Stribeck curve

The Stribeck curve is an overall view of friction variation in the entire range of lubrication, including the hydrodynamic, mixed, and boundary lubrication.

The Stribeck curve is an overall view of friction variation in the entire range of lubrication, including the hydrodynamic, mixed, and boundary lubrication.

Tribology is the science and technology of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear. By means of the Stribeck curve the transitions from boundary lubrication to mixed lubrication and the transitions from mixed lubrication to elasto-hydrodynamic lubrication can be predicted and subsequently the lubrication regime in which a particular contact operates can be predicted.

Hydrostatic pressure
The pressure distribution in the lubricating film is composed of a hydrostatic and a hydrodynamic pressure. The hydrostatic pressure arises due to the pressure difference between the pumped liquid side and the atmosphere side. The hydrodynamic pressure is generated as a pumping action due to the sliding motion of the surfaces.

Lubrication regimes for hydrodynamic pressure
At high velocities and not too high loads, the hydrodynamic pressure completely separates the sliding parts, allowing the formation of full-fluid-film lubrication. At lower velocities or higher loads, the hydrodynamic pressure is not sufficient to completely separate the sliding parts. In this situation, a mixed lubrication regime exists where part of the load is supported directly by the contact points of the surfaces.

Topography of the surfaces
The topography of the surfaces affects where the mixed lubrication regime is reached. At even lower velocities or higher loads, the generated hydrodynamic pressure becomes insignificant. This lubrication regime is called boundary lubrication. The thickness of the lubricating film of the mechanical shaft seal must be very small to avoid excessive leakage. Consequently, the seal is always in the mixed lubrication or boundary lubrication regime.





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