Ceramics kilns as heat treat furnaces?

[Senna]

Around here a guy see a lot of ceramics/pottery firing kilns for sale cheap but rarely a cheap heat treat furnace.

Can a guy effectively use a ceramics type kiln for the heat treatment of metallic parts?

I realize that I'd need to wrap steel items in SS foil to prevent carburization of the part but aside from not having a inert environment are these inexpensive kilns a viable alternative to a proper heat treating furnace?

 

[awander]

I've got one that I intend to use for color case-hardening. I can't see any fundamental reason why it wouldn't work.

Most ceramic kilns are top-loading, though, and not designed to be loaded or unloaded while they are hot. For metal treatment, we need to get the stuff out while the kiln is up to temperature, so I am laying mine on it's side, and making an angle-iron frame to reinforce/support it.

I have also heard that you need to be careful of burning out the heating elements due to gases from the stuff that you use for case-hardening.

 

[David Kirtley]

Absolutely not. It puts out a different kind of heat. (Yes, this is a joke)

They work just fine. Most can go much hotter than you would would ever want for heat treating. (Many could actually burn off steel.) The main difference is that many of the ceramic kilns don't have a pyrometer (temp gauge) but use cones or a kiln sitter instead. A kiln sitter is a strip of clay that gets soft at a certain temperature and will release a microswitch when it at temperature.

You can get front loading and top loading. The shape of a ceramic kiln is not that well suited for heat treating. You will end up with a lot of air space (which isn't that good of a thing) You can also roll your own. Soft insulated fire brick works very easily and you can just buy the heating elements. Personally, I wouldn't mess with a lot of brick. In a heat treating oven, you don't generally get a shape that makes effective use of the brick and really hard to make a good top. You can build one easily from ceramic fiber insulation (kaowool is one brand) in whatever shape you want. Something fancier, just get some castable refractory.

 

[xalky]

Hey Ken. I don't know if you remember this thread when I bought my kiln. http://www.hobby-machinist.com/showthread.php?t=19829&highlight=kiln

I haven't hooked it up yet. I'm in the process of setting up an area in my basement for this and my plasma table( ran out of space in the garage). I think it's gonna work out great.

 

[DennisK]

I made a forge out of an old BBQ grill and hooked up a Wet-Vac to blow instead of suck. Throw in some coal and you can get steel hot enough to glow bright orange. Cost next to nothing.

 

[John Hasler]

I made a forge out of an old BBQ grill and hooked up a Wet-Vac to blow instead of suck. Throw in some coal and you can get steel hot enough to glow bright orange. Cost next to nothing.

When needed I set up a field-expedient forge using a pile of cement blocks, scrap expanded metal, a small window fan, and a couple of bags of charcoal.

 

[Lynn]

Hi Senna, Like others here, I bought a round top-loading kiln to case harden. Had to redo the top hold-open to allow vertical lift of parts. Fabricated a heavy sheet metal container in which I could pack the parts in charcoal. Probably best to avoid the charcoal with built in starter. The container and contents have enough thermal inertia that moving to quench is easy to do without much cooling. Bought the cheapo relay, thermocouple and controller off e-bay for about $40 dollars and bypassed all but the on/off switch that came on the kiln. Found that the controller would do the job but the presets needed changing and it took a couple of tries to get that right. Hardening tool steel is ok because you can see the temp when you remove the part. Have found tempering to be more challenging and if I really needed to do much of that I would want an oven with less surplus internal volume and fewer air leaks plus a controller with some programmable features. So it's worked for me. Good luck.