Page 1694 - MiSUMi 2025

[Technical Calculation]
Calculation method and the concept of basic rating life of the Ball Bearing Excerpted from GB/T 6391—2010

1. ■ Life
Life (of a single set of rolling bearings) refers to the number of revolutions that one collar or washer of a bearing rotates relatively to
another collar or washer before the first sign of fatigue expansion appears on one collar or washer or rolling element material of the
bearing.
Note: Life can also be expressed in hours of operation at a given constant speed.

2. ■ Basic rating life
For bearings with currently used common high-quality materials, good processing quality and operating under normal operating
conditions, it refers to the rated life related to 90% reliability.

3. ■ Modified rating life
The rating life obtained by modifying the basic rating life considering 90% or other reliability levels, bearing fatigue loads and/or spe-
cial bearing performance and/or contaminated lubricants and/or other unconventional operating conditions.
4. ■ Basic dynamic radial load rating
It refers to the constant radial load that a set of rolling bearings can bear theoretically. The basic rated life of the bearing under this
load is one million revolutions.
Note: For a single row angular contact bearing, the load refers to the radial component of the load that causes the bearing rings to
produce pure radial displacement between each other.
5. ■ Dynamic equivalent radial load
It refers to a constant radial load, under which the rolling bearing has the same life as that under the actual load condition.

6. ■Dynamic equivalent radial load
6.1 Dynamic equivalent radial load of single set of bearings
The dynamic equivalent radial load of radial contact and angular contact ball bearings under constant radial and axial loads is:
Pr ＝XFr + YFa EEEEEEEEEEEEEEEEEEEEEEEEEEEEE （3）
See Table 1 on P.09-009 for X and Y values. These coefficients are applicable to bearings with raceway groove curvature radius
complying with requirements listed on P.09-009. For the curvature radius of the other raceway grooves, the X and Y values can be
calculated by 4.2 in ISO/TR 8646:1985.

6.2. Dynamic equivalent radial load of bearing group
■Single row angular contact ball bearing "back-to-back" or "face-to-face" configuration
Two sets of identical single row angular contact ball bearings are installed side by side on the same shaft in "back-to-back" or
"face-to-face" configuration, and rotate as a whole (installed in pairs). When calculating their dynamic equivalent radial load, it should
be considered as a set of double row angular contact bearings.
Note: If two sets of identical single row radial contact ball bearings operate in a "back-to-back" or "face-to-face" configuration, users
should consult the bearing manufacturer for the calculation method of their dynamic equivalent radial load.

7. ■Basic rating life
7.1 Life formula
The basic rating life formula for radial ball bearings is:
3
C r
L 10＝( ) EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE （4）
P r
The life formula is also applicable to the life estimation of a bearing group consisting of two or more sets of single row bearing group.
At this time, the rated load C r is calculated according to the whole bearing group, the equivalent load P r is calculated according to the
total load acting on the bearing group, and the X and Y values used are based on the requirements listed in 6.2.
7.2 Load limiting conditions of life formula
The life formula can give a satisfactory result in a wide range of bearing loads. However, excessive loads can produce harmful plastic
deformation at the point of contact between the ball and the groove. Therefore, when P r is greater than the smaller of C 0r or 0.5C r, the
user should consult the bearing manufacturer to determine the applicability of the life formula.
Too small load can cause other failure modes, which are not included in this standard.

B-049