The Design of Rolling Bearing Mountings

GlossaryEP additivesWear-reducing additives in lubricating greases and lubricatingoils, also referred to as extreme pressure lubricants.Equivalent dynamic load PFor dynamically loaded rolling bearings operatingunder a combined load, the calculation is based on theequivalent dynamic load. This is a radial load for radialbearings and an axial and centrical load for axial bearings,having the same effect on fatigue as the combinedload. The equivalent dynamic load P is calculated bymeans of the following equation:P = X · F r + Y · F a[kN]F r radial load [kN]F a axial load [kN]X radial factor (see FAG catalogues)Y thrust factor (see FAG catalogues)Equivalent static load P 0Statically stressed rolling bearings which operate undera combined load are calculated with the equivalent staticload. It is a radial load for radial bearings and anaxial and centric load for thrust bearings, having thesame effect with regard to permanent deformation asthe combined load.The equivalent static load P 0 is calculated with theformula:P = X 0 · F r + Y 0 · F a[kN]F r radial load [kN]F a axial load [kN]X 0 radial factor (see FAG catalogues)Y 0 thrust factor (see FAG catalogues)Factor a 1Generally (nominal rating life L 10 ), 10 % failure probabilityis taken. The factor a 1 is also used for failureprobabilities between 10 % and 1 % for the calculationof the attainable life, see following table.Failureprobability % 10 5 4 3 2 1Fatiguelife L 10 L 5 L 4 L 3 L 2 L 1Factor a 1 1 0.62 0.53 0.44 0.33 0.21Factor a 23 (life adjustment factor)The a 23 factor is used to calculate the attainable life.FAG use a 23 instead of the mutually dependent adjustmentfactors for material (a 2 ) and operating conditions(a 3 ) indicated in DIN ISO 281.a 23 = a 2 · a 3The a 23 factor takes into account effects of:– amount of load (stress index f s* ),– lubricating film thickness (viscosity ratio ),– lubricant additives (value K),– contaminants in the lubricating gap (cleanlinessfactor s),– bearing type (value K).The diagram on page 185 is the basis for the determinationof the a 23 factor using the basic a 23II value. Thea 23 factor is obtained from the equation a 23II · s (s beingthe cleanliness factor).The viscosity ratio = / 1 and the value K are requiredfor locating the basic value. The most important zone(II) in the diagram applies to normal cleanliness(s = 1).The viscosity ratio is a measure of the lubricating filmdevelopment in the bearing. operating viscosity of the lubricant, depending on thenominal viscosity (at 40 °C) and the operating temperaturet (fig. 1). In the case of lubricating greases, is the operating viscosity of the base oil. 1 rated viscosity, depending on mean bearing diameterd m and operating speed n (fig. 2).The diagram (fig. 3) for determining the basic a 23IIfactor is subdivided into zones I, II and III.Most applications in rolling bearing engineering arecovered by zone II. It applies to normal cleanliness(contamination factor V = 1). In zone II, a 23 can be determinedas a function of by means of value K.With K = 0 to 6, a 23II is found on one of the curves inzone II of the diagram.With K > 6, a 23 must be expected to be in zone III. Insuch a case conditions should be improved so thatzone II can be reached.FAG 184