Machinery's Handbook, 31st Edition
2482 Ball and Roller Bearings Bearing Failures, Deficiencies, and Their Origins.— The general classifications of fail ures and deficiencies requiring bearing removal are: 1) Overheating due to a) Inadequate or insufficient lubrication; b) Excessive lubrication; c) Grease liquefaction or aeration; d) Oil foaming; e) Abrasive or corrosive action due to contaminants in bearing; f) Distortion of housing due to warping, or out-of-round; g) Seal rubbing or failure; h) Inadequate or blocked scavenge oil passages; i) Inadequate bearing- clearance or bearing-preload; j) Race turning; k) Cage wear; and l) Shaft expansion-loss of bearing or seal clearance. 2) Vibration due to a) Dirt or chips in bearing; b) Fatigued race or rolling elements; c) Race turning; d) Rotor unbalance; e) Out-of-round shaft; f) Race misalignment; g) Housing resonance; h) Cage wear; i) Flats on races or rolling elements; j) Excessive clearance; k) Corrosion; l) False-brinelling or indentation of races; m) Electrical dis charge (similar to corrosion effects); n) Mixed rolling element diameters; and o) Out-of- square rolling paths in races. 3) Turning on shaft due to a) Growth of race due to overheating; b) Fretting wear; c) Improper initial fit; d) Excessive shaft deflection; e) Initially coarse shaft finish; and f) Seal rub on inner race. 4) Binding of the shaft due to a) Lubricant breakdown; b) Contamination by abrasive or corrosive matter; c) Housing distortion or out-of-round pinching bearing; d) Uneven shimming of housing with loss of clearance; e) Tight rubbing seals; f) Preloaded bear ings; g) Cocked races; h) Loss of clearance due to excessive tightening of adapter; i) Thermal expansion of shaft or housing; and j) Cage failure. 5) Noisy bearing due to a) Lubrication breakdown, inadequate lubrication, stiff grease; b) Contamination; c) Pinched bearing; d) Seal rubbing; e) Loss of clearance and preload ing; f) Bearing slipping on shaft or in housing; g) Flatted roller or ball; h) Brinelling due to assembly abuse, handling, or shock loads; i) Variation in size of rolling elements; j) Out-of-round or lobular shaft; k) Housing bore waviness; and l) Chips or scores under bearing race seat. 6) Displaced shaft due to a) Bearing wear; b) Improper housing or closure assembly; c) Overheated and shifted bearing; d) Inadequate shaft or housing shoulder; e) Lubrica tion and cage failure permitting rolling elements to bunch; f) Loosened retainer nut or adapter; g) Excessive heat application in assembling inner race, causing growth and shift ing on shaft; and h) Housing pounding out. 7) Lubricant leakage due to a) Overfilling of lubricant; b) Grease churning due to use of too soft a consistency; c) Grease deterioration due to excessive operating temperature; d) Operating life longer than grease life (grease breakdown, aeration, and purging); e) Seal wear; f) Wrong shaft attitude (bearing seals designed for horizontal mounting only); g) Seal failure; h) Clogged breather; i) Oil foaming due to churning or air flow through housing; j) Gasket (O-ring) failure or misapplication; k) Porous housing or clo sure; and l) Lubricator set at wrong flow rate. Load Ratings and Fatigue Life Ball and Roller Bearing Life.— The performance of ball and roller bearings is a func- tion of many variables. These include the bearing design, the characteristics of the mate- rial from which the bearings are made, the way in which they are manufactured, as well as many variables associated with their application. The only sure way to establish the satisfactory operation of a bearing selected for a specific application is by actual perfor - mance in the application. As this is often impractical, another basis is required to estimate the suitability of a particular bearing for a given application. Two factors are taken into consideration: the bearing fatigue life, and its ability to withstand static loading. Life Criterion: Even if a ball or roller bearing is properly mounted, adequately lubri cated, protected from foreign matter and not subjected to extreme operating conditions, it
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online