Mark & Sylvia Mondloch on thu 4 jan 01
I tried our new x-mas toy - a double probe pyrometer- in a bisque load =
in my propane MFT kiln. I put one probe in the bottom front wall and one =
in the top back wall. The front bottom lags behind in the early stages =
of firing and then catches up and actually fires hotter at the end in =
glaze firings. With the probes, I found that all the way up to bisque =
temp I have about 200F difference. The front is just starting to catch =
up at bisque temp.
I'm thinking that means that the front bottom area is actually getting =
a faster firing then when it plays catch-up and I think glaze faults =
have been more prevalent in that area so I'd like to even it out.
If I change target bricks to direct the flame to the front for the early =
part, I'm afraid that it will make the front even hotter at the end. My =
kiln chimney provides alot of draft and I know it helps to even out the =
temp if I damper it in to create some back-pressure, but I also =
understand that I need extra oxygen during bisque and early stages of =
glaze firing. So... my question is, how much extra oxygen do I need? I =
have an oxy probe so I should be able to damper in for back-pressure =
which will also give me a smaller amount of extra oxygen if a smaller =
amount is OK. If you bisque in a gas kiln do you always have the damper =
wide open? and in early stage of glaze loads? If you have an oxyprobe, =
what do you have it set at in the early part? If you fire a MFT do you =
notice this temp differential?=20
Thanks for any input,
Sylvia Mondloch =20
=20
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake, WI 53075
silvercreek@execpc.com
http://www.execpc.com/silvercreek
Jeff Lawrence on fri 5 jan 01
Sylvia was describing the temperature difference in her MFT:
Hello Sylvia,
I have the same situation in my kiln and have tried lots of bagwall
configurations from minimalist to byzantine. I kind of wanted to grab the
problem by the throat and subdue it. Finally, I've concluded that for me
other factors are more effective.
Things I've found that help are:
- fire slowly -- minimal gas and air will get fairly hot if you give it a
lot of time
- fire with a minimum of gas and air consistent with oxidation in early
stages and your damper will help even things out.
- check your flue bore -- I've bricked mine down to about 45 square inches
and that helped even things out a lot.
- loosen and even out the load
Best,
Jeff
Jeff Lawrence ph. 505-753-5913
Sun Dagger Design fx. 505-753-8074
18496 US HWY 285/84 jml@sundagger.com
Espanola, NM 87532 www.sundagger.com
Jennifer F Boyer on fri 5 jan 01
I think this pattern of cool bottom front in the beginning
stages is normal. I have a MFT shaped kiln, but didn't use the
flue system(use a neutral at, not reduction) and I have this
unevenness. It almost catches up by the end of a glaze cone 10
firing, but is way off at bisk temps. I messed with bagwalls,
and now have none, as they cooled the bottom even more . I have
a target brick that is set so it gives as much heat to the
front as possible without creating a cold spot near the flue
opening. But you have the tools to work on this problem. I
also have the 2 thermocouple pyrometer and an oxyprobe. If you
use the thermocouple setting that shows the difference between
the 2 thermocouple readings, you can get a pretty good idea of
what is helping even out the temps. You time the rate of change.
I've found that keeping the damper more closed in the early
stages will start the bottom catching up faster. You are still
below max pressure so have more leaway to skimp on draft without
getting into reduction. I think staying below .08 on the
oxyprobe should keep you out of reduction.
Jeff Lawrence wrote:
>
> Sylvia was describing the temperature difference in her MFT:
>
> Hello Sylvia,
>
> I have the same situation in my kiln and have tried lots of bagwall
> configurations from minimalist to byzantine. I kind of wanted to grab the
> problem by the throat and subdue it. Finally, I've concluded that for me
> other factors are more effective.
>
> Things I've found that help are:
> - fire slowly -- minimal gas and air will get fairly hot if you give it a
> lot of time
> - fire with a minimum of gas and air consistent with oxidation in early
> stages and your damper will help even things out.
> - check your flue bore -- I've bricked mine down to about 45 square inches
> and that helped even things out a lot.
> - loosen and even out the load
>
> Best,
> Jeff
>
> Jeff Lawrence ph. 505-753-5913
> Sun Dagger Design fx. 505-753-8074
> 18496 US HWY 285/84 jml@sundagger.com
> Espanola, NM 87532 www.sundagger.com
>
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Jennifer Boyer mailto:jboyer@adelphia.net
Thistle Hill Pottery
95 Powder Horn Glen Rd
Montpelier, VT 05602 USA
802-223-8926
http://www.thistlehillpottery.com/
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