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Over fired but kiln says otherwise


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I am at a loss. My L&L e23T kiln has been significantly over firing. Target is cone 6. But my cone packs (4-5-6) all show all the cones completely flat on three shelves. It  was then set to fire at cone 4 in an attempt to prevent over firing. Again cone packs 4,5 and 6 went completely down. The readout tells me the highest temperature reached was 2124 degrees.
 
Why would there be such disparity between the cones telling me the heat work was well over cone 6 and the highest temp reading was cone 4?
 
Rob Battey from L&L has been very patient with my questions and we want to try and work with the thermal couples offset  but I’d appreciate any insight you might have
Edited by Anne Lythgoe
Tyoos
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  • Anne Lythgoe changed the title to Over fired but kiln says otherwise

When you say 'completely flat' - do you mean they held their shape, but bent over, like they are laying on their side - or did they melt completely into a puddle ? (pic's might be helpful)

Have you had successful firings with this kiln in the past ?  If yes, look for what may have changed since the last successful effort:   

Any chance you got 04, 05, and 06 cones, instead of 4, 5, and 6 ?  Could the cones have gotten wet since the last time you used them ?  Did you accidentally add a soak to the end of your firing ? 

 

 

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As long as the cones are not defective then they represent the true heatwork done. After all they are simply made of glaze. Assuming they are not defective then electronic controllers try to approximate the heatwork by firing at a specific speed in prox. the last 200 f degrees of the firing. So, if the kiln is going the right speed then the temperature should end up to be approx the cone temp expected. Where this falls apart is when the kiln does not have sufficient fire power to maintain the speed and so this last segment begins to fire slower. Too slow and you get an error, but before that error it begins to overfire as it exceeds the controllers ability to compensate for the reduced speed.

Not saying this is the issue, but not all elements working, worn elements will cause the kiln to overfire. I would make sure they all work and are not worn beyond 10% of new resistance as well as confirm what is the final segment rate your kiln can maintain?

Edited by Bill Kielb
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@Anne Lythgoe Lots of possibilities, but first give us some more information:

1. How old is your kiln?

2. What firing schedule are you using?

3. What is the age of your elements and thermocouples?

4. What type of controller?

5. Have you changed the thermocouple offsets? What are they set at?

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14 hours ago, Rockhopper said:

When you say 'completely flat' - do you mean they held their shape, but bent over, like they are laying on their side - or did they melt completely into a puddle ? (pic's might be helpful)

Have you had successful firings with this kiln in the past ?  If yes, look for what may have changed since the last successful effort:   

Any chance you got 04, 05, and 06 cones, instead of 4, 5, and 6 ?  Could the cones have gotten wet since the last time you used them ?  Did you accidentally add a soak to the end of your firing ? 

 

REPLY:  Thanks for your reply....Here is a photo of my cone packs. they are not old, wet or wrong. cone 4,5,6.  To me, I would describe as collapsed!  The kiln was built in 2007, I acquired it in 2016. A that time I converted it  phase 1- 240 volt  kiln to make it fit the power outlet. that outlet was installed by a certified electrician with the help of L&L kilns.  I replaced the elements and power relays in 2019 in an attempt to solve some of the issues you (and others) have mentioned. the TC offset is at 20 in each level and the cone offset 05. Rob is suggesting I set all the TC offsets to 60 and try another firing.  I'll do that this weekend. any insights are welcome!

14 hours ago, Rockhopper said:

 

 

cone photo.jpg

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Yours are worse than mine. My first 2 firings of my new L&L is in this strand:

I am running a slow bisque with a preheat to ^08 to see if I come near^ 06. This may help me with firing to ^6 on Saturday after glazing the pieces. Hopefully I can get my situation figured out as will you.  I am new to this hocus pocus with a controller as I have always fired full manual with an old L&L that bit the dust after 36 years.

best,

Pres

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@Anne Lythgoe @47runner make sure your thermocouples are touching the ends of the protection tubes. To adjust them, loosen the screws in the porcelain block that holds the thermocouple, push the TC all the way forward until it hits the end of the tube, then tighten the screws. Also make sure that your thermocouple wire connections are tight, at the block, the terminal strip, and the controller.

Has this always been a problem, or is it a new issue? How many firings do you have on the thermocouples and elements?

That's a really old controller. That could be a problem. Old thermocouple wires can also cause problems.

Is the kiln over-firing at bisque temps, too? If it's only firing hot at cone 6, then I would not adjust the thermocouple offset, because then it will run cold at bisque temps. Either set the cone offset to a different temp, or do a firing with cones and watch the cones drop. When 6 goes down, note the temperature and turn off the kiln. Then set up a custom program that goes to that temp.

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15 hours ago, Rockhopper said:

When you say 'completely flat' - do you mean they held their shape, but bent over, like they are laying on their side - or did they melt completely into a puddle ? (pic's might be helpful)

Have you had successful firings with this kiln in the past ?  If yes, look for what may have changed since the last successful effort:   

Any chance you got 04, 05, and 06 cones, instead of 4, 5, and 6 ?  Could the cones have gotten wet since the last time you used them ?  Did you accidentally add a soak to the end of your firing ? 

 

REPLY:  Thanks for your reply....Here is a photo of my cone packs. they are not old, wet or wrong. cone 4,5,6.  To me, I would describe as collapsed!  The kiln was built in 2007, I acquired it in 2016. A that time I converted it  phase 1- 240 volt  kiln to make it fit the power outlet. that outlet was installed by a certified electrician with the help of L&L kilns.  I replaced the elements and power relays in 2019 in an attempt to solve some of the issues you (and others) have mentioned. the TC offset is at 20 in each level and the cone offset 05. Rob is suggesting I set all the TC offsets to 60 and try another firing.  I'll do that this weekend. any insights are welcome!

Quote

 

 

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14 hours ago, neilestrick said:

@Anne Lythgoe Lots of possibilities, but first give us some more information:

1. How old is your kiln?   2007

2. What firing schedule are you using?   I don't have that with me now.... but typically use either slow or fast glaze schedule offered on the controller.

3. What is the age of your elements and thermocouples?   Under 4 years old, I only fire a few times a year. Thermocouples.... not sure, but they do no have protective sheaths on them.

4. What type of controller? DynoTrol original equipment

5. Have you changed the thermocouple offsets? What are they set at? they are set at 20

 

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1. How old is your kiln?   2007

2. What firing schedule are you using?   I don't have that with me now.... but typically use either slow or fast glaze schedule offered on the controller.

3. What is the age of your elements and thermocouples?   Under 4 years old, I only fire a few times a year. Thermocouples.... not sure, but they do no have protective sheaths on them.

4. What type of controller? DynoTrol original equipment

5. Have you changed the thermocouple offsets? What are they set at? they are set at 20

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2 hours ago, 47runner said:

I replaced the elements and power relays in 2019 in an attempt to solve some of the issues you (and others) have mentioned. the TC offset is at 20 in each level and the cone offset 05. Rob is suggesting I set all the TC offsets to 60 and try another firing.  I'll do that this weekend. any insights are welcome!

I would suggest measuring your element resistance and seeing how worn they are. Easy to do and you will know for sure at what stage of wear they are at. If they have risen in resistance by 10% or more, time for replacement. Offsets can help, but if elements are worn too much your kiln will not fire fast enough (degrees per hour) in the final segment for an offset to continue to work well with the controller.

Easy to check and get out of the way IMO

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Just wanted to echo on watching cones. If possible, place a cone where you can see it through a peep. Try moving it to where you can see the profile of the cone, paint that side with a thin line of iron oxide, use the small cone - it's smaller!

Just note, the small cone bend is a few degrees offset from the large - depending on the cone number. For watching live heat work, it's not enough difference to be concerned with, unless doing very narrow/specific heat objective stuff. The smalls are also cheaper - not by much (can ship for less though, heh).

Glasses, rated for yellow hot kiln viewing, necessary.

Edited by Hulk
glasses
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Thermocouples - I work with Skutt Kilns and L&L kilns. Skutt kiln thermocouples are exposed while L&L thermocouples are in a ceramic tube.  (My kilns anyway.) The Davinci kilns have closed tubes while the E23 has an open end. You mention that your thermocouples are not in a tube. Can you provide a picture?  

A newer thermocouple looks like a metal rod bent into a "U" shape. An old thermocouple looks black on the end and has a mass of metal on the tip. As the thermocouple is the link between the kiln chamber and the controller its vital that they be in good condition.

A thermocouple can become dysfunctional for a variety of reasons. Age is one. Sometimes glaze will fall onto the tip and affect its ability to read temperature correctly? Sometimes a kiln is packed tightly, around the thermocouple, and that will affect its functioning?

I've spoken with Rob many times and he's a terrific resource.  Usually he's been able to solve my problems. Have you used a meter yet? That can greatly aid the process. 

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2 hours ago, Jeff Longtin said:

The Davinci kilns have closed tubes while the E23 has an open end.

They started using open end tubes this last year, as they could no longer find closed end tubes that were of consistent thickness. All models use the same tubes, it just depends on when they were built.

I'm actually surprised that this 2007 kiln doesn't have protection tubes.

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