[Clayart] silicon carbide shelves

[Jeff Lawrence]

Hello,
I got some 12 X 24 X .390" nitride bonded kiln shelves for my current small
kiln, but as cracking takes its toll, have been pondering alternatives.
While this may be a sign it's time to start a gradual upgrade to Advancers,
I've been tempted by the idea 24" X 24" shelves so that I can fire larger
platters spanning two not-so-flat shelves (and yes, I know the Advancers
would probably address that issue, too).
My sense is that a 24 X 24 X 5/8" shelf should probably stay as flat as it
was when I got it, since I'm only firing to cone 6. But I don't want to
risk getting them if they're going to be as bowed as my current ones. Does
anyone know how flat they are, though?
Another issue is posting - my stacking footprint is 24X24. Since I don't
really want monster shelves all the way up, what about the transition from
the big boys to 12X24 - would the posts for the smaller shelves that
weren't positioned above other posts cause the big guys to warp?
Thanks in advance for informed commentary.
Jeff
Jeff Lawrence
jeff...@gmail.com
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[Hank Murrow]

On Aug 11, 2013, at 1:38 PM, Jeff Lawrence wrote:

> Hello,
> I got some 12 X 24 X .390" nitride bonded kiln shelves for my current small
> kiln, but as cracking takes its toll, have been pondering alternatives.
> While this may be a sign it's time to start a gradual upgrade to Advancers,
> I've been tempted by the idea 24" X 24" shelves so that I can fire larger
> platters spanning two not-so-flat shelves (and yes, I know the Advancers
> would probably address that issue, too).

Hank here:

For the Record, I have fired tiles up to 24x24 on two 14x28 Advancers, carefully shimmed so that they were on the same plane. Cone 11 Reduction with a soak in Ox.

> My sense is that a 24 X 24 X 5/8" shelf should probably stay as flat as it
> was when I got it, since I'm only firing to cone 6. But I don't want to
> risk getting them if they're going to be as bowed as my current ones. Does
> anyone know how flat they are, though?

I would be cautious of 24x24 shelves of any material, but YMMV.

> Another issue is posting - my stacking footprint is 24X24. Since I don't
> really want monster shelves all the way up, what about the transition from
> the big boys to 12X24 - would the posts for the smaller shelves that
> weren't positioned above other posts cause the big guys to warp?

I have another suggestion if you will email me.

Cheers, Hank in Eugene

[Kathi]

My question is, why are your shelves cracking? Are they cracking during firing? Is it a handling issue? I traded a friend pots for his store for twenty if these shelves. I've done fifteen firings with them and only broke one from mishandling. I have altered my firing schedule so that I have a very light flame at the beginning. But, once I'm at 800 degrees I let it rip.

Kathi

Sent from my iPad

[William & Susan Schran User]

Jeff,
Have you been flipping your shelves or is the flame path impinging on your
shelves?
Are the shelves solid or do they have slits built into them?
I've heard from others that the solid nitride bonded Sic shelves have had
cracking issues.
If you have any flame on the shelves this will cause uneven heating and
lead to cracking, same with Advancer shelves.

I don't know if Sic shelves come in 24 x 24 size, I have seen 18 x 24, in
any case, this large size needs to be 3/4" thick if oxide bonded SiC.

I suggest you read the section I wrote on kiln shelves for Mel's kiln book
and is available on Smith Sharpe's web site:
http://kilnshelf.com/Websites/kilnshelf/Images/Kiln%20Shelf%20Options%20by%
20Schran.pdf

Bill
--
William "Bill" Schran
wsc...@cox.net
wsc...@nvcc.edu
http://www.creativecreekartisans.com

On 8/11/13 4:38 PM, "Jeff Lawrence" <jeff...@gmail.com> wrote:

>Hello,
>I got some 12 X 24 X .390" nitride bonded kiln shelves for my current
>small
>kiln, but as cracking takes its toll, have been pondering alternatives.
>While this may be a sign it's time to start a gradual upgrade to
>Advancers,
>I've been tempted by the idea 24" X 24" shelves so that I can fire larger
>platters spanning two not-so-flat shelves (and yes, I know the Advancers
>would probably address that issue, too).
>My sense is that a 24 X 24 X 5/8" shelf should probably stay as flat as it
>was when I got it, since I'm only firing to cone 6. But I don't want to
>risk getting them if they're going to be as bowed as my current ones. Does
>anyone know how flat they are, though?
>Another issue is posting - my stacking footprint is 24X24. Since I don't
>really want monster shelves all the way up, what about the transition from
>the big boys to 12X24 - would the posts for the smaller shelves that
>weren't positioned above other posts cause the big guys to warp?
>Thanks in advance for informed commentary.

[David Woof]

Hi Jeff, Everyone,

I'm sure you will get plenty of information re shelves and posts settings so I will offer an alternative solution to the problem of warped and out of true shelves that in the long run do not stay absolutely true even if you flip every few firings.

My solution is to Elmer's glue refractory balls (Epk, fine sawdust, alumina) to bottom of the platter; using ample size balls to allow heat/air flow under the platter and to meet the uneven shelves terrain, and plastic enough to deform slightly and fill the voids as the weight of the platter presses and levels. One may replace the alumina with silica at cone 6 and when not sodium firing at higher temps.

The attraction also is that one may place the balls at selected spots in center and anywhere under the platter to help evenly distribute the weight so as to also prevent the platter from warping during the pyroplastic stage.

When I consider the technical problems associated with production of large platters as expressed over time here on Clayart the small time it takes to use the "Smart Pills" is for me good insurance and applied common sense.

David Woof

> Date: Sun, 11 Aug 2013 14:38:52 -0600
> From: jeff...@gmail.com
> To: cla...@ceramicist.org
> Subject: [Clayart] silicon carbide shelves

[Jeff Lawrence]

Hello,
Thanks for the input. No expansion slits, though most arrived new with
annoying minor cracks and slight bows. I killed two very first firing
(using beefy cordierite made me too casual about thermal shock). Since then
(over a year and a half) two others succumbed for no obvious reason.
Stack set back from ports by 1.5-2" so I don't think it's flame
impingement, but what I call crash cooling is cutting the gas with the
damper open to drop from 2200F to 1800F for another soak. Does that
constitute shelf abuse?
Another annoyance is that bricking away extravagant glaze blebs has eroded
the surface on several. I wonder if mine were made on a Monday morning?
Bill - good article! thanks for the link.
Jeff

[Kathi]

My shelves came from Bailey and had expansion slits. All were absolutely flat. After fifteen firing there is no deformity, no surface erosion. The few drips that I had we're easily removed with a grill brick.

My kiln is an Abernathy design. So, it has no bag walls and no chimney. I was concerned about rapid heat up affecting the shelves. I decided to do a slow warm up for the first hour. That has served me well.

Kathi LeSueur

Sent from my iPad

[William & Susan Schran User]

An anecdote - few years back after the Chinese made nitride bonded Sic
shelves cane on the market, had a talk with Paul Geil of Geil kilns about
shelves. He said he bought a huge shipment of them to offer as
alternatives to his 1" high alumina shelves. Every single shelf cracked
and he had to eat the cost and replace the shelves. He has since gone with
the Corelite shelves.

I still have two of the Chinese made nitride bonded SiC shelves I got when
I began testing. Both have expansion slits in them and I don't use any
kiln wash on them. We have 20 Advancer shelves that are our workhorse
shelves. I also have a couple Corelite shelves and some old warped oxide
bonded SiC shelves that we use in a pinch.

If I received a shipment of shelves and some were cracked, I would be on
the phone with the supplier to replace them before I finished unpacking.
Quality control of the cheaper nitride bonded shelves is a big issue!

Bill
--
William "Bill" Schran
wsc...@cox.net
wsc...@nvcc.edu
http://www.creativecreekartisans.com

[Jeff Lawrence]

Thanks for the tip, Kathi. Sounds like Bailey has better quality for the
same price, though I'm still mulling over progressing piecemeal to
Advancers.
FWIW, the ones I'm not so satisfied\ with are Axner/Laguna shelves - the
local clay store is a Laguna supplier so I went with free shipping on their
truck. The minor edge cracks and bowing were represented to me as typical
(these are the only ones I've bought) and all rang sound when I took
delivery. Since then, I got involved with another potter whose shelves
seemed harder, flatter, and free of those defects; at the same time,
they're also more like 1/2" thick.
Live and learn, I suppose. Could be either that 40-50 firings is their
limit or that mine are closer to that older stock Bill describes.
Jeff Lawrence
jeff...@gmail.com

[jonathan byler]

Why did bailey stop with the expansion slits? we have a large number of these nitride bonded shelves that we got for a very good price from larkin refractory. our also have slits, and I have never had a bit of trouble except when I dropped one on the edge once and it shattered. But that is to be expected from such mishandling! I have never taken any precautions to keep ramp up slow from the start. we go easy for the first half hour/45 minutes after an overnight preheat with just the pilots to drive off any residual water. Then it's go time! never had a single crack.

I was very happy with the shelves from larkin, but when I went to buy more (we want to up our shelf size to 4 18x24's per layer instead of 6 12x24's per layer), I was told that they were looking for a new supplier of the shelves.

is there any consensus of bailey's shelves (now with no slits) vs. the axner shelves that have the slits? Bailey lists the weight as 21 lbs per shelf, whereas axner lists the shelf weight as ~14-1/2 lbs ea for 18x24 nitride bonded SiC shelves.

I want to get these larger shelves to make stacking easier, but spending close to $3000 on shelves that I have to baby is not really an option.

Any arguments for shelves with slits vs. shelves without slits?

Thanks,
jon

[jonathan byler]

Where did this other potter buy their shelves?

[Kathi]

Not sure if you are addressing me, Jonathan. If you are, the potter I traded pots for shelves with bought them from Bailey. He felt that the shelves were affecting his rate of cool down and decided to go back to cored rite. I was happy to take them off of his hands and have fired them weekly since March with no problems, no warping.

Kathi

Sent from my iPad

[William & Susan Schran User]

Neither Bailey's nor Axner make the kiln shelves they sell.
The cheap nitride bonded SiC shelves these suppliers sell all come from
China.
Some suppliers have probably given up sourcing the shelves from some
manufacturers due to the many customer problems.
They began to engineer expansion slits into many of these shelves in an
attempt to deal with the cracking issue.
The big issue, IMHO, is material and manufacturing quality control.
I still have one of these shelves from my testing a few years back that is
still in use.
Others cracked and broke in time.
I wrote a section for Mel's kiln book on shelves.
Smith-Sharpe has it on their site if you haven't read it yet:
http://kilnshelf.com/Websites/kilnshelf/Images/Kiln%20Shelf%20Options%20by%
20Schran.pdf

Bill
--
William "Bill" Schran
wsc...@cox.net
wsc...@nvcc.edu
http://www.creativecreekartisans.com

On 9/10/13 2:43 PM, "jonathan byler" <jeby...@gmail.com> wrote:

>Why did bailey stop with the expansion slits? we have a large number of
>these nitride bonded shelves that we got for a very good price from
>larkin refractory. our also have slits, and I have never had a bit of
>trouble except when I dropped one on the edge once and it shattered. But
>that is to be expected from such mishandling! I have never taken any
>precautions to keep ramp up slow from the start. we go easy for the
>first half hour/45 minutes after an overnight preheat with just the
>pilots to drive off any residual water. Then it's go time! never had a
>single crack.
>
>I was very happy with the shelves from larkin, but when I went to buy
>more (we want to up our shelf size to 4 18x24's per layer instead of 6
>12x24's per layer), I was told that they were looking for a new supplier
>of the shelves.
>

[jonathan byler]

Yes, thanks!

[jonathan byler]

The ones I already have from Larkin have done rather well for us, and I would happily buy the same ones from them again, but alas… supplier trouble. The worst part about the slits that they have is that sometimes kiln wash and glaze build up in them, and I have concerns about that falling on pots below. They also make it difficult to put down a layer of sand/grog for placing under uneven or large items to give support and/or allow for easier movement. They have held up admirably in both our soda kiln and our ^10 gas reduction kiln, without a single casualty after more than a few years of use now - even with some really terrible glaze runs.

I hate to go all in on these from Bailey or Axner, as neither one of them offers any sort of warranty on them (not that I blame them). Still given the quality control issues people have had in the past, it gives me pause to buy these, and then have thousands of dollars of shelves just be a heap of junk…

[Jeff Lawrence]

On Wed, Sep 11, 2013 at 6:00 AM, <clayart...@ceramicist.org> wrote:

> On Sep 10, 2013, at 12:03 AM, Kent Tool <kent...@icloud.com> wrote:
>
> > We use and love the advancer shelves in our gas and electric kilns at
> our community ceramics studio. After several years use and numerous thin
> coats of kiln wash, these shelves are a bit uneven and certainly badly
> stained.
> >
> > Is there a way to clean these shelves? We use a grinding stone to
> remove glaze drips and post debris but this doesn't really clean the
> surface of stains and built up kiln wash.
>

Hi,
I recommend applying and firing a really high temperature glaze on your
stained shelves - formulate it for cone 32 - and consider adding colorants
so the shelves match your decor. If you have avocado appliances, you might
try some line blends of chrome oxide and RIO.
aesthetically yours,
Jeff
Jeff Lawrence
jeff...@gmail.com