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Skutt kiln is heating unevenly


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I have a 3 year old Skutt electric kiln and it had  been firing hot for a little while before Covid and then I could no longer access it due to its location. I was setting it to cone 5 with a 10 minute hold to get cone 6 to drop. I did my first firing in awhile last week and put cone packs in the top, middle, and bottom. The top and bottom went to almost 7 and because it was a test run I loaded it with deglazed stuff and junk bisque. Has anybody dealt with such a difference between temperature in areas of their kiln the tests came out great in the middle but the re-fires blistered and got bleached of all color.

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If it's single zone, then you have to load it to take advantage of hot spots and cold spots. If an area is running hot, load that area more densely. If it's running cold, load it looser.

Also, are all of your elements the same age? If not, you could have some elements that are more worn out than others, resulting in uneven heating.

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My elements are all the same age and the kiln only has maybe 60 firings on it, more of which are bisque. For awhile, I would take them to my friends place and use her glazes and reduction kiln. It’s a pretty big kiln, for an electric. I replaced the thermocouple, there is only one and it is where all my tests were and they did very well. I’m a bit confused and at least I can program it to be done preheating and climbing by the time I arrive in the am. I will program in cone 5 and give it a good soak there while monitoring the cones. My next firing is a bisque and I will set it on the softer side. Gonna have to go old school for now. 

 

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5 hours ago, Johnmicheal said:

Does your kiln have zone control, are there three thermocouples or just one?

I don’t know about the zone control. Just one thermocouple 

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"Zone control" is when the computer views each section as a "zone" and varies the firing progress to maintain an even temperature throughout the kiln. It's only available when you have three thermocouples. (With only one thermocouple the computer reads the entire kiln as one "zone".) At the pottery shop where I work we have many 1231PK's.  (31 being the depth.) With the added depth the zone control is a useful tool.  Zone control is useful when firing a glaze kiln but not so necessary when firing bisque. The one bummer with zone control is that you have to make sure your thermocouples are in good working order. If they're not the computer will throw back an error message and/or delay/stop the firing. Skutt recommends you change thermocouples after 60 firings.  It seems tedious but its a simple fix to keep the kilns in good running condition.

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36 minutes ago, Jeff Longtin said:

Skutt recommends you change thermocouples after 60 firings.

That's good idea if you want to make sure you're never experiencing any sort of temperature drift at all due to aging thermocouples, but in reality most people go 100-150 firings without any big issues. How long they last depends on how hot you're firing, if you're doing long soaks at high temp, what type of clay you're firing, if the kiln is vented or not, etc. A visual check of the TC condition and the occasional use of cones to check accuracy is really the best way to know when to change them.

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The differences you describe are pretty typical. Like Neal pointed out, you load your kiln to take care of these idiosyncrasies. You can help this with a soak, and varying the cone your firing too. The hotter you fire too, the more noticeable the fluctuation. I used to fire a kiln sitter with multiple thermocouples, titrating the control manually. Drove me crazy, trying to get that perfect even firing. If your interested in having more control with your skutt controller, you can add zone control to your existing controller. For the cost of a couple more thermocouples, and drilling two more holes, the controller will keep those zones alittle more even.

 

 

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One nice feature of Zone Control is that it allows you to test amperage, on each section,  easily and quickly.  A simple command: Enter_diag_Enter_Amps_Enter activates a simple diagnostic.  On a Skutt 1231PK I'm looking for 28-22-28. If those numbers don't appear it gives me an indication which section may be problematic.  (Unfortunately with a  1231 there are three different element thicknesses so experience helps determine which element needs replacing.) 

If the numbers are below the ideal it tells me an element is old. If the numbers are higher than the ideal it tells me the wrong element was used.  If I get a "0" in any section it tells me the element has a break and needs to be replaced. 

While I don't think all three thermocouple kilns automatically have the ability to run an Amp Test its easy to install a Current Sensor such that you can.  

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