jonathan byler on tue 16 sep 08
I had written before about having trouble with one of our gas kilns
not heating evenly top to bottom. Nils Lou and some others suggested
that the flue opening may be too large.
So off I went and measured the flue opening on the larger kiln of
similar design that fires off much more evenly. It measured 45" sq.
the burners output about 590,000 btu/hr. The smaller kiln outputs
360,000 btu/hr. So I used my handy (but sadly minimal) algebra
skills and decided that about 27" sq would be the ideal size for the
flue. unfortunately, the opening is also 45" sq, just like on the
bigger kiln. So I cut some bits of brick, and closed the opening to
make it a little over 30" sq as I didn't want to go too much too
soon. Both kilns are soft brick construction.
I am currently firing the smaller kiln, and already have positive
results to report. by the time I got it up to reduction temperature
(1650F-1700F) the color in the kiln was much more even. before the
top would be glowing a nice orange, whilst the bottom was a good dull
red at best. Hopefully the rest of the firing will go as smooth. I
have noted that the previous settings are no longer 100% valid for
ideal firing conditions. damper position and gas pressures have
changed a fair bit from before, which I had expected.
thanks to those who had offered help,
jon
p.s. I also discovered in firing this kiln before, that lengthening
the bagwall served to make the front/bottom hotter at the expense of
temperature at the bottom/back. It made me think that moving the
bagwall will mostly affect the conditions in the bottom of the kiln,
and mostly gives control front to back.
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
jonathan byler on wed 17 sep 08
So I have not looked in the kiln yet, it is still cooling, but it
looks like the reduced flue opening did the trick. I may try making
it ever so slightly smaller still, along with a couple of other minor
tweaks. With a minimum of effort and fussing, I got cone ten on the
top almost flat (I, like mel, fire to a hard ^10), and the ^10 on the
bottom is almost touching. probably all in all only one cone
difference, top to bottom, and I actually shaved over an hour off of
my previous firing times. I attribute the time saving to the fact
that I didn't have to stall the kiln much in order to even it out.
With a few more firings, I should be able to work out better gas/air/
damper settings and speed things up a little bit more, while still
keeping an even firing.
-jon
jon byler
3-D Building Coordinator
Art Department
Auburn University, AL 36849
On Sep 16, 2008, at 5:42 PM, jonathan byler wrote:
> I had written before about having trouble with one of our gas kilns
> not heating evenly top to bottom. Nils Lou and some others
> suggested that the flue opening may be too large.
>
> So off I went and measured the flue opening on the larger kiln of
> similar design that fires off much more evenly. It measured 45"
> sq. the burners output about 590,000 btu/hr. The smaller kiln
> outputs 360,000 btu/hr. So I used my handy (but sadly minimal)
> algebra skills and decided that about 27" sq would be the ideal
> size for the flue. unfortunately, the opening is also 45" sq, just
> like on the bigger kiln. So I cut some bits of brick, and closed
> the opening to make it a little over 30" sq as I didn't want to go
> too much too soon. Both kilns are soft brick construction.
>
> I am currently firing the smaller kiln, and already have positive
> results to report. by the time I got it up to reduction
> temperature (1650F-1700F) the color in the kiln was much more
> even. before the top would be glowing a nice orange, whilst the
> bottom was a good dull red at best. Hopefully the rest of the
> firing will go as smooth. I have noted that the previous settings
> are no longer 100% valid for ideal firing conditions. damper
> position and gas pressures have changed a fair bit from before,
> which I had expected.
>
> thanks to those who had offered help,
>
> jon
>
> p.s. I also discovered in firing this kiln before, that lengthening
> the bagwall served to make the front/bottom hotter at the expense
> of temperature at the bottom/back. It made me think that moving
> the bagwall will mostly affect the conditions in the bottom of the
> kiln, and mostly gives control front to back.
>
>
>
> jon byler
> 3-D Building Coordinator
> Art Department
> Auburn University, AL 36849
>
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