William & Susan Schran User on thu 8 feb 07
Just got off the phone, a hour long conversation with Marshall Brown at
Smith-Sharpe. He worked with Saint Gobain (formally Carborundum) in the
development of the Advancer shelf for top-loading electric kilns.
I had forwarded some of the messages on Clayart about silicon nitride bonded
shelves. I wanted to hear from the folks that make and sell some of these
Besides the testing St. Gobains did with these shelves, they also had Skutt
also go through rigorous testing of the shelves. Marshall said he is working
on an article about this testing. FYI - Saint Gobains went through a series
of tests putting slits in nitride bonded shelves. For their products, they
found the slits did nothing to relive stress.
What is the difference between Advancers and the nitride bonded shelves
manufactured in China?
Advancers are made up of fine powdered materials and then slip cast. These
shelves are fired twice. The 2nd firing involves the nitride process and the
formation of a glassy oxide layer that protects the silicon carbide from
oxidation. The thin profile and fine particle make-up allows for rapid heat
transfer. But because of this tightness, Advancers are not to be used in
situations where they come into direct contact with flame. They would not be
appropriate for use in former electric kilns that have been converted to
updraft gas fired kilns.
Marshall said he is not aware of any failures of Advancers in electric kiln
applications and they have about 2,000 shelves out with users. I had asked
him about a very fast firing rate, ^6 in 4 hours. He thought the Advancer
shelves would take that abuse, but doesn't recommend that as any silicon
carbide shelf will expand and contract with heating/cooling.
He also stated that many tests were run with elements in contact with the
Advancers shelves and did not have any of the shelves conduct electricity.
This is mainly due to that glassy oxide layer. He also stated that there
have been no issues with using direct venting systems and Advancers. Saint
Gobains did some testing of their Advancers that had only been fired once
and found these shelves did not conduct electricity.
Because Advancers are slip cast, there is more time and handling that goes
into the making of each shelf. Also they are fired twice. The fact that
there is high quality control and that there is a greater overhead for labor
as the shelves are made in the US, they simply can't produce a shelf for $30
or $40. Each shelf is checked before leaving the factory for warpage. Should
the shelf exceed 3/1000" per 1" in deflection, it doesn't pass inspection.
Now you know why Advancers cost so much.
Marshall couldn't address some specifics as he is not involved in the
production of Chinese manufactured silicon nitride bonded shelves, but he
did share his understanding of their process - shelves are ram pressed of
larger particle sized silicon carbide and are probably fired once. Marshall
believes issues with these shelves may be the bonding of the materials and
that the silicon carbide is of a larger particle size. They are thicker,
heavier (though much lighter than cordierite) and have a higher porosity.
There may be issues with these shelves conducting electricity.
I think the main thing folks need to understand is that NOT all silicon
carbide nitride bonded shelves are alike. It's like the recent discussion
about angle grinders. You get what you pay for. A less expensive kiln shelf
may work perfectly fine for one person, but for somebody else, expecting the
cheaper shelf to perform the same way, well, they may be disappointed.
Marshall has passed along my questions to Mike Arbini, one of the tech guys
at Saint Gobains, and asked him to respond. When I get that information I'll
pass it along.
I hope this information will help everyone make an informed decision when it
comes to purchasing kiln furniture.
William "Bill" Schran
Hank Murrow on thu 8 feb 07
On Feb 8, 2007, at 12:51 PM, William & Susan Schran User wrote:
> Just got off the phone, a hour long conversation with Marshall Brown at
> Smith-Sharpe. He worked with Saint Gobain (formally Carborundum) in the
> development of the Advancer shelf for top-loading electric kilns.
> I had forwarded some of the messages on Clayart about silicon nitride
> shelves. I wanted to hear from the folks that make and sell some of
> Besides the testing St. Gobains did with these shelves, they also had
> also go through rigorous testing of the shelves. Marshall said he is
> on an article about this testing. FYI - Saint Gobains went through a
> of tests putting slits in nitride bonded shelves.
> I hope this information will help everyone make an informed decision
> when it
> comes to purchasing kiln furniture.
Dear Bill et al;
Back in the early days of nitride bonded SiC setters, I ordered a set
of Crystar shelves from Norton through Firebrick Supply in MN. This was
19 pcs. 14" x 28" for around $136 per shelf...... approx. $2500. The
shelves were great for around 50 firings, when one cracked right in
half falling on the pots below. This continued until the last one
failed at firing 105. I was in contact with FBS and (by then) St.
Gobain about the reasons for this. I sent a big package of pieces to
FBS so that Marshall and Mike could confer over the real thing.
There seemed to be no explanation other than, "We don't recommend
Crystars for periodic kilns anymore". It was decided that no recompense
was called for. I bought Advancers from them in two batches to use
while the remaining Crystars failed. The Advancers have been holding up
fine except for one which cracked. I do feel like I was a sort of
'unwilling tester' for the Crystars, and $2500 is a high tuition for a
potter to pay, IMHO. I imagine that an Industrial Account might have
fared better than a sole proprietor/potter such as myself. That said, I
still buy my Advancers from FBS, and have enjoyed good service from
Lauren Bellero on fri 9 feb 07
thanks so much for the effort and the info. i look forward to
the follow up information from mike arbini.
i had attempted to research this info myself, getting very
helpful info about the advancers from dona at smith-sharpe, but
was thwarted by folks at geil regarding their NSiC shelves. i
called geil 3 times. the first time, i was told they had that info
ready to be emailed. what i rec'd was an email with 1 sheet of
specs copied from the advancer webiste and one sheet on
'moisture caution'. no usable info to make a comparison. so i wrote
back with specific questions and when i got no response i called geil 2
more times being, what would have been any salesperson's dream, a customer
begging to be 'sold'. both calls went unanswered. so
my current plan is to go to nceca and talk to the vendors there.
but, for all their good rep with kilns, you can bet money 'if and when'
that i won't be buying from geil.
the other part of my plan is to see what plays out here on clayart
and in the clayart room in louisville. so again, thanks for sharing
all the best,
Lauren Bellero, Mudslingers Pottery
Red Bank, NJ
William & Susan Schran User on fri 9 feb 07
On 2/9/07 12:58 PM, "Lauren Bellero" wrote:
> getting very
> helpful info about the advancers from dona at smith-sharpe, but
> was thwarted by folks at geil regarding their NSiC shelves. i
> called geil 3 times. the first time, i was told they had that info
> ready to be emailed. what i rec'd was an email with 1 sheet of
> specs copied from the advancer webiste and one sheet on
> 'moisture caution'. no usable info to make a comparison. so i wrote
> back with specific questions and when i got no response i called geil 2
> more times being, what would have been any salesperson's dream, a customer
> begging to be 'sold'. both calls went unanswered.
Marshall told me Geil used to sell Advancers some time back but apparently
there was some hoo-ha between them and Saint Gobain's, so Geil went to the
Chinese manufactured shelves.
FYI - Marshall told me Advancers were originally developed for the sanitary
ware manufacturers, ceramic toilets and the like, because they needed a
shelf that weighed less but would support the weight of a toilet.
William "Bill" Schran