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Shell to Tire Clearance

What is the clearance between chairs and the inner diameter of tire ring?

The clearance between the chairs and the tire is specific for each tire and is specified in the OEM documents (kiln assembly drawings) as cold clearance. The cold clearance will be different for each tire as stated because it is based on the designer's expected shell temperatures at each tire. During operation, when the shell is at "normal" operating temperature the clearance at each tire will have diminished due to differential shell to tire expansion, but now it is reasonable to expect that they all be approximately the same. To determine what this hot clearance is, measure the tire creep and divide by PI(). Typically for any tires and shell chairs that are in good condition the tire creep will be in the range of 6 to 12mm meaning that the theoretical clearance will be 2 to 4 mm if the tire and shell were truly circular. But if you were to instantly stop the kiln and measure the gap at the top it would be about 50% larger because of shell ovality. (The circular relationship of dividing creep by PI() does not prevail since the shell is not round but more like an oval with a pronounced flattening at the top.)

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