Gail Dapogny on tue 4 may 04
Hey guys (oops, excuse me, Mel), I'm feeling left out. I wrote a
request ---see below -- for info on kiln posts and no one....but no one
answered. It went more or less like this:
I need advice on kiln posts for a large, cone 10 reduction gas kiln. I
thought I had read that the Acme Marl material used in shelves is high
alumina and different from cordierite, but in the archives several
people implied
that they are the same material. Yet, somewhere (Vince perhaps?), I
believe that I read that cordierite is less refractory and not so good
at cone 10 as high alumina. How about those dry-pressed alumina posts
at Bailey's?
What do you all use at high temps, big kilns (lots of weight), and
frequent firings?
ANY and ALL help greatly appreciated!
...Gail in Ann Arbor
Gail Dapogny gdapogny@umich.edu
Richard Aerni on tue 4 may 04
On Tue, 4 May 2004 00:11:30 -0400, Gail Dapogny wrote:
>
>What do you all use at high temps, big kilns (lots of weight), and
>frequent firings?
>ANY and ALL help greatly appreciated!
>...Gail in Ann Arbor
Hi Gail,
Yes, cordierite is a very different animal from the dry pressed high
alumina shelves like those that Acme Marls make. I've had the equivalent
of the Acme Marls for years and don't have warping.
For kiln posts, I use fire brick. My shelves are 14 x 28, I use four
posts, and mostly use half brick I've sawn, soaps (2 x 2 1/4 x 9), pieces
of splits and pieces of silicon carbide kiln shelves (and combinations of
the above). I wad them with wet clay rolled in alumina oxide, and have no
sticking problems.
Hope this helps.
Richard Aerni
Rochester, NY
David Hendley on tue 4 may 04
Gail, I hesitated to respond because I think you, and everyone who
has been around Clayart for a while, knows that I make my own kiln
posts, and I think they are better than any I can buy.
I hate to sound like a preacher extolling the virtues of doing-it-yourself
and the eternal damnation of buying things.
Anyway, here is how I make them:
I use a 2" square hollow extruder die, remove the center section and
replace it with a small washer - so the resulting extrusion is mostly
a solid square, but with a small hole in the center.
The "recipe" for kiln posts is crushed insulating fire bricks and fireclay.
Crush the bricks to "window screen mesh", add enough clay to make
the mixture extrudable (probably about 1/3 by volume or 1/2 by
weight). For wood or salt kilns, add 10% alumina. Don't worry about
"drag marks" when extruding, there will be some.
Cut some lath boards the proper length for each length of post (add
about 10% to the length you want to end up with). Use these to
cut each post to length. If they are a little long or short of standard
measurement it doesn't matter, as long as they are consistent.
After the posts are cut to length, roll them in a tub of hydrated
alumina, so all 6 surfaces are coated. Use a stamp to impress the
length measurement on each post.
Fire to your top kiln temperature before using them to support
kiln shelves.
I also use firebricks that I got from the firebrick factory before
they were fired as kiln posts. If you have a factory nearby, you
might consider this.
I cut them to length with a miter saw. Use an old dull blade - it
will be very dusty, but easy to cut. I made soaps, half-soaps
(4 1/2" tall), 7" tall soaps, and 1/8 bricks, which use the thickness
of the brick (2 1/2") as the critical measurement.
Before firing, I dunked them in water and then in a bucket of
kaolin/alumina kiln wash.
David Hendley
david@farmpots.com
http://www.farmpots.com
Ron Roy on tue 4 may 04
Hi Gail,
Richard means hard brick by the way - still - make sure it can take the
heat you are firing to and more. Certainly not soft (IFBs) brick.
I cut mine with a hammer and chisel (the 4 or 5" kind brick layers use) on
a bed of sand - tap turn, tap turn, tap turn. Four 4.5" supports from a
2.5 x 4.5 x 9" brick - eight 2.5 " supports from the same size.
Over 800 cone 10 gas firings on mine now and still no problems.
RR
>>What do you all use at high temps, big kilns (lots of weight), and
>>frequent firings?
>>ANY and ALL help greatly appreciated!
>>...Gail in Ann Arbor
>
>Hi Gail,
>
>Yes, cordierite is a very different animal from the dry pressed high
>alumina shelves like those that Acme Marls make. I've had the equivalent
>of the Acme Marls for years and don't have warping.
>
>For kiln posts, I use fire brick. My shelves are 14 x 28, I use four
>posts, and mostly use half brick I've sawn, soaps (2 x 2 1/4 x 9), pieces
>of splits and pieces of silicon carbide kiln shelves (and combinations of
>the above). I wad them with wet clay rolled in alumina oxide, and have no
>sticking problems.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Gail Dapogny on tue 4 may 04
Ah, David, Thank you for overcoming your shyness! I did see your
formula in the archives and was going to add a
P.S. in my earlier post: "David, Please don't tell me to make my own
posts!!!!!!"
Only kidding: I'm touched that you bothered. And it's very impressive.
Do you crush the firebricks by hammering them?
---Gail
On May 4, 2004, at 10:48 AM, David Hendley wrote:
> Gail, I hesitated to respond because I think you, and everyone who
> has been around Clayart for a while, knows that I make my own kiln
> posts, and I think they are better than any I can buy.
> I hate to sound like a preacher extolling the virtues of
> doing-it-yourself
> and the eternal damnation of buying things.
>
> Anyway, here is how I make them:
> I use a 2" square hollow extruder die, remove the center section and
> replace it with a small washer - so the resulting extrusion is mostly
> a solid square, but with a small hole in the center.
>
> The "recipe" for kiln posts is crushed insulating fire bricks and
> fireclay.
> Crush the bricks to "window screen mesh", add enough clay to make
> the mixture extrudable (probably about 1/3 by volume or 1/2 by
> weight). For wood or salt kilns, add 10% alumina. Don't worry about
> "drag marks" when extruding, there will be some.
>
> Cut some lath boards the proper length for each length of post (add
> about 10% to the length you want to end up with). Use these to
> cut each post to length. If they are a little long or short of standard
> measurement it doesn't matter, as long as they are consistent.
>
> After the posts are cut to length, roll them in a tub of hydrated
> alumina, so all 6 surfaces are coated. Use a stamp to impress the
> length measurement on each post.
>
> Fire to your top kiln temperature before using them to support
> kiln shelves.
>
> I also use firebricks that I got from the firebrick factory before
> they were fired as kiln posts. If you have a factory nearby, you
> might consider this.
> I cut them to length with a miter saw. Use an old dull blade - it
> will be very dusty, but easy to cut. I made soaps, half-soaps
> (4 1/2" tall), 7" tall soaps, and 1/8 bricks, which use the thickness
> of the brick (2 1/2") as the critical measurement.
> Before firing, I dunked them in water and then in a bucket of
> kaolin/alumina kiln wash.
>
> David Hendley
> david@farmpots.com
> http://www.farmpots.com
>
> _______________________________________________________________________
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Ivor and Olive Lewis on wed 5 may 04
Dear Gail,
Cordierite contains Magnesium in its composition and this does have an
effect on the ultimate melting point, giving it a lower fusibility
than Quartz (+1600=BA C)
Sillimanite has no Magnesium in its composition and may be thought of
as 3Al2O3. 2SiO2 which accounts for its refractoriness. Kyanite is
another mineral with the same chemical composition. Melting point at
about 1850 =BA C
I believe the rule is that for high temperatures you go for the
highest alumna content and for high loads for thicker shelves.
A good detail to consider, and the manufacturer should be able to
quote this for you is the PCE factor, or Pyrometric Cone Equivalent
table of these should be somewhere in Google. From memory I thing the
ball park figure is about 35 for pottery refractory furniture. This is
not the melting point but describes bending behaviour of the Cone
Best regards,
Ivor Lewis. Redhill, South Australia
Steve Mills on wed 5 may 04
Hi Gail,
I didn't see your original post.
Acme Marls (now known as Dyson Ceramic Systems) use a mixture which is
mostly Cordierite, but with some Mullite in it. The resulting mix is
good for high temperatures. The ultimate very high temperature material
is Mullite. Shelves made of this material are almost white and about as
rare as Rocking Horse crap! I have used the Cordierite/Mullite Batts for
years now and never had a problem; I gas fired consistently to cone 9
plus, and now do the same with wood only a bit higher!
Steve
Bath
UK
In message , Gail Dapogny writes
>Hey guys (oops, excuse me, Mel), I'm feeling left out. I wrote a
>request ---see below -- for info on kiln posts and no one....but no one
>answered. It went more or less like this:
>I need advice on kiln posts for a large, cone 10 reduction gas kiln. I
>thought I had read that the Acme Marl material used in shelves is high
>alumina and different from cordierite, but in the archives several
>people implied
>that they are the same material. Yet, somewhere (Vince perhaps?), I
>believe that I read that cordierite is less refractory and not so good
>at cone 10 as high alumina. How about those dry-pressed alumina posts
>at Bailey's?
>
>What do you all use at high temps, big kilns (lots of weight), and
>frequent firings?
>ANY and ALL help greatly appreciated!
>...Gail in Ann Arbor
>Gail Dapogny gdapogny@umich.edu
--
Steve Mills
Bath
UK
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