Marcia Selsor, on 24 December 2012 - 03:32 PM, said:
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 '
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.
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.