wayneinkeywest on fri 2 apr 04
In the latest edition of "Pottery Production Practices" which is
a special supplement to Ceramic Industry Magazine is an
article entitled ""Lighten Up" dealing in kiln furniture and
shelves.
In it, the differences between cordierite, silicon carbide,
advanced nitride bonded silicon carbide, recrystallized
silicon carbide and reaction-sintered, silicon infiltrated
silicon carbide shelves is explored with an eye toward
energy saving and strength. Fascinating article.
From that article, I quote:
"Advanced NSiC kiln shelves can be used in soda firing
when soda is introduced indirectly into fireboxes using
wet or dry methods. Due to the extremely low porosity
of the shelves, soda drips are usually easy to remove by
hand scraping after each firing. However, advanced
NSiC shelves are not recommended for applications where
water/soda combinations are sprayed directly onto the shelf,
because they are susceptible to thermal shock failure under
these conditions.
In these cases a thicker, traditional SiC
shelf should be used. Advanced NSiC kiln shelves have
also been used successfully in wood-fired kilns. However,
the shelves must be placed so they are not subjected to
direct flame impingement or uneven temperatures. In
wood-fired kilns with multiple chambers, the shelves have
been used successfully in the second and third chambers,
where temperature rises are gradual and direct flame
impingement is not an issue. If these chambers are
stoked with wood at the later stages of the firing, it is
important that the teperatures are already high enough to
allow for a gradual increase, and/or that the shelves are
stacked or shielded in a way that prevents direct flame
impingement. A combination of advanced NSiC shelves
and traditional SiC shelves is often a good option in areas
where temperature uniformity is a problem.
It is also worth noting that an advanced NSiC (Advancer, BTW)
shelf is likely to exhibit more profuse glass dripping from the
alkalis present in wood-fired atmospheres. A traditional SiC
shelf will exhibit a certain amount of glass dripping in wood-fired
atmospheres due to oxidation; however, the problem is
compounded with an advanced NSiC shelf because of its
higher surface area of silicon carbide (ie., fine grain sizing
and low porosity). An advanced NSiC shelf also has a
protective oxide (glass) layer, which is intentionally formed
during manufacturing to further protect the shelf from the
destructive effects of oxidation. When excessive alkais
are present, which is the case when wood is a fuel source,
the alkalis will flux the glass layer and lower its viscosity,
causing the glass to drip or foam more readily. The effect
is less pronounced in second or third chambers where
direct wood stoking is minimal."
PHEW!
Be careful with your testing Tony. Don't need no dripping,
exploding shelves. Kinda takes the fun out of it.
Wayne Seidl
> clennell wrote:
>
> >The rich folks out there have the fancy Advancer kiln shelves.
Way to
> >expensive for those of us without trust funds. I'm testing thin
silicon
> >carbide shelves for the local pottery supply house imported from
China. What
> >is interesting about these 14" x 28" shelves is that they have
2- 6 inch
> >cuts into the length and 2- 3 inch cuts into the width. i figure
this is to
> >prevent warping and possibly stress cracks.
> >
clennell on sat 3 apr 04
Sour Cherry Pottery
> In the latest edition of "Pottery Production Practices" which is
> a special supplement to Ceramic Industry Magazine is an
> article entitled ""Lighten Up" dealing in kiln furniture and
> shelves.
Wayne; I know I not supposed to use the list to say thanks, but thanks.
Great information on the Advancer shelves. My wood kiln is my toy and I
can't ever imagine spending big bucks for shelves to get the liven crap
kicked outta them. i tumblestack and use oldies that are recycled from my
gas kiln. the woodkiln is their last resting place where they serve me
until they are broken up as kiln post spacers.
The one shelf they gave me was free, so it will visit hell compliments of
someone else's pocketbook.
Thanks again- good stuff.
Cheers,
Tony
| |
|
