karen terpstra on mon 10 nov 03
To bagwall or not to bagwall....sometimes when I disagree with Mel, I
run it by Nils Lou. (Both Mel and Nils have waaaaaay more years in
experience with kilns than I do. If you add their ages together, they
are older than dirt. :) )
Here's what I received from Nils on the bagwall discussion:
"Obviously, muddy minds need the Lou filter. Mel is correct in his
bagwall
theory so long as the flame trench is parallel to the flame path. For
instance the ubiquitous Alpine kiln of vintage years fires infinitely
better when the arched tubes and "bagwall" are removed. Kilns with side
burner design firing directly into the ware load are archaic, in my
opinion, but do need a baffling to prevent flame impingement. But this
baffling is not, technically, a bagwall; it is really a target baffle
and
contributes to the heat mass sucking up Btu's, hence a poor design. Many
kilns have massive bagwalls along the flame path when all that may be
needed are a few well placed bricks to control flame splash. Just
because
the kiln is "manufactured" doesn't mean it was engineered for optimum
performance--or even that the designer has ever fired a kiln! Experiment
with your kiln and you will probably learn how to make it perform
better.
Know your equipment. I think Vince and Richard would agree."
We fire our Bailey with a set of target bricks and baffle bricks and in
that situation....Nils is right...not technically a bagwall. Students
have neglected to replace the target and baffle bricks on occasion after
cleaning the bottom row of shelves. We experienced "flame impingement"
on the ware in the back bottom shelves (warping and glaze
discoloration). The rest of the work was fine.
We have a new salt kiln with Lou's burners, hard brick inside, soft
outside. Works like a charm without the bag walls. But we want flashing
etc. so variations would be throughout the kiln anyway. The flame trench
is a bit wider than in comparison to the Baily. We haven't noticed
warping.
Our wood kiln requires bagwalls in both chambers because of the way we
like to fire and type of work we put in it. They help control the flame
pattern in the first chamber and the bagwall in the second chamber helps
keep the charcoal under control.
We (including Marta) will unload the wood kiln tomorrow...and, the
low-fire salt kiln load that Marta did last week with the students.
I'll write about it later this week. Marta has been the highlight of
the semester, btw.
Karen Terpstra
La Crosse, WI
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