pam pulley on wed 12 jul 00
Our last firing of our "dragon" kiln (Alpine Updraft) which is outside her
in mid-Michigan had a real problem. We all take turns/shifts during the
candling and firing, but the last group could not getit up to Cone 6. Open
the damper, close damper, more gas and less gas, do nothing etc. Now the
problem I think was that it was really humid that day. Can someone explain
how that could effect the firing? Shouldn't we be able to compenstate for
that? and then ofcourse it rained on and off? After 19 hours the crew said
"no more" and shut it down about cone 4.
The dragon does have a little metal roof over the top to keep direct rain
out.
Thanks for information.
Pam
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Chris Trabka on wed 19 jul 00
Pam,
Firing on a humid day is a pain. Last summer I almost gave up after 20 hours; 2
hours later cone 10 finally went over. The next day I did a lot of thinking. Here
are my conclusions:
On a humid there are two problems to overcome extra water vapor in the air and less
oxygen (displaced by the water vapor). The main culprit is less oxgyen. I
compensate by opening the damper more. If I still have too much reduction I will
lower the gas pressure until I get the "correct" amount of reduction. Unfortunately
because of the reduced gas pressure the firing will take a bit longer.
My damper has 1 inch marks going from 1 (completely closed) to 10 (wide open).
About two weeks ago I fired when the relative humidity was about 90% (the dew point
was about 65 degrees most of the day). I normally have the damper some where
between 5 and 7; on the humid day it was at 9. Further I usually have about two and
three quarter inches of water column pressure; on the humid day I reduced the
pressure to two and one quarter inches. The firing took one hour longer than usual
- but the reds were spectacular.
Chris
pam pulley wrote:
> Our last firing of our "dragon" kiln (Alpine Updraft) which is outside her
> in mid-Michigan had a real problem. We all take turns/shifts during the
> candling and firing, but the last group could not getit up to Cone 6. Open
> the damper, close damper, more gas and less gas, do nothing etc. Now the
> problem I think was that it was really humid that day. Can someone explain
> how that could effect the firing? Shouldn't we be able to compenstate for
> that? and then ofcourse it rained on and off? After 19 hours the crew said
> "no more" and shut it down about cone 4.
>
> The dragon does have a little metal roof over the top to keep direct rain
> out.
>
> Thanks for information.
>
> Pam
>
> ________________________________________________________________________
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Earl Brunner on thu 20 jul 00
Alpine Updrafts are notorious for this I think, they used to
give us fits back in college. One thing that has not been
addressed in response to this post (at least so far) is the
stack inside the kiln. If you crowded or choked the top of
the kiln near the flue then that can cause problems. The
other thing I have recently come to realize (since I got a
digital pyrometer) is that with the alpine we used to move
the damper in and out anywhere from a half an inch to 2-3
inches at a time. You couldn't really see what that was
doing to the firing with the old needle type pyrometer. The
digital pyrometer shows right away (with in less than a
minute, although I usually allow a little more time) whether
what you did will cause the kiln to continue to climb, stall
or lose temperature. What I have found is that adjustments
as little as an 1/8th to a 1/4 of an inch can stall the heat
climb. The kiln is much more sensitive to small changes
than I ever realized. Add to that the humidity, which may
compound the problem along with the stack inside the kiln
and who knows?
>
> pam pulley wrote:
>
> > Our last firing of our "dragon" kiln (Alpine Updraft) which is outside her
> > in mid-Michigan had a real problem. We all take turns/shifts during the
> > candling and firing, but the last group could not getit up to Cone 6. Open
> > the damper, close damper, more gas and less gas, do nothing etc. Now the
> > problem I think was that it was really humid that day. Can someone explain
> > how that could effect the firing? Shouldn't we be able to compenstate for
> > that? and then ofcourse it rained on and off? After 19 hours the crew said
> > "no more" and shut it down about cone 4.
> >
> > The dragon does have a little metal roof over the top to keep direct rain
> > out.
> >
> > Thanks for information.
> >
> > Pam
> >
> > ________________________________________________________________________
> > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.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.
>
> ______________________________________________________________________________
> 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.
--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Hank Murrow on fri 21 jul 00
>Pam,
>
>Firing on a humid day is a pain. Last summer I almost gave up after 20
>hours; 2
>hours later cone 10 finally went over. SNIP___
>On a humid there are two problems to overcome extra water vapor in the air
>and less
>oxygen (displaced by the water vapor). SNIP___ on the humid day I reduced the
>pressure to two and one quarter inches. The firing took one hour longer
>than usual
>- but the reds were spectacular.
>
>Chris
Dear Chris & Pam; Ohio State University did some nice studies(Bulletins 202
& 204) about the beneficial effects of water vapor on reduction. At high
temps the hydrogen disassociates and grabs the oxygen atoms from the oxides
in the ceramic materials, so your humid day may have helped the reds. BTW,
there is watervapor in natural gas; but much less in propane; perhaps
propane stokers could try a water drip to aid reduction. I imagine this
also has bearing on the effects of watervapor in wood fired kilns. Regards,
Hank in Eugene
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