Machinery's Handbook, 31st Edition
Ball and Roller Bearings 2483 can ultimately fatigue. Under ideal conditions, the repeated stresses developed in the con tact areas between the balls or rollers and the raceways eventually can result in the fatigue of the material which manifests itself with the spalling of the load-carrying surfaces. In most applications the fatigue life is the maximum useful life of a bearing. Static Load Criterion: A static load is a load acting on a non-rotating bearing. Perma- nent deformations appear in balls or rollers and raceways under a static load of moder- ate magnitude and increase gradually with increasing load. The permissible static load is, therefore, dependent upon the permissible magnitude of permanent deformation. It has been found that for ball and roller bearings suitably manufactured from hardened alloy steel, deformations occurring under maximum contact stress of 4,000 megapascals (580,000 pounds per square inch) acting at the center of contact (in the case of roller bear- ings, of a uniformly loaded roller) do not greatly impair smoothness or friction. Depend- ing on requirements for smoothness of operation, friction, or sound level, higher or lower static load limits may be tolerated. Ball Bearing Types Covered.— AFBMA and American National Standard ANSI/ABMA 9-1990 sets forth the method of determining ball bearing Rating Life and Static Load Rat- ing and covers the following types: 1) Radial, deep groove and angular contact ball bearings whose inner ring raceways have a cross-sectional radius not larger than 52 percent of the ball diameter and whose outer ring raceways have a cross-sectional radius not larger than 53 percent of the ball diameter. 2) Radial, self-aligning ball bearings whose inner ring raceways have cross-sectional radii not larger than 53 percent of the ball diameter. 3) Thrust ball bearings whose washer raceways have cross-sectional radii not larger than 54 percent of the ball diameter. 4) Double row, radial and angular contact ball bearings and double direction thrust ball bearings are presumed to be symmetrical. Limitations for Ball Bearings.— The following limitations apply: 1) Truncated contact area. This standard* may not be safely applied to ball bearings sub jected to loading which causes the contact area of the ball with the raceway to be truncated by the raceway shoulder. This limitation depends strongly on details of bearing design which are not standardized. 2) Material. This standard applies only to ball bearings fabricated from hardened good quality steel. 3) Types. The f c factors specified in the basic load rating formulas are valid only for those ball bearing types specified above. 4) Lubrication. The Rating Life calculated according to this standard is based on the assumption that the bearing is adequately lubricated. The determination of adequate lubrication depends upon the bearing application. 5) Ring support and alignment. The Rating Life calculated according to this standard assumes that the bearing inner and outer rings are rigidly supported and the inner and outer ring axes are properly aligned. 6) Internal clearance. The radial ball bearing Rating Life calculated according to this standard is based on the assumption that only a nominal interior clearance occurs in the mounted bearing at operating speed, load and temperature. 7) High-speed effects. The Rating Life calculated according to this standard does not account for high-speed effects such as ball centrifugal forces and gyroscopic moments. These effects tend to diminish fatigue life. Analytical evaluation of these effects frequently requires the use of high-speed digital computation devices and hence is not covered in the standard. * All references to “standard” are to AFBMA and American National Standard “Load Ratings and Fatigue Life for Ball Bearings” ANSI/ABMA9-1990.
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