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Electric Kiln Firing


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#1 Suby

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Posted 27 July 2010 - 03:29 PM

I have an L&L Liberty Bell kiln with Vent Sure attachment. I have been struggling for months trying to find the right program so my pieces will fire to maturity. We fire to 06, 05, 04, and 6. I have called L&L throughout this time and they keep telling me to adjust temp. I have 3 shelves and try to fill them evenly. Two usually over fire and one under fires or comes close to firing the correct temperature according to the free standing Orton cones. I keep adjusting the temperature, but can't get glazes that do not have a range of firing temperatures to work out. Since the thermocouple is at the top, I have decided that all three shelves will never fire to the same temperature. I am beginning to think that I have to use Stroke and Coats or Underglazes that have a wide temperature range. Does anyone have any suggestions or are experiencing the same problem? Thank you.

#2 Seasoned Warrior

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Posted 27 July 2010 - 04:49 PM

Are your shelves solid? It sometimes helps internal circulation to have 1/2 shelves and keeping a slot open in the center.

#3 Suby

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Posted 27 July 2010 - 08:45 PM

Are your shelves solid? It sometimes helps internal circulation to have 1/2 shelves and keeping a slot open in the center.



#4 Suby

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Posted 28 July 2010 - 08:38 AM

We use solid shelves. We will try staggering 1/2 shelves in the middle. Thank you for advice.

#5 hansen

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Posted 31 July 2010 - 02:55 PM

I have an L&L Liberty Bell kiln with Vent Sure attachment. I have been struggling for months trying to find the right program so my pieces will fire to maturity. We fire to 06, 05, 04, and 6. I have called L&L throughout this time and they keep telling me to adjust temp. I have 3 shelves and try to fill them evenly. Two usually over fire and one under fires or comes close to firing the correct temperature according to the free standing Orton cones. I keep adjusting the temperature, but can't get glazes that do not have a range of firing temperatures to work out. Since the thermocouple is at the top, I have decided that all three shelves will never fire to the same temperature. I am beginning to think that I have to use Stroke and Coats or Underglazes that have a wide temperature range. Does anyone have any suggestions or are experiencing the same problem? Thank you.


This is not outside the window that electric kilns normally fire to, the one & two cone difference. "Soak, hold, and ramp down" is what the best advice is. That and find glazes with broader ranges, or ones that will still be nice slightly over-fired. You don't want under-fired. Try going a cone higher, say cone 7. Usually electric kilns because they fire so fast and have no thermal mass to speak of, as gas kilns with all those pots & shelving & soaps, etc. get a lot more maturing time for the glazes. Your approach is correct, just hang in there!! This happens to everybody
h a n s e n



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#6 Suby

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Posted 01 August 2010 - 09:32 PM

Thank you. We were thinking that the top does not reach maturity because air leaks in at the top and the vent is pulling the heat down. We were also thinking that we needed to use glazes and clay that have a range of temp. If we bisqued at 05, then maybe the over fired parts would be at 04 which would be fine. If we fired to cone 5, then the over fired parts would be cone 6 which is what we want. We are going to run a bisque firing this week. Thank you for your advice. Suby

#7 Marcia Selsor

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Posted 01 August 2010 - 10:18 PM

Try putting a kiln shelf inside at the top to hold heat. Try some fiber on the outside top if you have any available.
USE cone packs to monitor the heat. Try rearranging the ware. Dense here, sparse there. Stagger shelves arrangements.
Fire slow, soak at glazes temp. and soak again at 1800 F. or so. Make it work.
Marcia

#8 Rob Battey

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Posted 02 August 2010 - 02:02 PM

Hi Suby,

All the suggestions given so far are good ones.

The 8-sided, 18 inch tall, L&L Liberty Belle kiln is very simple in that it just has one thermocouple and all the elements are turned on and off at the same time.

With just one thermocouple there is no attempt by the digital controller to keep the temperature even from top to bottom in this kiln.

With that in mind, there remains only a couple variables that can have anything to do with the evenness in temperature top to bottom in this kiln. They are: Loading, Speed of Firing, Convection, and Heat Loss.

Loading and Speed of Firing go hand in hand. It is ok to load a lot of ware into a kiln, it will just need to be fired more slowly to keep the heat-work reasonably the same throughout the kiln . Always center your shelves and never load anything past the edge of the shelf. Loading ware too close to the elements will overheat them.

Convection, or air movement, is important. Most of the heat in the kiln is radiant heat not heated air, but pulling the heated air downward with the downdraft vent system helps to even out heat-work. If most of the air coming into the kiln is coming in around the lid it is possible to see the top shelf a little cooler, especially if it is close to the top of the kiln. The suggestion earlier of using a top shelf like a cap on top of the load is a good one. Also be sure the hinge is adjusted high enough so that the lid will sit flat when it gets hot.

Heat Loss through the firebrick is happening all over the kiln. More and more heat is lost the hotter the kiln gets. The sides of the kiln have elements producing heat, but the top and bottom have no elements. Ware on the very bottom and very top of the kiln will be cooler, compared to the center of the kiln because of the extra heat that is being lost through the top and bottom. The effects of heat loss on this little kiln are best combated by a lighter load, a slower firing, and the air movement.

Suby, feel free to call/ email me directly to discuss more.

Best Regards,

Robert Battey
Technical Sales and Support
L&L Kiln Mfg Inc.
800-259-1423 X 106
rob@hotkilns.com
www.hotkilns.com

#9 JBaymore

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Posted 02 August 2010 - 03:02 PM

In the category of "assumptions we make"............ couple of questions about stuff that could be affecting this also:

Are you certain that all the banks of elements are working?

Did you change some of the elements, but some other sets are older?


And a more general question.........

How long are you taking overall (I realize it is not linear climb) to get to cone 04 or to cone 6 in hours of total climb time?


That additional information could serve to help everyone debug this stuff for you. But Rob is "on target".

best,

................john
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#10 AndyL

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Posted 02 August 2010 - 06:42 PM

Ok, a few questions about your Vent Sure. Refer to the PDF http://www.hotkilns....re-instruct.pdf if you live in the USA. Do you have more then 4 90ยบ turns in the ductwork? Have you tried adjusting the ventsure's sliding adjustment on the bypass box under the kiln? Are you venting thru your wall as per the vent sure's instruction? Are you venting into preexisting ductwork? If you are is the preexisting ductwork the correct size to support your kiln?




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