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Cone Different Top To Bottom


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#1 LesleyWilson

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Posted 10 August 2010 - 12:57 AM

Hello,

I just got a new (used) kiln and am hoping to get some help as I am new to operating kilns. The kiln is a Skutt KM1227 with a vent. I got it all set up and fired it yesterday at 04 medium speed with just the shelves, posts and cones to test it out. I mostly do time consuming sculpture and didn't want to put anything in it without knowing if it was working right. It seemed like it was firing correctly, I followed the ramp in the manual and it seemed the same. The only problem is it seems to be about a cone cooler near the bottom of the kiln then at the top. It was just a little hotter than 04 at the top and about 05 at the bottom. Could it be caused by an old element? All of the elements are getting hot but I don't know how to tell if they need to be replaced anyway. If I used it the way it's firing now will it cause problems?

Thank you for your help!

#2 Chris Campbell

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Posted 10 August 2010 - 10:14 AM

This is fairly standard for a regular cone firing.
Most electric kilns cool quickly through the bottom and top.

There are ways to adjust and compensate for it.
If you control cool ... or fire down ...You can achieve more even results.

You can hold at the top temp for ten minutes to get the bottom hotter but this will
also heat up the center ... Sometimes all you want is for the whole kiln to hit the
right temp and a little hotter in the center is not critical.

Some people add more insulation to the outside to slow cooling and keep the heat in
the bottom and top.

Most of the time getting to temp is the most important part and a little over is not as bad
as a little under.

But ... You might need bang on temps in which case I would recommend firing down as
well as up. There should be a program for this in your manual.

Chris Campbell
Contemporary Fine Colored Porcelain
www.ccpottery.com

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#3 LesleyWilson

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Posted 10 August 2010 - 12:59 PM

Okay, what would be a good rate of cooling down? My manual says how to program a controled cool down but doesn't have a set program.

Thanks

#4 Chris Campbell

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Posted 10 August 2010 - 01:57 PM

My manual had a ramp program but if yours does not, go to the skutt site and see if there is one you can download.

Chris Campbell
Contemporary Fine Colored Porcelain
www.ccpottery.com

TRY ...   FAIL ...  LEARN ...  REPEAT


#5 LesleyWilson

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Posted 10 August 2010 - 03:05 PM

My maunal says

Controlled Cooling
Normal firing to cone 5, rapid* cooling to 1950° with a 30 minute hold. Slow cooled to 1100°, then normal cooling to room temperature. This is a useful profile when glaze firing to ensure gentle cooling and avoid cracking or crazing.

As an exmaple? I can't find anything else on the Skutt site but maybe I'm missing something?



#6 Seasoned Warrior

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Posted 10 August 2010 - 04:53 PM

Hello,

I just got a new (used) kiln and am hoping to get some help as I am new to operating kilns. The kiln is a Skutt KM1227 with a vent. I got it all set up and fired it yesterday at 04 medium speed with just the shelves, posts and cones to test it out. I mostly do time consuming sculpture and didn't want to put anything in it without knowing if it was working right. It seemed like it was firing correctly, I followed the ramp in the manual and it seemed the same. The only problem is it seems to be about a cone cooler near the bottom of the kiln then at the top. It was just a little hotter than 04 at the top and about 05 at the bottom. Could it be caused by an old element? All of the elements are getting hot but I don't know how to tell if they need to be replaced anyway. If I used it the way it's firing now will it cause problems?

Thank you for your help!


Hi:

Most of your question has been answered well but just as an aside one of the ways of telling if a heating coil is efficient and operating correctly is to take a resistance measurement when the coil is new and then monitor the resistance throughout its life. As a coil ages it becomes slightly less condiuctive through oxidation of its outer skin and as the resistance increases it uses mmore electricity to get the same amount of heat out of it also the oxidation can increase the thermal transfer between the coil and the kiln atmosphere. There is a time in my opinion where it is better to replace the coil since it costs more to operate. As long as a coil conducts electricity and has resistance it will heat. An open coil on the other hand needs to be relpaced immediately because it won't heat. I use a digital multimeter to monitor my coils and a multimeter is a handy device to have around the studio for other things. I have a clamp-on amp-meter attachement, an incident light meter, and I can use any thermocouple with it by knowing what the junction consists of and then measuring the milliamps output.

#7 Chris Campbell

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Posted 11 August 2010 - 10:56 AM

If you do not have computer controls, it will be challenging as you have to watch the temp ...
and control the heat.
Someone else might know more about how to do this manually ... Mine have computers.

Generally, you can let it cool quickly to about 1900 F ... from 1900 to 1100 cool by 150 per hour ...
then turn it off.

Chris Campbell
Contemporary Fine Colored Porcelain
www.ccpottery.com

TRY ...   FAIL ...  LEARN ...  REPEAT


#8 LesleyWilson

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Posted 22 August 2010 - 10:55 PM

Okay I just had an epiphany. Since I plan on bisque firing to cone 04 and glaze firing to cone 05, can't I just put geenware on the top part of the kiln and glaze coated bisque on the bottom? Is there anything wrong with this plan?

#9 bciskepottery

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Posted 23 August 2010 - 07:24 PM

Okay I just had an epiphany. Since I plan on bisque firing to cone 04 and glaze firing to cone 05, can't I just put geenware on the top part of the kiln and glaze coated bisque on the bottom? Is there anything wrong with this plan?


At the studio where I teach, we fire bisque (05) and low fire glazed items in the same kiln without any problems. We follow the slow bisque program loaded in the kiln controller. Just remember not to open the kiln too soon or you could get some pinging/crazing on the glazed items.

#10 LesleyWilson

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Posted 25 August 2010 - 01:48 AM

Thank you everyone for your help!




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