Elongating electric kiln for heat treating

ScottRoush

ScottRoush

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Jan 10, 2010
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I will shortly have access to a top loading kiln that I would like to investigate the feasibility of converting to a vertical sword heat treat kiln. I'm still awaiting the specs.. but I'm told that it has an 18" deep firebox and runs off of 220v. I would like to just go ahead and buy a new unit... But I REALLY want it to be vertical..and I'm not aware of a commercial vertical unit.

My crude plan at this juncture would be to use the current firebox and lid to be the top.. and then build an extension from firebricks.

First.. is this madness?

Second.. I don't yet know the manufacturer... but I'm assuming that I could get the necessary heating elements from them?

Third... I have over 200 firebricks from an abandoned boiler that are in excellent shape... would it be kosher to grind in the grooves in which to lay the elements and use these as the basic foundation?

Fourth... I currently have a PID/thermocouple box with 110V pigtail (built from the sticky on this forum) that I was going to use for solenoid forge control. What would I need to do to convert this for the use of a 220v device (as I said.. I don't yet have the specs, amps, etc)?

Fifth.. is this quite over my head?

Sixth... would it make more sense to use the kiln for low temp salts... since I don't yet have a good method for tempering swords.. (my vertical gas forge is sufficient for quenching.. just not 'Cadillac')? And I do have a smaller 110 V kiln that could also be used for the salt bath.

Thanks in advance!
 
It's difficult to give good advice without at least seeing some pictures of the thing you may be modifying, but......

First: Maybe, but I find it quite enjoyable.

Second: The elements are not necessarily at all expensive; search for "Kanthal furnace element" on ebay. I find 16 ga Kanthal A1 seems to work well. The price will probably be much higher if you need the elements to fit something specific though.

Third: What sort of firebricks do you have? If you have Insulating Fire Bricks, it's easy to cut grooves and fit elements. I have welded frames for the HT ovens I've made out of 1" x 1" x 1/8" angle and 1" x 1/8" flat steel to hold the IFBs in place. I filed in the element grooves on the first 2. Now I cut the grooves with a router. If you have hard firebricks, look for a source of IFBs.

Fourth: I'm not familiar with your power supply setup, being in Europe, but I'd expect it to be easy enough to drive a contactor from the 110V output your current pigtail PID controller has, and run the 220V through the contactor. Just in case the terminology changes mid-Atlantic, a contactor is basically a big relay. If you already have an SSR on the output, that should handle switching 220V without modification.

Fifth: I don't know. Ask someone who knows you:D.

Sixth: It's hard to judge. If it's currently either useful or sellable, I'd be inclined to keep it as it is for as long as possible.

A couple of my efforts:

http://s667.photobucket.com/albums/vv31/timmgunn1962/Mark 3 Oven with Salt Capability/

http://i667.photobucket.com/albums/vv31/timmgunn1962/Sword-Length HT Oven/P1210157.jpg

http://i667.photobucket.com/albums/vv31/timmgunn1962/Sword-Length HT Oven/DSCF0046.jpg
 
Thanks a lot... I will check out your images.

No.. I don't have insulating. I have hard. Will the hard fire bricks work if I get the groove in or is it just easier to cut in the groove? I have so many (and enough space) that I'm thinking of staggering the bricks to leave the necessary gap rather than cut it in. This would also lead to double the insulation... Any sense to that at all?
 
Scott, you need the insulating variety of fire bricks. As the other gentleman stated, as long as you have a power source compatible to power both the controller and the elements, your good. The controller will not be driving the elements directly, but switching either a contactor or relay. The conttoller most likely cannot directly switch a load above 3 amps.
 
I would suggest not trying what you are describing. It has many problems.
It sounds like this is not your normal thing, so research it a lot and understand everything before doing anything.


Making a low temp salt pot is a good idea, and will require very little modification to the kiln . The PID control you have can be used to run an SSR to control the kiln and that will give you a digitally controlled salt pot. You will make a hole in the top for the salt tube to go through and insulate the section of tube that sticks above the lid. Kaowool is the simplest way to do that. Because the low temp salt pot is only operating at 300-500F range, it is a pretty safe and very useful shop addition. High temp pots are another thing entirely.


Vertical HT ovens are commercially available. Many people buy the Sugar Creek (or other brand) kilns that have sections. Each section is independent, and you can order the number you need, stack them vertically, and get the size oven desired. My friend has four stacked. To make them vertical, just cut a hole in the door and make a round cap from two insulating firebricks.
Sugar Creek ( or the company you decide on) will work with you and build it the way you want.
http://www.sugarcreekind.com/kilns-knife-kilns-c-273_312.html
 
Okay... Thanks a lot.

Yeah.. Like I said.. I do have a SUFFICIENT means for austentizing long blades... but I have no good method for tempering. Sounds like low temp salt may be the way to go.

And thanks for the Sugarcreek link.... that helps a lot.
 
I'll try and describe it in words.

Make or purchase a stainless low temp salt tube. The walls should be 1/8-1/4" thick and the bottom welded professionally. The salts and tube can be purchased from High Temp Tools and Supplies.
Take the kiln top and cut a hole about 5-6" wider than the salt tube. ( eg. - 4" tube, 8-9" hole)
Make a 1/4" thick base for the salt tube that fits in the kiln and covers most of the kiln floor ( keeping away from the coils). Center the tube on it and weld it to the tube base in 3-4 spots.
Make a sheet metal shell that fits on the kiln top and extends to a height three inches short of the tube end. It should be 4" wider than the hole in the top (eg. - 8-9" hole, 12-13" shell). If that is close to the top size, it may be simplest ( and look best) to make it the size and shape of the top. It should have ears that fit on the top or sides to allow screwing in place.
Place the tube in the kiln, and close the top. If it sits solidly and is straight, good. If not, lift the tube up and pour some satanite or other refractory cement in the bottom. Then set the tube back down and brace the tube straight while the refractory sets.
Place the shell on the top and secure well with sheet metal screws.
Line this shell with 2" Hi-Z kaowool to within an inch of the top. Since there is no air flow or flames, it isn't necessary to coat the wool with refractory, but rigidizer is a good idea. Cut some kaowool into a long 3" wide strip and wrap around the tube to close the opening between the tube and the insulation jacket. Again, rigidizer is helpful. Some wire "hair pins" pushed into the shell insulation jacket will help keep this seal from sliding down.
Make a top from 1" Insuboard that fits snugly over the tube and sits on the extension shell. Mark the insuboard around the shell and trim so it snugly slips into the shell and seats on the insulation...thus making a top.


When running the salt pot, place a stainless steel or monel TC in the salts with a clip on the tank lip. The tip of the TC should be about halfway down the tube. The PID should control an SSR ( or two if 220VAC) and the SSR should be wired to a socket that matches the kiln cord. Plug the kiln into the socket and set the kiln to HIGH. Set the PID to about 50 degrees below the desired temp and turn on. After the salts melt and have become evenly heated, raise the temp to the tempering temperature. Let stabilize for a while ( a stir or two with an iron rod won't hurt), and insert the sword for tempering.

BTW, quenching from austenitization into the salt pot at 400F is a superb way to quench a long blade (unless doing a water quench steel). It rapidly and evenly drops the temperature due to the thermal properties of the molten salts. The sword can sit there for 5-10 minutes and then be removed to check for warps. These can be straightened, returning it to the salt pot as needed to keep it hot. Once straight and all is right, let sit for a few more minutes and then take out and let cool to room temp. Check again for warp, and place back in the salt pot for the first temper...cool...second temper...done!

When not in use, cover the salt pot with a tight rubber cap, as the salts are hygroscopic.
 
Wow I appreciate this Stacy...

The only thing I'm not clear on is using the two SSRs for a 220 system. And I suppose I would have to rig up a heat sink since my unit currently doesn't have one (it's for propane).

Like I mentioned... I do have a kiln that can attain 1200F. It's 110V and I don't use it very often due to the small firebox.. only 10". If it's feasible to use THAT for the salt pot.. then if I acquire the other kiln (the one I was thinking of converting)..then I would use that for austentizing most of the bladework I do since it has an 18" box. This one is 220V...
 
Scott, I'm sure Stacy will be along shortly to clarify. But the reason for 2 relays on US version of single phase 220 is that both legs are 'hot'. Controlling both legs removes the chance of you being the return path of 120v if you touch an element controlled by just one leg, etc. Your controller should have sufficient control output current to drive two SSRs simultaneously on a single channel. Please verify, tho, by reading the specs..
 
Yes, that is why. On a closed unit, like a salt pot, actually, one would be fine.

A heat sink would be needed.

You could probably use the 115V kiln for the salt pot if the tube is 18". However, you were talking about swords, so I am not sure what you are planning.

If I was to make this decision in the same circumstances, I would build a low temp salt pot that would quench and temper most all the blades you will do. The larger kiln sounds like it would handle a 30" tube easily ( which would handle 24" blades). Then ,I would purchase a good 24" knifemakers HT oven with a programmable controller to do your austenitization.
 
Ouch... Only 24" blades on the larger kiln eh?

Okay.. I really need to get the full specs on this kiln that's coming my way so there aren't so many question marks.. I will try to run out and look at it tomorrow....

But I really need something that will handle up to 34" blades for tempering.
 
For 3 foot long swords ,you will need specialized equipment. The cost grows considerably as the length does. That is why many good sword makers farm out the HT and tempering.

I'm not saying you can't build it, but it requires some engineering and fabrication skills.

Some folks do it neo-tribal and others do it high tech. Not saying one is better ( OK, I do think Hi Tech is better), but the cost difference is usually the deciding factor.
 
okay... back to the drawing board. Thanks Stacy....

One of the links above does have kilns that get into the range for my sword lengths.... or at least a means for adding extensions. So one solution would be to just get a long kiln and use it for austentizing AND tempering until I get the equipment for a long salt tube. This seems to be the simplest solution.

I agree that high tech is the way to go for many applications.. especially in performance oriented blades. Historical reproductions... may be overkill and I do believe there is a place between the 'neo-tribal' and the 'high tech' spectrum when it comes to simple 10xx steels.

But... I have a blade I'm making for a Battle of the Nations contest.. sort of the ultimate test for a 'battle ready' sword. So I do need to get a better set up. Or farm it out I suppose.
 
One thing that is possible is :
If you have a vertical electric HT oven the size for a sword ( sugar creek 4-5 sections), you can make/get an extra top door with a hole to fit a salt tube. The sword would be hardened and oil quenched as normal. Then the oven would be allowed to cool, and the tube placed in it with the top changed. Set the controller to 450°F ( or whatever the temper will be) and let the salts melt.

In theory this could work as a high temp salt pot too, but there are many more issues to be dealt with when corrosive and conductive 1500°F salts are around red hot kanthal elements charged with 220VAC.
 
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