Lubricating film

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With ideal lubrication , a thin film of lubricant forms between two surfaces , on which the surfaces slide past each other without touching.

The main influencing factors are the viscosity of the lubricant , the temperature and the sliding speed . A lubricant with a low viscosity is required at high sliding speeds . At high temperatures, an agent with a slightly higher viscosity is required, since the viscosity of a lubricant usually decreases with increasing temperature. For this reason there are different lubricating oils for summer and winter in cars, for example . If the working area is left, the lubricant film may tear (oil film tear, lubricant film tear ) and wear increases significantly.

Unwanted lubricating film

The railways fear the formation of a lubricating film from leaves and moisture . The braking distance is longer and trains can get stuck on inclines due to insufficient wheel-rail contact (friction). As a result, a reduced loading / utilization of freight trains is indicated as a preventive measure in autumn . As a countermeasure, the sand spreading device is used (to a limited extent) to increase the friction and thus to shorten the braking distance. On steep gradients, pushing locomotives or multiple traction are also required to avoid loss of tractive power, for example due to the drive wheels skidding (spinning).

More detailed physical relationships, including EHD contact and the resulting elastohydrodynamic lubricating film, see lubrication ( tribology ) under the term hydrodynamic lubrication .

literature

  • Wolfgang Weißbach: Materials science. Structures - Properties - Examination, 18th edition, Vieweg + Teubner Verlag, Wiesbaden 2012, ISBN 978-3-8348-1587-3 .
  • Helmut Schaefer (Hrsg.): VDI-Lexikon Energietechnik . Springer-Verlag Berlin Heidelberg GmbH, Berlin Heidelberg 1994, ISBN 978-3-642-95749-9 , pp. 1043-1044.
  • Rainer Köhnlechner: Investigations into the thickness of the lubricating film in compressed air cylinders. Springer Verlag, Berlin Heidelberg 1980, ISBN 978-3-540-10375-2 .

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