Bearing life and load ratings
Bearing life and load ratings In industrial applications, bearing size is usually determined by its load carrying capacity relative to the load, required life and required reliability of the application. For machine tool applications, bearing size is almost always determined by other factors such as system rigidity, fixed dimensions of the spindle as well as the speed and feed parameters of the application. For super-precision bearing arrangements, determining the actual load is particularly complex as it involves many influencing factors. SKF Spindle Simulator is a sophisticated computer program to analyse statically indeterminate spindle bearing systems. It supports the analysis of spindles and contains detailed models of super-precision bearings. For add itional information, contact the SKF application engineering service or visit SKF Engineering Consultancy Services at skf.com.
Dynamic bearing loads and life The general information about bearing life calculation and basic load ratings provided under Selecting bearing size in the SKF catalogue Rolling bearings, or at skf.com, is also valid for super-precision bearings. It should be noted that all life calculations based on ISO 281 are valid for normal speeds. For applications where the speed factor A ≥ 500 000 mm/min, contact the SKF application engineering service.
Basic dynamic load rating The basic dynamic load rating C is used for life calculations involving dynamically stressed bearings, i.e. bearings that rotate under load. It expresses the bearing load that will result in an ISO 281 basic rating life L 10 of 1 000 000 revolutions. It is assumed that the load is constant in magnitude and direction and is radial for radial bearings and axial, acting centrically, for thrust bearings. Values for the basic dynamic load rating C are listed in the product tables. Equivalent dynamic bearing load To calculate the basic rating life for a bearing using basic dynamic load ratings, it is necessary to convert the actual dynamic loads into an equivalent dynamic bearing load. The equivalent dynamic bearing load P is defined as a hypothetical load, constant in magnitude and direction, that acts radially on radial bearings and axially and centrically on thrust bearings. This hypothetical load, when applied, would have the same influence on bearing life as the actual loads to which the bearing is subjected. Information and data required for calculating the equivalent dynamic bearing load is provided in each product chapter.
A = n dm where A = speed factor [mm/min] dm = bearing mean diameter [mm] = 0,5 (d + D) n = rotational speed [r/min] Rated bearing life can be calculated for fatigue conditions based on statistical assumptions. For detailed information, refer to Basic rating life in the SKF catalogue Rolling bearings, or visit skf.com.
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