Gene Arnold on thu 21 feb 08
This may be a crazy question but I need to ask. What is the distance a =
venture burner should be placed from the opining in the kiln??? Mine are =
set 1 1/2 inches back from the opening in the back of the kiln. And does =
the distance they are set at play a part in reduction???
I have fired this MFT 5 times now and I continue to get good reduction =
through out the kiln except in the bottom front of the kiln, where I get =
little to no reduction. I have flame and good pressure at the top peep, =
the bottom peep has flame but little pressure. The flame seems to be =
licking around in a lazy pattern inside the kiln on the bottom. If I =
close the damper enough to get good pressure at the bottom peep then the =
temperature starts to drop or just stalls the kiln all together.=20
Could I be getting air from some hidden place in the front that keeps =
the kiln in oxidation in the bottom front?? The door seems to fit good =
as best as I can tell. Or should I be looking for something else??=20
So I'm looking for any thing that might be keeping me from getting =
reduction in that area of the kiln.
Any suggestions??? Any help!!!
Gene=20
mudduck@mudduckpottery.net
www.mudduckpottery.net
vpitelka on fri 22 feb 08
Gene Arnold wrote -
"This may be a crazy question but I need to ask. What is the distance a
venture burner should be placed from the opining in the kiln??? Mine are set
1 1/2 inches back from the opening in the back of the kiln. And does the
distance they are set at play a part in reduction???"
Gene -
Not a crazy question at all. 1.5" away from the port face is appropriate
for a salt or soda kiln, but much farther than necessary for a reduction
kiln. I place my burner tips 1/2" from the port face. Any more than that
gives you less control.
Make sure that there are no air leaks at the bottom of your door. I am
assuming that this is a downdraft kiln. Do you have a flue tunnel? It's
simple to arrange. Just place your lowest shelves about four inches off the
floor, and then trim down some IFBs to fit under those shelves from front to
back on either side of the flue opening so that the flue draws at least
partially from the front of the kiln. You may need to close off part of the
flue draw at the back of the kiln between the bottom shelf and the flue
opening in order to get it to draw some at the front of the kiln.
Don't choke off the air to the burners when you are in reduction. You need
some turbulence to get even reduction, and people often choke off the
primary air, and that is a mistake. You should not have to change the
primary air (the air drawn into the back end of the burners) at all.
Reduction should be accomplished by closing the damper which decreases
secondary air and creates the atmosphere rich in carbon monoxide and
hydrogen that does the work.
We do not know the particulars of your kiln, but I have been able to get
even reduction in a wide variety of updraft and downdraft kilns. It is just
a matter of adjustments. You may need a little more back pressure than what
you have been using in the past. Heavy reduction accomplishes nothing, but
a good steady partial reduction from body-reduction temperature up to
maturation with a good oxidation cleanup at the end usually gives good
results.
- Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
Kurt Wild on fri 22 feb 08
Gene:
If something bothers and you have a question =96 it=92s not crazy;
to someone else mayb, but should not be to you.
Anyway, I had the same problem =96 light or no reduction in the
back corners (opposite the burners). My burners are 1-1/4=94
from the face of the burner port (kiln wall). My exit flue is
between two venturi burners. Like yours, my flame seemed
to be moving around lazily.
I pretty much, but not totally, solved the problem by placing a
slab (1-1/2=94 x 6=94 x 12=94) lengthwise along the inner side of both
flameways (along the side of the shelf stack). The idea was to
keep the flame from taking the shortest path to the flue. Some
potters use a deflector brick in the flameway to prevent this and
to deflect the flame against the outside wall and toward the back
of the kiln. After those adjustments my kiln is even from top to
bottom.
Another thing I=92ve done is to set my bottom shelf up 2-1/2=94 from
the floor.
Kurt Wild
email: kurtwild@sbcglobal.net
web: www.kurtwildpottery.com
patsgreenpots on sat 23 feb 08
Hey there Gene,
I cannot speak to your speciffic burner, and I can only speak from
experience. So anyone feel free to correct any misleading info.
Personally I found I like the burner to be fairly close to the
opening, I do think it has some bearing on the reduction. I found if
it was too far back it would tend to reduce outside the kiln some,
which is just unpleasant. As to the reduction location questions here
is what my experience has told me.
I find that, when firing glazes like shinos, most kilns have low
carbon zones where you will get little to no actual carbon trapping,
on the other hand those same zones tend to be quite nice for celadons,
as you end up with a nice clean, smooth, clear blue surface there. On
every downdraft kiln I have fired these zones do happen towards the
front bottom and rise in sort of a cone---ish manner to say mid kiln.
Of course the size change due to other factors(shelf arrangment, pot
shapes, bagwalls)
Make no mistake these places still get pretty good reduction so
temmokus, celladons, etc go well there be even on my hardest
reductions I still have a few clean areas so those get standard
glazes. and the places where carbon is heavy I put low soda shinos(As
they will get plenty and need no help) and where its lighter I put
carbon trapping( as they will tend to grab more then the regular shinos)
Of course you may indeed have a leak up front there. To find this out
here is what I would do(mind you this is with an empty cool kiln).
Shut the damper completely and build a little smoke fire on a kiln
shelf. Then shut the whole thing up like you were firing it. As the
kiln fills with smoke from the fire you will see every single little
gap and openning that might be loosing you reduction. It is
surpriseing at how many little places air can wiggle out.
Beyond that it is really tough to tell.
I hope this helped some.
Patrick Andrew Green,
Remember what Plutarc said, "The mind is not a vessel to be filled,
but rather a fire to be kindled."
--- In clayart@yahoogroups.com, Gene Arnold wrote:
>
> This may be a crazy question but I need to ask. What is the distance
a venture burner should be placed from the opining in the kiln??? Mine
are set 1 1/2 inches back from the opening in the back of the kiln.
And does the distance they are set at play a part in reduction???
>
> I have fired this MFT 5 times now and I continue to get good
reduction through out the kiln except in the bottom front of the kiln,
where I get little to no reduction. I have flame and good pressure at
the top peep, the bottom peep has flame but little pressure. The flame
seems to be licking around in a lazy pattern inside the kiln on the
bottom. If I close the damper enough to get good pressure at the
bottom peep then the temperature starts to drop or just stalls the
kiln all together.
>
> Could I be getting air from some hidden place in the front that
keeps the kiln in oxidation in the bottom front?? The door seems to
fit good as best as I can tell. Or should I be looking for something
else??
>
> So I'm looking for any thing that might be keeping me from getting
reduction in that area of the kiln.
>
> Any suggestions??? Any help!!!
>
>
> Gene
> mudduck@...
> www.mudduckpottery.net
>
>
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