>> P.23
ABCDEFGHIJKLMLife adjustment factor for operating conditionsa3This factor helps take into account the effects of oper-Correction of basic dynamic for temperature and hardnessload rating ating conditions, especially lubrication on the bearing.Temperature factorThe bearing life is limited by the phenomenon of fatigue which occurs, in general, beneath surfaces The operating temperature for each bearing is deter-subjected to repeated stresses. Under good lubrica-mined according to its material and structure. If spe-tion conditions where the rolling element and raceway cial heat treatment is performed, bearings can be surfaces are completely separated by an oil lm and used at temperatures higher than +150°C. As the surface damage can be disregarded, a3 is set to be 1. However, when conditions of lubrication are not good, allowable contact stress gradually decreases when the bearing temperature exceeds 150°C, the basic namely, when the viscosity of the lubricating oil is low dynamic load rating is lowered and can be obtained or the peripheral speed of the rolling elements is by the following equation:especially low, and so on, a3< 1 is used.lubrication On the other hand, when is especially good, a value of a3 > 1 can be used. When lubrica-tion is not good and a3 < 1 is used, the life adjustment factor a2 cannot generally exceed 1.Ct = ftC …………………………………… (7)where,Ct : Basic dynamic load rating considering temperature rise, N : Temperature factor (See Fig. 4.)ftC : Basic dynamic load rating, NWhen selecting a bearing according to the basic dynamic load rating, it is recommended that a suitable Temperaturevalue for reliability factor a1 is chosen for each appli-the cation. The selection should be made using (C/P) or fh values determined by machine type and based upon the actual conditions of lubrication, tem-perature, mounting, etc., which have already been °C150200250ft1.00.950.90.850.80.75Fig. 4 Temperature factorexperienced and observed in the same type of Further, if the bearing is used at high temperature, i.e. machines.Limiting conditions120°C or above, the amount of dimensional displace-ment gets larger. So special heat treatment is neces-sary. If needed, please contact IKO.These bearing life equations are applicable only when Hardness factorthe bearing is mounted and lubricated normally with-out intrusion of foreign materials and not used under When the shaft or housing is used as the raceway sur-extreme operating conditions.face instead of the inner or outer ring, the surface Unless these conditions are satised, the life may be hardness of the part used as the raceway surface shortened. For example, it is necessary to separately should be 58〜64HRC.consider the effects of bearing mounting errors, exces-If it is less than 58HRC, the basic dynamic load rating is sive deformation of housing and shaft, centrifugal lowered and can be obtained by the following equation:force acting on rolling elements at high-speed revolu-tion, excessive preload, especially large radial internal clearance of radial bearings, etc.When the dynamic equivalent load exceeds 1/2 of the basic dynamic load rating, the life equations may not be applicable.CH = fHC…………………………………… (8)where, CH : Basic dynamic load rating considering hardness, NfHC: Hardness factor (See Fig. 5.): Basic dynamic load ratingNHardness of raceway surfaceHRC6050403020fH10.80.60.40.20.1Fig. 5 Hardness factorA20
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