The theoretical service life is only achieved in practice when all of the following conditions are met:
- Careful determination of the magnitude and direction of the permanent loads
- Constant operating speed
- Constant temperature not exceeding 100 deg. C
- Maximum cleanliness during installation and operation
- Careful selection and precise dosing of the lubricant
- Installation in strict compliance with the instructions in the "Handling and installation" section
In more complex applications or in cases of doubt, we recommend that you seek our technical advice.
We use the formulas and theories of the ISO and AFBMA standards to calculate the load ratings and the theoretical service life of ball bearings.
1. Service Life of Radial and Axial Ball Bearings
L10 = (C / P)3
| Definitions | |
|---|---|
| L10 | Service life in millions of revolutions |
| C | Dynamic load rating in N |
| P | Dynamic equivalent load in N |
| C/P | Load safety factor |
2. Service Life in Hours
L10h = L10 x 106 / (n x 60)
| Definitions | |
|---|---|
| L10 | Service life in millions of revolutions |
| n | Speed in 1/min (rpm) |
Conversion of units:
1 N = 1 kg m/s2
1 kgf (= 1 kp) = 9.81 N
3. Definitions
| L10 | Service life in millions of revolutions |
| L10h | Service life in hours, which is the life achieved by 90% of a large number of identical ball bearings operating under the same conditions. 40% of them achieve a service life that is more than five times longer. |
| C | The basic dynamic load rating is the constant, unchanging load at which the bearing achieves a basic rating life of one million revolutions. For radial bearings, the basic radial dynamic load rating Cr refers only to the constant, unchanging radial load. For axial bearings, the axial dynamic load rating Ca refers to the constant, purely axial load acting along the bearing axis. For each bearing, the load ratings Cr and Ca are specified in the dimension tables; their values depend on the bearing size, the number of rolling elements, the material and the bearing design. The load ratings were determined in accordance with the STN ISO 281 standard. |
The dynamic load rating takes into account:
- The repeated deformation of the various components of the ball bearing (raceways and balls) depending on the mechanical resistance of their materials and their geometric shapes
- The frequency of the loads
- An empirical probability factor
| P | Dynamic equivalent load. It is a fictitious load that combines the axial and radial load components in such a way that, when calculating the theoretical service life, the same result is obtained as if only a pure radial load (for radial bearings) or a pure axial load (for axial bearings) were acting. |
| C0 | Basic static load rating. For radial bearings this is a radial load, and for axial bearings a constant axially directed load, at which a permanent deformation of no more than 0.1 per mille of the rolling element diameter occurs at the most heavily loaded contact point. Operating conditions:
|
| P0 | Equivalent static load |
4. Calculation of the Dynamic Equivalent Load
4.1 Radial Deep Groove Ball Bearing, Single Row
P = X . Fr + Y . Fa
| Definitions | |
|---|---|
| P | Dynamic equivalent load in N |
| Fr | Radial component of the load in N |
| Fa | Axial component of the load in N |
| X | Radial factor of the bearing (see table below) |
| Y | Axial factor of the bearing (see table below) |
4.2 Axial Deep Groove Ball Bearings
P = Fa
5. Calculation of the Static Load Rating
C0 = S0 . P0
| Definitions | |
|---|---|
| C0 | Basic static load rating in N |
| P0 | Equivalent static load in N |
| S0 | Static load safety factor |
The value of the static load safety factor can be selected from the table below, depending on the operating conditions and the requirements placed on the bearing:
| S0 Value | Application |
|---|---|
| 0.5 to 0.7 | Low requirements, smooth vibration-free operation |
| 1.0 to 1.2 | Normal requirements, smooth vibration-free operation |
| 1.5 to 2.0 | High requirements, subject to impact loads |
6. Calculation of the Equivalent Static Load
6.1 Radial Deep Groove Ball Bearing
P0 = X0 . Fr + Y0 . Fa
| Definitions | |
|---|---|
| P0 | Equivalent static bearing load in N |
| Fr | Radial component of the largest static load in N |
| Fa | Axial component of the largest static load in N |
| X0 | Radial load factor = 0.6 |
| Y0 | Axial load factor = 0.5 |
Note: If the equivalent static bearing load P0 < Fr determined by this formula, use P0 = Fr.
6.2 Axial Deep Groove Ball Bearings
P0 = Fa
7. Duplex Bearing
When two single-row radial deep groove ball bearings are used in a duplex arrangement (X, O or tandem), the following relationships must be taken into account when calculating the basic dynamic load rating and the dynamic equivalent load.
7.1 Duplex Arrangement X or O
Basic Dynamic Load Rating
Cd = (2 · cos α)0.7 · C
L10 = (Cd / P)3
| Definitions | |
|---|---|
| Cd | Basic dynamic load rating for a pair of ball bearings in N |
| α | Contact angle |
| C | Basic dynamic load rating for a single ball bearing in N |
| L10 | Service life in millions of revolutions |
| P | Dynamic equivalent load in N |
Dynamic Equivalent Load
P = X . Fr + Y . Fa
| Definitions | |
|---|---|
| P | Dynamic equivalent load in N |
| Fr | Radial component of the load in N |
| Fa | Axial component of the load in N |
| X | Radial factor for a pair of ball bearings |
| Y | Axial factor for a pair of ball bearings |
Duplex Arrangement X or O with Preload
Fa = 0.8 (Fap + Fa1)*
| Definitions | |
|---|---|
| Fa | Effective axial load in N |
| Fap | Preload of the ball bearing pair in N |
| Fa1 | External axial force acting on the preloaded ball bearing pair in N |
* Note: The ratio of preload Fap to axial force Fa1 must be selected appropriately so that no bearing is completely unloaded. Within the radial clearances and contact angles recommended by myonic, this requirement is met if:
Fap ≥ 0.35 Fa1
Duplex Arrangement X or O without Preload or with Low Axial Play
In these cases, the calculation must be carried out using the formulas listed under point 7.1. When determining the factors X and Y from the table, the total number of balls of both bearings must be taken into account (represented here by the "2" in the denominator).
f0 . Fa / (2 . Z . Dw2)
| Definitions | |
|---|---|
| Z | Number of balls |
| Dw | Diameter of the balls in mm |
7.2 Tandem Arrangement
Basic Dynamic Load Rating
Ct = C . N0.7
| Definitions | |
|---|---|
| Ct | Dynamic load rating of the tandem arrangement in N |
| C | Dynamic load rating of a single ball bearing in N |
| N | Number of ball bearings |
The dynamic equivalent load and the rating life are calculated using Ct, in the same way as for a single bearing with one row of balls. The factors X, Y and e can be found in the table at the bottom of this page.
8. Calculation Example
Example 1
Calculation of the theoretical rating life Lh of the radial deep groove ball bearing R 2570X under the following operating conditions:
| Radial load | Fr = 5.7 N |
| Axial load | Fa = 2.8 N |
| Speed | n = 8000 rpm |
| Radial clearance | 2 / 5 μm |
Step-by-Step Calculation
Step 1: Determine the limit value e
(from the X/Y table: radial clearance 2–5 μm, suffix 2/5)
Step 2: Compare Fa/Fr with e
→ Use X = 0.56, Y = 2.77
Step 3: Calculate the dynamic equivalent load P
P = 0.56 · 5.7 + 2.77 · 2.8 = 3.2 + 7.8 = 11 N
Step 4: Calculate the service life L10
L10 = (C/P)³ = 12.9³ = 2,147 million revolutions
Step 5: Convert to hours L10h
= L10h = 4,473 hours
Values of X and Y for Radial Ball Bearings
For the radial factor X, the axial factor Y and the limit value e used to calculate the dynamic equivalent load, please refer to the official myonic data sheets. If Fa/Fr ≤ e, use X = 1 and Y = 0.
Need help?
For detailed calculations or assistance with a specific application, please contact the myonic technical support team.