Fred Parker on tue 3 apr 07
I am not sure why electric heating elements fail in reducing atmospheres,
but the ongoing quest for reduction results in an electric kiln prompts me
to ask what the result might be of injecting an inert gas -- such as
argon -- into a hot kiln. In welding, an inert shield protects a molten
weld puddle from atmospheric oxygen, nitrogen and other reactive
contaminants, thereby preventing (or minimizing) formation of unwanted
oxides, nitrides and such in the weld metal. Has this been tried in
electric kilns?
I know nothing about the metallurgy of heating elements, but if it is not
the reduction itself that damages them -- possibly other contaminants
carried as products of combustion of whatever fuel is used to produce the
reducing atmosphere -- it would seem that an argon-injected electric kiln
might be a low-cost solution to many potters' needs.
Comments from the illuminati...?
Fred Parker
Fredrick Paget on tue 3 apr 07
Sorry , argon is indeed inert and will not reduce the glazes.
However there was a PhD thesis on line awhile back from a man in GB
who used 5 percent hydrogen in nitrogen to do reduction. You could
use 5 percent hydrogen in argon as well but it is more expensive. The
reason for the 95 percent non reactive or inert gas is that at that
concentration hydrogen is not explosive. I don't recommend this at
home as you may have an explosion if things get out of control.
The reason reduction is hard on Kanthal elements is that they depend
on a thin oxide coating that is formed in the first firing to protect
the bulk of the element from oxidation and failure. If you remove
that coating by reducing it, the element forms more oxide and it does
not take long for that treatment to develop thin places which have a
higher resistance and heat up more than the rest of the element -
soon melting and failure occurs.
There are elements that are not affected by reduction. Globars
(silicon carbide ) elements are an example. If you have lots of money
have a special kiln built with those elements.
The ITC method seems to work if everything goes right and the
elements are the right alloy. Since there are several different
Kanthal alloys maybe some one of them is more prone to failure under
ITC.
Also the ITC must not be knicked through to the bare Kanthal or there
is a spot for attack.
Fred Paget
--
Twin Dragon Studio
Mill Valley, CA, USA
Arnold Howard on tue 3 apr 07
From: "Fred Parker"
> but the ongoing quest for reduction results in an electric
> kiln prompts me
> to ask what the result might be of injecting an inert
> gas -- such as
> argon -- into a hot kiln.
Argon gas is routinely injected into Paragon knifemaking
furnaces to prevent scaling on knives during heat treating.
We sell a gas inlet flow meter for this purpose.
However, I've never used argon gas with a kiln, so I don't
know how much to use during firing or how much element life
is reduced.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
Lee Love on wed 4 apr 07
On 4/4/07, Fredrick Paget wrote:
> There are elements that are not affected by reduction. Globars
> (silicon carbide ) elements are an example. If you have lots of money
> have a special kiln built with those elements.
Globars are the elements you usually find in Japanese kilns. I
wonder, if there is enough demand, if someone like Shimpo could export
these kilns to the USA?
I think of Shimpo, because the only coil element type kiln I have seen
in my narrow experiences in Japan has the Shimpo label on it. Maybe
they can get Globar kilns to America.
The other way to go might be to buy the Globar elements from Kanthal
and build your own kiln:
http://www.kanthal.com/sandvik/0971/internet/s003237.nsf/index/5A90E8FB896EC8B7C12570AE00302A0C?OpenDocument
PDF Specs:
http://www.kanthal.com/sandvik/0971/internet/s003237.nsf/DDE6A857C0FA1F78C12570C20051578C/$file/10-C-2-3%20-%20Kanthal%20Globar%20SG%20SR.pdf?OpenElement
http://www.kanthal.com/sandvik/0971/internet/s003237.nsf/DDE6A857C0FA1F78C12570C20051578C/$file/10_B_2_3Globar%20SD.pdf?OpenElement
from this page:
http://www.kanthal.com/
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
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