Ball and Roller Bearings Machinery's Handbook, 31st Edition
2492
(17) where f c = a factor which depends on the geometry of the bearing components, the accu racy to which the various parts are made, and the material. Values of f c are given in Table 32 l eff = effective length, mm (inches) Z = number of rollers in a single row, single direction, thrust roller bearing D = roller diameter, mm (inches) (mean diameter for a tapered roller, major diam eter for a spherical roller) α = nominal contact angle, degrees For thrust roller bearings with two or more rows of rollers carrying loads in the same direction the magnitude of C a is found by the formula: C f l Z D for a c eff ! α α α = ° ^ h 7⁄9 3⁄4 29⁄27 , cos tan 90
Z 1 l eff 1 C a 1 --------
Z 2 l eff 2 C a 2 --------
9 2 ⁄
9 2 ⁄
=
Z 1 l eff 1 Z 2 l eff 2 … Z n l effn + + + ( )
+
… + +
C a
(18)
–2 9 ⁄
Z n l effn C an --------
9 2 ⁄
where Z 1 , Z 2 , … , Z n = the number of rollers in respective rows of a single direction, multi- row bearing C a 1 , C a 2 , … , C an = the basic load rating per row of a single direction, multi-row, thrust roller bearing, each calculated as a single row bearing with Z 1 , Z 2 , … , Z n rollers respectively l eff 1 , l eff 2 , … , l effn = effective length, mm (inches), or rollers in the respective rows In applications where rollers operate directly on a surface supplied by the user, such a surface must be equivalent in all respects to the washer raceway it replaces to achieve the basic load rating of the bearing. In case the bearing is so designed that several rollers are located on a common axis, these rollers are considered as one roller of a length equal to the total effective length of contact of the several rollers. Rollers as defined above, or portions thereof which contact the same washer-raceway area, belong to one row. When the ratio of the individual roller effective length to the pitch diameter (at which this roller operates) is too large, a reduction of the f c value must be anticipated due to ex- cessive slip in the roller-raceway contact. 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 defined by Formula (18). If, for some techni cal reason, the unit may be treated as a number of individually interchangeable single-row bearings, this consideration does not apply. The magnitude of the equivalent thrust load, P a , in pounds, for thrust roller bearings with α not equal to 90 degrees under combined constant thrust and constant radial loads is given by the formula: (19) where F r = applied radial load, newtons (pounds) P XF YF a r a = +
F a = applied axial load, newtons (pounds) X = radial load factor as given in Table 34 Y = axial load factor as given in Table 34
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