>> P.42
∆δ=α∆tE …………………………………(29)Fitwhere, ∆δ : Reduction of radial clearance, mmα : Coefficient of linear expansion for Purpose of fit ≒12.5×10-6 1/°Cbearing steel∆tE : Temperature difference between the outer ring and the inner ring plus rolling elements considered as one unit, ° C Bore diameter of outer ring, mm:The temperature difference ∆t is considered to be 5〜10°C under normal operating conditions and 15〜 20°C at high rotational speeds. Therefore, when the temperature difference is great, a correspondingly larger radial internal clearance must be selected.To achieve the best performance of needle roller bearings, it is important that the bearing rings are cor-rectly tted onto the shaft and into the housing.The purpose of fit is to provide the appropriate amount of interference required between the inner ring and the shaft or between the outer ring and the housing, to prevent harmful mutual slippage.If the interference is insufficient, it will cause a harmful relative displacement, known as creep, between the fitted surfaces in the circumferential direction. This may lead to abnormal wear of tted surfaces, intru-sion of wear particles into the bearing, generation of abnormal heat, vibration, etc. Therefore, a suitable t must be selected.Table 20 Nature of radial load and fitNature of the loadRotating conditionsInner ringOuter ringFitInner ring : RotatingOuter ring : StationaryLoad direction : FixedRotating load on inner ringStationary load on outer ringInterference fitClearance fitInner ring : StationaryOuter ring : RotatingLoad direction : Rotating with outer ringInner ring : StationaryOuter ring : RotatingLoad direction : FixedRotating load on outer ringStationary load on inner ring Clearance fitInterference fitInner ring : RotatingOuter ring : StationaryLoad direction : Rotating with inner ringThe load direction is not fixed, including cases where Inner ring : Rotating or stationaryDirectionally ndeterminate ladthe load direction is fluctuat-Outer ring : Rotating or stationaryInterference fitInterference fiting or there is an unbal-Load direction : Not fixedanced load. A39
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