Nikom Chimnok on wed 20 nov 96
I need to know about a technique (perhaps industrial) for drying large
amounts of pots. Problem is this: We have a red clay with a very small
particle size (80% less than 4 microns) and it appears to be montmorillonite
based. Basically it just won't get dry until it's put into the kiln. After 2
months of drying, it will explode. The bottom is always the last thing dry,
and that is what explodes the most.
The setting is tropical--high humidity and temperatures all the time.
They've been making pots here for 200 years plus. The traditional way of
firing is to build a fire of huge logs outside the mouth of the kiln and let
it smolder away for about 48 hours, gradually drawing more of the smoke and
heat into the kiln. And then a very slow firing, and a very slow
cooling--about 7 days in all.
Now that we're producing for export, this is much too slow.
Is there a way to build a drying room to dry this clay out before it's put
into the kiln and so reduce the pre-warming time.
And please remember that this is huge production, not a few pots.
Containerloads, several per month. Thank you for your help.
Dave and Pat Eitel on thu 21 nov 96
The traditional way of
>firing is to build a fire of huge logs outside the mouth of the kiln and let
>it smolder away for about 48 hours, gradually drawing more of the smoke and
>heat into the kiln. And then a very slow firing, and a very slow
>cooling--about 7 days in all.
Any change of alter ing the traditional way of firing and using a smaller
fire to dry the ware more slowly so it doesn't explode? What about
changing the claybody so it will dry more easily--add some grog or
something--or some larger particle-size clay?
>Now that we're producing for export, this is much too slow.
>Is there a way to build a drying room to dry this clay out before it's put
>into the kiln and so reduce the pre-warming time.
Maybe you could design a very lage version of a drybox I use. It is a
refrigerator sized crate with gaps between the boards. Inside are shelves
made of slats, upon which the ware sits. At the bottom are three 350-watt
lightbulbs. At the top is a very low velocity fan (which I very seldom
use). In the summer I can dry a12 cu. ft. of pots from very soft leather
hard to bone dry--despite humidity in the 85+ range.
On the other hand, are containerloads, as in the huge containers they load
on ships and boxcars? If so, it would seem to make more sense to alter the
production cycle in some way, rather than try to build a humongous drybox.
Later...Dave
Dave Eitel
Cedar Creek Pottery
Cedarburg, WI
pots@cedarcreekpottery.com
http://www.cedarcreekpottery.com
Louis Katz on thu 21 nov 96
It is important to determine if the explosions are happening early in the
firing before 150 degrees celcius, near red heat or between the two.
Often the bottom of a kiln will remain cool quite longer than the top.
Things to try if the bottom is remaining cold and these pots are the ones
that blow up are:
1. place all pots on prefired stands.
2. close off the damper partway so that cold drafts aren't sucked in
along with the flame.
3. increase the turbulence in the kiln (not sure how)
4. load pots with the rims down instead of the flat bottom.
***************************************************
*Louis Katz lkatz@falcon.tamucc.edu *
*Texas A&M University Corpus Christi *
*6300 Ocean Drive, Art Department *
*Corpus Christi, Tx 78412 *
*Phone (512) 994-5987 *
**************************************************
Jeff Lawrence on fri 22 nov 96
Nikom Chimnok writes:
>I need to know about a technique (perhaps industrial) for drying large
>amounts of pots.
Nikom,
Harry Fraser's "Ceramic Faults and their Remedies" talks about humidity
drying, which sounds like what you need. To show the value of this book, I
quote two paragraphs below (to moderators: I'm not reproducing illicitly,
just taking advantage of the copyright law exceptions granted for purpose of
review):
"The viscosity of water rapidly decreases with increasing temperature and
the higher the temperature the more easily water will transfer from the
inside to the outside of the piece. Drying at higher temperatures therefore
reduces the moisture gradient in drying clay ware, thus reducing drying
stresses. The actual speed of drying of the surface of the clay ware can be
controlled by contrlling the humidity of the atmosphere. Humidity drying
i.e., maintaining high drying tempreatures under high atmospheric humidity
to prevent excess drying speed, reduces risk of cracking and distortion
since the ware dries much more evenly."
"Humidity drying also permits faster drying, especially so with wares of
thicker section. Thicker areas take disproportionately longer to dry,
particularly as the moisture content drops towards the leatherhard state and
beyond. By decreasing the humidity as the ware becomes drier a more rapid
drying rate can be maintained without damage to the ware."
The book is invaluable, though irritating. I hate finding out how much
energy I've spent doing things wrong. Plus, Fraser writes so clearly that
things seem obvious, giving rise repeatedly to the question, "Why didn't I
think of that myself?" Get it yesterday if not sooner.
Jeff Lawrence
Route 1 Box 394L
Espanola, NM 87532
jml@sundagger.com
505-753-5913 vox/fax
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