orion on fri 6 nov 98
Subject: Re: Marathon Car Kiln - even heating
Folks may suggest that you to raise bagwalls, lower bagwalls, fiddle with
gas pressure, raise the chimney, lower the chimney, etc., etc. -- but I
believe that (if your kiln is evenly insulated, without one wall less
insulated than the others, or without a "heat leak" at a poor door seal, for
instance) ... the best two ways to improve even heating are:
a) Keep the "mass" of the load as even as possible -- which may mean
putting your tallest work at the bottom. The weight of the kiln shelves
and posts is usually heavier (by far) than the sum of the ware! Sometimes,
I'll actually put an extra layer of unoccupied shelves in the kiln at a
spot I want to "slow down" -- and, I nearly always place an empty "cap"
(deck) of shelves above the top shelf with ware. It's amazing how
effective "mass management" can be!
b) Ensure good circulation of hot gases through the load by taking care not
to load too tightly. Also, load lower work at the outside edges of each
deck of kiln shelves -- this will allow free circulation of hot gas to the
core of the load.
We've really worked hard at perfecting even firing in our kiln (about 50
cu.ft.) because we're sometimes forced to fire an architectural piece in
more than one firing -- really need those pieces to end up at the same cone!
We've actually ended up with a top/bottom difference of only 4'F (!) with
identical Cone 10's everywhere... Well, that was once!
You might want to experiment with the balancing the mass, etc. first --
before fiddle-faddling with the basic configuration/design of flame
deflection, etc. & flow-through.
Best of luck!
Ellen Baker - Glacier, WA
orion@telcomplus.net
PS -- a nice long soak at the end always seems to help
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