super precision bearings

Modified Life Calculation L hnaStress Index f s*Bearing ComponentTemperature LimitsThe stress index is a measure foranticipating whether a bearing canbe fail-safe in a specific application.Precise individual calculationcan be made of the load distributionand the Hertzian contact pressureas well as the comparisonwith known limits. Provided thatthe further conditions κ ≥2 andV = 0.3 are met, a modified life calculationis not required.f s* = C 0 /P 0*P 0* can be calculated using theequations for the static equivalentload, however using the same dynamicloads as for the equivalentload.Cage 100 °CSeal 100 °CLubricantsee chapter “Lubrication”Bearing rings 150 °C16: Temperature limits of bearing componentsModified Life CalculationFAG has developed an extendedlife calculation which considers theoperating and environmental influencesto a substantially larger degreethan the standard calculation.The calculated modified life doesnot necessarily correspond to thebearing service life as it may be reducedby the service life of the lubricant.In this case the life of thelubricant (see Diagram 26) tallieswith the bearing life:L hna = a 1 · a 23 · L h10Factor a 23Factor a 23 considers the influencesof material, bearing type, loading,lubrication and cleanliness. Superprecision bearings are dimensionallystable up to 150 °C. Up to thisvalue, the influence of temperatureon the material properties neednot be taken into account. Temperaturelimits of cage, sealing and lubricanthave to be observed (seeTable 16). For applications of superprecision bearings at highertemperatures, please consult FAG.For the effects of load the stress indexf s* should be ascertained. Iff s* > 8, the bearing can be fail-safe.Factor a 1Bearing failures due to material fatigueare subject to statistical laws.The failure probability is taken intoconsideration by factor a 1 .Factor a 1 = 1 corresponds to a10-percent failure probability andis usually used for the modified lifecalculation.Endurance StrengthMaximum Hertzian contact pressure= 2000 MPa for 100Cr6 ballbearings and 2500 MPa for X30.EngineeringFAG · 137