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My kiln is running and going down in temp instead of up! What to do now?


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I come to the studio to monitor the last 50 degrees (and cones) usually. Last time I did, the temp fell a bit and but was able to come back up to my goal temp eventually and the cones fell but in the end but things looked over fired. This time I have my doubts that it will get up to temperature. I think it got up to 1168 before I came here (my husband set up a webcam for me to see my old kiln computer). At 11:30 it was 1133 C. At 11:45 it was 1122 C. At 12:00 it was 1114 C and now it is 12:15 and it’s 1110 C. I'm trying to fire to 1205 C with a 2 min hold. What now? How long should I let it try to get up to temperature? When should I shut it off? I guess my cones won't fall from heat work if there is more time but such a low temperature? Also I don't want to take the peeps out to check and make it even colder in there :( Based on previous conversations here, we thought I wouldn’t have to replace the elements for awhile. But this is surely an element problem, right? Or could it be a problem with the thermocouple? It’s one of those covered end thermocouples. Looks like ceramic covering the tip. Now it’s 1107 C at 12:27.  Thanks!

Edited by feistyfieryceramics
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Sounds like elements or at least a bad element that is totally not working so either way your kiln does not have the power to finish. I would shut it off and diagnose the issue. It’s not going to get warmer so I definitely would check the cones as well but if your last load did the same thing but ended on heatwork and over fired  I would say at best this will be the same.

A general rule is your elements should be less than 10% greater in resistance than when new. As they age their resistance increases so less wattage is available to heat your kiln, especially at top temperature where shell losses are highest.

If they all happen to measure as good and there are more than one (often three or more) then are they all powered or is there a bad relay?  If you have a three element kiln it will not make top temperature with only two of the three working.

From there we check voltage, always look for bad connections etc..... Measuring each element resistance gives you a good place to start though and can be done with the kiln unplugged but wares still loaded inside.

From memory this was the kiln with the bad lid switch(s) that would warp when heated, are you sure all elements are working? 

Edited by Bill Kielb
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1 hour ago, Bill Kielb said:

@Bill KielbSounds like elements or at least a bad element that is totally not working so either way your kiln does not have the power to finish. I would shut it off and diagnose the issue. It’s not going to get warmer so I definitely would check the cones as well but if your last load did the same thing but ended on heatwork and over fired  I would say at best this will be the same.

A general rule is your elements should be less than 10% greater in resistance than when new. As they age their resistance increases so less wattage is available to heat your kiln, especially at top temperature where shell losses are highest.

If they all happen to measure as good and there are more than one (often three or more) then are they all powered or is there a bad relay?  If you have a three element kiln it will not make top temperature with only two of the three working.

From there we check voltage, always look for bad connections etc..... Measuring each element resistance gives you a good place to start though and can be done with the kiln unplugged but wares still loaded inside.

From memory this was the kiln with the bad lid switch(s) that would warp when heated, are you sure all elements are working?

@Bill Kielb You have a good memory! I checked and the "pacman" is not compressing any of the lid switches. 

We have a contactor instead of relays.

Never did order those spare elements that I meant to. Was too overwhelmed with other things. I'm kicking myself for that now. But I just ordered a set this very minute so that will be nice to be able to start with a fresh set and then know if the resistance is getting too high in the future.

Now the kiln is down to 1096. None of the cones have fallen. It appears to still be running, but I peaked in the peep holes, and I think maybe the top elements aren't working, the kiln is glowing but they don't seem to be. And the bottom shelf, which is usually the coldest, looks hotter than the top. 

So do you think I should turn off the kiln, unplug, and check all the resistances and connection right away and then try to turn it on again if I find a loose connection? Also how to I check the voltage? Do you mean the voltage coming out of the wall? Can I check that with a multimeter and not electrocute myself? :)

Thank you!

Caitlin

Edited by feistyfieryceramics
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That’s right, you have switches. I would not try and finish this firing, I would turn it off now. You have switches if I recall which you likely leave on high and yes I remember the contactor so it is unlikely there is a bad leg there. Don’t measure any live voltage till you are comfortable doing so, do the resistance check first with no power, Based on those results we can take some next steps. Right now You are likely wasting electricity.

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7 hours ago, Bill Kielb said:

That’s right, you have switches. I would not try and finish this firing, I would turn it off now. You have switches if I recall which you likely leave on high and yes I remember the contactor so it is unlikely there is a bad leg there. Don’t measure any live voltage till you are comfortable doing so, do the resistance check first with no power, Based on those results we can take some next steps. Right now You are likely wasting electricity.

Okay. Thank you! I will start with using the multimeter on the unplugged kiln.

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@Bill Kielb I did the paper test and the top element didn't heat. I also checked the element ends with a multimeter and current couldn't pass through it. So yay! We know what the problem is! I have ordered a new set of elements. Would you recommend replacing them all at once since it is a used kiln, we don't know it's back story, and moments like this are so stressful!? Or should I only replace the broken one? Then I should monitor the resistance of the elements and when the resistance changes by >10% then I should change them again?

I'm also not sure if the glazes are under or over fired. The cones didn't fall. Is it possible for it to be over fired if the if it never got up to temperature and the cones didn't fall, but the kiln was kind of stuck at between 1000-1150 C a long time (I think I turned off the kiln at 13:26 and 1087 C). The glazes don't look like they normally do. I have a brownish red that normally comes out quite glassy but in this firing it looks thinner, more brown, and not as shinny. I have an "ocean" blue that usually has lots different colors with in it that break up beautifully over texture, but this time came out less shiny and less complex...kind of one note and dark. One piece has pinholes or popped bubbles....not sure which.

 

Thank you!

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If the cones didn't drop then it didn't reach temperature.

If the element died because it's old and worn out, then replace all of them. If it died prematurely, then just replace the one.  I'd go ahead and order a whole set, measure the resistance, and see where the others are at. If they're showing signs of wear, then just do them all and start fresh.

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2 hours ago, feistyfieryceramics said:

Would you recommend replacing them all at once since it is a used kiln, we don't know it's back story, and moments like this are so stressful!? Or should I only replace the broken one? Then I should monitor the resistance of the elements and when the resistance changes by >10% then I should change them again?

Change them all, they basically wear together. We are pretty sure your glazes are underfired as well as the claybody so once you get new elements I would fire them to cone. There is some risk they will not come out well though so you should be aware.

As your elements age your kiln will take longer and longer to get to the cone temp. Often folks notice at some point it takes so long that their pieces come out looking over fired even though they are still just making cone.

Going too slow in the final segment (say 25f per hour) is just too slow for many glazes. It’s really not as hard as it sounds. Most notice their firing times beginning to change by hours, so an eight hour schedule maybe becomes becomes nine, then ten, then eleven hours. It’s pretty obvious if you know your kiln you will need elements and you will simply order in advance.

when you get the new elements measure and record each on the kiln. As firing times get longer, measure and note some way. The 10% rule is very general and applies to the average kiln. Yours is a fiber kiln I believe, so it’s final replacement measure might be 11, 12, 15%...... we don’t really know, but you will know it best just with a little diligence and recording.

 

Edited by Bill Kielb
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@Bill Kielb @neilestrick

8 hours ago, neilestrick said:

I'd go ahead and order a whole set, measure the resistance, and see where the others are at. If they're showing signs of wear, then just do them all and start fresh.

Cool. That is what I was thinking too. It feels good to have a marching plan.

 

8 hours ago, Bill Kielb said:

Change them all, they basically wear together. We are pretty sure your glazes are underfired as well as the claybody so once you get new elements I would fire them to cone. There is some risk they will not come out well though so you should be aware.

I'm going to attached pictures of the cones and of to glazes on some student work. Unfortuntely I only had cone 7 and 8 on the top shelf. The top shelf is always hotter than the bottom so I didn't think getting to cone 6 would be a problem. Of course this is the time that the top elements break! On the bottom shelf I had cones 6,7,8. It looks like 6 was beginning to fall. 

In the video you see on the "Christmas" tree the brown read glaze fired to temperature. The other piece was in this firing. The glaze looks thin. I usually describe this glaze as chubby :) 

The other video shows the ocean blue. The first piece is when the glaze is fired to temperature, the second shows it from this firing with little holes and it lacking dimension (although the glaze looks better on the inside of the pot). 

When you say I should fire them to cone but they may not come out well, I feel like I should offer the option to students that their pieces can stay as is or I can re-fire them to see what happens (I will test re-fire my own pieces that were in this kiln load first so I can try to show them the results, but I don't have any of my own pieces in that blue). Will the glazes likely come out the same as now after re-firing? Or worse than now? Does re-firing also risk the glaze running off of them onto the kiln shelves? And if the pieces won't come out better, are there any risks to leaving them as is? Like the might not hold water? Or they might not be safe to eat or drink from?

Dang. The glaze video files are too big but I can't make them smaller right now because I have students coming. I'll send them this afternoon.

Thanks!

cones.jpeg

Edited by feistyfieryceramics
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6 hours ago, feistyfieryceramics said:

When you say I should fire them to cone but they may not come out well, I feel like I should offer the option to students that their pieces can stay as is or I can re-fire them to see what happens (I will test re-fire my own pieces that were in this kiln load first so I can try to show them the results,

I like your plan, those definitely melted. Makes me wonder what the glaze firing range really is.

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@Bill Kielb @neilestrick Here is the clay I have in the studio: https://www.potterypassion.com/products/0254 

The website says :

Water absorption
1070 C 9%
1140 C 6%
1240 0,4%
 
I think the kiln got up to about 1165 at 11:20 and then it  had fallen to about 1087 C at 13:30 when I turned it off. 
 
So they clay will be weak (easy to chip) and absorb water if it didn't mature? And based on this information it would absorb somewhere between 0.4 and 6%? Does that mean if someone had it sitting in a sink of water and then microwaved it that the steam would explode it or something?
 
The red brown glaze says recommended firing temperature is 1220- 1280C.
The blue glaze says recommended firing temperature is  1220- 1260C
My green glaze looks after this firing about just like it always does. So I guess it has a wide maturation range? The sample board at the local shop I bought it at says simply 1255 C.
 
When I glaze fire I use a 150 C rate of rise to 1205 and then a 20 minute hold and this makes cone 7 fall even though the Orton cone chart says that at 150 C per hour Cone 7 should fall around 1255 C... but I guess that 150/hr on the chart refers to the last 100 C and not the whole firing? Soooo... I don't know.
 
When I do a bisque I use a 150 C rate of rise to 1011 with a 1 hr hold and that makes cone 06 fall. 
 
I'm learning so much every day. Ha!
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52 minutes ago, feistyfieryceramics said:

So they clay will be weak (easy to chip) and absorb water if it didn't mature? And based on this information it would absorb somewhere between 0.4 and 6%? Does that mean if someone had it sitting in a sink of water and then microwaved it that the steam would explode it or something?

If absorption is over 2%, then the clay will absorb water through any exposed clay (foot ring) when you run it through the dishwasher, then it will weep that clay out and leave water ring in cabinets, on tables, etc. If the glaze is crazed, then it can absorb liquids through the cracks in the glaze, where it may become trapped and get funky, or weep out the foot. Ideally I like to be under 1.5% absorption.

54 minutes ago, feistyfieryceramics said:

When I glaze fire I use a 150 C rate of rise to 1205 and then a 20 minute hold and this makes cone 7 fall even though the Orton cone chart says that at 150 C per hour Cone 7 should fall around 1255 C... but I guess that 150/hr on the chart refers to the last 100 C and not the whole firing? Soooo... I don't know.

The rate of climb figure for cone only applies to the last 100C of the firing, but holding temp adds heatwork, about one cone per 20 minutes.

 

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2 hours ago, feistyfieryceramics said:
 
When I do a bisque I use a 150 C rate of rise to 1011 with a 1 hr hold and that makes cone 06 fall. 
 
I'm learning so much every day. Ha!

Yes, hard to predict all that. They may absorb, we just don’t know. Your solution of giving them the option to refire after seeing yours  I think is a good one, these may not be done and should not be considered functional. As far as firing, firing fast will be more uneven than slow. So most use the center of the Orton chart which puts the firing rate at 60c per hour for the last 100c of the firing.

This will be more even throughout the kiln than a faster speed. A hold or soak at the top temperature often has the effect you described, it fires to the next cone and still somewhat unevenly because whatever was leading in heatwork because it could “see” the elements still receives more heatwork. 

Anyway, a last segment of approximately 60c per hour over about the last 100c is a popular one to get the cone to drop  and a nice rate to keep things even for average thickness wares.

So for example  to get to cone 6 I would go into my table find my top temperature 1222 for cone 6 and subtract 100c. My last segment would start at 1122, fire at a rate of 60c per hour to 1222 or about 1 hour and forty minutes.

I have attached common firing schedule speeds in degre c. They follow the Orton chart for the most part in the last segment  and only go faster for very thin items that heat fairly evenly. Bisque schedules are generally slower and there are other reasons so go slow such  as removing all chemically bound water, quartz inversion, complete burnout of organics which takes time at a temperature etc.....

 

023A816A-97FF-4FEB-9114-3C9CD7226BAC.jpeg

B7AD028E-B25D-40BC-8595-DD42F34FF1E4.jpeg

Edited by Bill Kielb
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@Bill Kielb @neilestrick

 

Thanks for the info guys! This is great! I look forward to having more even firings. I feel like the positive side to all of this is it feels like the kiln elements will be a fresh start and a change to change and perfect firing schedules.

Do you guys recommend bisque firing to cone 04? When I began that was my plan as I believe that is what the studios I attended before fire their bisque to, but someone advised me against it and said I should instead fire to 06.

I'm trying to understand these firing schedule tables you have here.  So looking at this my first thought is the that the first 4 tables are bisque firing schedules due to the header that says "firing profiles cone 04" and the goal temp of 1063 on all the schedules. But then the tables on the right say "(glaze larger pieces or bisc [I assume this means bisque] thin)" and "(glaze thin pieces)"...why do they say "glaze" if these are bisque firing schedules.

Another question I have is how should I adapt these schedules to the fact that my kiln has a very simple computer that allows only two different rates of rise, a hold, and a slow cool. And would you recommend a slow cool? I was watching a Washington Street Studios video and I believe he said that was good for matt glazes and for healing bubbles that may have formed during the hold.

Thank you!

Caitlin

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18 minutes ago, feistyfieryceramics said:

Do you guys recommend bisque firing to cone 04? When I began that was my plan as I believe that is what the studios I attended before fire their bisque to, but someone advised me against it and said I should instead fire to 06.

I prefer 04. Less chance of not getting everything burned out in stoneware bodies, fewer glaze problems.

 

19 minutes ago, feistyfieryceramics said:

I'm trying to understand these firing schedule tables you have here.  So looking at this my first thought is the that the first 4 tables are bisque firing schedules due to the header that says "firing profiles cone 04" and the goal temp of 1063 on all the schedules. But then the tables on the right say "(glaze larger pieces or bisc [I assume this means bisque] thin)" and "(glaze thin pieces)"...why do they say "glaze" if these are bisque firing schedules.

They just put the same labels on every chart, but what they mean is that the slower schedules are better for bisque, faster schedules are ok for glaze.

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7 hours ago, feistyfieryceramics said:

I'm trying to understand these firing schedule tables you have here.  So looking at this my first thought is the that the first 4 tables are bisque firing schedules due to the header that says "firing profiles cone 04" and the goal temp of 1063 on all the schedules. But then the tables on the right say "(glaze larger pieces or bisc [I assume this means bisque] thin)" and "(glaze thin pieces)"...why do they say "glaze" if these are bisque firing schedules.

Basically bisque on the left and glaze on the right. So for lowfire clay folks @04 they bisque to 04 using the schedule on the left and lowfire glaze to 04 with the schedule on the right

bique to cone six is not really a thing so the bottom left hand schedule would be more appropriate to once fire work from green to glaze at cone six

The popular schedules cone 6 midfire -

  • slow & medium bisque to 04
  • medium glaze  to cone 6 , or fast glaze to cone 6 when your glazes will tolerate it.

So if you do not glaze to cone 04 or once fire to cone 6   ...... use the top left column of  tables and on the bottom the right column of tables.

Sorry rushed to put in the Celsius values for someone and just left them all 

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On 3/16/2021 at 3:04 PM, neilestrick said:

I prefer 04. Less chance of not getting everything burned out in stoneware bodies, fewer glaze problems.

Thanks! I have been wondering if some of the problems I'm having of little bubbles might be from bisque firing to a lower temperature. Organics burning out during the glaze firing and bubbling though the glaze?

 

On 3/16/2021 at 10:07 PM, Bill Kielb said:

Sorry rushed to put in the Celsius values for someone and just left them all 

C is perfect for me!

 

@Bill Kielb @neilestrick 

So my glaze temps are as follows:

The red brown glaze says recommended firing temperature is 1220- 1280C.
The blue glaze says recommended firing temperature is  1220- 1260C
For the rest of my glazes, the sample board at the local shop I bought it at says simply 1255 C. But maybe that is the max temperature?
 
When I was younger, I know the studio I attended fired to cone 6 and that seems to be a mid range standard? But I have been firing to cone 7 because of the "1255 C" and because the other glazes can handle that temp. Should I fire instead to cone 6? But then for my clay the absorption is listed as 1140 °C - 6% and 1240 °C - 0,4% so then my clay absorption would be unknown but something in that range.
 
Coils are supposed to come today! I'll try to manage with YouTube videos. LOL. But you may get more questions :) soon. Maybe some day I'll have learned so much that I'll be able to help people on here. That would be pretty cool!
 
Thanks!

 

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@Bill Kielb @neilestrick Oh man. So disappointed. So I got the new elements this afternoon.

While removing the old elements we saw where the top element had gotten scrunched up and burned out. We also saw what looked like a mini tooth of porcelain stuck to the bottom element but that element was still operational according to the paper test.

Anyway. We took those out and vacuumed everything  and installed the new elements. It seemed very straight forward given our kiln is old only has one thermocouple, etc. I was feeling really proud! But then I tried to do the paper test to make sure all the elements were working and it switched the breaker for the whole studio! Maybe it's because I had it on a very fast ramp for that, 500 C per hour, but that is what I did with the last paper test and it didn't flip the breaker.

When I ordered the elements, the guys at Cromartie asked me if I havd 220 or 240 V. I called the electrician who installed the 3 phase plug for us and he said it didn't matter because it was 3 phase. I told that to the Cromartie guy and he didn't seem convinced. So he looked it up for our region and said it was 220 V. So Cromartie made me (and this is what the label says) a CTL 75, 5 kW, 220V element set. The resistance of the new elements was 27.4-27.6 Ohm.

The element was quire long and we had to sit it in the groves like a loaded spring to get it to fit, but it's supposed to be the correct length for the CTL 75, so I guess that's normal?

Any idea why the breaker might have flipped?

Edited by feistyfieryceramics
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18 minutes ago, feistyfieryceramics said:

Any idea why the breaker might have flipped?

First what size is the breaker? Second we will need to measure your voltage, eventually. Third, not a good thing for an electrician to say actually IMO.
So the difference between 220v and 240v ought to be 24 amps at 220 volts and 26 amps at 240 volts with the elements you have. What is your breaker size? Normally breakers are sized here in the states not to exceed 80% of their rating  so looking at the numbers this  is about an 8% increase (24 amps vs 26 amps)  I am actually surprised the breaker would trip unless it was previously sized very close to the rated load or the breaker is becoming worn.

So there may be a way to use what you have but it will take a little bit of thinking and confirming to be sure. And you should do it to make sure other things are sized correctly, such as the wiring. Before I comment  what does the nameplate on the kiln say with respect to rated wattage, voltage and expected amperage?

Edited by Bill Kielb
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@Bill Kielb  Here is the name plate on the kiln

CromartieTag.jpg

I'm not in the studio right now but I took this picture of the breaker when I was there and sent it to the electrician, but he works for the company we rent from so I don't expect we will hear back until Monday. I'm pointing to the switch that flipped. The "T" (test) button says 25 A above it. Is taht the number you're looking for? Here is also a wider shot, but it is kind of blurry. ItBreaker.jpg

Should I ask the electrician to measure the voltage if I get him into the studio next week? Should I just hire an independent electrician? I feel so confused still about electricity that when he said "it doesn't matter," I just assumed I asked a dumb question.

This was on a different breaker, but one of the breakers has previously has flipped with two hair dryers on. Is that normal? Even when I turned off everything else I could think of on that circuit.

 

Thanks!

 

63787970974__DF50F03F-1656-455A-BD34-DDA93598847C.jpg

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