>> P.43
1N=0.102kgf=0.2248lbs.1mm=0.03937inchABCDEFGHIJKLMConditions for determination of fitWhen determining a suitable t for a bearing, it is nec-essary to consider various conditions such as nature and magnitude of the load, temperature, required rota-tional accuracy, material/nish grade/thickness of the shaft and housing, ease of mounting and dismounting, etc.as ∆T, the temperature difference between the inner ring and the shaft can be estimated to be (0.1〜0.15) ∆T. Accordingly, the amount of reduction of the inner ring interference is obtained by the following equation. ∆dT= (0.1〜0.15) ∆Tαd≒0.0015 ∆Td×10-3…(32)where, ∆dT : Reduction amount of inner ring interference due to temperature 1 Nature of load and fitBasically, the appropriate t depends on whether the load direction is rotational or stationary in relation to the inner and outer rings.The relationship between the nature of radial loads and the t is, in general, based on Table 20.2 Load amount and interferenceThe greater the load, the larger the interference must be.When selecting an interference between the inner ring difference, mm∆T: Temperature difference between the inside of the bearing and the outside of the housing, °Cα : Coefficient of linear expansion for bearing steel ≒12.5×10-6 1/ °Cd : Bore diameter of inner ring, mm4 Shaft finish grade and interferenceSince peaks of surface roughness of the tted surface and the shaft, it is necessary to estimate the reduction are crushed down when tting the bearing, the effec-of interference due to the radial load. The amount of tive interference becomes smaller than the apparent reduction of interference is obtained by the following interference obtained by measurements, and it is gen-erally obtained by the following equations.・For ground shaft ∆de= ∆df …………………………(33)dd+2・For machined shaft ∆de= ∆df …………………………(34)dd+3where, ∆de : Effective interference of inner ring, mm d: Bore diameter of inner ring, mm∆df Apparent interference, mm:5 Minimum interference and maximum interferenceWhen the load direction is rotating in relation to the inner ring, the inner ring is tted with interference to the shaft. For solid ground steel shafts, the minimum interfer-ence (required apparent interference) ∆df is expressed by the following equation which is deduced from equa-tions (30) or (31), (32) and (33).∆df ≧ (∆dF+0.0015 ∆Td×10-3) …(35)d+2d∆dF=0.08 F r×10-3………………(30)dB・When Fr>0.2C0∆dF=0.02 ×10-3FrB ……………………(31)where, Fr C0∆dF d B :Radial load applied to bearing, N :Basic static load rating, N:Amount of reduction of inner ring interference, mm:Bore diameter of inner ring, mm:Width of inner ring, mm3 Temperature conditions and change of interferenceThe interference of tted surfaces is also inuenced by the temperature difference between the bearing and the shaft and housing. For example, when steam is owing through a hollow shaft, or when the housing is made of light metal, it is necessary to take into consid-eration the differences in temperature, the coefficient of linear expansion and other such factors.equations.・When Fr≦0.2C0Usually, the interference of the inner ring decreases It is desired that the maximum interference should be as the bearing temperature increases during opera-less than 1/1000 of the shaft diameter. In the case of tion. If the temperature difference between the inside the outer ring, the effective interference varies accord-of the bearing and the outside of the housing is taken ing to the housing material, thickness, shape, etc., so it is determined empirically.A40
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