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Building an Expedient Kiln


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#1 rleeq

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Posted 24 December 2012 - 12:43 PM

Hi All:

My name is R'Lee and I'm an absolute beginner at working with clay. After a long career as a neerdowell, I've retired and decided to turn my talents to clay, as I've always been pretty good with my hands as well as somewhat artistic.

Posted Image

I found the above raku kiln plans at http://www.brackers.com/kilns/bracker

I want to build something about half again as large as this kiln. I'm thinking an 3" wire mesh frame Arch design lined with a double layer of wool, top and sides . The bottom being a 3" wire mesh box deep enough to accommodate the burner. 2 layers of wool on the sides of this box and 1 layer will line the bottom, then a floor made of refractory cement 1.5" thick. 1 kiln shelf elevated above the floor on 4 refractory cement bricks. This bottom box will comprise the fire box which will be propane fired.

So...I recently bought a 50' (2x25x1.5) roll of 2300 Deg. Kaowool #8 and some refractory cement rated to 2200 deg.

A couple of questions I have are as follows.


1. I found the plans on the web for this raku kiln but I don't want to be limited to just raku. I want to do stoneware as well as porcelain. The plans for the above kiln call for one layer of wool. As the blanket I bought is rated at 2300 deg, I'm wondering...if I double the thickness will this increase the temperature I can take the kiln to?

2. If I can increase the temp by double layering the wool, will it also increase the amount of time it can be held at higher temperatures?

3. How long can I expect the wool to last? (Like how many firings will it take before it looses it's thermal barrier ability's...(give or take?))

4. My plan is to build as carefully as I can (seems like a simple enough plan) with overlapping seams ONLY where absolutely necessary, but I am concerned about heat leakage as I've only a small space to work in ( concrete slab backyard about 25' x 15') and I have a wooden fence. Don't want to burn the place down...

So there you have it. Any input will be deeply appreciated.

R'
Want to make God Laugh? Tell Him your plans!

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#2 Marcia Selsor

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Posted 24 December 2012 - 03:32 PM

Dear R,

1. I found some plans on the web for a raku kiln but I don't want to be limited to just raku. The plans for the above kiln call for one layer of wool. As the blanket I bought is rated at 2300 deg, I'm wondering...if I double the thickness will this increase the temperature I can take the kiln to?


This link shows a kiln built with 1" thick 8# density roll 24" x 25 '
http://ceramicartsda...wimage&img=2221
If you double the thickness you may have a capacity that could probably contain less than 2 five gallon buckets of space..
You don't mention your fuel or burner choice, the material for the floor and a moisture barrier for the floor.

2. If I can increase the temp by double layering the wool, will it also increase the amount of time it can be held at higher temperatures? In my opinion
you need greater thermal mass to hold at a higher temperature. If you are not removing your pieces in a raku process or protecting them in saggars you run the risk of dunting from thermal shock by cooling too quickly.<br style="color: rgb(28, 40, 55); font-family: arial, verdana, tahoma, sans-serif; line-height: 19px; background-color: rgb(250, 251, 252); "><br style="color: rgb(28, 40, 55); font-family: arial, verdana, tahoma, sans-serif; font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252); ">3. How long can I expect the wool to last? (Like how many firings will it take before it looses it's thermal barrier ability's...(give or take?))

Thermal barrier is not the concern. I had high temperature doors insulated on the interior with fiber which lasted years firing to ^6-7 semi-weekly during an academic year. The structural integrity becomes fragile over time but can be prolonged using rigidizer, a commercial product designed for this purpose.

4. My plan is to build as carefully as I can (seems like a simple enough plan) with overlapping seams ONLY where absolutely necessary, but I am concerned about heat leakage as I've only a small space to work in ( concrete slab backyard about 25' x 15') and I have a wooden fence. Don't want to burn the place down...<br style="color: rgb(28, 40, 55); font-family: arial, verdana, tahoma, sans-serif; font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252); ">

Because you don't mention things like burners, fuel, foundation material, this is tough to call. Fiber shrinks when fired so overlaps are absolutely necessary.

What is it you are trying to do? What firing range or process do you want to achieve?
Look into some home made castable refractory recipes to develop thermal mass. My biggest concern would be this: when dealing with high temperatures, "expedient" is not a good way to go.Or you might just be burning the place down.

This jpg is a look at a raku kiln at 1850 degrees F.using 1" 8 # density fiber. This is the kiln shown being constructed in my gallery on this forum.
Just to give you an idea of heat transfer with one layer.
I did have a friend build a test kiln using fiber about 1/4 the size of a shoe box firedone test tile at a time with a bunsen burner. So you can reach temperature...efficiently? , at what size?, using what fuel?, sitting of what type of foundation? These variables are significant.

Marcia

#3 Marcia Selsor

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Posted 24 December 2012 - 04:11 PM

Hi All:

My name is R'Lee and I'm an absolute beginner at working with clay. After a long career as a neerdowell, I've retired and decided to turn my talents to clay, as I've always been pretty good with my hands as well as somewhat artistic.

Posted Image

I found the above raku kiln plans at http://www.brackers.com/kilns/bracker

I want to build something about half again as large as this kiln. I'm thinking an 3" wire mesh frame Arch design lined with a double layer of wool, top and sides . The bottom being a 3" wire mesh box deep enough to accommodate the burner. 2 layers of wool on the sides of this box and 1 layer will line the bottom, then a floor made of refractory cement 1.5" thick. 1 kiln shelf elevated above the floor on 4 refractory cement bricks. This bottom box will comprise the fire box which will be propane fired.

So...I recently bought a 50' (2x25x1.5) roll of 2300 Deg. Kaowool #8 and some refractory cement rated to 2200 deg.

A couple of questions I have are as follows.


1. I found the plans on the web for this raku kiln but I don't want to be limited to just raku. I want to do stoneware as well as porcelain. The plans for the above kiln call for one layer of wool. As the blanket I bought is rated at 2300 deg, I'm wondering...if I double the thickness will this increase the temperature I can take the kiln to?

2. If I can increase the temp by double layering the wool, will it also increase the amount of time it can be held at higher temperatures?

3. How long can I expect the wool to last? (Like how many firings will it take before it looses it's thermal barrier ability's...(give or take?))

4. My plan is to build as carefully as I can (seems like a simple enough plan) with overlapping seams ONLY where absolutely necessary, but I am concerned about heat leakage as I've only a small space to work in ( concrete slab backyard about 25' x 15') and I have a wooden fence. Don't want to burn the place down...

So there you have it. Any input will be deeply appreciated.

R'

It seems you edited your version while i took an hour to rewrite mine after losing the first attempt

I didn't see this pic when I responded to your questions. This kiln is not using 1" fiber judging from the edge visible where there are peep holes cut away.<div>On the kilns I posted, they are using hardware wire 1/2" or mesh from home depot.One is attached to a welded frame, the other is using bolts to attach the mesh to steel straps.</div><div>You can see more detail at my gallery on this forum under Raku.http://ceramicartsdaily.org/community/index.php?app=gallery&amp;module=images&amp;section=viewimage&amp;img=2221


Marcia






#4 rleeq

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Posted 24 December 2012 - 04:16 PM

Dear R,

1. I found some plans on the web for a raku kiln but I don't want to be limited to just raku. The plans for the above kiln call for one layer of wool. As the blanket I bought is rated at 2300 deg, I'm wondering...if I double the thickness will this increase the temperature I can take the kiln to?


This link shows a kiln built with 1" thick 8# density roll 24" x 25 '
http://ceramicartsda...wimage&img=2221
If you double the thickness you may have a capacity that could probably contain less than 2 five gallon buckets of space..
You don't mention your fuel or burner choice, the material for the floor and a moisture barrier for the floor.

2. If I can increase the temp by double layering the wool, will it also increase the amount of time it can be held at higher temperatures? In my opinion
you need greater thermal mass to hold at a higher temperature. If you are not removing your pieces in a raku process or protecting them in saggars you run the risk of dunting from thermal shock by cooling too quickly.<br style="color: rgb(28, 40, 55); font-family: arial, verdana, tahoma, sans-serif; line-height: 19px; background-color: rgb(250, 251, 252); "><br style="color: rgb(28, 40, 55); font-family: arial, verdana, tahoma, sans-serif; font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252); ">3. How long can I expect the wool to last? (Like how many firings will it take before it looses it's thermal barrier ability's...(give or take?))

Thermal barrier is not the concern. I had high temperature doors insulated on the interior with fiber which lasted years firing to ^6-7 semi-weekly during an academic year. The structural integrity becomes fragile over time but can be prolonged using rigidizer, a commercial product designed for this purpose.

4. My plan is to build as carefully as I can (seems like a simple enough plan) with overlapping seams ONLY where absolutely necessary, but I am concerned about heat leakage as I've only a small space to work in ( concrete slab backyard about 25' x 15') and I have a wooden fence. Don't want to burn the place down...<br style="color: rgb(28, 40, 55); font-family: arial, verdana, tahoma, sans-serif; font-size: 13px; line-height: 19px; background-color: rgb(250, 251, 252); ">

Because you don't mention things like burners, fuel, foundation material, this is tough to call. Fiber shrinks when fired so overlaps are absolutely necessary.

What is it you are trying to do? What firing range or process do you want to achieve?
Look into some home made castable refractory recipes to develop thermal mass. My biggest concern would be this: when dealing with high temperatures, "expedient" is not a good way to go.Or you might just be burning the place down.

This jpg is a look at a raku kiln at 1850 degrees F.using 1" 8 # density fiber. This is the kiln shown being constructed in my gallery on this forum.
Just to give you an idea of heat transfer with one layer.
I did have a friend build a test kiln using fiber about 1/4 the size of a shoe box firedone test tile at a time with a bunsen burner. So you can reach temperature...efficiently? , at what size?, using what fuel?, sitting of what type of foundation? These variables are significant.

Marcia


Marcia:

Thank you for your prompt response. You're right I failed to mention those things, and quite likely others. As I've been researching this most of the day I've tried to edit my posting to address those.

A picture is worth a 1000 words. The entire kiln will be build on a concrete slab and the moisture barrier of cinder blocks to raise it off the ground.
The "Firebox" part of the affair will be wire frame 3" mesh about 6" deep Maybe a little deeper. The flat bottom will have one layer of wool as well as a cast floor of refractory cement1.5' thick. The sides of the box I'll double the wool with plenty of overlap sewn together with tungsten wire (6000deg).
Propane will be the fire source with a weed burner type torch with a flame control knob. I think the one I have is rated up to 200,000 BTU but I can get one rated to 500,000 BTU. Some control of temp can be achieved by moving the burner closer or farther from the fire port. Pyrometric cones will be used in abundance to help me control the temp until I can get a GOOD pyrometer.

As for capacity...The arch I want to construct will be about 4' high, 3' front to back and 3' wide in the fire box. Even with double layering of the wool I think this will come to about 15 cubic feet...maybe less. Not really a big consideration as I'm doing this for myself so to speak, I want to see just what I can do with clay of all kinds.I can always make the arch wider at the top, but 3' wide and 3' front to back is about as big as I think I want for the fire box.

Now to what I'm trying to accomplish. This is harder to explain. As I stated. I am entirely new to ceramics. I've done some serious reading on the web as well as some good books I've bought. What I have done so far is to turn one of my bedrooms into a studio (of sorts). The kiln will be setup in my backyard. What I want it to do is have a wide enough range to do raku work some times and Stoneware and Porcelain at others.
I know that it would be best if I could build a brick kiln with a magic door which would open and close quickly but I am constrained by economics. So...When I do porcelain that is all that will be fired nothing else. Raku firings will be a day dedicated to raku and nothing else.

I am also aware that this is a tall order using the materials I am confined to using but such is as it is.

Want to make God Laugh? Tell Him your plans!

About Me: Rude Crude & Socially Unacceptable.

I Roll my own Cigars
I make my own Whiskey
And when the Rattlesnake Bit Me
After three days of pain he finally died.

#5 Marcia Selsor

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Posted 24 December 2012 - 04:38 PM

[attachment=1805:rakukilnsMT copy.jpg]I swear I thought mi fiber was 1.5 inches after I unrolled it but the carton said 1".
I am prejudice about weed burners and I have used them earlier in my raku experiences. Maybe if you use a good regulator , you can control them better but I think they are very inefficient for gas consumption and freezing tanks. JMHO.

In this photo I made these kilns from a single roll 1" x 2' x 25'.
I used them to take to workshops. They are connected to three tanks in tandem. That helped avoid freezing tanks. Without a good regulator, you may run into freezing tank problems using a weed burner. My burners were from Marc Ward. He advertises in CM I believe.
You could google Ward burners.

Marcia

#6 Marcia Selsor

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Posted 25 December 2012 - 10:04 PM

Here is a slide show from Craig Rhodes from last year. He built a fiber kiln.
http://craigrhodes.u...hodes/Kiln.html

He did a great job on the frame, burner ports, etc.
Thought you might like seeing this.

Marcia

#7 Marcia Selsor

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Posted 27 December 2012 - 09:58 PM

dear Rleeq,
I have been thinking about yor project and two other things to thik about.
1. Doubling the thickness of the ceramic blanket does not increase it 's temperature range. What is rated for 2300 degrees still is rated at 2300 degrees on the hot surface.

2. Tungsten wire? Why? hat seems very extravagant for an expedient project. you can get kanthal wire from the Clay store at the a
Archie Bray Foundation in Helena, Mt. they sell it by the foot. You can get thinner gauges on eBay..

the kiln design by Craig Rhodes in a previous post, looks to me like it is the direction you might consider. It eliminates the concrete blocks, and gives you a nice circulation from below and still have a downdraft out the rear.
anyway,kiln designs are a whole world unto themselves and very fascinating to experiment with.

Marcia




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