Self-Lube Hand book - NSK Europe - #9

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SELF-LUBE® BEARINGS 9 Bearing load ratings and endurance Basic dynamic radial load rating Cr This is defined as the load that can be applied to the bearing to give a basic L10 rating life of one million revolutions. This is the life associated with 90% reliability which has been found by experience to be acceptable for normal engineering bearing applications. The majority of the bearings attain a much longer life and the median life is approximately five times the L10 life. Ratings for each series are given in the bearing tables and are used to calculate life for radial loads of constant magnitude and direction. Equivalent dynamic radial load Pr For applications where axial and radial loads are present they must be converted into a single equivalent radial load Pr and calculated as follows, where: Fr = actual radial load (N) Fa = actual axial load (N) Y = axial factor from table 18.2 Cor = basic static load rating Cr = dynamic radial load rating fo = axial load factor Note: Axial load Fa must not exceed 0.5 Cor. Select fo from table 18.1 for the appropriate bearing insert. Calculate f0 Fa and obtain the value of Y from table 18.2. Calculate Pr where: Pr = Fr or Pr = 0.56 Fr + YFa Use whichever Pr value is the greatest. Relationship between load and life Having determined the equivalent load Pr the nominal L10 bearing life is calculated as follows: L10 life in hours = ( Cr )3 • 106 where n = bearing operating speed (rev/min). Alternatively, by using the loading ratio Cr the bearing L10 life can be estimated by reading off directly from the tables on page 9 under the appropriate speed column. Basic static load rating Cor This value is calculated in accordance with ISO standard 76. Ratings for each series are given in the bearing tables. Static equivalent radial load Por When static axial and radial loads are applied to a bearing these must be converted to an equivalent static radial load Por where: For = actual static radial load (N) Foa = actual static axial load (N) Calculate Por where: Por = For or Por = 0.6 For +0.5 Foa Use whichever Por value is greater, but this value should not exceed the bearing static radial load rating Cor. Service factors It is customary when calculating bearing life to include application factors which allow for fluctuations in loading that occur in service, and from experience the following may be used as a guide. For steady and light shock loads multiply load by 1.2 to 1.5. For moderate shock loads multiply load by 1.7 to 2.0. When selecting the size of bearing for a given load, the calculated life should conform to the L10 lives shown in the next column: ››Machines in use 8 hours/day – not fully utilised – 10,000 to 20,000 hours ››Machines in use 8 hours/day – fully utilised – 20,000 to 30,000 hours. ››Machines in use 24 hours/day – 40,000 to 80,000 hours. ››Machines in seasonal use – 4,000 to 8,000 hours. Limiting loads The axial load Foa must not exceed half the basic static load rating Cor. Housing strengths must also be considered as a limiting factor - see detail on page 19. Basic bearing insert f0 1017 13.1 1020 13.1 1025 13.9 1030 13.8 1035 13.8 1040 14.0 1045 14.1 1050 14.4 1055 14.3 Basic bearing insert f0 1060 14.3 1065 14.4 1070 14.4 1075 14.7 1080 14.6 1085 14.7 1090 14.5 3095 13.6 fo Fa Cor Y 0.172 2.30 0.345 1.99 0.689 1.71 1.03 1.55 1.38 1.45 2.07 1.31 3.45 1.15 5.17 1.04 6.89 1.00 Cor Pr Pr 60n