Machinery's Handbook, 31st Edition
2490 Ball and Roller Bearings Radial Roller Bearings: The magnitude of the Rating Life, L 10 , in millions of revolu tions, for a radial roller bearing application is given by the formula: (12) where C = the basic load rating in newtons (pounds), see Formula (13); and, P = equivalent (13) where f c = a factor which depends on the geometry of the bearing components, the accu racy to which the various bearing parts are made, and the material. Maximum values of f c are given in Table 31 i = number of rows of rollers in the bearing l eff = effective length, mm (inches) α = nominal contact angle, degrees Z = number of rollers per row in a radial roller bearing D = roller diameter, mm (inches) (mean diameter for a tapered roller, major diam eter for a spherical roller) When rollers are longer than 2.5 D , a reduction in the f c value must be anticipated. In this case, the bearing manufacturer may be expected to establish load ratings accordingly. In applications where rollers operate directly on a shaft surface or a housing surface, such a surface must be equivalent in all respects to the raceway it replaces to achieve the basic load rating of the bearing. When calculating the basic load rating for a unit consisting of two or more similar single-row bearings mounted “in tandem,” properly manufactured and mounted for equal load distribution, the rating of the combination is the number of bearings to the 7 ⁄ 9 power times the rating of a single-row bearing. If, for some technical reason, the unit may be treated as a number of individually interchangeable single-row bearings, this consider- ation does not apply. The magnitude of the equivalent radial load, P , in newtons (pounds), for radial roller bearings, under combined constant radial and constant thrust loads is given by the formula: (14) where F r = the applied radial load in newtons (pounds) F a = the applied axial load in newtons (pounds) radial load in newtons (pounds), see Formula (14). For radial roller bearings, C is found by the formula: X = radial load factor as given in Table 33 Y = axial load factor as given in Table 33 Table 33. Values of X and Y for Computing Equivalent Radial Load P for Radial Roller Bearing L P C 10 = a k 10 ⁄ 3 cos C f il c eff = ^ Z D h 7⁄9 3⁄4 29⁄27 α P XF YF r a = +
F F
F F
r a
r a 2
e
e
#
Bearing Type
X
Y 0
X
Y
Single Row Bearings Double Row Bearings a 0.4
Self-Aligning and Tapered Roller Bearings a α ≠ 0 °
1 1
0.4 cot α
0.67
0.45 cot α
0.67 cot α
a For α = 0°, F e = 1.5 tan α
a = 0 and X = 1.
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