Lubrication of a ship's steam engine crankshaft. The two bottles of lubricant are attached to the piston and move while the engine is operating.
This article's lead section contains information that is not included elsewhere in the article. If the information is appropriate for the lead of the article, this information should also be included in the body of the article. (December 2021) (Learn how and when to remove this template message)

Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology.

Lubrication mechanisms such as fluid-lubricated systems are designed so that the applied load is partially or completely carried by hydrodynamic or hydrostatic pressure, which reduces solid body interactions (and consequently friction and wear). Depending on the degree of surface separation, different lubrication regimes can be distinguished.

Adequate lubrication allows smooth, continuous operation of machine elements, reduces the rate of wear, and prevents excessive stresses or seizures at bearings. When lubrication breaks down, components can rub destructively against each other, causing heat, local welding, destructive damage and failure.

Lubrication mechanisms

Fluid-lubricated systems

As the load increases on the contacting surfaces, distinct situations can be observed with respect to the mode of lubrication, which are called lubrication regimes:[1]

Besides supporting the load the lubricant may have to perform other functions as well, for instance it may cool the contact areas and remove wear products. While carrying out these functions the lubricant is constantly replaced from the contact areas either by the relative movement (hydrodynamics) or by externally induced forces.

Lubrication is required for correct operation of mechanical systems such as pistons, pumps, cams, bearings, turbines, gears, roller chains, cutting tools etc. where without lubrication the pressure between the surfaces in close proximity would generate enough heat for rapid surface damage which in a coarsened condition may literally weld the surfaces together, causing seizure.

In some applications, such as piston engines, the film between the piston and the cylinder wall also seals the combustion chamber, preventing combustion gases from escaping into the crankcase.

If an engine required pressurised lubrication to, say, plain bearings, there would be an oil pump and an oil filter. On early engines (such as a Sabb marine diesel), where pressurised feed was not required splash lubrication would suffice.

See also


  1. ^ Hamrock, Bernard J. (2004). Fundamentals of fluid film lubrication. Steven R. Schmid, Bo O. Jacobson (2nd ed.). New York: Marcel Dekker. ISBN 0-8247-5120-5. OCLC 55739786.
  2. ^ San Andrés. L. "Introduction to pump rotordynamics, Part i. Introduction to hydrodynamic lubrication". ("MEEN626 Lubrication Theory Class:Syllabus FALL2006"). [1][permanent dead link] (11 Dec 2007)
  3. ^ tribonet (2017-02-16). "Hydrodynamic Lubrication". Tribology. Retrieved 2017-02-23.
  4. ^ Singh, Kushagra; Sadeghi, Farshid; Russell, Thomas; Lorenz, Steven J.; Peterson, Wyatt; Villarreal, Jaret; Jinmon, Takumi (2021-09-01). "Fluid–Structure Interaction Modeling of Elastohydrodynamically Lubricated Line Contacts". Journal of Tribology. 143 (9): 091602. doi:10.1115/1.4049260. ISSN 0742-4787. S2CID 230619508.
  5. ^ tribonet (2017-02-05). "Elastohydrodynamic Lubrication (EHL)". Tribology. Retrieved 2017-02-23.
  6. ^ Popova, E.; Popov, V. L. (2015). "On the history of elastohydrodynamics: The dramatic destiny of Alexander Mohrenstein-Ertel and his contribution to the theory and practice of lubrication". Zeitschrift für Angewandte Mathematik und Mechanik. 95 (7): 652–663. Bibcode:2015ZaMM...95..652P. doi:10.1002/zamm.201400050.
  7. ^ Bosman R. and Schipper D.J. Microscopic Mild Wear in the Boundary Lubrication regime. Laboratory for Surface Technology and Tribology, Faculty of Engineering Technology, University of Twente, P.O. Box 217, NL 7500 AE Enschede, The Netherlands.
  8. ^ Ewen, James. "Boundary Lubrication". Trbonet.
  9. ^ Akchurin, Aydar; Bosman, Rob; Lugt, Piet M.; Drogen, Mark van (2015-05-31). "On a Model for the Prediction of the Friction Coefficient in Mixed Lubrication Based on a Load-Sharing Concept with Measured Surface Roughness". Tribology Letters. 59 (1): 19. doi:10.1007/s11249-015-0536-z. ISSN 1023-8883.