Bearings
Bearings and loads
Bearings play a crucial role in supporting and guiding motion of shafts in machines. Depending on the application, bearings are subjected to different ypes of loads, such as radial and axial forces, as well as static and dynamic loads. Choosing the right bearing is crucial for optimal performance and a long lifespan.
What are radial and axial loads?
Bearings are subjected to forces from the operation of machinery. These forces are classified into two main categories: radial and axial loads.
Radial loads
A radial load is a force acting perpendicualr to the shaft of the bearing. This means that the load is perpendicular to the shafts of rotation. Applications in which radial loads are common incude:
- Conveyors
- Electric motors
- Bike hubs
Many bearings, such as ball bearings and spherical roller bearings, are specifically designed to absorb axial forces, but some types can also tolerate limited axial forces.
Axial loads
An axial load is a force acting on the bearings in the longitudinal direction of the shaft. Axial forces can occur at:
- Lifting and hoisting systems
- Aircraft turbines
- Worm gear transmission
Certain bearings, such as angular contact bearings and thrust roller bearings, are specifically designed to accommodate axial forces. However, many applications involve combined loads, with both radial and axial forces acting simultaneously.
Which bearings are suitable for radial and axial forces?
Not every bearings is suitable for absorbing as much radial as axial forces. Below is an overview of commonly used bearing types and their suitability:
| Bearing type | Radial load | Axial load |
|---|---|---|
| Groove ball bearing | Yes | Limited |
| Angular contact bearing | Yes | Yes |
| Cylinder roller bearing | Yes | Limited |
| Spherical roller bearing | Yes | Yes |
| Axial roller bearing | No | Yes |
In applications where both radial and axial forces occur, angular contact bearings or spherical roller bearings are often used because they can accommodate both load types.
Static and dynamic loads
In addition to radial and axial forces, bearing technology also distinguishes between static and dynamic loads.
Static loads (Co-value)
A static load means that the bearing does not move or rotates only at a very low speed. This type of load occurs with:
- Static structures with high loads
- Bearings that are stationary for long periods of time with load
- Very slow moving applications
For static loads, the bearing is evaluated based on its static load rating (Co), which indicates how much load the bearing can withstand without permanent deformation.
Dynamic load (C-value)
A dynamic load occurs when the bearing rotates under load. This occurs in virtually all machines in which bearings are used, such as:
- Automotive engines
- Industrial machinery
- Train wheels
For dynamic loads, the dynamic load rating (C) is used, which indicates how long a bearing will last under a given load. This load rating is calculated according to ISO standards and based on a life of 1 million rotations.