aluminium casting using pottery kiln? Heat-treating?

Hi guys, dumb question for you all. I have a plethora of pottery kilns that
have shown up in my shop (building a pottery studio for my wife, she put her
net out for cheap/free kilns, she got four...).
These go up to 2000 degrees F. Can I use them as a heat source for
melting/casting aluminium? they are pretty controllable and I have a
temperature probe, can I use them as a heat-treat oven for steel?
Thanks,
Brian
Reply to
Brian
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I use my pottery kiln for normalising and tempering steel regularly and this should not be an issue. From what I have heard in the past though you should not use it for melting metal unless the elements are sealed such as in a muffle furnace. The issue as far as I know is the metal vapour that comes off will kill the exposed elements.
Brian wrote:
Reply to
David Billington
Yes you can. In fact, electric furnaces have the advantage that you can purge the kiln with argon gas and get much higher quality heats (as opposed to gas fired).
You would probably want to put some sheetmetal down in the bottom of it because you will be dripping things into it, and it would be very difficult to get it out of there. The other possibility would be to line the bottom with an inch of loose sand.
You'll have to figure out a safe way to pull your crucubles out.
Might even be able to melt bronze. I'd stay away from brass though, unless it's outdoors.
Reply to
Mensch
The main problem with pottery kilns it that they are usually top loaders. That's no problem with pottery since the kiln is allowed to cool before being opened. But you want to take things out while they're still at full heat and heat rises so you're working over the door into hell! You're also worried about bumping crucibles against exposed heating elements and splashing hot metal about.
Yes you can do it, but a purpose-built front loader is better. Could a small pottery kiln be turned on its side and its heating elements relocated I wonder?
Reply to
John Ings
It would be a good idea to coat the heating elements with ITC-213. In fact, even the kilns used for ceramics would probably benefit.
There are other ITC products that can help keep the kilns functioning.
Try this URL, I can't seem to find one directly for ITC:
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No connection just a satisfied customer.
Cheers,
Kelley
Reply to
Kelley Mascher
Kelley,
...mmm.. I understand that you want to coat the elements to stop them oxidising, but isn't ITC going to reduce their life by slowing down their radiant losses into the kiln, and hence making the element run hotter than it is designed for? A brief look through the ITC site gave me the impression it's a good thermal insulator whereas you need an oxygen barrier that is a good heat conductor. Kanthal elements iirc have aluminium as a sacrificial constituant - the aluminium oxide rises to the surface and forms a good barrier to stop further oxidisation. In pottery applications they try to keep a reducing atmosphere to give the elements long life.
Andrew Mawson Bromley, Kent, UK
Reply to
Andrew Mawson
The opposite, actually - electric kilns are run in oxidation (to maintain that oxide coating), except by people who are trying to replicate gas kiln work (reduction) and those are generally silly people who are not going to be stuck replacing the kiln elements when they fail (ie, students or others who have their hands on a "shared" kiln). Anyone who's gone though element replacing and is going to be stuck paying for it will generally stick to working within the envelope where the kiln will live a long time, and get a fuel kiln if they must do reduction.
Reply to
Ecnerwal
Quite right. From reading the information you can get from Kanthal placing coating the elements will reduce their ability to radiate heat and so cause them to run hotter so shortening their life. The normal method I have seen for mounting elements in a ceramic kiln is to place them in grooves in the wall. According to the Kanthal info this is already the least efficient method in terms of the heat loading you can place on the element due to the shrouding effect of the groove. The heat loading being the number of watts/mm2 of element surface area you can safely use.
Andrew Maws>
Reply to
David Billington
I can't see a single reason in the world why it couldn't simply be flipped on its side and run like that. The only problems I can envision would be purely mechanical - "Now that it's on its side, how do I open the lid and keep it open while I get the thing loaded/unloaded???" or "This WAS a round kiln - but then it rolled away..." and that sort of thing.
Reply to
Don Bruder
You should have no problem using it for aluminum. Most pottery kilns use Kanthal for the heating elements. It is a iron aluminum alloy and depends on the aluminum forming an oxide coating that protects the element from further oxidation and other chemicals that might be in the glazes. So I don't think there is any problem with using it to melt aluminum or bronze.
I would not use an inert gas to purge the kiln. Kanthal needs an oxidizing atmosphere to maintain that protective layer. Using a gas to purge the kiln will not lead to immediate failure, but will shorten the life of the elements.
Dan
Reply to
Dan Caster
And where do you put the load? Some sort of shelf?
Are they robust enough to lie on their sides? I've seen the things but never actually moved one around or operated one. Some seem to be sort of slab-sided, hexagonal maybe...
Reply to
John Ings
Right. You've got the idea as far as the problems I can see with the idea - Purely mechanical (as opposed to operational) considerations.
(Kiln shelves, standoff posts, and other kiln layup stuff is readily available from any pottery supply place worthy of the name)
Most of them that I've encountered have been "round-ish" - Basically hexagonal or octagonal firebrick/whatever-that-stuff-is-properly-called slabs wrapped in what amounts to a more-or-less round tube of sheet metal stuffed with fiberglass/rockwool/similar.
As far as moving them, they're bulky and awkward, but the washing machine-sized one that I helped move wasn't at all heavy (at least compared to what you'd guesstimate from just looking at its dimensions) - If there had been a decent way for me to grab it, I probably could have literally just picked it up and carried it to where it was supposed to go. I'd say the "stripped" (no shelving inside, lid and counterweights moved separately, etc) weight of the thing was under 125 pounds, but that's just an estimate. Because it was so bulky, and there was no decent way to get a grip on it, it ended up being a three man job to shift it from one end of the room to the other.
Reply to
Don Bruder
Depending on the kiln and the pinning of the elements in the grooves, if any, you may have problems with the elements falling out. It may be necessary to get some kanthal wire or similar and pin the upper elements at frequent intervals.
D>>
Reply to
David Billington
Gee, almost *ALL* ameteur crucible furnace designs are top-loading, for one. That's what leather gloves are for, dude.
I'd be more worried about the melt time, but that's an advantage because you can ram a mold or two in the 2+ hour melt time. Just relaxing, no hurry.
For anything but silicon bronze, I'd be worried about not having enough power. Simple heating time aside, you may not have the power to counter the evaporative cooling of all that zinc. I'll admit my only experience with bronze is melting it in a hollowed-out firebrick with my small burner. I've never done it with a molten glass cover so I wouldn't know...
Should work great for heat treating. Just remember that pottery is meant to be heated very slowly so it doesn't crack; the object of metalwork is to do it fast so it doesn't burn up on you. Annealing aside...
Tim
-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @
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Reply to
Tim Williams
My 2 cents worth...
A front-loading ceramic kiln is typically called a "glass kiln" because glass users are more likely than ceramic users to open it while hot and muck around with the contents.
They typically have elements on the back and two sides but not the door, this is OK for glass but ceramic folks don't like it because of the uneven firing. Glaze will be different on 1/4 of a large workpiece, the corners are cooler than the sides etc. They can be bought with an additional element string in the door but I've never seen one and that's its own set of issues particularly with respect to opening the door while hot.
The door of a front-loading is built heavier, particularly with a stronger hinge structure, otherwise the construction is basically the same.
For melting aluminum, it ought to work for a small quantity like a few lbs but it would take forever to melt a large crucible. Would love to hear from someone who has actually done it.
As for heat treating, a small ceramic or glass kiln with a computer controller is a terrific heat treat oven. Program whatever ramps and soaks you need with good assurance that it will happen within a few degrees of what you tell it.
Reply to
Bob Powell
I've used ITC-100 and as a high temperature reflective coating it works very well. ITC-213 is a different animal, I've never used it, but it's more of a protective coating and is meant to be applied in a very thin coating. I can't say whether there are problems with its application to heating elements but ITC, literally a mom and pop company, has been selling it for many years and has an exemplary reputation.
Here's a URL from someone who has used it.
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Speculation about the product's method of operation and side-effects are, well... , speculation. Personally, I can't imagine ITC continuing to promote a product for an application where it had the opposite of the desired effect.
Cheers,
Kelley
Reply to
Kelley Mascher

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