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Excessive Pressures.

(2) Bearing pressures will be regarded as excessive whenever they are greater than intended in the design of the bearing, or greater than permissible in good practice. Overload on a machine is, therefore, an evident cause of excessive bearing pressures.

Incorrect alignment is a common cause of excessive bearing pressures. This may occur through the incorrect position of the bearing either horizontally or vertically; or the bearing may be twisted on its foundation. Correct alignment of bearings is the first essential of satisfactory installation and should not be neglected.

Heavy belt pull or unnecessarily tight driving chains result in excessive pressures and should be corrected in order to avoid trouble. Worn gears often result in heavy radial forces and vibratory loads on the bearing.

Excessive end thrust on a shaft, caused by expansion or contraction of a long lineshaft with changing temperature sometimes brings a heavy pressure on a thrust collar not intended for a heavy load, thus causing friction and heating.

Excessive pressures, such as have been described, often cause failure of the oil film, resulting in metallic contact, rapid wear and excessive frictional heat which may destroy the bearing. They should be overcome by mechanical correction wherever possible. When heavy pressures are unavoidable, the resultant troubles may be relieved by the use of a heavy-bodied oil. Heavy-bodied compounded oils, due to their superior adhesive qualities, are useful for extreme bearing pressures, provided the method of lubrication does not involve repeated use of the oil.