William & Susan Schran User on fri 4 jun 10
On 6/4/10 6:34 PM, "Bob Johnson" wrote:
> I have been having trouble getting the bottom shelf of my kiln up to temp
> without overheating the top in reduction firing of my downdraft kiln. A
> friend suggested that, instead of controlling reduction with the damper, =
I
> could control it with the primary air vents on my burners--making the fla=
me
> a bit "dirty." Have any of you tried that?
> FYI, my previous approach was as follows: After using the damper to produ=
ce
> a little back pressure at the peep during glaze reduction, I would take t=
he
> kiln up to the next-to-last cone (for me that would be ^7). At that point=
I
> would put the kiln back in oxidation (by opening the damper until the bac=
k
> pressure disappears) and adjusting the gas to hold the temp on the pyrome=
ter
> until the heat work caused the target cone (cone 8) to fall. If I were to
> use my friend's method, I would not manipulate the damper for back pressu=
re,
> but rely only on the primary air adjustments on the two burners for
> reduction.
I will tell you what I do to fire our Geil kiln at school using natural gas
to get even temperatures top to bottom. 24 cu ft, 8 burners.
Shelf configuration is three stacks of 12 x 24 shelves, side by side..
I now fire to ^6, firings are 7 - 8 hours. Start at low pressure, increase
each hour, after 3 hours it is at top gas pressure we use, about half what
the manufacturer recommends.
All burners have primary air open about 1/4" - stay that way all the time.
Have pencil marks on damper. Start firing at 2 7/8 mark,
at 1800F close to 2 1/2 mark, about 1900F back to 2 7/8, at 2000F pull out
to 3, sometimes 3 1/4. There is never any smoke or flame coming out of the
chimney.
So, after pressure has been turned up, only thing touched is damper. Never
more than 1/2 cone difference top to bottom.
Here's what I figured out in my situation to get even temperatures - it's
all in the stacking of the shelves. There are 3 shelves that sit on the kil=
n
floor, then the first set of stacked shelves are all as high or higher than
the flue opening. I also try to stack all low bowls, plates, etc in the
upper half of the kiln.
I'd suggest before changing firing settings that you try stacking taller
pots at the bottom and shorter at the top and see how that works.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Bob Johnson on fri 4 jun 10
I have been having trouble getting the bottom shelf of my kiln up to temp
without overheating the top in reduction firing of my downdraft kiln. A
friend suggested that, instead of controlling reduction with the damper, I
could control it with the primary air vents on my burners--making the flame
a bit "dirty." Have any of you tried that?
FYI, my previous approach was as follows: After using the damper to produce
a little back pressure at the peep during glaze reduction, I would take the
kiln up to the next-to-last cone (for me that would be ^7). At that point I
would put the kiln back in oxidation (by opening the damper until the back
pressure disappears) and adjusting the gas to hold the temp on the pyromete=
r
until the heat work caused the target cone (cone 8) to fall. If I were to
use my friend's method, I would not manipulate the damper for back pressure=
,
but rely only on the primary air adjustments on the two burners for
reduction.
Comments? Suggestions?
Thanks--from Southern Oregon,
Bob
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