Michael McDowell on wed 2 oct 02
Dear Randy,
I have been firing a small updaft kiln of similar dimensions for
many years now. It's not easy, but it can be fired just about even
in temperature from bottom to top. Mine actually has yet another 4
1/2 inches in height, so it's not too tall. First, be sure to allow
about 4" below the bottom shelf as a "mixing area" for burner
gasses. Then stack all your shelves butted together in the center
for maximum flow up the sides. Then try to get your top shelf about
1" from the top of the kiln. Finally, you should be dampering the
opening at the top with soft bricks. I don't know how big the
opening is on your kiln, but you want to use lots of damper. I take
about 14 hours to fire the kiln to cone 11, with about 150-250
degrees Fahrenheit/hour as the general target when not reducing or
reaching terminal temperature (those are of course much slower).
Good luck,
Michael McDowell
Whatcom County, WA
Michael@McDowellPottery.com
http://www.McDowellPottery.com
ranmcc on wed 2 oct 02
Any one out there with a 2831g. I have tried various changes in shelf
stacking, but no matter how I change the shelves I still get about a 4 cone
difference between the top and bottom shelf. It is always much hotter on
the 2nd shelf from the top than the bottom shelf. No ware is put on the top
shelf and I try to put it between 2 and 3 inches from the top port. I have
tried firing on about a 7.5 hour schedule to an 11 hour schedule.
I have 8 half round shelves. These are the following configurations I have
tried. About and inch apart except the top shelf which I butted together.
FIRST ______ 1
____ ____ 2
____ ____ 3
____ ____ 4
Second Olympic said to move the shelves out closer to the burners. Tried
that and no difference.
Kickwheel said to put the shelves in a pyramid shape.
____ ____
____ ____
____ ____
____ ____
Still no difference.
One thing I have not tried is to alternate shelves open and
closed??????????? Or not using a top shelf.
________
____ ____
________
____ ____
This kiln has 4 burners on the bottom edges. Should the round shelves be
placed very close to the burners where the top round part of the shelve is
center over the burner?
I would really appreciate any help!!!!!!!!!! and any suggestions as I want
to do a glaze fire tomorrow.
Randy
Clio, South Carolina
Michael Wendt on thu 3 oct 02
Randy,
In an updraft like this, you should make the damper setting tight enough so
that in a darkened room, you see an occasional flicker of flame. My oxyprobe
shows a neutral flame when this happens and that slows the intake of cold
air at the bottom which most likely is the cause of the cold bottom layer.
Second, you can place flame spreader tiles made of broken kiln shelf in the
path of the flames up 2.5" from the bottom and about 1.5" from the side
walls of the kiln and move them in or out as needed until you balance the
top and the bottom. Place cone sets throughout the load each time you fire
and keep records of all changes made. The best thing is to try only one
change at a time to learn how it affects the firing and master that. Then
once you have optimized a parameter, play with another. Sometimes two
changes counteract each other and you get no worthwhile result.
I also added 1" of kaowool on the bottom inside the kiln to reduce heat loss
out the bottom.
Stack a tall layer (7" or taller) in the bottom. Short bottom layers don't
fire very well. The same is true at the top, stack a taller top layer (5" or
taller). Be sure you use a top shelf set about 1.5" below the lid and seal
the seam between the shelves with thin clay cover strips to keep damper
brick chips off the pots. We fire more than 100 loads a year with this kind
of kiln and it takes 4-5 hours to reach cone 10 after we pass read heat.
There is no reason to fire slower unless you are breaking and cracking work.
See the results at wendtpottery.com
Regards and Good Luck!
Michael Wendt wendtpot@lewiston.com
Wendt Pottery
2729 Clearwater Avenue
Lewiston, Idaho 83501
1-208-746-3724
wendtpottery.com
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