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How Fast Is Your Kiln Heating Up And Cooling Down?

kiln firing cooling charts

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#1 Mart

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Posted 26 October 2013 - 11:55 AM

I wanted to know how fast my kiln is actually heating up and cooling down so I decided to record the temperature changes while kiln was in regular used. Fully loaded and set to run our typical program.

I used a simple webcam and pointed it at the hand controller (Bentrup TC88).
Webcam took 1 frame per minute and recorded it to my HD (actually a DropBox folder so I can see from home, what was/is happening).

Bisque firing was as expected. Nothing interesting there.
Attached File  79-bzg_to987.png   39.15KB   1 downloads


Glaze firing was a bit different but also nothing unexpected.
From the ambient to 600C, at 120 C per hour was not a problem.
Going from 600 to 1258, at 150 per h started out fine but slowed down after reaching 1123 C (2053.4 F). It did not climb 25C (77 F) per every 10 min any more.
From 1123C on it slowed to 22, then 20, 18, 19, 17, 16C per 10 minute before reaching 1257C (2294.6F), holding this was not a problem.

Attached File  79-gls_to1257.png   45.77KB   1 downloads


Cool down was more "interesting". Coming down from 1257/1256C, temperature dropped 55C (131F)in first 10 min. 10 more minutes and kiln was at 1160C. Additional 37C degrees was lost in following 10 minutes.
Following charts show loss of temperature per 10 minutes and compares bisque and glaze firing.
Attached File  78-bzgvsglz.png   33.95KB   2 downloads

In one hour, kiln was 1032C and had lost 224C. 140C was lost in the following hour.
24h from the start of firing, kiln was at 221C and cooling has slowed to a crawl. This is where I usually pull the plugs to speed up the cool down unless I am in so hurry.

Bentrup TC88 can slow down cooling if needed. It allows me to program some really tricky firing schedules, with 10 segments, if needed. It can save ... mmm I thing 16 programs, each with up to 10 segments.

This charts shows the drop in temperature in percentages per 10 minutes.
Attached File  79-bzgvsglz_prc.png   36.59KB   1 downloads

#2 Mart

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Posted 26 October 2013 - 02:01 PM

I was almost sure we fire our glazes about cone 7. I tested with a cone #7 and it was flat on it's face.
Now, because I know the last hour we go at 100C and not 150C, we are probably firing to cone 8.5 or 9.
I am going to buy some cones (absurdly expensive around here) and see what is really going on.

#3 neilestrick

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Posted 26 October 2013 - 04:36 PM

Is your controller set up to fire to a specific cone, or to a temperature set point?


Neil Estrick
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#4 Mart

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Posted 27 October 2013 - 04:49 AM

Is your controller set up to fire to a specific cone, or to a temperature set point?


Temperature set point. It knows nothing about cones :) BTW, I am almost sure that none of the modern electric/gas kilns, built in/for EU, use cones any more. Glazes, clay etc. sold around here usually never even mentions "cone".
Thermocouples give way more flexibility, no matter what direction you are firing - heating, controlled cooling, heating again, holding at certain temperature etc.
Because US produces so much interesting materials about ceramics in English, I have to be acquainted with the cone system.
I think I have few cones left somewhere. I'll use those to see, is my guess about the cone number is correct.

#5 Wyndham

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Posted 27 October 2013 - 07:16 AM

Cones, as I'm sure you know, measure heat work and T/C's temperature. As you fire according to the controller program, the heat curve will change with aging of element. It is always good to have cones as a  backup to verify what you get in the end.

If you kiln has a programmable cone fire controller,such as Orton or Bartlett, there should be a page in the manual or online that gives the pre-programed ramp segments to compare to what you found in your test.

 

Even if your controller is different you can go to these companies and download their manuals for their controllers and see what they have programed their controllers for different temperature set points.

The Orton foundation's website has a great deal of information on cones, heatwork and the way these interact.

Wyndham



#6 Mart

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Posted 27 October 2013 - 08:46 AM

Cones, as I'm sure you know, measure heat work and T/C's temperature. As you fire according to the controller program, the heat curve will change with aging of element. It is always good to have cones as a  backup to verify what you get in the end.

Controller measures temperature and time and makes adjustments accordingly. To program it, I need to insert time and temperature for each segment.
For example, 5 h to reach 600 C, next segment 4h 30 min to reach 1257C, hold 10 min etc.
Aging heating elements are not as dangerous as failing thermocouple but engineers have thought about it so it will shut down.

If elements get older and it can not keep up with the schedule, controller will let me know. I agree, it is a good idea to use conses once in while to make sure that everything is OK.
 

If you kiln has a programmable cone fire controller,such as Orton or Bartlett, there should be a page in the manual or online that gives the pre-programed ramp segments to compare to what you found in your test.


As mentioned in my reply to neilestrick, TC88 knows nothing about cones.
BTW on page 27, Appendix B: Preset Standard Cone-Fire Schedules - °C has a nice time/temp/cone table.
I am going to adjust my last hour of firing from 150 to 100C.

We use locally mixed glazes (and mix some stuff ourselves in local Arts Academy lab). Firing instructions for those glazes never mention "cone". I have few glazes mixed in Germany and none of those have any information about cones. What they do have is recommended firing temperature range and this already considers heat work. Those instructions are actually exactly the same for me as "fire to cone Q and soak Y minutes" to you.
You know, almost like pints and liters. ;)


If you like to watch paint dry or kiln temperature change :) , here is little video compiled form webcam jpeg's. yawn... output03.avi
Going form 600C to 1257 and back down to 1000C. 3 kiln minutes per one video second.

#7 JBaymore

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Posted 27 October 2013 - 02:34 PM

 

What they do have is recommended firing temperature range and this already considers heat work.

 

WOW.  This statement, as written, goes against everything that I have understood for 44+ years as a ceramics professional and professor of ceramics. 

 

"Heat work" (as used in ceramic applications) is basically defined as the impact of the application of heat enery over time to ceramic materials.  Temperatue is simply the result of the application of an amouint of heat energy to a particlarr physical mass that possesses a certain specific heat property. 

 

Can you provide the technical literature to explain this above statement?

 

best,

 

.......................john


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Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

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#8 Mart

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Posted 27 October 2013 - 03:25 PM

What they do have is recommended firing temperature range and this already considers heat work.

 
WOW.  This statement, as written, goes against everything that I have understood for 44+ years as a ceramics professional and professor of ceramics. 
 
"Heat work" (as used in ceramic applications) is basically defined as the impact of the application of heat enery over time to ceramic materials.  Temperatue is simply the result of the application of an amouint of heat energy to a particlarr physical mass that possesses a certain specific heat property. 
 
Can you provide the technical literature to explain this above statement?
 
best,
 
.......................john


English is not my first language. It's possible something was lost in "translation".
BTW, text you quoted, unless I am misunderstanding it again, has the answer to your question.

If I receive instructions to heat something for time X, rising temp by rate R until temp T is reached, how is this different from "fire it to cone Y"? The result is the same.

Those magical cones do what they do because this is exactly what is happening - they get heated for time X, rising temp by rate R until temp T is reached. If you speed up (change) one of the variables, other will change too. But this is unimportant at the moment, unless you like to complicate things.

So, I am not sure what are you WOW'ing about. I did not tell you anything new.

#9 JBaymore

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Posted 27 October 2013 - 04:07 PM

It is likely the translation issue.

 

Saying "What they do have is recommended firing temperature range and this already considers heat work." and saying that the COMBINATIION of firing at a specific rate from one firing temperature to the next are two different things.  The missing part in the statement I quoted was the fact that you were tallking about the combination of the two

 

It was not clear in that single posting.  If someone did not read back through all of the earlier thread postings, it would not have been clear.  I did read back, and still did not get the correct impression.

 

Remember that this approach of not using cones assumes that the mass of wares and the air surrouneding the thermocouple probe are increasing at the same rates.  Likely this is the case (with the wares lagging behind the termocouple reading a tad)..... but there is the thermal lag factor to consider a bit on the end point.

 

best,

 

........................john

 

PS:  The last NCECA had some fascinating information about heat work from the ceramic engineering folks....... and will result in the controller manufacturers changing their proggramming in the coming time.


John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

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#10 Min

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Posted 27 October 2013 - 06:47 PM

 

PS:  The last NCECA had some fascinating information about heat work from the ceramic engineering folks....... and will result in the controller manufacturers changing their proggramming in the coming time.

 

John, would you elaborate on this? Would be very interesting.

Thanks,

Min



#11 Mart

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Posted 06 November 2013 - 02:56 PM

I adjusted our glaze firing schedule to following:

1) 1:00h to 120°C @ 120°C/h
2) 3:10h to 600°C @ 150°C/h
3) 3:40h to 1160°C @ 150°C/h (will merge 2 and 3)
4) 1:30h to 1249°C @ 60°C/h
5) hold 10 min at 1249°C
6) cool-down

Total 9h 20 min
I also found 2 cones we had left over form summer. 8 and 9. Lets see what they will show.

#12 Mart

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Posted 08 November 2013 - 06:14 AM

I think they look sad. Or is this happy for pyrometric cones?
Attached File  IMG_2859_v1.JPG   35.02KB   0 downloads

8 and 9

#13 clay lover

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Posted 08 November 2013 - 06:36 AM

THEY LOOK LIKE they went to ^10 AND ^11 FROM WHAT I CAN SEE OF THE 9.

#14 Mart

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Posted 08 November 2013 - 08:14 AM

Really hard to believe, because 10 is somewhere in the neighbourhood of >1300C, but all glazes etc are just fine. No signs of over firing.
Maybe those cones have gone bad, past expiration date perhaps... must be cispondial phenomena. <- joke!

#15 JBaymore

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Posted 08 November 2013 - 09:37 AM

Hard to see the tip of the 9 but....... it looks more like about 8.75 - 8.8 to me.

 

http://ortonceramic....Guide_Cones.pdf

 

FYI......... Orton self supporting cones at 150C hr ROC are cone 8 at 1271 C and cone 9 at 1280C.

 

best,

 

.......................john


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Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#16 neilestrick

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Posted 08 November 2013 - 09:40 AM

Looks like cone 9 almost.


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#17 Mart

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Posted 08 November 2013 - 04:01 PM

JBaymore, I used 60°C in the program because I found out this kiln can not do 150°C/h after reaching 1123C (see my first post)

I'll be firing more stuff in few days so looks like I have to buy more cones and also a #10.
My top temperature is set to 1249°C. Additional 30°C in those levels is a HUGE deal.

Maybe I need to buy ceramic temperature measurement rings to really find out wtf is going on. I hope kilns thermocouple is not out of whack.
I think I am going to reduce the 10 min soak to 5 minutes because our kiln is so tiny and possible lag is minimal.

#18 Mark C.

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Posted 08 November 2013 - 09:11 PM

Fiber kilns tend to cool very fast compared to bricks or at least all I have made did.

My glaze fire to cone 11 takes 12-15 hours and at high temps climbs very slowly-hence heat work kicks in-The walls  are soft brick inside with hard brick outside(I like the look of this wall makeup)  the arch is two layers soft with fiber on top of that with a metal roof -this tends to hold heat and releases it slowly. The car kiln door is 7-8 inch's of various fiber densities with a metal exterior.

This kiln cools slowly-the hard brick floor and large bag walls help in this as well.

I like a two day cool unless pressured then it can be 16-24 hours

Mark


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#19 Mart

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Posted 09 November 2013 - 05:46 AM

Mark C, lucky you. Sounds like you have a serous kiln over there :) We are planning to get something in the range of 250 liters (9 cu f). 

So far, I can not complain about our little kiln loosing heat to fast. If it was any slower, temmoku glaze will probably turn in to ugly red... brrr horror!

I can always slow down the cooling to a crawl or stall it at what ever temperature, if I have to.

We use Witgert Nr 11 clay. (max firing at 1300°C) <- How do you translate this to cone-speak?

With a chemical composition:
SiO2   73.4
Al2O3  21.6
TiO2    1.2
Fe2O3   1.0
CaO     0.1
MgO     0.3
Na2O    0.1
K2O     2.3






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