Over fired but kiln says otherwise

[Anne Lythgoe]

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

[Bill Kielb]

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?

[neilestrick]

@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?

[47runner]

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:

 

 

[Pres]

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

[neilestrick]

@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.

[47runner]

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

 

 

[47runner]

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

 

[47runner]

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

[Bill Kielb]

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

[Hulk]

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.

[Jeff Longtin]

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. 

[neilestrick]

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.

[Roberta12]

I have been doing a search through the forum, trying to figure out what to do with my kiln E23T firing hotter than programmed.  I found this thread.   Since he has been mentioned, Rob Battey has been my kiln support for 10 years and we have had numerous conversations via email and phone this last week.  Because neither Rob or I could properly diagnose the issue,  my husband and I changed the elements and thermocouples on Saturday.  I ran a fast glaze cone 5 empty load to season the elements.  Cone 5 cone was down.  Perfect, I thought.  I loaded a cone 6 glaze load and monitored carefully.  It completed in 8.17 hours.  I peeked at the top cone pack this morning and it went to cone 7.  Rob had suggested TC offset adjustments.  But since I have new thermocouples in there, would that be the best course of action??  (I am trying to cut Rob some slack by asking you guys....he's pretty slammed).  I have taken care with loading, and this problem is fairly recent.  Maybe 10 firings ago I started having a problem??  What do you all think?  My kiln is 10 years old. The oldest relay is 2 years old.   Thanks for any insight.  Yeah, and naturally I am getting ready for a show.  

Roberta

[neilestrick]

@Roberta12 Do a TC offset if it's off at low temps, too. Do a cone offset if it's just off at cone 6. But first also make sure all your thermocouple wire connections are tight along the entire system. Make sure the wires aren't broken under the screws on the porcelain blocks at the kiln. It's not unusual to need some sort of calibration.

Are you using a hold at the peak?

[Roberta12]

3 hours ago, neilestrick said:

@Roberta12 Do a TC offset if it's off at low temps, too. Do a cone offset if it's just off at cone 6. But first also make sure all your thermocouple wire connections are tight along the entire system. Make sure the wires aren't broken under the screws on the porcelain blocks at the kiln. It's not unusual to need some sort of calibration.

Are you using a hold at the peak?

No, no hold.  I will read the manual on cone offsets.  I  have only been reading about the TC offsets.  I will recheck the wires.  But we did just change the TC and elements Saturday.  I opened the panel last week and the yellow tc wire on the #3 tc was out of the bracket.  In fact the entire bracket was loose and wobbly.  I tightened all the screws, put the tc wire back and thought that might have been the problem, but no, it wasn't.   Thanks for the reassurance that it's not unusual to need some sort of calibration.  I do have 900 firings on my kiln but we have been faithful with maintenance.  Replacing not only elements and thermocouples and relays, but tc wires also.  Thanks @neilestrick

[Roberta12]

@neilestrick I read through the instructions for cone offset and tc offset on the hotkilns site.  I have to confess that I have never put cones in my bisque.  So, I just now ordered 04/05/06 because I have no idea whether bisque is firing properly or not.  Would a work around for a cone 6 firing be to program cone 5 and add hold time?? 

 

[neilestrick]

Just now, Roberta12 said:

@neilestrick I read through the instructions for cone offset and tc offset on the hotkilns site.  I have to confess that I have never put cones in my bisque.  So, I just now ordered 04/05/06 because I have no idea whether bisque is firing properly or not.  Would a work around for a cone 6 firing be to program cone 5 and add hold time?? 

 

If your bisque is off by a cone it's not usually a big deal unless you're really picky about the absorbency when you glaze, or have burnout issue with dark clay. That said, it's not a bad idea to calibrate for low and high temps.

Yes, the hold would be a good workaround. Or do a custom schedule with a lower final temp than the pre-programmed firing.

[Bill Kielb]

10 hours ago, Roberta12 said:

  I ran a fast glaze cone 5 empty load to season the elements.  Cone 5 cone was down.  Perfect, I thought.  I loaded a cone 6 glaze load and monitored carefully.  It completed in 8.17 hours

That it worked empty and then did not full is an indication that near top temperature it is firing at a considerably slower rate than expected. Assuming both were fast glaze programs it may be a tad too fast for the kiln / load to achieve.  IF all that is true, big IF there, then there maybe some things that you can check. If those were fast glaze firings, I would try a slow glaze speed firing just to see if the controller is happier and lands more squarely on its cone. In addition If you can monitor the speed at the end of the firing and record it (say last 100 - 150 degrees) as well as see how even the zones are, those numbers could provide real insight into a few easy things to check.

An example would be  that the controller on slow glaze is expecting the last 200 degrees to be about 120 degrees per hour. If the kiln fires slower, say 50- 80 degrees per hour it likely over fires more towards cone 7 on the Orton chart. On fast glaze the controller expects 200 degrees per hour, empty this might be doable, but full again things start to overfire because it takes more time than the controller is programmed for. Sort of like a built in hold. 

So, if we find out the why, then it is much easier to figure the what to check and how to check it. Tc offsets might work, but making sure the kiln fires as designed is usually a more lasting stable basis to work from.

As boring as it sounds, I always suggest folks learn what your kiln is doing in the last few hundred degrees. It’s very valuable knowledge thats tedious and  boring, and therefore no one does it. It is extremely valuable though.

[neilestrick]

If it's firing slower than the program, the controller should compensate the peak temp to still arrive at the proper heat work.

I would not be at all surprised if it was firing more accurately at cone 5 than at cone 6. There seems to be a breaking point there for accuracy in some kilns, including one of mine. Cone 5 to cone 6 is 65F degrees, one of the biggest temperature jumps in cones, so I wonder if that has something to do with it.

[Bill Kielb]

1 hour ago, neilestrick said:

would not be at all surprised if it was firing more accurately at cone 5 than at cone 6. There seems to be a breaking point there for accuracy in some kilns, including one of mine.

Not sure - that’s why the ifs above, but it is interesting that it finishes spot on unloaded and at least 3 hours long loaded. IF it was a fast glaze. Not a whole bunch of kilns I run into fully loaded will keep schedule with the fast glaze schedule though so kudos to most controllers, they are pretty tolerant. I find rate is definitely  something super handy to know though at the top end it often reveals potential issues. Again lots of ifs there though.

[Roberta12]

13 hours ago, Bill Kielb said:

That it worked empty and then did not full is an indication that near top temperature it is firing at a considerably slower rate than expected. Assuming both were fast glaze programs it may be a tad too fast for the kiln / load to achieve.  IF all that is true, big IF there, then there maybe some things that you can check. If those were fast glaze firings, I would try a slow glaze speed firing just to see if the controller is happier and lands more squarely on its cone. In addition If you can monitor the speed at the end of the firing and record it (say last 100 - 150 degrees) as well as see how even the zones are, those numbers could provide real insight into a few easy things to check.

An example would be  that the controller on slow glaze is expecting the last 200 degrees to be about 120 degrees per hour. If the kiln fires slower, say 50- 80 degrees per hour it likely over fires more towards cone 7 on the Orton chart. On fast glaze the controller expects 200 degrees per hour, empty this might be doable, but full again things start to overfire because it takes more time than the controller is programmed for. Sort of like a built in hold. 

So, if we find out the why, then it is much easier to figure the what to check and how to check it. Tc offsets might work, but making sure the kiln fires as designed is usually a more lasting stable basis to work from.

As boring as it sounds, I always suggest folks learn what your kiln is doing in the last few hundred degrees. It’s very valuable knowledge thats tedious and  boring, and therefore no one does it. It is extremely valuable though.

Good thoughts @Bill Kielb, however I always run a slow glaze program.  The only time I run a fast glaze is to season the elements or to do the paper test.    When I realized the kiln was overfiring (yep, I had some bloating on some dark clay that previously had been fine) I started putting cone packs in very consistently instead of "oh yeah, let's put some cones in there!" and monitoring the ramps and times and which relays were clicking on and off and what the TCs were reading.  Rob B. asked to me take a serious look at how I was loading.  Not overloading the bottom and making certain I had 2 rows of elements to do the heating for each TC.  Then the slow glaze program began taking first an hour then 2 hours then almost 3 hours longer than normal.  At the last ramp instead of 120 per hour, it was 80 then 64 then quick jump to 100 then back to 80 then back to 64.  It seemed to be struggling.  I also noticed the #3 relay was staying on the whole time.  Which, since that TC was reading 20 degrees cooler sort of made sense.  Then I wondered if that relay was having an issue.  But with all the signs pointing to element wear, that's what we did. Even though they only had 38 firings on them.  And they did look bad, laying down in several places.  And we changed TCs also.  (we did not change the #3 relay, although I noticed it makes a softer clicking noise than the other 2) The last cone 6 slow glaze load I ran before changing everything, was for a friend, and I monitored very very closely.  The kiln was really struggling, and the ramp was flipping all over the place starting at 1900 degrees or so.  I just kept monitoring, knowing that his work would be fine with a cone 5 firing and at 2188 I shut it off.  9.5 hours.  In the morning, cone 5 was all the way down and 6 had started to bend.  So that's the story.  I would never have questioned anything that happened if I hadn't had the bloating on that dark clay and if those elements had more firings on them.  When the 04,05,06 cones get here I will take a serious look at whatever calibration I need to do.  I want to know if this overfiring is happening on all programs or just cone 6.  

I really appreciate you all for listening and responding.  I know I have said this before, but living in a remote area, with no kiln repair people and really no other people around that have kilns, my husband and I have jumped into the world of kiln maintenance.  It is wonderful to have others to lend an ear and advice.  Thanks @neilestrickand @Bill Kielb

[neilestrick]

2 hours ago, Roberta12 said:

But with all the signs pointing to element wear, that's what we did. Even though they only had 38 firings on them.

The elements should last a lot longer than that. Like 100 firings more if you're doing bisque and cone 6. The fact that the ramp speed was jumping around points to the problem being something other than the elements, like a thermocouple issue, or possibly a relay that's sticking and unsticking, although they don't typically come on and off when they're sticking, they usually just stick. It could also be an electrical interference problem, although that is rare. If you don't mind checking something- open up your control box and see if there are two wires coming off the Center Tap tab on the controller circuit board, one of which goes directly to the grounding screw at the bottom of the box.

[Roberta12]

36 minutes ago, neilestrick said:

The elements should last a lot longer than that. Like 100 firings more if you're doing bisque and cone 6. The fact that the ramp speed was jumping around points to the problem being something other than the elements, like a thermocouple issue, or possibly a relay that's sticking and unsticking, although they don't typically come on and off when they're sticking, they usually just stick. It could also be an electrical interference problem, although that is rare. If you don't mind checking something- open up your control box and see if there are two wires coming off the Center Tap tab on the controller circuit board, one of which goes directly to the grounding screw at the bottom of the box.

I have extra relays.  I could change that #3.  And I am getting ready to load a bisque firing right now, I will open it up and look at the wires coming off the Center tab.  And I should have added, I am direct wired.  And mostly that #3 relay is staying on.  Specifically when the temp is higher.  Isn't that sort of normal?   Rob B said firing dark clay and clay with manganese (Speckled Buff) can shorten the life of your elements.  Have you found that to be true?  I am about half dark clay and half porcelain.  And I usually get somewhere around 80 firings on elements.  

[neilestrick]

41 minutes ago, Roberta12 said:

I have extra relays.  I could change that #3.  And I am getting ready to load a bisque firing right now, I will open it up and look at the wires coming off the Center tab.  And I should have added, I am direct wired.  And mostly that #3 relay is staying on.  Specifically when the temp is higher.  Isn't that sort of normal?   Rob B said firing dark clay and clay with manganese (Speckled Buff) can shorten the life of your elements.  Have you found that to be true?  I am about half dark clay and half porcelain.  And I usually get somewhere around 80 firings on elements.  

Dark clay can certainly shorten element life some, but not by 100 firings. Are you running a downdraft vent? Even 80 firings seems short for that kiln, although I have a couple of other customers that get  about that, too. I assume you're firing bisque, too, correct? The bottom relay will stay on for most of the second half of the firing. The top will run a lot, too. The middle will run about 50% of the top and bottom.  It's more about number of cycles than time on, though, so if it's staying on it's actually wearing less than the others which are cycling more.

Kill the breaker and inspect all the wiring connections where the power cord meets the wall. Feel your power cord during the next firing and see that it's not heating up.