Rated load and rated life of precision bearings

Rated static load
Rated static load refers to the central axial static load or radial load equivalent to the following calculated contact stress at the contact center of the rolling element bearing the maximum load and the raceway.
Self-aligning ball bearing: 4600MPa
Other ball bearings: 4200MPa
All roller bearings: 4000MPa
The total permanent deformation of the rolling element and the raceway under the above contact stress is about 0.0001 times the diameter of the rolling element.
For a bearing group consisting of 1 set of identical angular contact ball bearings, the rated static load is 1 times the rated static load of a single set of bearings.
Equivalent static load
2.1 Radial equivalent static load
The radial equivalent static load of angular contact ball bearings is the larger of the values calculated by the following two formulas.
Por = Xo Fr + Yo Fa
Por=Fr
In the formula: Por–radial equivalent static load, N
Xo—radial static load coefficient, see the table below
Yo—Axial static load series, see the table below
Fr — bearing radial load, or the radial component of the actual bearing load, N
Fa—bearing axial load, or the axial component of the actual bearing load, N
Coefficients Xo and Yo of angular contact ball bearings
Contact angle Xo Yo
15° 0.5 0.46
25° 0.5 0.38 Equivalent radial static load of cylindrical roller bearings
Por = Fr
2.2 Radial equivalent static load
For ball screw support bearings with a contact angle of 60°, the equivalent axial static load is calculated according to the following formula:
Poa = 2.3Frtg α + Fa ie Poa = 4Fr + Fa
For double direction thrust angular contact ball bearings, the axial equivalent static load
Poa = Fa
Static load safety factor
According to the stability of bearing operation, friction requirements and the geometry of the actual contact surface, the allowable equivalent static load can be less than, equal to or greater than the rated static load. However, for high-speed precision bearings, the ratio of the recommended static load rating to the equivalent static load should not be less than 3.
Rated dynamic load
The rated dynamic load refers to the constant radial load or constant central axial load that a set of rolling bearings can bear hypothetically. Under this load, the basic rated life of the rolling bearing is 100 complete revolutions.
For single row angular contact ball bearings, this load refers to the radial component of the load that causes the rings of the bearing to have a pure radial displacement relative to each other.
For ball screw support bearings, the dynamic load rating refers to the axial component of the load that causes the axial displacement of the bearing rings relative to each other.
Equivalent dynamic load
5.1 Equivalent dynamic load of angular contact ball bearings
Pr = X Fr + Y Fa
In the formula: Pr–radial equivalent dynamic load, N
X—Radial dynamic load coefficient, see the table below
Y—Axial dynamic load series, see the table below
Fr — bearing radial load, or the radial component of the actual bearing load, N
Fa—bearing axial load, or the axial component of the actual bearing load, N
Factors X and Y for angular contact ball bearings
Contact angle Fa/Core Fa/Fr ≤ e Fa/Fr ＞ e
X Y X Y
15° 0.015 0.38 1 0 0.44 1.47
0.029 0.40 1 0 0.44 1.40
0.058 0.43 1 0 0.44 1.30
0.087 0.46 1 0 0.44 1.23
0.12 0.47 1 0 0.44 1.19
0.17 0.50 1 0 0.44 1.12
0.29 0.55 1 0 0.44 1.02
0.44 0.56 1 0 0.44 1.00
0.58 0.56 1 0 0.44 1.00
25° — 0.68 1 0 0.41 0.87 For a set of preloaded angular contact ball bearings:
(1) If the bearing only bears external radial load, then the Fa value is the preload value Fa.
(2) If the bearing bears external radial and axial combined loads Fr’ and Fa’
When the group of bearings is rigidly preloaded, if Fa′ ≤ 3Fao, then Fa= 2/3 Fa′+Fao
If Fa′ ＞ 3Fao, Fa=Fa′
When the group of bearings is elastically preloaded, then Fa=Fa′+Fao
The radial equivalent dynamic load of cylindrical roller bearings:
Pr=Fr
5.2 Equivalent axial dynamic load
Due to the axial load mainly borne by the ball screw support bearing, usually, when the radial Fr’ and axial Fa’ loads act together, Fr'<0.47Fa’, therefore, the axial load of the ball screw support bearing Equivalent dynamic load Pa=Fa’.
Basic rating life
For a single set of rolling bearings or a group of nearly identical rolling bearings operating under the same conditions, the basic rating life is the life associated with 90% reliability, commonly used materials and processing quality, and normal operating conditions.
The basic rating life L10 of a grouped angular contact ball bearing is
L10=i2.1[Cr/Pr]3 (million revolutions)
Or L10h=i2.1[Cr/Pr]3×106/60n (hour)
In the formula, i—the number of bearing sets in a set of bearings
Cr—the radial dynamic load rating of a single set of bearings, N
Pr—the radial equivalent dynamic load of a single set of bearings, N
n—bearing speed, r/min
For bidirectional thrust angular contact ball bearings and ball screw support bearings, the axial load should be used when calculating their life.
For cylindrical roller bearings, the basic rating life is
L10=[Cr/Pr]10/3 (million revolutions)
Or L10h=[Cr/Pr]10/3×106/60n (hour)
The life calculated above refers to the fatigue life of the bearing. For high-speed precision spindle bearings, the life of the bearing generally refers to the precision life, that is, the maintenance time of the bearing precision. After the precision bearing has been used for a period of time, due to the wear of the rolling elements, ring raceways, and cage, the bearing accuracy is reduced and cannot be used. At this time, the bearing may not have fatigue damage, but we think that the bearing life has expired. Therefore, calculating the fatigue life of bearings can be used as a reference for the service life of high-speed precision bearings.
The relationship between the contact angle of the spindle bearing and the speed and load: the larger the angle of the angular contact ball bearing, the greater the axial load and the lower the speed; the smaller the contact angle, the smaller the axial load and the lower the speed. The higher the value, the greater the radial load; for example, for the same type of angular contact ball bearing, the rigidity of the C angle bearing is about 45% of the rigidity of the AC angle bearing, and the rigidity of the paired bearing mainly depends on the pairing and preload of the spindle bearing In terms of force, it also depends on the rigidity of the shaft and housing. Preload: The relationship between spindle bearing preload and contact angle is similar, and it is one of the important factors related to the performance of spindle bearings. Generally, there are three types of preload for angular contact bearings: light preload A (L), medium preload B (M), and heavy preload C (H). Under different preload conditions, the greater the preload, the greater the radial rigidity and axial rigidity, the corresponding increase in the temperature rise of the spindle, the corresponding decrease in life and limit speed, and the excessive preload will cause bearing damage. Unfavorable problems such as loud noise and bearing channel burns occur.