>> P.41
1N=0.102kgf=0.2248lbs.1mm=0.03937inchABCDEFGHIJKLMSelection of clearance∆C=∆F+∆E………………………………(24)Radial clearances of needle roller bearings change according to bearing fit, temperature difference between bearing rings and rolling elements, loads, etc., and these factors greatly inuence bearing life, accuracy, noise, generation of heat, etc. If radial clearances are too large, noise and vibration will increase, and if they are too small, abnormally great forces are exerted on the contact areas between raceways and rolling elements, resulting in abnormal-where,∆C:Amount of reduction of the radial clearance, mm∆F:Amount of expansion of the out-side diameter of inner ring, mm∆E :Amount of shrinkage of the bore diameter of outer ring, mm1Amount of expansion of the outside diameter of inner ringly high heat generation and a decrease in bearing life. ・With solid shaft∆F=∆de ………………………………(25)dF・With hollow shaft1-(di/d)21-(d/F)2 (di/d)2dF∆F=∆de ……(26)where,∆de:Effective interference of inner ring, mmd:Bore diameter of inner ring, mmF:Outside diameter of inner ring, mmdi:Bore diameter of hollow shaft, mm2Amount of shrinkage of the bore diameter of outer ring ………………………………(27)ED∆E=∆De・With steel housing(D0≠∞) ……(28)1-(D/D0)21-(E/D)2 (D/D0)2ED∆E=∆Dewhere,∆DeDE D0 :Effective interference of outer ring, mm :Outside diameter of outer ring, mm:Bore diameter of outer ring, mm:Outside diameter of housing, mm・With steel housing(D0=∞)Reduction of radial clearances due to temperature differences between inner and outer ringsFrictional heat generated by rotation is dissipated through the shafts and housings as well as through oil and air. Under general operating conditions, heat dis-sipation is larger on the housing side compared with Therefore, in the ideal case, the clearance provided before mounting should be such that it will become zero or slightly larger when the bearing has reached steady-state operation and the temperature has become constant (saturation temperature). However, it is difficult to achieve this ideal state for all bearings. Under general operating conditions, bearings with CN clearance are most widely used, and are manufac-tured to provide satisfactory performance when tted according to Tables 21 and 22.When radial internal clearances other than CN are used, refer to Table 19.Table 19 Examples of selecting radial internal clearances other than CN clearanceOperating conditionsSelection of clearanceWhen heavy loads and shock loads are applied, and amount of interference is great.When directionally indeterminate loads are applied, and a tight fit is required for both inner and outer rings.When temperature of inner ring is much higher than that of outer ring.When shaft deflection and/or mounting error to the housing are great.When less noise and vibration are required. C3 or larger clearance When a loose fit is required for both inner and outer rings. C2 or smaller clearanceWhen preload is required. Reduction of radial clearances by fitWhen the inner or outer rings are interference fitted that on the shaft side, and the temperature of the onto shafts and into housings, respectively, they outer ring is usually lower than that of the inner ring. expand or shrink due to elastic deformation. As the During operation, the temperature of the rolling ele-result, the radial clearances are reduced. These ments is the highest, followed by that of the inner ring reduced radial clearances are called residual (internal) and that of the outer ring. The amount of thermal clearances.expansion, therefore, varies, and the radial clearances The amount of reduction is obtained by the following are reduced. This reduced radial clearance is called equation, and it is generally 70 to 90% of the interfer-the effective (internal) clearance, and the amount of ence amount.reduction is obtained by the following equation:A38
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