mel jacobson on fri 7 nov 03
up draft, down draft, i do not use them.
i think they are throw a back to wood fired kilns.
people think they need them to protect the ware.
i do not share that reasoning.
in three kilns that i have fixed for folks, i just
ripped them out.
the kiln fired so much better, and the ware was
not affected.
no kiln that we have at the farm, here at home, or
the dozen or so that i have built for folks have
bag walls.
they all fire very well.
mel
From:
Minnetonka, Minnesota, U.S.A.
web site: my.pclink.com/~melpots
or try: http://www.pclink.com/melpots
new/ http://www.rid-a-tick.com
mel jacobson on sat 8 nov 03
yes, richard, in certain cases, the bag wall saves a kiln.
but, in the cases i have mentioned, it was just a heat damn.
and, i am a charter member in the small flu/full gas/flattop club.
goes back to 1965.
many people do not have a clue why they install
bagwalls.
they just do it because they saw it once in a kiln.
it must be done for a specific reason...often that is not
the case.
you know what you are doing, are a veteran of many thousands
of firings. nothing i say applies to you.
you have a professional agenda.
mel
From:
Minnetonka, Minnesota, U.S.A.
web site: my.pclink.com/~melpots
or try: http://www.pclink.com/melpots
new/ http://www.rid-a-tick.com
Richard Aerni on sat 8 nov 03
On Fri, 7 Nov 2003 21:28:46 -0600, mel jacobson wrote:
>up draft, down draft, i do not use them.
>
>i think they are throw a back to wood fired kilns.
>people think they need them to protect the ware.
>
Sorry, Mel...two of my last posts have been directly contradictory to your
opinions...
The size and placement of my bagwalls make a huge difference in how my kiln
fires. I think it all depends upon the type of kiln you build. I suspect
that you are building the Nils Lou model of kiln, with the overpowered
burners and small flues creating a pressurized box of heat. Mine relies
more on finesse, and the bag wall is essential...not just to deflect the
heat, but also to distribute it. Without the bagwall, my flame path would
be straight across the kiln bottom and out.
Just my opinion, but I've tried most of the alternatives, and I don't care
what anyone says, I'm going to do what works for me...
Now, I really should go down and get ready for my sale...
Richard Aerni
Bloomfield, NY
Vince Pitelka on sat 8 nov 03
> The size and placement of my bagwalls make a huge difference in how my
kiln
> fires. I think it all depends upon the type of kiln you build. I suspect
> that you are building the Nils Lou model of kiln, with the overpowered
> burners and small flues creating a pressurized box of heat. Mine relies
> more on finesse, and the bag wall is essential...not just to deflect the
> heat, but also to distribute it. Without the bagwall, my flame path would
> be straight across the kiln bottom and out.
I have to agree with Richard Aerni. Mel has obviously perfected some kilns
that fire beautifully without bagwalls, but a blanket condemnation of
bagwalls as "heat dams" is unwarranted. Many kilns have the burners
directed through the side walls, pointing towards the wares, and without a
bagwall the wares in front of the burners would get scorched. And aside
from that, many downdraft kiln designs benefit from bagwalls to simply
direct the heat upwards, so that it circulates more effectively throughout
the kiln. This is an old issue that many kiln designers have struggled
with, and there are many situations where bagwalls are beneficial.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Office - wpitelka@tntech.edu
615/597-6801 x111, FAX 615/597-6803
http://iweb.tntech.edu/wpitelka/
John K Dellow on sun 9 nov 03
>
>
I wonder if haveing the burners pointing up is the reasion Mel does not use bag walls. My burners are horozontal from each corner ( 8 burners) and I need a low bag wall , 8 inches, and a deflection brick on each side.
John Dellow "the flower pot man"
From the land down under
Home Page http://www.welcome.to/jkdellow
http://digitalfire.com/education/people/dellow/
John K Dellow on sun 9 nov 03
Another thought about burners pointing up . The tip of the flamb is the hottest ,so if the burners is pointing up this point will be near the top of the kiln .If the burners is horozontal the the hottest point of the flamb is at the bottom shelf level .
So pointong up has less of a flashing affect on the wear . Point horozontal can cause flashing low down near the burners . This is veary
apparent with terra-cotta.
John Dellow "the flower pot man"
From the land down under
Home Page http://www.welcome.to/jkdellow
http://digitalfire.com/education/people/dellow/
Clay Mudman on sun 9 nov 03
----- Original Message -----
From: "Richard Aerni"
> The size and placement of my bagwalls make a huge difference in how my
kiln
> fires. I think it all depends upon the type of kiln you build.
I agree. It depends on how your burners are directed and where
the flue is. With the setup like Mel is talking about, with the burners
on each side of the chimney, bagwalls are not necessary.
Also, bag walls are not always necessary in wood kilns. My wood
kiln does not have bag walls. The flame enters the ware chamber at the
back of the kiln and there is space for the flame to come up without
obstruction and there is also space on both sides so the flame can flow
around the sides of the kiln.. The flue exit is a channel under the
floor, between the two firechambers, so it is a true downdraft kiln (flue
exit is below the level of the flame entry.) Most gas shuttle kilns here
have the flue exit under the floor of the shuttle.
--
Lee In Mashiko, Japan
http://Mashiko.org
Web Log (click on recent date):
http://www.livejournal.com/users/togeika/calendar
Kathi LeSueur on sun 9 nov 03
I don't think there is a potter in Ann Arbor who has a bagwall on their
kiln and there are lots of gas kilns in and around this town. What most
of us do have is 7 inches of space from the wall of the kiln to each
side of the shelves. But then again, we don't have chimeny's either.
Kathi
Lee Love on sun 9 nov 03
----- Original Message -----
From: "Vince Pitelka"
> bagwalls as "heat dams" is unwarranted. Many kilns have the burners
> directed through the side walls, pointing towards the wares, and without a
> bagwall the wares in front of the burners would get scorched.
The commercial gas kilns here all have the side burner ports on the
bottom of the kiln, against each side wall, so the burners point up.
Venturi burners are the norm. The space needed is much smaller, so that
if there is a bag wall, it is very narrow and takes up little space.
Clay
iandol on mon 10 nov 03
Dear Friends,
I recall there was an article some years ago in CM, early eighties, =
which had a lot to say about Bag Walls and Tuning a Kiln to get the =
optimum use of all of the heat which was pumped into a kiln.
Bag walls are a feature of many industrial kilns where they are used to =
serve specific purposes. They are essential in a true down draft kiln =
where gases are drawn out of the kiln through a chequer work floor to =
prevent a short circuit in the flow pattern of the burning fuel. Nor =
need a bag wall be a solid structure. Again, chequer work assists in =
controlling the distribution of heat in a cross draft kiln. And though =
Nils Lou has several references to Bag Walls, he seems more concerned =
with the economics of heating hard brick rather than exploring =
alternative options or reasons for using or not using this in kiln =
control or other purposes for which they might be used. As an example, =
in a wood fired kiln openings in a chequer work bag wall can be used as =
a columbarium where small pots can be put to roost to get additional =
heat and ash.
Best regards,
Ivor Lewis. Redhill, South Australia
Clay Mudman on mon 10 nov 03
----- Original Message -----
From: "John K Dellow"
> I wonder if haveing the burners pointing up is the reasion Mel does not
>use bag walls.
John, the MFT design I think Mel uses has two burners pointing in,
horizontal, from the back wall on each side of the chimney. The kilns
that Donovan Palmquist built at Northern Clay Center, where I used to gas
fire, are of a similar design, but with an arch. If I remember
correctly, the kilns at Northern had short bag walls with target bricks in
the middle.
Most of the Japanese kilns I've looked at, with the up pointing
burners along the side walls, don't have bag walls. My teachers two gas
kilns had short bag walls, a little taller than a yunomi. His large kiln
had eight venturi burners, four on a side, and us apprentices were allowed
to put work inside the bag wall, between the burners. There were 10 spots
and 5 apprentices, so we could put in two yunomi each firing. I usually
filled my spots with glaze tests.
--
Lee In Mashiko, Japan
http://Mashiko.org
Web Log (click on recent date):
http://www.livejournal.com/users/togeika/calendar
Nils Lou on sat 5 mar 11
first, if the burners are firing down the length of=3D20
your kiln along the wall there is no reason to have a
bagwall. just adds more mass to heat. probably don't need=3D20
a brick in the flame path either, but it gives you something to
play with. a split brick at the end set at a 45 degree can
help deflect the flame upward. fiber in the flame trench tends
to "break up" the flame. I don't use it in the MFT, but it
really helps in the Alpine which has a much shorter trench
length. Mian thing with the Alpine is to get rid of the stupid
curved baffles. That helps more than anything.
nils lou, professor of art
http://nilslou.blogspot.com
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