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Cannot dial in middle of kiln, running too hot (new'ish l&l)


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I am about ~38 firings into my new eQuad pro and I thought I had everything dialed in but I guess not. 

When I first got it I ended up doing a cone offset of 35 degrees in order to get my cones perfectly aligned at the base of the self supporting cones. I began testing some newer glazes and started having some issues on the middle shelves...sometimes nothing to bad just could tell it was getting hotter there...which I also know is normal.

So I put some cones on every shelf the past few firings (sides and middle of shelves) and top and bottom fire perfectly ^6 and the middle is a hot cone 6 (if not hotter), they are touching the shelf and then some. Some of my glazes will not handle this extra heat, run, crawl etc.

I read back on old threads and have done quite a bit of testing based off them so new info would be greatly appreciated (waiting on a response from l&l).

I just ran a fast firing to ensure all the elements were glowing normal, check. All diagnostics seem ok, no errors etc.

I have changed the way I load the kiln and that did not work. I added dense pots in the middle as well to try and help there and that did not work.

I do not have a vent system and simply use the peep and lid to let moisture out but part of me thinks the middle thermocouple is done. They look ok, somewhat corroded but nothing bad bad. 

My firing is 04 slow and for glaze a slow glaze + 5min hold on the top with built in cool down.

Not sure what to test next but kinda tired of ruining pots in the middle of the kiln testing it. 

Do an empty load with cones just to rule out how I am loading it?

Do an additional TC offset on #2?

Replace the TC's already?

 

PS - TO make matters even a bit more frustrating is I have the same problem on my ^04 (no offsets or anything) but it happens to be hotter in the middle giving me a perfect ^04 in the middle and just barely begins to move the bottom and top cones. Since it is a bisque I have not worried too much about that but alas.

Edited by Morgan
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Are you doing a drop before going into the cooling cycle? If you're cooling from the peak instead of dropping 100F or so, you're going to get some extra heat work, and the middle is going to get more than the top or bottom since it's insulated by the top and bottom.

The beauty of the TC offset is that you don't have to set them all the same. Go ahead and adjust the middle if you need to.

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Posted (edited)

The built in cooling drops from peak to 1900 then control cools to 1500 or so I believe.

Ok, I will try the TC offset, thanks Neil (as always)!

PS - What is a good starting number for ~half a cone off degree wise? Start with say, shaving off 15 degrees and see how she does?

Edited by Morgan
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2 hours ago, Morgan said:

PS - What is a good starting number for ~half a cone off degree wise? Start with say, shaving off 15 degrees and see how she does?

If you have temperature sensitive glazes you may want to shoot for just short of cone 6. Cones are very sensitive toward the end of firing so maybe shoot for the four or five o’clock position. A few degrees heatwork per section is a tough ask for any kiln IMO. When we design glazes we tend to get rid of or correct those that are overly temp sensitive for just that reason. Cone bend chart below for your reference

I would also lose the 5 min hold at peak unless I had a real proven reason it is needed. The center is already overfiring very slightly.

 

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Edited by Bill Kielb
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The difference between perfect 6 and hot 6 is generally no big deal for most pottery situations, meaning there’s nothing wrong with your kiln. But if your glazes are picky then I would add a TC offset to the middle TC too. 

Also you said you tried packing the middle more densely but how much denser did you try? In my kiln, I make my bottom shelf and top shelf 7 or 8 inches tall, and pack the middle with a bunch of short shelves. I don’t do TC offsets and my kiln fires evenly, and my glazes are picky too. 

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IMO glazes should be able to handle 1/2 cone difference and still be acceptable. If they're pickier than that I would reformulate to give them a broader melting range. I notice in my kiln that I'll have up to 1/2 cone difference in a particular part of the kiln from load to load just because it's loaded with different work every time. I used to have a glaze that was dry at cone 5, slightly runny at cone 6, and running off the pot at cone 7. It was a pain to work with, and resulted in a lot of ruined work simply because it required far more precision in application and firing than was realistic.

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I guess I should have elaborated on that…I agree a half a cone should be fine and for the most part they are I am just the one picky haha.

they just do not come out how I want them. Some need pretty thick applications to get some of the proper colors and blending etc and that extra heat (it’s going more than a half a cone too btw) will cause some problems in the middle at times. Of coarse I also agree with you all that part of me should just accept this, pack different stuff there and compensate for it and move on, change glazes, but I thought this was a bit more than your “middle running hotter is normal”. There could be some application issues on my end that are adding to that maybe but regardless it’s getting overly hot.

as far as how dense, it was about as dense as I could with mugs, cylinder type shapes on a couple of 7ish posts while getting them as close together as I legally can :)

at the end of the day I’m pretty neurotic admittedly and I feel like getting proper cones throughout the kiln should not be that tall of an order :)

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Go ahead and adjust the middle thermocouple 10 degrees and see if that helps. Also verify that your thermocouples are all the same distance from the end of the tubes (I'm assuming you have open tubes). If they're closed tubes, the thermocouples should be touching the ends of the tubes.

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