MudFire - Luba & Erik on wed 27 apr 05
Time to turn to my friends and experts!!!
I'm firing my Bailey downdraft for the 4th time today. On this go-round, I
seem to have tweaked and fine tuned a bunch of small issues and questions
through extremely detailed logs and note-taking... but this quandry...
well... I just don't know how to tackle it.
The scenario:
I'm firing a 38 cubic foot downdraft with forced air. Here's the schedule
that's worked well in the past and so far today....
Candle in the AM for about 2 hours
Fire about 250 degree/hour through cone 012 (low gas pressure, medium air,
1/2 dampered-in)
Push damper in for a medium-strong (.8 on oxyprobe/about 8" backpressure
flame) body reduction at cone 012
Stop body reduction after one hour and attempt to maintain what's been
refered to me as "climbing reduction" (.65 oxyprobe) all the way to
temperature at about 120degree/hour (or faster if possible). This occurs
with the damper about 1/2 closed in, gas pressure at 2" W.C. and forced air
at "full". The idea is to get to cone 10 this way. But it never quite
happens.
At around 1800F everything slows down!!! Right now I'm at 1940F and it's
been crawling up there at about 30 degrees/hour (per pyrometer reading).
Reduction is reading the same (on the oxyprobe AND backpressure/kiln
atmosphere color) But the temperature rise has all but stopped. This has
happened each time I've fired and I tried everything to get out of the stall
(damper in, damper out, more/less air, more/less gas) and no combination
seems to work.
I tried dampering in to "keep the heat in" and the high reduction atmosphere
sends the temperature tumbling downwards.
I tried increasing gas pressure to "heat it up"... same result (I don't have
any more air to give it - it's maxed out).
I even tried creating an oxidizing atmosphere "to get the fire moving"
(despite the fact that there's a ton of copper reds in the kiln, and I'd
rather just keep in mild reduction the whole way up).... Regardless, the
temperature just stalls.
I know that all kilns are completely different, so I'm not asking "what
exactly I should do"... but rather, I wonder if anyone could share their
firing theory in this situation. I'm overlooking some rather crucial
consideration... but have run out of ideas. Or am I completely crazy and
30degrees an hour is the best I can expect at that temperature????
Any thoughts would be VERY appreciated!!
(a slightly over-heated) Luba
MudFire Clayworks and Pottery Center
Open Studio * Gallery * Workshops
www.mudfire.com
Donald G. Goldsobel on thu 28 apr 05
I suggest you reduce the gas pressure slightly to decrease the velocity of
the gases in the kiln. Increasing the pressure only increases the velocity
and you need oxygen to burn the gas to increase the temperature.The gas is
leaving the kiln without being burned. Try opening the damper a bit, give
the gas more air so it can burn and give off heat. Right now it is starving
for air and that is why when you increase the gas it drops the temp.
D
----- Original Message -----
From: "MudFire - Luba & Erik"
To:
Sent: Wednesday, April 27, 2005 4:32 PM
Subject: some gas kiln firing theory please
> Time to turn to my friends and experts!!!
>
> I'm firing my Bailey downdraft for the 4th time today. On this go-round,
> I
> seem to have tweaked and fine tuned a bunch of small issues and questions
> through extremely detailed logs and note-taking... but this quandry...
> well... I just don't know how to tackle it.
>
> The scenario:
>
> I'm firing a 38 cubic foot downdraft with forced air. Here's the schedule
> that's worked well in the past and so far today....
>
> Candle in the AM for about 2 hours
> Fire about 250 degree/hour through cone 012 (low gas pressure, medium
> air,
> 1/2 dampered-in)
> Push damper in for a medium-strong (.8 on oxyprobe/about 8" backpressure
> flame) body reduction at cone 012
> Stop body reduction after one hour and attempt to maintain what's been
> refered to me as "climbing reduction" (.65 oxyprobe) all the way to
> temperature at about 120degree/hour (or faster if possible). This occurs
> with the damper about 1/2 closed in, gas pressure at 2" W.C. and forced
> air
> at "full". The idea is to get to cone 10 this way. But it never quite
> happens.
>
> At around 1800F everything slows down!!! Right now I'm at 1940F and it's
> been crawling up there at about 30 degrees/hour (per pyrometer reading).
> Reduction is reading the same (on the oxyprobe AND backpressure/kiln
> atmosphere color) But the temperature rise has all but stopped. This has
> happened each time I've fired and I tried everything to get out of the
> stall
> (damper in, damper out, more/less air, more/less gas) and no combination
> seems to work.
>
> I tried dampering in to "keep the heat in" and the high reduction
> atmosphere
> sends the temperature tumbling downwards.
> I tried increasing gas pressure to "heat it up"... same result (I don't
> have
> any more air to give it - it's maxed out).
> I even tried creating an oxidizing atmosphere "to get the fire moving"
> (despite the fact that there's a ton of copper reds in the kiln, and I'd
> rather just keep in mild reduction the whole way up).... Regardless, the
> temperature just stalls.
>
> I know that all kilns are completely different, so I'm not asking "what
> exactly I should do"... but rather, I wonder if anyone could share their
> firing theory in this situation. I'm overlooking some rather crucial
> consideration... but have run out of ideas. Or am I completely crazy and
> 30degrees an hour is the best I can expect at that temperature????
>
> Any thoughts would be VERY appreciated!!
>
> (a slightly over-heated) Luba
>
> MudFire Clayworks and Pottery Center
> Open Studio * Gallery * Workshops
>
> www.mudfire.com
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
Frank Colson on thu 28 apr 05
Luba-
Your firing problems don't seem so overwhelming if you understand kiln
firing systems. I suggest that you go to the following site, scroll down on
the front page and click on "KILN THEORY". www.R2D2u.com This will give
you some substantial information on how to approach your firings!
Frank Colson
www.R2D2u.com
----- Original Message -----
From: "MudFire - Luba & Erik"
To:
Sent: Wednesday, April 27, 2005 7:32 PM
Subject: some gas kiln firing theory please
> Time to turn to my friends and experts!!!
>
> I'm firing my Bailey downdraft for the 4th time today. On this go-round,
I
> seem to have tweaked and fine tuned a bunch of small issues and questions
> through extremely detailed logs and note-taking... but this quandry...
> well... I just don't know how to tackle it.
>
> The scenario:
>
> I'm firing a 38 cubic foot downdraft with forced air. Here's the schedule
> that's worked well in the past and so far today....
>
> Candle in the AM for about 2 hours
> Fire about 250 degree/hour through cone 012 (low gas pressure, medium
air,
> 1/2 dampered-in)
> Push damper in for a medium-strong (.8 on oxyprobe/about 8" backpressure
> flame) body reduction at cone 012
> Stop body reduction after one hour and attempt to maintain what's been
> refered to me as "climbing reduction" (.65 oxyprobe) all the way to
> temperature at about 120degree/hour (or faster if possible). This occurs
> with the damper about 1/2 closed in, gas pressure at 2" W.C. and forced
air
> at "full". The idea is to get to cone 10 this way. But it never quite
> happens.
>
> At around 1800F everything slows down!!! Right now I'm at 1940F and it's
> been crawling up there at about 30 degrees/hour (per pyrometer reading).
> Reduction is reading the same (on the oxyprobe AND backpressure/kiln
> atmosphere color) But the temperature rise has all but stopped. This has
> happened each time I've fired and I tried everything to get out of the
stall
> (damper in, damper out, more/less air, more/less gas) and no combination
> seems to work.
>
> I tried dampering in to "keep the heat in" and the high reduction
atmosphere
> sends the temperature tumbling downwards.
> I tried increasing gas pressure to "heat it up"... same result (I don't
have
> any more air to give it - it's maxed out).
> I even tried creating an oxidizing atmosphere "to get the fire moving"
> (despite the fact that there's a ton of copper reds in the kiln, and I'd
> rather just keep in mild reduction the whole way up).... Regardless, the
> temperature just stalls.
>
> I know that all kilns are completely different, so I'm not asking "what
> exactly I should do"... but rather, I wonder if anyone could share their
> firing theory in this situation. I'm overlooking some rather crucial
> consideration... but have run out of ideas. Or am I completely crazy and
> 30degrees an hour is the best I can expect at that temperature????
>
> Any thoughts would be VERY appreciated!!
>
> (a slightly over-heated) Luba
>
> MudFire Clayworks and Pottery Center
> Open Studio * Gallery * Workshops
>
> www.mudfire.com
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Edouard Bastarache Inc. on thu 28 apr 05
Try giving more air to the kiln by keeping 1 or 2 peepholes unplugged
(Naturally it depends on the size of these holes).
In steelmills, after a certain time, melters give more air to the furnace
by opening the door.
In my case, after clay redux and reoxidation at C/08 I leave the upper
plug removed when the wind is strong enough, if the wind is not strong
enough, I unplug, at least partially, the middle peephole.
But my burners are of the Venturi type, not air-forced.
"Ils sont fous ces quebecois"
"They are insane these quebekers"
"Están locos estos quebequeses"
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.digitalfire.com/education/toxicity/
----- Original Message -----
From: "MudFire - Luba & Erik"
To:
Sent: Wednesday, April 27, 2005 7:32 PM
Subject: some gas kiln firing theory please
> Time to turn to my friends and experts!!!
>
> I'm firing my Bailey downdraft for the 4th time today. On this go-round,
> I
> seem to have tweaked and fine tuned a bunch of small issues and questions
> through extremely detailed logs and note-taking... but this quandry...
> well... I just don't know how to tackle it.
>
> The scenario:
>
> I'm firing a 38 cubic foot downdraft with forced air. Here's the schedule
> that's worked well in the past and so far today....
>
> Candle in the AM for about 2 hours
> Fire about 250 degree/hour through cone 012 (low gas pressure, medium
> air,
> 1/2 dampered-in)
> Push damper in for a medium-strong (.8 on oxyprobe/about 8" backpressure
> flame) body reduction at cone 012
> Stop body reduction after one hour and attempt to maintain what's been
> refered to me as "climbing reduction" (.65 oxyprobe) all the way to
> temperature at about 120degree/hour (or faster if possible). This occurs
> with the damper about 1/2 closed in, gas pressure at 2" W.C. and forced
> air
> at "full". The idea is to get to cone 10 this way. But it never quite
> happens.
>
> At around 1800F everything slows down!!! Right now I'm at 1940F and it's
> been crawling up there at about 30 degrees/hour (per pyrometer reading).
> Reduction is reading the same (on the oxyprobe AND backpressure/kiln
> atmosphere color) But the temperature rise has all but stopped. This has
> happened each time I've fired and I tried everything to get out of the
> stall
> (damper in, damper out, more/less air, more/less gas) and no combination
> seems to work.
>
> I tried dampering in to "keep the heat in" and the high reduction
> atmosphere
> sends the temperature tumbling downwards.
> I tried increasing gas pressure to "heat it up"... same result (I don't
> have
> any more air to give it - it's maxed out).
> I even tried creating an oxidizing atmosphere "to get the fire moving"
> (despite the fact that there's a ton of copper reds in the kiln, and I'd
> rather just keep in mild reduction the whole way up).... Regardless, the
> temperature just stalls.
>
> I know that all kilns are completely different, so I'm not asking "what
> exactly I should do"... but rather, I wonder if anyone could share their
> firing theory in this situation. I'm overlooking some rather crucial
> consideration... but have run out of ideas. Or am I completely crazy and
> 30degrees an hour is the best I can expect at that temperature????
>
> Any thoughts would be VERY appreciated!!
>
> (a slightly over-heated) Luba
>
> MudFire Clayworks and Pottery Center
> Open Studio * Gallery * Workshops
>
> www.mudfire.com
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
Vince Pitelka on thu 28 apr 05
> Stop body reduction after one hour and attempt to maintain what's been
> refered to me as "climbing reduction" (.65 oxyprobe) all the way to
> temperature at about 120degree/hour (or faster if possible). This occurs
> with the damper about 1/2 closed in, gas pressure at 2" W.C. and forced
> air
> at "full". The idea is to get to cone 10 this way. But it never quite
> happens.
Luba -
Why the forced air at "full?" It sounds like you are just pumping too much
air into the kiln. I can't imagine any other reason why it would stall like
that. You can expect to have to turn up the burners as the temperature
increases, because as the kiln gets hotter, it requires more and more input
of heat to get it to continue to climb. If you leave it at one setting, you
will often reach a plateau where it won't climb any farther. But I cannot
imagine a climbing reduction with the blowers on "full." It doesn't make
sense. I cannot imagine any circumstance on that kiln where you would want
to fire with the blowers on full.
Did this kiln come with firing instructions, and if it did, what do they
say? Have you talked to Bailey about this problem? Tell us more, and we
might be able to help.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
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