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
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:
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.
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?
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
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
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.
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>
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.
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
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...
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.
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>>
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 @
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.
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
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