Judith Frederick on thu 9 may 02
Hi all,
We have an Alpine gas updraft kiln at school. Our question is this, on the
left side of the kiln there is a whole in the wall. It is about 8" off the
floor and about 12" from the back wall. What is it for? We have it covered
with wool fiber and bricks. We are firing tonite. We are having trouble
getting the top and bottom temperatures to even out. After 5 hours or so we
have a 300 degree diference between the top and bottom. The gas is at about
3.5, and the blower is about 40. The kiln manual says to leave both peep
holes close.
Any info would be greatly appreciated. Thanks. Judy in Baltimore.
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Craig Clark on thu 9 may 02
Judith, I learned how to fire by using an old 60 cubic foot Alpine
updraft. Did this consistently and evenly for close to ten years. We could
take the cone pats from the top and bottom after a firing and they would be
pretty close to each other.
If you are having trouble with uneven firing it has to do with the
length of your flame which is primarily determined by the adjustment of your
dampers and the ratio of primary air to fuel.
Before I go into the explanation of what worked for us I have a
question, is your Alpine one of the old models where you are able to
independently adjust the speed of the blowers and the pressure of the fuel
or is it one of the new-fangled computer contolled things? If it's computer
controlled I don't know anything about them.
Those holes that you are refering to are not the peep holes (which are
located in the door.) I don't know what they are called but we always left
ours open. When we were after a nice heavy reduction during part of the
firing the gas and blower speeds were adjusted so that enough back pressure
was created in the kiln to result in a small lick of flame coming out of the
ports.
Another thing that we would do to check on "eveness" of firing during
reduction would be to open the peep holes and look at the flame coming form
them. If things were proceeding well there would be flame coming out of both
the top and bottom holes. Once again this was accomplished by adjusting the
ration of fuel to air and the dampers.
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
----- Original Message -----
From: "Judith Frederick"
To:
Sent: Wednesday, May 08, 2002 10:13 PM
Subject: Re: Alpine kiln question
> Hi all,
>
> We have an Alpine gas updraft kiln at school. Our question is this, on
the
> left side of the kiln there is a whole in the wall. It is about 8" off
the
> floor and about 12" from the back wall. What is it for? We have it
covered
> with wool fiber and bricks. We are firing tonite. We are having trouble
> getting the top and bottom temperatures to even out. After 5 hours or so
we
> have a 300 degree diference between the top and bottom. The gas is at
about
> 3.5, and the blower is about 40. The kiln manual says to leave both peep
> holes close.
> Any info would be greatly appreciated. Thanks. Judy in Baltimore.
>
> _________________________________________________________________
> Send and receive Hotmail on your mobile device: http://mobile.msn.com
>
>
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Jeff Tsai on thu 9 may 02
Judy Wrote:
We have an Alpine gas updraft kiln at school. Our question is this, on the
left side of the kiln there is a whole in the wall. It is about 8" off the
floor and about 12" from the back wall. What is it for? We have it covered
with wool fiber and bricks. We are firing tonite. We are having trouble
getting the top and bottom temperatures to even out. After 5 hours or so we
have a 300 degree diference between the top and bottom. The gas is at about
3.5, and the blower is about 40. The kiln manual says to leave both peep
holes close.
Any info would be greatly appreciated. Thanks. Judy in Baltimore.
Hi Judy,
We also use a kiln almost exactly like that at our school. The hole, which
has a name that right now eludes me, doesn't need to be plugged up and
really
doesn't cause significant amount of differences in your kiln that it is the
cause of your temperature difference. YOu don't need to have the whole
plugged. We use it as a sign of too heavy of reduction in reduction gas
firings (I assume this whole is very low down, lower than the bottom peep
hole and along the side of the lowest part of the bag wall. When we damper
into reduction, if we see flames shooting out of this hole, we know we've
gone further than we need to in reducing the glazes.
The temperature difference is simply caused by the design of the kiln
itself.
It's just a common updraft problem. I don't know what sort of firing you
plan
on doing. For bisque firings, I keep the flame as low as possible in the
kiln
so the bottom will heat up and convection will cause the top to heat as
well.
Basically, what you want is for the hottest part of the flame, especially
during the first few hours of firing, to be at the bottom of the kiln. Since
the hottest part is the tip, you simply try to combust as much of the gas at
the base of the kiln as possible so the flame doesn't shoot up towards the
damper seeking oxygen. This will help keep the kiln more even during later
stages.
If the kiln gets hot for a bisque and it's really hot at top and cold at
bottom, I do the same thing. I turn the gas way way down and turn the blower
way up. I then damper down until I kiln is almost in reduction. The idea
again is for the combustion of the gas to occur at the base of the kiln,
thus
heating up the kiln at the bottom while the top is held soaking at its
temperature while the bottom catches up. I usually will do this if I see,
say, a cone 010 cone go down at top and I'm firing to 06, but the bottom
color looks like it hasn't passed 1400 degrees F.
Glaze firings are a little different. Again it's about getting the bottom
hot
and keeping it hot first. But the disparity tends to happen anyway in
updrafts. IN regular reduction high fires, I just use the top cones to tell
me when to put it into reduction, but usually during the reduction, the kiln
evens out because dampering in at that point forces a lot of heat to the
bottom of the kiln.
good luck,
-jeff
vince pitelka on thu 9 may 02
> hole and along the side of the lowest part of the bag wall. When we damper
> into reduction, if we see flames shooting out of this hole, we know we've
> gone further than we need to in reducing the glazes.
> The temperature difference is simply caused by the design of the kiln
itself.
> It's just a common updraft problem.
Jeff and Judy -
That firebox port is a very valuable indicator, and it need never be
plugged. There is no reason to have such a temperature differential in any
updraft, especially an Alpine. I don't much like Alpines, but I got good at
firing them during my six years at UMass Amherst (three as grad student,
three as studio tech). We had three of them. The challenge with any
updraft is to maintain enough back pressure to get even temperatures without
over reducing. Natural draft updrafts usually have a network of burners
under the floor or around the perimeter, and a low, slow flame will usually
still heat the whole kiln fairly evenly. That is not true on an Alpine,
which just has the two power burners at the bottom front. I found that by
maintaining good airflow from the power burners while dampering down
considerably, I could create plenty of turbulence in the kiln, which is
essential to getting even temperatures in an Alpine.
The side port does not serve any purpose until you reach red heat. After
that, you can balance the blower intake shutter and rheostat settings, the
gas pressure, and the damper to get a small blue flame at the firebox
side-ports. That will give you even temperatures without excessive
reduction. When you want body reduction, close the damper slightly and
increase the gas slightly (and if necessary, close the air shutters
slightly) until the small flames at the firebox ports go orange, with a good
corresponding orange flame at the spyholes and the damper. After body
reduction, back off to decrease the flame slightly, but keep it a little
orange/yellow at the damper and all ports for a partial or climbing
reduction to get up to temperature. If you do this there is no need for a
glaze reduction.
Hope this helps -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Cantello Studios on thu 9 may 02
Hi Judy
I'm not sure that you will get this note in time but in up draft kilns the
top is always hotter in the first part of the
firing. Though 300 degrees is a big difference 100 to 150 being the norm. I
am assuming the top is hotter? You did not say?
If this is the case it sounds like you have the flue open to much 2" is
about right until the kiln reaches about 1500
than you can damper down to about 1 1\2 inch. I need to say that I fire
venture up drafts I must say that blowers
are pains and I don't use them, regardless you need to push the heat down to
the bottom of the kiln and that is done
by closing down the damper some. Most kilns will even out by the time they
reach 1800 or so by doing this. What this
does is cause back pressure, forcing the heat down it also starts the first
stage of reduction. As for the large hole in
the side of the kiln I thing they were put there to help keep the bottom of
the kiln cooler in the later stages of the
firing that's because the bottom will get hotter as you reach some where
around 2300. My ceramics teacher used these
holes to throw tennis balls filled with motor oil in them to luster his pots
at 1400 after cone 10 or max temp was reached
and the kiln had cooled down.
Good Luck Chris
From Cantello Studios
Snail Scott on wed 15 may 02
Let's not forget the importance of stacking. Those
Alpine updrafts can definitely be fired to even
temperatures throughout, and even hot on the bottom
if you overdo it a bit! (Of course, hot on the bottom
is a lot easier to correct for than the opposite,
once it happens!) All the flame and damper control in
the world won't overcome an inappropriate stacking
job, though.
As several other people have mentioned, turbulent
flow at the bottom of the kiln goes a long way
toward evening out the temperature, but this is
difficult to achieve if the bottom of the kiln is
packed tightly with the shelves and ware close
together.
Pack the bottom shelf loosely, to allow for airflow
through this level. The second shelf should be at
least 9" above the bottom and also loosely packed.
Save the tight packing and short shelf-posts for
higher in the kiln. If there is not enough ware to
really fill the kiln, leave the bottom shelf or
shelves empty, rather than having a short stack.
It's almost impossible to even out a load that
doesn't fill the kiln to near the top, so put your
empty space at the bottom instead.
-Snail
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