David Hendley on mon 18 mar 02
If you have enough power coming in, and a way to let it
out again, you can make a kiln just about any shape, and
it will "work". It's just a box to hold heat.
That said, it does matter what shape the kiln is. Particularly
if, like most of us, you want more than to just heat the
ware to temperature.
I'm assuming that you want a kiln that fires evenly, within
a half-cone difference throughout the kiln. Some designs you
see, particularly wood-fired cross-draft or groundhog
designs, are not striving for consistency.
I'm certainly no kiln expert, but, by the same token, the
engineering types often do not know what we potters are
trying to do with our "furnaces". I don't think many of them
have much experience with wood firing and natural draft
kilns without blowers. And seldom are commercial designers
concerned with reduction firings. There's a difference.
I would not stray too far from the notion that a small potter's
kiln should have a chamber that is close to being a cube.
It doesn't matter if the top is flat or arched, as long as it is
close to the "cube" relationship. Talk about an arch "guiding"
the flames is pure speculation, and, in fact, we want our kilns
to have turbulence, so the heat and firing effects (reduction,
salt, soda, ash) will be well-distributed.
Don't cut corners with your design. Always design your kiln
with extra space around the shelves, to give the flame plenty
of room to maneuver.
As for arches, shaped bricks are always better than straight
bricks in an arch. They just are; the taper hold them in place.
On the other hand, for centuries people have been building
arches with ONLY straight bricks, using mortar and rubble
to fill in on the top of the arch to hold the bricks in place.
On a small kiln, you will usually need to use some straight
bricks in your arch, if you buy pre-shaped bricks.
I would rather buy straight bricks and cut my arch bricks with
a table saw, so they are all arch bricks, cut at an angle specifically
for my kiln. No, these are IFBs, not hardbricks.
A bonded arch is certainly better than a ring arch.
The half-round arch proposed by Mr. Wunch at the NCECA
session should work, but in order to keep the kiln dimensions
within the "cube" parameter, the arch will have to start awfully
low on the walls so it's top will still be within the cube. If the
arch is stuck on top of a cube, the top of the kiln will be cold
in a downdraft kiln. I once built a kiln with a high arch because
all I had was #1 arch bricks (hard bricks).
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
John Jensen on mon 18 mar 02
My 15 cubic foot catenary doesn't fire evenly at all...or rather I don't
fire it evenly. One way or the other I have a two cone range at least. I
chose the cat to build partly because it was supposed to be an even firing
design, but also because I'd always wanted to build an arch since I first
read about them in fourth grade history class about the Greek Aquaducts and
how they were supported. Maybe someday I'll learn to make it fire evenly.
John Jensen, Mudbug Pottery, Annapolis
mudbug@toad.net, www.Toadhouse.com
Hank Murrow on mon 18 mar 02
David hendley wrote;
>If you have enough power coming in, and a way to let it
>out again, you can make a kiln just about any shape, and
>it will "work". It's just a box to hold heat.
>That said, it does matter what shape the kiln is. Particularly
>if, like most of us, you want more than to just heat the
>ware to temperature.
>I'm assuming that you want a kiln that fires evenly, within
>a half-cone difference throughout the kiln. Some designs you
>see, particularly wood-fired cross-draft or groundhog
>designs, are not striving for consistency.
>
>I'm certainly no kiln expert, but, by the same token, the
>engineering types often do not know what we potters are
>trying to do with our "furnaces". I don't think many of them
>have much experience with wood firing and natural draft
>kilns without blowers. And seldom are commercial designers
>concerned with reduction firings. There's a difference.
>I would not stray too far from the notion that a small potter's
>kiln should have a chamber that is close to being a cube.
>It doesn't matter if the top is flat or arched, as long as it is
>close to the "cube" relationship. Talk about an arch "guiding"
>the flames is pure speculation, and, in fact, we want our kilns
>to have turbulence, so the heat and firing effects (reduction,
>salt, soda, ash) will be well-distributed.
>Don't cut corners with your design. Always design your kiln
>with extra space around the shelves, to give the flame plenty
>of room to maneuver.
>
>The half-round arch proposed by Mr. Wunch at the NCECA
>session should work, but in order to keep the kiln dimensions
>within the "cube" parameter, the arch would have to start awfully
>low on the walls so it's top will still be within the cube. If the
>arch is stuck on top of a cube, the top of the kiln will be cold
>in a downdraft kiln. I once built a kiln with a high arch because
>all I had was #1 arch bricks (hard bricks).
David writes from experience in the potters' realm;
And his post is a fine description of what a gas firer needs
in a kiln. I came to many of the same conclusions awhile back, and
you may visit http://www.murrow.biz/hank for a look at my 'take' on
this problem. When you reach the site, just click on the 'Kiln and
Tools' page. For a longer discussion of the design, click on the
first link on that page to check out the CM article. I really
appreciate David's thoughtful response to this thread.
Best, Hank in Eugene
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