Donald MacDonald on wed 6 apr 05
I am hoping that someone on the list has some
information on cross draft kilns. The kiln is small,
about 8 cu. ft. stacking space, two burners one side,
chimney the other. The previous owner fired it for
years, living with uneven top and bottom, and less
than adequate reduction. It is natural gas fired. I
am used to downdraft kilns, four burners, where the
burners come in and the flame is initially in a
firebox, with bagwalls along the sides. I looked in
Daniel Rhodes book about Kilns, and in the Kiln book
by Frederick Olsen, Rhodes has a diagram of how the
bagwall should be, but it doesn't work in this kiln.
The top reached temp., but the bottom did not, and
reduction was spotty. Any ideas or information will be
gratefully received.
June
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Kurt Wild on thu 7 apr 05
June;
you wrote: "......Rhodes has a diagram of how the
bagwall should be, but it doesn't work in this kiln.
The top reached temp., but the bottom did not, and
reduction was spotty...................
Have you tried leaving more openings in the bag wall at the lower level
and/or lowering the height of the bag wall itself?
Kurt
Marcia Selsor on thu 7 apr 05
I built a cross draft catenary arch kiln about 60 cu. ft. back in the
70's and fired with oil. You can see a diagram of it and the burner in
the old Studio Potter Book under alternative fuels. Play around with
the bag wall. Maybe open it up with little gaps to get some heat down
at the bottom. Use your primary air control and dampper to elongate the
flame and heat. Our kiln was fairly even if I remember but oil is a
different breed of flame). We switched sides for the burner ports and
actually knocked out new ones on the opposite side and plugged up the
old ones. That was gutsy (scary) ..to hammer out two big holes in the
side of the base of the kiln. Maybe you should try that. Get two more
burners and see if that could be a possible solution. What is the wall
made of. Ours was hard brick, not mortared.
Marcia Selsor
On Apr 6, 2005, at 5:55 PM, Donald MacDonald wrote:
> I am hoping that someone on the list has some
> information on cross draft kilns. The kiln is small,
> about 8 cu. ft. stacking space, two burners one side,
> chimney the other. The previous owner fired it for
> years, living with uneven top and bottom, and less
> than adequate reduction. It is natural gas fired. I
> am used to downdraft kilns, four burners, where the
> burners come in and the flame is initially in a
> firebox, with bagwalls along the sides. I looked in
> Daniel Rhodes book about Kilns, and in the Kiln book
> by Frederick Olsen, Rhodes has a diagram of how the
> bagwall should be, but it doesn't work in this kiln.
> The top reached temp., but the bottom did not, and
> reduction was spotty. Any ideas or information will be
> gratefully received.
>
> June
Gary Navarre on fri 8 apr 05
Hello June,
Pictures are worth a thousand words and a few hunderd words need to be
read. I'll quote from my Rhodes 1st. edition, 2nd. printing, p.129>133.
On Wed, 6 Apr 2005 23:55:05 -0400, Donald MacDonald
wrote:
>I am hoping that someone on the list has some
>information on cross draft kilns. The kiln is small,
>about 8 cu. ft. stacking space, two burners one side,
>chimney the other.
"All downdraft and crossdraft kilns require a chimney tofurnish sufficent
draft ir pull to draw the gasses downward or across through the setting.the
hot products of combustion will only travel upwards unless induced by a
draft to do otherwise. Therefore, the design and construction of the
chimney is a critical factor."
Try adding a foot or two to the stack.
>Rhodes has a diagram of how the
>bagwall should be, but it doesn't work in this kiln.
>The top reached temp., but the bottom did not,
"A valuable feature of downdraft and crossdraft circulation is the ease
with which the flow of heat can be changed or redirected to secure more
even temperatures. If the kiln fires too hot in the lower part, this may be
overcome by raising the height of the bag wall, forcing mor of the flame
toward the top of the kiln.On the other hand, if the kiln is firing too hot
in the top, the reverse remedy is tryed, I.E., lowering the bag walls or
making larger openings in them so more of flame will pass directly into the
lower part of the setting."
In my Hobalectric wood fired conversion I had a brick or two for a bag
wall which didn't work well and it took up space so I stacked the bottom
with short posts and tight. Still it got hotter,^11 on the bottom, and ^10
in top, but I got more pots out. (Can't remember the ULR so just click my
link to see the results, about half way down the albums.)
>and
>reduction was spotty.
I would imagine after you get the kiln more even you can adjust the
reduction. Generally when we fine tune a kiln it is a good practice to only
change one aspect at a time or we won't know what cause created what effect.
Damper manipulation is another factor. I start wide open to get the heat
to the stack, dry the pots, and keep the kiln cooler. Once the draft is
established I nudge it in some to start keeping the heat in the chamber but
not so much as to loose draft.
Are you using forced air or atmospheric burners?
Of course, I could be blowing smoke up my stack since I don't fire gas
anymore but I think the same principles apply. Thanks for reading, good
luck, and stay in there!
G in da U.P.
Navarre Pottery
Norway, Michigan, USA
http://public.fotki.com/GindaUP/
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