Plain bearing working method and functional systems

Plain bearings are used to absorb and convey forces between components that move relative to one another. They determine the position of the moved components in relation to one another and ensure accuracy of the movement. Plain bearings must satisfy many requirements. They must be capable of tolerating high mechanical loads to the greatest possible extent, while suffering only minimal wear throughout their service life. Likewise, they must withstand high sliding speeds and be insensitive to disturbances from the bearing environment.

Influences in a tribological system

Intermediate material

  • Solid lubricant, grease, liquid, viscosity,
  • Ageing resistance


  • Amount and load type (static, dynamic)
  • Load time (constant, with intervals), circumferential load, concentrated load

Interacting sliding part

  • Material, hardness, surface roughness, thermal conductivity

Relative movement

  • Rotating, oscillating, linear
  • Sliding speed, duration of movement

Base body

  • Material, hardness, surface roughness, wear resistance, limp-home capability,
  • Chemical resistance

Ambient conditions

  • Temperature, medium, dirt
1. Intermediate material
2. Stress
3. Interacting sliding part
4. Relative movement
5. Base body
6. Ambient conditions

Functional systems

In terms of the operating mode, we distinguish between three different functional systems:

Hydrodynamically operated plain bearings

Plain bearings that work on the principles of hydrodynamics can satisfy the various requirements comparatively well. In this way, oil-lubricated plain bearings, in particular, can be designed for optimum, reliable operation with the aid of modern calculation methods.

Grease-lubricated, low-maintenance plain bearings

Low-maintenance plain bearings are generally lubricated with grease. The quantity of grease applied during installation is normally sufficient for the entire service life.

Due to the many influencing factors, however, calculating the expected service life of grease-lubricated plain bearings is fraught with uncertainty and can only be used as a guide.

Dry-running, maintenance-free plain bearings

But in many cases, lubrication using oil or grease is not possible or not permitted. In cases like this, maintenance-free, dry-running plain bearings are employed. Here, too, calculating the service life is not sufficiently precise.

The common practice of calculating service life using simple methods and taking into account influencing factors (such as specific load, sliding speed, temperature, etc.) can provide only approximate guide values. It is therefore recommended to verify the design and layout of both maintenance-free, dry-running plain bearings and low-maintenance ones through field-oriented tests.