there instead?

In the past I had considered the Evenheat Oven salt pots Tim Zowada sells, but the smallest is 9" deep, which is about double what I need, and the $1300 price tag put me off as well.

 

[Stacy E. Apelt - Bladesmith]

That is a melting pot for casting, not a salt pot. I don't think it wouldt last long as a salt pot.

What does work well is taking a small pottery kiln and making a hole in the lid for a salt tube to go through. Have the tube come about 4" above the kiln lid. The heavy walled stainless tubes can be purchased from several sources, or made up by a welding shop.

I suspect from your description, you want to do smaller carbon steel blades and other small parts. A converted pottery kiln will do this well. Just add a PID controller and SSR and you will be able to enter a number and let the machine do the rest.

These kilns are often available for almost nothing ... sometimes free. The small ones can be either floor or tabletop units, and the large ones will be floor models. The larger ones can often hold a 24" salt pot.

An even better setup is to make two small salt pots and have one for the high temp salts and the other for low temp salts for the quench (marquenching), tempering, and for heat bluing. It is an identical setup as the high temp pot.

Some tips for those considering this:
Use as heavy a tube as you can get.
Make a tight fitting cap to cover it when cooled and not in use. The salts will soak up atmospheric moisture if not closed tight.
Weld a small collar on the tube that is just below the rim. It should extend 3" out from the tube. Make some larger drip plates that will slip over the tube and sit on the smaller rim. The larger plate catches the drips and gives a place to clamp the TC. After a HT, you can remove it and wash the drips off. It can be mild steel, but stainless will last longer. I would suggest that the drip plates have a diameter of the tube size plus 12" ( that would usually be about 16"). The center hole should be 1/4" wider than the tube diameter. Many of the online metal suppliers will cut these donut plates for you for a very low price. ( also a great way to get perfect fitting forge ends for round forges)
Check pawn shops, trader papers, Craig's list, etc. for pottery kilns. Also check with the folks at local pottery shops and craft centers. They may know of someone who is selling or giving away one.

The plus on doing this is perfect heating with NO overheating, no decarb, clean blades that need very little cleanup ( allowing thinner blades to be done), and reduced or eliminated warp.

 

[the possum]

The plus on doing this is perfect heating with NO overheating, no decarb, clean blades that need very little cleanup ( allowing thinner blades to be done), and reduced or eliminated warp.

Yes, that's exactly what I'm after. Something that will do a great job on tiny, super-thin steel that's 99% finished already. That won't ruin it after I've invested many hours of tedious work. In the past I've tried just eyeballing it with a torch, and had some success, but know it's not a great job, and had disappointing failures as well.

That is a melting pot for casting, not a salt pot. I don't think it would last long as a salt pot.

Maybe I should have asked this first- does anyone make a small plug & play salt pot about 5" deep, for around $200-$500? 'Cause I just assumed nobody makes something like this & I would have to modify or make something, or spend a whole bunch of money. I was surprised when I came across the above unit (didn't know such a thing existed) and though it might be workable with minimal effort. I was thinking maybe it would need some stainless sheet with a hole through the middle to protect the insulation from drips, and maybe need a stainless vessel welded up with a flange/collar on top as well. I think the vessel could be done for less than $40 locally.

What would need to change to make it last longer? I don't anticipate firing it up more than like 10 times a year. (I'm just a hobbyist with minimal "free time".) I could remove the salt vessel and clean everything afterwards before storage.

A converted pottery kiln will do this well. Just add a PID controller and SSR and you will be able to enter a number and let the machine do the rest.

These kilns are often available for almost nothing ... sometimes free. The small ones can be either floor or tabletop units, and the large ones will be floor models.

If ya find one that would work, I'd be happy to pay you to ship it over here. I've been keeping an eye out for over a decade and haven't seen one locally. How many more years should I wait? My dad averages going to at least one estate auction per week as well, and hasn't seen one. Seems other folks have all the luck finding cool stuff.

 

[timgunn1962]

I built something very similar and traded it with a maker of slipjoints some years ago, though I don't know whether he ever used it in anger.

http://s667.photobucket.com/user/ti... Crucible Furnace/240V salt pot?sort=3&page=1

The graphite crucible will certainly work for at least a fairly limited number of cycles with Neutral high-temperature salts. I'd be doing considerably more research if intending to use Nitrate salts though.

I just used Low-Sodium salt for testing and I took it up to 1100 degC (2012 degF) several times. The crucible seemed fine, with just a bit of a colour change on the outside from black to grey. I was unsure whether it was a clay/graphite crucible or a graphite crucible, though the ebay listing just said Graphite. At 1100 degC, the lo-salt level seemed to drop quite fast: maybe one or two millimetres/hr? I presume it was vapourising and would not recommend running it in a shop full of tools unless you really want them all rusty.

The little details that are not clear from the link in the OP are likely to be what decides whether it's just a bit meh or very good indeed for HT. The thermocouple location and controller tuning can make a big difference to the temperature control. Reading between the lines, I suspect many of the problems noted in the reviews are down to insulation damage when handling hot crucibles. For HT, that is not going to be an issue.