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Kiln Information And Sources


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#1 harleyweigle

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Posted 04 January 2017 - 11:48 PM

Hello Everyone,

 

I would like to develop and understanding of  the whys and hows concerning gas fired kilns. I don't necessarily have questions I just want to fully understand and gather as much information as possible. If anyone could give me any insights or resources, such as books, to the following subjects I would be incredibly grateful! 

 

1. Downdraft & Updraft Kilns

 

2. Forced Air Vs. Natural Draft Kilns

 

3. Flame Paths Inside Kilns

 

4. BTU Distribution Inside Kilns

 

Thank you very much!

 

-Harley



#2 Marcia Selsor

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Posted 05 January 2017 - 08:50 AM

Harley,

here is a simplistic response from my personal experiences with gas kilns since 1967. Didn't fire kilns in '66, just made things.

 

1. Downdraft & Updraft Kilns

I prefer down drafts for easier control of getting even reduction in the kilns. I learned to fire on home made downdrafts while in College in the 60s. I built several down drafts in Grad school for soda and salt firings and and oil burning kiln fired with modified burners. Also fired 2 Alpine updrafts in grad school..and found they needed a different approach to stacking to help even the bottom with the top. All this comes from repeated firings regularly and through different weather conditions. In 2011-12 I fired a huge Olsen updraft with 14 burners entering from the bottom. With the guide of a 20 year kiln log from the previous professor, it fired perfectly even. I'd say updrafts with burner ports coming through the floor are preferable . I still prefer downdrafts. I designed and built all the kilns I used during my 25 years of teaching in Montana. -2 burner downdrafts: a catenary Arch and a Sprung Arch. .First 5 years were forced air. Second 20 years were venturi burners on a large car kiln and a sprung arch.When I taught in Hawaii, they had a program of hundreds of students and we were firing many dozen or so updrafts during the week.- team firing.The success is dependent on stacking and balancing the burner output with the dampers.

 

2. Forced Air Vs. Natural Draft Kilns

In higher altitudes I think forced air is a benefit. you need a higher stack (chimney) if you are using a natural draft. Mandatory.

 

 

3. Flame Paths Inside Kilns-

flame paths are dependent on the stacking. Cross drafts, updrafts, downdrafts all follow the maze through the ware to the flu. In the kilns I fired for 20 years, downdrafts with ventures (and all kilns are unique) I stacked tighter along the back wall, 9" on the bottom course and tighter in the middle and top front.  Think maze and flow path when stacking.

 

4. BTU Distribution Inside Kilns 

The BTU distribution? Not sure what you mean unless you are referring to hot spot. BTU needs are measured by the type of insulation the kiln has. BTU measurement is the burner output.

For example, a kiln with quality insulation brick requires (ballpark) 14,000 BTUs per cubic  ft. at max capacity. A hard brick kiln requires 30,000 BTU output because the hard bricks have mass density and need to be heated up more. 

Just my experience. I fired regularly in east coast Philadelphia, Midwest Carbondale, Ill. and Billings, Montana (3500 ft ) , Honolulu, Banff (6,000 ft) up state NY. Also the differences of propane and natural, diesel,  can determine firing behavior. Diesel burns inefficiently when it enters a cold kiln. Need to avoid carbon clinker buildup. Wood is another case all together.

A book you might want to read is  "The Art of Firing " by Nils Lou.

 

At NCECA in the past, many conversations occur regarding your many questions. I think the conference will be help in 2018 in Pittsburgh. You should try to attend.

 

Marcia


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[http://www.marciaselsorstudio.com

#3 Marcia Selsor

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Posted 05 January 2017 - 10:20 AM

Just wanted to add that I fired 2 kilns, each twice a week beginning of the 3 third week of the semester. Sometimes more by the end of the semester. 

The last 20 years of teaching in Montana I built a hinged door on the sprung arch and a roll shut door on the car kiln because by 1980 I needed carpal tunnel surgery from what I think was bricking up and un bricking heavy hard brick doors on the kins.

 

Marcia


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#4 Magnolia Mud Research

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Posted 05 January 2017 - 12:15 PM

Two books that will give you some insights on your topics:
 
21ST Century Kilns
edited by Mel Jacobson
http://www.21stcentu....com/index.html
 
The Art of Firing
by Nils Lou
Publisher; Bloomsbury Publishing Plc, 1998
ISBN; 0713647418, 9780713647419
Length 96 pages
It is available from various book sellers.
 
LT



#5 Magnolia Mud Research

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Posted 05 January 2017 - 01:03 PM

The CAD book store has a sale on now for Fred Olsen's The Kiln Book, 3rd Edition. 

http://ceramicartsda...nline-specials/

 

Fred does a good job of explaining how kilns operate and discusses the differences among them.  It is also a good resource for your topics.

 

LT



#6 Marcia Selsor

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Posted 05 January 2017 - 03:17 PM

 

Two books that will give you some insights on your topics:
 
21ST Century Kilns
edited by Mel Jacobson
http://www.21stcentu....com/index.html
 
The Art of Firing
by Nils Lou
Publisher; Bloomsbury Publishing Plc, 1998
ISBN; 0713647418, 9780713647419
Length 96 pages
It is available from various book sellers.
 
LT

 

My raku kiln in my avatar is in Mel's book.

Marcia


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#7 Marcia Selsor

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Posted 06 January 2017 - 11:47 AM

The CAD book store has a sale on now for Fred Olsen's The Kiln Book, 3rd Edition. 

http://ceramicartsda...nline-specials/

 

Fred does a good job of explaining how kilns operate and discusses the differences among them.  It is also a good resource for your topics.

 

LT

One thing Fred left out of his earlier editions was the need for taller stacks at high altitude. 1993. We were firing a fast freddie wood kiln at Banff which was built to his specs. It stalled out at 1900 degrees. Finally Les Manning called Fred for help. The stack wasn't tall enough for the altitude. It is difficult to generalize about kilns because there are so many differing conditions.


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#8 Magnolia Mud Research

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Posted 06 January 2017 - 04:24 PM

Marcia said:
"... the need for taller stacks at high altitude. ... It is difficult to generalize about kilns because there are so many differing conditions".

Yeah, too many of the 'scientific topics' in studio ceramics discussions get over-simplified and lose sight of the fact that such things as scfm air flow and acfm air flows do not mean the same amount of air. They are the same only when the actual air pressure is the same as the standard air pressure.  (physics 101). 
 
Combustion devices (aka kilns) should always be reviewed carefully using balanced fuel and air in and gases out, and in molar or mass units instead of volumes.

 

His book is still a useful resource.

 

LT



#9 Marcia Selsor

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Posted 06 January 2017 - 04:47 PM

LT,

I agree his book is a valuable resource, but as you say, many factors also need to be considered for individual situations.

Marcia


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#10 Marcia Selsor

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Posted 07 January 2017 - 09:11 PM

One of my basic kiln books was a small paper handout by Paul Soldner. I still have it but it mat still be in Texas.

Marcia


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#11 Marcia Selsor

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Posted 16 January 2017 - 11:09 PM

I am going to embark on some experimental kilns in the Spring based on Ian gregory's book of alternative kilns. There is a small soda fired kiln that sounds like an interesting project.

 

Marcia


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