Gay Judson on mon 10 aug 09
Snail,
You have challenged what I have determined to be the cause of uneven
heating in my Skutt 1027 (computerized with 3" brick and vent in the
bottom). For the first 100 firings I got incredibly even heat top to
bottom--as demonstrated by the 3 cone packs I put into the kiln. I
had to replace the elements and now I get incredibly UNeven heating in
my kiln. Most noticeably when I have had tall pieces to fire along
with more regular sized pieces. I have always put the tallest pieces
on the top so I don't have to worry about posting for a shelf over the
tall pieces. But after getting very uneven heating (top with no
movement in the ^5 cone when firing to ^6 and the bottom with ^6 flat)
I decided it was because there was so much space in the top. I have
gone to all sorts of gyrations to put the tall pieces in the middle
having to stack posts on top of each other to cover the tall pieces
with a shelf for another layer of ware. There was enough of an
improvement that I felt I had found the solution. Of course, there
are other variations like the amount of additional ware and size of
other ware. I would much rather load the kiln in the manner you
describe--so that is what I will do and see how it comes out.
I have thought that the reason I got such even heating before is
because most of my ware was all one size--mugs and bowls. Now I have
grown into making some taller pieces--vases, pitchers and handbuilt
pieces--so the shelves are not all separated by the same distance.
I don't watch the cone packs while firing. I use them for after-the-
fact information. I have not developed the skill of being able to see
the cones when the kiln is firing so brightly.
Finally, will a longer soak--maybe even a slower ramp rate, I use 108
for the last 100 degrees--also promote a more even firing?
Gay Judson
On Aug 10, 2009, at 11:06 AM, Snail Scott wrote:
> On Aug 9, 2009, at 8:43 PM, Carol Baker Cotton wrote:
>> ...my top shelf fired cooler....5 3/4..the others were a 6 all the
>> way
>> down. It is usually the bottom that is cooler. I have a Skutt
>> 1231PK. If I put shelves over my top shelf might that even out the
>> firing so that I am getting a full 6 on top also?
>
>
> No; it will probably make it worse. Top shelves
> often fire cooler because there are no elements
> in the lid; just that vast surface radiating away
> all your heat. Adding a cover shelf works with
> updraft kilns because it slows the exit of the hot
> air as it rushes past and out. With an electric kiln
> it mainly acts as a heat-sink, soaking up a lot of
> your heat and making that top shelf even cooler.
>
> When I have this problem, I wait until the kiln is
> about 1 or 2 cones away from the final one, then
> turn my lower and middle elements back to
> 'medium' until it even out. Then, I turn everything
> back to 'high'. With a computer-controlled kiln,
> this is not really possible, but I have solved that
> by putting a 1" slab of kaowool board on the lid
> during firing. That little extra bit of insulation
> works like a charm!
>
> If your loading allows for it, try to make the top
> shelf space a big one, exposing the work to
> several rows of elements, and try to load loosely
> on the top. Same for the bottom, if that's cool.
> Keep the short or tightly packed shelf spaces in
> the middle of the kiln.
>
>>
>> And...one more question. I usually watch the cones from the top
>> hole.
>> What happens if I pull a plug from a lower shelf to check the cones.
>> Will there be much heat loss or a draft that would change things?
>
>
> Not really. You can't get a draft without an
> 'in' and an 'out' for the air to move through.
> (I keep trying to explain that to my husband:
> the bathroom fan won't work for s**t if you
> keep the door shut with a towel under it!)
>
> People often note that heat rises, but for it to
> do this, there must be a temperature gradient -
> a cool mass of air to sink and a hotter mass to
> rise. If all the air is the same temperature (as
> we hope for inside an electric kiln) there is
> no convection current of heat rising; the air
> is still. So, it simply doesn't matter whether
> you pull an upper plug or a lower one or
> one in the middle, or all of them (though not
> at the same time!)
>
> The momentary heat loss of any peephole-
> checking will be quickly equalized, regardless
> of which plug you pull.
>
> -Snail
Lee Love on tue 11 aug 09
I read about putting shelves over the last layer at the top, to help
even things out. It worked when I tried it.
--
--
Lee Love, Minneapolis
"The tea ceremony bowl is the ceramic equivalent of a sonnet: a
small-scale, seemingly constricted form that challenges the artist to
go beyond mere technical virtuosity and find an approach that both
satisfies and transcends the conventions." -- Rob Sliberman
full essay: http://togeika.multiply.com/journal/item/273/
Arnold Howard on tue 11 aug 09
From: "Gay Judson"
> You have challenged what I have determined to be the cause
> of uneven
> heating in my Skutt 1027 (computerized with 3" brick and
> vent in the
> bottom). For the first 100 firings I got incredibly even
> heat top to
> bottom--as demonstrated by the 3 cone packs I put into the
> kiln. I
> had to replace the elements and now I get incredibly
> UNeven heating in
> my kiln.
Gay, I believe your Skutt kiln is similar to the Paragon
design and requires two types of elements. If you
inadvertently reverse a center element with a top/bottom
element, the kiln will fire very unevenly. The kiln should
fire just as evenly with the new elements as it did with the
old ones.
Sincerely,
Arnold Howard
Paragon Industries, L.P., Mesquite, Texas USA
ahoward@paragonweb.com / www.paragonweb.com
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