The forces and torques acting on the bearing position are decisive for selecting the optimum bearing size and guaranteeing the required service life.
Direction and Distribution of Forces
Pure Radial Load Fr
Loads that must be taken into account:
- Weight of the moving part
- Centrifugal force (imbalance)
- Dynamic load (acceleration, deceleration)
- Force due to energy transmission (pulley, gears, etc.)
- Preload for duplex bearings1
Load Distribution Case 1
Load Distribution Case 2
Radial Load Formula:
Fr = Qr / 2
(Assuming load is centered between two bearings)
Pure Axial Load Fa
Fa = Q (alternating load)
Fa = Q (unidirectional load)
Fa = Q (alternating load)
Fa = Q (alternating load)
Note: To ensure that an axial load can be supported by several ball bearings, they must be arranged in pairs1, either ring to ring or with very precisely manufactured intermediate rings.
Combined Loads (Radial and Axial)
1) see duplex installation
| Load Component | Formula | Application |
|---|---|---|
| Radial Component Qr | Qr = Q . cos ß | Radial bearing load |
| Axial Component Qa | Qa = Q . sin ß | Axial bearing load |
Normal Installation
Fa = Qa (the axial load is absorbed by only one ball bearing)
Duplex Installation in Tandem Design (Intermediate Ring)
Load distribution:
- Fr = Qr
- Fa = Qa
Preload Fap
Ball bearings in duplex form1 (O arrangement or X arrangement) have a preload (Fap) that is above or below the axial load Fa.
This preload Fap must be adjusted to the operating conditions and the desired life expectancy.
Reference: 1 See Preload and Duplex Installation page for detailed information on duplex bearing arrangements.
Equivalent Dynamic Load (P)
The equivalent dynamic load P is used to calculate the rated service life (L10). It converts actual radial and axial loads into a single hypothetical load with equivalent effect on bearing life.
Calculation Formulas
| Bearing Type | Formula (P) |
|---|---|
| Radial Deep Groove Ball Bearings | P = X . Fr + Y . Fa |
| Axial Deep Groove Ball Bearings | P = Fa |
About Coefficients X and Y:
These coefficients depend on the ratio Fa / Fr and the relative axial load f0 . Fa / C0. Refer to the coefficient tables on the "Service Life Calculation" page for specific values.
Equivalent Static Load (P0)
Used to verify bearing load capacity at standstill or very low speeds (n < 10 rpm), ensuring no permanent deformation occurs.
Calculation Formulas
| Bearing Type | Formula (P0) | Coefficient Values |
|---|---|---|
| Radial Deep Groove Ball Bearings | P0 = X0 . Fr + Y0 . Fa Note: If P0 < Fr, then P0 = Fr |
X0 = 0.6 Y0 = 0.5 |
| Axial Deep Groove Ball Bearings | P0 = Fa | - |
Static Load Safety Factor (S0)
The static safety factor S0 represents the ratio of the basic static load rating C0 to the equivalent static load P0, used to evaluate safety margins.
Calculation Formula:
S0 = C0 / P0
Or to determine required C0: C0 = S0 . P0
S0 Guideline Values
| Operating Conditions | S0 Range |
|---|---|
| Low Requirements Smooth operation, no vibrations | 0.5 ... 0.7 |
| Normal Requirements Standard operating conditions, no significant vibrations | 1.0 ... 1.2 |
| High Requirements Impact loads, high reliability requirements | 1.5 ... 2.0 |