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Product data Page ............. 3 Bearing size Page ............. 24

Selection of bearing size

Bearing life

Life modification factor a
SKF Table 1 This factor represents the relationship between the fatigue load limit ratio (P
Degree of Factor c For modern high quality bearings thebasic rating life can deviate signifi- cantly from the actual service life in a given application. Therefore ISO 281:1990/Amd 2:2000 contains a modified life equation to supplement the basic rating life, which now makes predicting the bearing life of SKF Explorer bearings more precise. This life calculation makes use of amodification factor to account for the amount of contamination, the viscosity of the lubricant, and the fatigue limit of the material. The SKF life modification factor a
cleanliness/ for bearings with u /P), the lubrication condition (viscosity ratio
contamination mean diameter d (mm) ) and the contamina-tion level in the bearing (
m 100> 100 c ). Values forthe factor a
SKF can be obtained from .Guideline values when selecting
Cleanliness diagram
1 as a function of
c (P
u /P)for SKF standard and SKF Explorer cylindrical roller bearings and for differ- entvalues of the viscosity ratio
Extreme11 High0,8 .. 0,60,9 .. 0,8Normal0,6 .. 0,50,8 .. 0,6 Equivalent dynamic bearing load
Contamination Slight0,5 .. 0,30,6 .. 0,4 Typical0,3 .. 0,10,4 .. 0,2Severe0,1 .. 00,1 .. 0 When dynamically stressed cylindrical roller bearings are used as non-locat- ing bearingsP = F
c aregiven in Diagram table
1 has been drawn up for a safety factor commonly used in fatigue life considerations and is valid for lubri- cants without EP additives. If a lubricant containing such additives is used, reference should be made to the SKF General Catalogue or the SKF Interactive Engineering Catalogue, available on CD-ROM or online at www.skf.com. . More detailed infor-mation can be found in the SKF General Catalogue or the SKFInteractive Engineering Catalogue, available on CD-ROM or online at www.skf.com.
Guideline values for factor c for contamination level SKF applies to the standardizedconcept. The SKF rating life of a roller bearingaccording to ISO 281:1990/Amd 2:2000 is
1 where e = limiting value= 0,2 for bearings in the 10, 2, 3 and 4 series= 0,3 for bearings in the 22 and 23 seriesY = axial load factor= 0,6 for bearings in the 10, 2, 3 and 4 series= 0,4 for bearings in the 22 and 23 seriesSince axially loaded cylindrical rollerbearings only operate satisfactorily when they are subjected to a simultan- eously acting radial load, the ratio F
1 0/3 L
nm = a
1 a
SKF

(

C PIf the speed is constant, the life can beexpressed in operating hours, using the equation

)

10/3 L
nmh = a
1 a
SKF 1 000 000 60 nPwhereL

(

C

)

r nm = SKF rating life (at 100 – n % reliability), millions of revolutionsL If cylindrical roller bearings with flangeson both the inner and outer rings are used to locate a shaft in one or both directions, the equivalent dynamic bearing load can be calculated usingP = F
a /F
r should not exceed 0,5.
nmh = SKF rating life (at 100 – n % reliability), operating hoursa Equivalent static bearing load
1 = life adjustment factor for reliabil-ity according to ISO 281:1990, normally a For statically stressed cylindrical roller bearingsP
1 = 1a
SKF = SKF life modification factor (
r when F
a /F
r eP = 0,92 F
= F
r âž” diagram
1 )C= basic dynamic load rating, kN P= equivalent dynamic bearingload, kNn= rotational speed, r/min
r + YF
a when F
a /F
r > e 16