Vince Pitelka on thu 22 may 97
At 12:13 PM 5/21/97 -0400, you wrote:
>----------------------------Original message----------------------------
>At 11:57 AM 5/20/97 EDT, you wrote:
>>I am using 21" round kiln shelves. They are 21"x21"x5/8".
>>During the past year few of the shelves developed cracks up to 10 cm long
>>from the edge inside.
>>Is this a normal phenomena?
>Hey, I'd quit using them when I first saw the crack. I haven't the
>foggiest idea what caused it but I consider any shelf with a crack showing
>unsafe.
Actually, it is no problem using cracked shelves, as long as you use some
common sense as well. If they are cracked more than half-way across their
width, recycle them as smaller shelves or cut them up as shims. Shelves
always crack from the outer edge towards the center, usually from
excessively abrupt heating and/or cooling. When you stack the kiln, place a
post as close as possible to the point where the crack meets the edge of the
shelf, if possible directly beneath and above the crack. This will be no
problem with full-round shelves, since you can always rotate them so that
the crack is directly above a post. Once they are cracked, the stress is
relieved, and it is likely that they will not crack more for a long time.
In production in California I fired and cooled my car kiln dangerously fast
a few times, and cracked a great many nice new 14x28 silcar shelves. I quit
firing so fast, but I also I kept using most of the cracked shelves for
another seven years.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
APGreenLA on wed 28 may 97
You might also want to consider patching the cracks with some type of
patching mortar. This should increase the life.
>Actually, it is no problem using cracked shelves, as long as you use some
>common sense as well. If they are cracked more than half-way across
their
>width, recycle them as smaller shelves or cut them up as shims. Shelves
>always crack from the outer edge towards the center, usually from
>excessively abrupt heating and/or cooling. When you stack the kiln,
place a
>post as close as possible to the point where the crack meets the edge of
the
>shelf, if possible directly beneath and above the crack. This will be no
>problem with full-round shelves, since you can always rotate them so that
>the crack is directly above a post. Once they are cracked, the stress is
>relieved, and it is likely that they will not crack more for a long time.
>In production in California I fired and cooled my car kiln dangerously
fast
>a few times, and cracked a great many nice new 14x28 silcar shelves. I
quit
>firing so fast, but I also I kept using most of the cracked shelves for
>another seven years.
>- Vince
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