William & Susan Schran User on sat 12 jul 08
On 7/11/08 1:31 PM, "Barrie Gross" wrote:
> We have two gas kilns: one updraft and one downdraft. We do mostly
> reduction firings with a rare oxidation firing. I am curious if anyone has
> any feedback about use of the imported nitrite bonded shelves in gas kilns.
> Does anyone have any experience to share? Curious about overall
> performance, cracking, total failure, ease of cleaning glaze, kiln wash (yes
> or no), different experiences based on different sizes, length of shelf life
> (no pun intended), etc.
There will be more specific information about nitride bonded SiC shelves to
be found in Mel's kiln book due out this fall.
So far the testing of these shelves, based on real and anecdotal information
points to both good and bad.
The bad - Geil kilns stopped offering the nitride bonded shelves due to
multiple customer complaints about cracking. Paul told me he's still sitting
on a load of them and is uncertain what he'll do with them. I noted in Geil
ads that he has gone to the Corelite shelves, which are high alumina
cordierite.
The representative of Chinese manufacturer, Ashine Industries, who made
those nitride bonded shelves told the shelves cracked because of flame
impingement or rapid heating/cooling.
I suspect issues have been due to lack of quality materials used in making
the shelves and poor quality control. This is based on that I have been told
by some that the shelves are great, no problems and others that cracking
occurred in the first firing. On the other hand, Advancer shelves undergo
strict material and quality controls. If an Advancer shelf comes out of a
firing with a deflection greater than .03" it is destroyed. The nitride
bonded shelf I'm testing already shows signs of warping.
Another issue that may point to problems is when the nitride bonded shelves
first came out, they were solid. Now the manufacturer has introduced
expansion slits, created during the forming process - ram pressing - to
relieve, according to the manufacturer, heat expansion issues.
I have been test firing, to ^10 reduction, several types of kiln shelves
over the past 6 months Geil kiln. Shelves are moved around the kiln each
firing - top, bottom, in the middle and close to burners.
The nitride bonded shelf supplied to me by PSH/Euclid's has the expansion
slits. The shelf looks and feels very similar to a SiC oxide bonded shelf
and has about the same absorption rate as the oxide bonded shelf, about 15%.
One would expect the shelf would need to be coated with kiln wash, but with
my testing, I decided not to apply kiln wash. So far all of the student
glaze accidents have come off with putty knife and a light going over with
an angle grinder.
So, should you get the cheaper nitride bonded shelves?
If you can afford to buy Advancer shelves, they are my recommendation.
If money is an issue, then get the cheaper shelves, but only get a few from
a reliable distributor that you trust. Test them and see if they fit your
needs.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Lee Love on sat 12 jul 08
I have the Japanese version of these kiln shelves I use in my
woodkiln. They are retired from a commercial pottery factory in
Seto. They cost me less than $10.00 each and are fantastic. At that
price, I am Going to try and ship them back to the States, if I can
ship by sea container.
They are light, easy to clean and are durable. If there is any
problem with the Chinese imports, it isn't inherent in the type of
shelve, but due to their manufacturing process.
--
Lee Love in Minneapolis
http://mashikopots.blogspot.com/
http://claycraft.blogspot.com/
"Let the beauty we love be what we do.
There are hundreds of ways to kneel and kiss the ground." --Rumi
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