Machinery's Handbook, 31st Edition
2494 Ball and Roller Bearings When a 3 is less than 1 it may not be assumed that the deficiency in lubrication can be overcome by using an improved steel. When this factor is applied, L 10 ′ = a 3 L 10 . In most ball and roller bearing applications, lubrication is required to separate the roll- ing surfaces, i.e., rollers and raceways, to reduce the retainer-roller and retainer-land fric- tion and sometimes to act as a coolant to remove heat generated by the bearing. Factor Combinations: A fatigue life formula embodying the foregoing life adjustment factors is L 10 ′ = a 1 a 2 a 3 L 10 . Indiscriminate application of the life adjustment factors in this formula may lead to serious overestimation of bearing endurance, since fatigue life is only one criterion for bearing selection. Care must be exercised to select bearings which are of sufficient size for the application. Ball Bearing Static Load Rating.— For ball bearings suitably manufactured from hard ened alloy steels, the static radial load rating is that uniformly distributed static radial bearing load which produces a maximum contact stress of 4,000 megapascals (580,000 pounds per square inch). In the case of a single row, angular contact ball bearing, the static radial load rating refers to the radial component of that load which causes a purely radial displacement of the bearing rings in relation to each other. The static axial load rating is that uniformly distributed static centric axial load which produces a maximum contact stress of 4,000 megapascals (580,000 pounds per square inch). Radial and Angular Contact Groove Ball Bearings: The magnitude of the static load rat ing C o in newtons (pounds) for radial ball bearings is found by the formula: (20) where f o = a factor for different kinds of ball bearings given in Table 35 i = number of rows of balls in bearing Z = number of balls per row D = ball diameter, mm (inches) α = nominal contact angle, degrees This formula applies to bearings with a cross sectional raceway groove radius not larger than 0.52 D in radial and angular contact groove ball bearing inner rings and 0.53 D in radial and angular contact groove ball bearing outer rings and self-aligning ball bearing inner rings. The load-carrying ability of a ball bearing is not necessarily increased by the use of a smaller groove radius but is reduced by the use of a larger radius than those indicated above. Radial or Angular Contact Ball Bearing Combinations: The basic static load rating for two similar single row radial or angular contact ball bearings mounted side by side on the same shaft such that they operate as a unit (duplex mounting) in “back-to-back” or “face- to-face” arrangement is two times the rating of one single row bearing. The basic static radial load rating for two or more single row radial or angular contact ball bearings mounted side by side on the same shaft such that they operate as a unit (duplex or stack mounting) in “tandem” arrangement, properly manufactured and mounted for equal load distribution, is the number of bearings times the rating of one single row bearing. Thrust Ball Bearings: The magnitude of the static load rating C oa for thrust ball bearings is found by the formula: (21) where f o = a factor given in Table 35 Z = number of balls carrying the load in one direction D = ball diameter, mm (inches) α = nominal contact angle, degrees cos C f ZD oa o 2 = α cos C f iZD o o 2 = α
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