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Kiln shelves breaking SiC & Mullite

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diskullman

Industrial
Oct 6, 2005
298
Our customer asked us to source sandwich tiles for kiln shelves. Kiln shelves are typically made of Silicon Carbide. Our customer prefers a sandwich tile, which is still silicon carbide, with a surface coating of Alumina. Our source overseas could only provide this tile with a mullite coating. The tiles are 12" x15" withe 2 expansion relief cuts approximately 3/4" deep into each side. Our source molded the expansion cuts into the SiC, then coated the entire tile in mullite, hiding the expansion cuts. We are having lots of tiles breaking, extending from the expansion cuts.
My heory is that the mullite that fills in these cuts is expanding at a greater rate than the SiC, wedging open the expansion cut, and cracking the tile all the way through. Can anyone confirm this?
Also, on a kiln shelf that small are expansion cuts even needed?

Russell Giuliano
 
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