Load Ratings and Life Calculations

General Notes About Bearing Life
NMB Ball Bearings are used in a wide variety of applications. Many contain several application and environmental variables, all of which have an influence on bearing performance and life. Therefore it is extremely important to select the correct Bearing for each application in order to obtain the best possible results. These values are calculated according to JIS Specs as follows:

Basic Life Rating
The Basic Life Rating (L10) is defined in specification JIS B1518 "Dynamic load ratings and rating life for rolling bearings" as follows:

The Basic Life Rating is the life obtained with 90% reliability, when an individual bearing or an identical group of bearings are manufactured with common materials, common manufacturing processes and quality, and operate under the same conventional conditions. L10 Life is the accumulated rotation where 90% of survive without material flaking when they are operated under fixed conditions, of a population of bearings.

The calculation formula for the Basic Life Rating is the following.
  Formula for Basic Life Rating in revolutions Basic Life Rating in revolutions : Basic Life Rating in millions of revolutions
Basic Dynamic Load Rating : Basic Dynamic Load Rating
Equivalent Dynamic Radial Load Factor : Equivalent Dynamic Radial Load Factor

There is a relationship between the Basic Life Rating (revolutions) and Basic Life (time).
  formula of relation between Basic Life Rating (revolution) and Basic Life (time) Rotation Speed : Rotation Speed (min-1)
hours : Time (hours)


Basic Dynamic Load Rating (Cr)
The method for calculating the Basic Dynamic Load Rating can be found in JIS B1518 and is based on an endurance test of 1,000,000 revolutions.


Dynamic Equivalent Radial Load Factor (Pr)
The Dynamic Equivalent Radial Load Factor is defined as "the direction and magnitude to the bearing, which is able to obtain the same life under the actual load and rotation conditions".
From the calculation formula and the table below, the axial and the radial loads are replaced by the Dynamic Equivalent Radial Load Factor (Pr).
   

Pr = XFr + YFa
X and Y are taken from the table below
Fr = Radial load (N or kgf)
Fa = Axial load (N or kgf)
 
Axial Load Ratio Load Ratio Load Ratio e
Units X Y X Y
N {kgf}
Axial Load Ratio 1 0 0.56 2.30
1.99
1.71
1.55
1.45
1.31
1.15
1.04
1.00		 0.19
0.22
0.26
0.28
0.30
0.34
0.38
0.42
0.44
0.172
0.345
0.689
1.03
1.38
2.07
3.45
5.17
6.89		 { 0.0175 }
{ 0.0352 }
{ 0.0703 }
{ 0.105 }
{ 0.143 }
{ 0.211 }
{ 0.352 }
{ 0.527 }
{ 0.703 }

i : No. of rows
Z : No. of balls
Dw : Ball Diameter (mm)
The values for X andY that are not in the above table shall be calculated by linear interpolation.


Basic Static Load Rating (Cor)
The formula for the Basic Static Load Rating and the Static Equivalent Radial Load Rating of ball bearings is defined in specification JIS B1519 as follows:

Basic Static Load Rating (Cor) :
The Basic Static Load Rating is the amount of static radial load that will cause a total permanent deformation (ball and raceway) on the most heavily stressed ball/raceway contact area (the center) that equals to 0.0001 of the ball diameter under a stress level of 4200 MPa.

Static Equivalent Radial Load (Por) :
The Static Equivalent Radial Load is a static radial load that would cause the same total permanent deformation on the most heavily stressed ball/raceway contact as the actual load.

The largest value obtained from the following two formulas will be used.

P0r = X0Fr + Y0Fa
P0r = Fr

X0 and Y0 are defined in specification JIS B1519 Table 2 (the coefficient values of X0 and Y0                  of radial ball bearing)
X0=0.6; Y0=0.5
Fr= Radial Load (N or kgf)
Fa= Axial Load (N or kgf)



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