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Kiln Firing Unevenly

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My kiln fires very unevenly, and I'm wondering if there's something I can do. I have four 'levels' of shelves, evenly spaced apart (ie I usually use a similar height of shelf stilts between levels). I leave about a 1/2 inch space in the middle of each half kiln shelf to try to move air between levels. The bottom three layers have half kiln shelves, the very top layer I use a full kiln shelf. I also use an envirovent. The kiln pack on the bottom layer shows a fully fallen cone 5 and a 1/4 way fallen cone 6. The next layer up shows a fully fallen cone 6, with 1/4 fallen cone 7. The next layer shows a completely fallen cone 6, and almost a fully fallen cone 7. The top layer is a completely fallen cone 7, and in fact I suspect goes higher as I was getting some serious bloating on a couple of pieces. I do a slow to medium speed ramp, hold for 15 mins at 2185 degrees and slowly cool. I have experimented with slightly lower and higher temps, but always get the same difference in temps between kiln shelf layers. Any thoughts? Is it simply the envirovent? Thank you!!

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The Envirovent actually helps. The problem is that you have a single zone kiln. The computer only knows how hot the middle is. Most kilns with single zones have graded elements, meaning the very top and very bottom elements run hotter than the rest, to account for heat loss out the lid and floor. Assuming your elements are correct, you need to adjust how you load the kiln. To cool down the top, pack it tighter. To heat up the bottom, pack it looser. The more pots there are on a shelf, the cooler that area will run. Put big pots at the bottom, put the little ones at the top.

 

What brand and model of kiln is it? What cone are you actually trying to hit?

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From my experience the biggest factor in firing a single zone kiln consistently came from always having a shelf a few inches above the probe. You may also get a more even firing if the half shelf heights are staggered. This, of course, changes the way you have been loading the kiln.

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Thanks for the responses! It's a Skutt 1027 and I'm aiming for a cone 6. Thanks!

This kiln is suppose to have tuned elements to take care of this problem.  Maybe they were changed at some point and not put in as they were supposed to be.  Also even shelf spacing may not  work that well.  You want to have at least 2 elements between shelves. 

David

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Even with graded elements, Skutt kilns are known to fire unevenly. You'll likely have to adjust your loading. To see if you have graded elements, turn the kiln on full blast (Ramp/Hold, 1 segment, rate of 9999 to 1000 degrees). The top and bottom elements should glow before the rest.

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I find that my Skutt 1027 is usually within a ½ cone But my Olympic 1827 is terrible with almost a 2 cone difference. All the elements resistance are good o it should not be he elements. I am thinking of just selling it and keep just the Skutt.

Both are using a sitter at this time.

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Pretty much any single zone kiln can have issues. The controller really only knows the temperature in the middle, so load density can throw off the rest of the kiln very easily. It's not that expensive or difficult to upgrade to multi zone control.

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