Lubrication

Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load (pressure generated) between the opposing surfaces. The interposed lubricant film can be a solid, (eg graphite, MoS2) [www.engineersedge.com/lubrication/applications_solid_lubrication.htm - 14k] a solid/liquid dispersion, a liquid, a liquid-liquid dispersion (greases) or exceptionally a gas.

In the most common case the applied load is carried by pressure generated within the fluid due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces.

Lubrication can also describe the phenomenon such reduction of wear occurs without human intervention (aquaplaning on a road). The science of friction, lubrication and wear is called tribology.

When we talk about (adequate) lubrication smooth continuous equipment operation is assumed, with only mild wear, and without excessive stresses within the lubricated conjunctions to cause seizure at the conjunction, or break of any part of the equipment, and when such a catastrophic event does occur it means that the lubrication has broken down.

The regimes of lubrication

When progressively increasing the load between the contacting surfaces three distinct situations can be observed with respect to the mode of lubrication, which are called regimes of lubrication:

*Fluid film lubrication is the lubrication regime in which through viscous forces the load is fully supported by the lubricant within the space or gap between the parts in motion relative to one another (the lubricated conjunction) and solid-solid contact is avoided. [San Andrés. L. "Introduction to pump rotordynamics, Part i. Introduction to hydrodynamic lubrication". ("MEEN626 Lubrication Theory Class:Syllabus FALL2006"). [http://phn.tamu.edu/me262/Notes_pdf/Introduction.pdf] (11 Dec 2007)]
**Hydrostatic lubrication is a special case of fluid film lubrication in which an external pressure is applied to keep the lubricant in the conjunction, enabling it to support the external load.
**Hydrodynamic lubrication is also a special case of fluid film lubrication which occurs when the lubricant is able to support the load without external pressure, through hydrodynamic forces alone, which deform the shape of the interposing lubricant film into a wedge shape and drags the lubricant into the film, so that the externally applied load can be supported.
*Elastohydrodynamic lubrication: The opposing surfaces are separated but there occurs some interaction between the raised solid features called "asperities", and there is an elastic deformation on the contacting surface enlarging the load bearing area whereby the viscous resistance of the lubricant becomes capable of supporting the load.

*Boundary lubrication (also called boundary film lubrication): The bodies come into closer contact at their asperities; the heat developed by the local pressures causes a condition which is called stick-slip and some asperities break off. At the elevated temperature and pressure conditions chemically reactive constituents of the lubricant react with the contact surface forming a highly resistant tenatious layer, or film on the moving solid surfaces (boundary film) which is capable of supporting the load and major wear or breakdown is avoided.

:Boundary lubrication is also defined as that regime in which "the load is carried by the surface asperities rather than by the lubricant" [cite book|author= Bosman R. and Schipper D.J.|title=Microscopic Mild Wear in the Boundary Lubrication regime|edition=|publisher=Laboratory for Surface Technology and Tribology, Faculty of Engineering Technology, University of Twente, P.O. Box 217, NL 7500 AE Enschede, The Netherlands |year=|id=] .

Beside supporting the load the lubricant may have to perform other functions as well, for instance it may have to cool the contact areas, or to remove wear products, and for 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 pistons, pumps, cams, bearings, turbines, cutting tools etc where without lubrication the pressure between the surfacers in close proximity would generate enough heat for rapid surface damage which in a coarsened condition literally weld the surfaces together, causing seizure.

References

ee also

* Lubricant
* Lubrication theory
* Bearing (mechanical)
* Grease (lubricant)
* Fluid management
* Oils
* Society of Tribologists and Lubrication Engineers
* Penetrant


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Look at other dictionaries:

  • Lubrication — Lu bri*ca tion, n. The act of lubricating; the act of making slippery. [1913 Webster] …   The Collaborative International Dictionary of English

  • Lubrication — Lubrication. См. Смазка. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

  • lubrication — (n.) 1640s, act of lubricating, noun of action from LUBRICATE (Cf. lubricate) (v.). Earlier were lubifraction (1540s) …   Etymology dictionary

  • lubrication — See lubricate. * * * Introduction of any of various substances between sliding surfaces to reduce wear and friction. Lubricants may secondarily control corrosion, regulate temperature, electrically insulate, remove contaminants, or damp shock.… …   Universalium

  • lubrication — A type of friction reducing agent like oil or grease. Also see central chassis lubrication chassis lubrication clean oil lubrication dry sump lubrication forced feed lubrication petroil lubrication pressure lubrication pump fed lubrication …   Dictionary of automotive terms

  • Lubrication — (Roget s Thesaurus) >Absence of friction. Prevention of friction. < N PARAG:Lubrication >N GRP: N 1 Sgm: N 1 smoothness smoothness &c. 255 Sgm: N 1 unctuousness unctuousness &c. 355 GRP: N 2 Sgm: N 2 lubrication lubrication lubrification …   English dictionary for students

  • lubrication — n. liquor. D A little lubrication would help this party a lot. □ Wally has had a little too much lubrication …   Dictionary of American slang and colloquial expressions

  • lubrication — tepimas statusas T sritis fizika atitikmenys: angl. lubrication vok. Schmieren, n; Schmierung, f rus. смазка, f; смазывание, n pranc. graissage, m; lubrification, f …   Fizikos terminų žodynas

  • lubrication — lubricate ► VERB ▪ apply oil or grease to (an engine or component) to minimize friction. DERIVATIVES lubrication noun lubricator noun. ORIGIN Latin lubricare make slippery , from lubricus slippery …   English terms dictionary

  • lubrication — noun see lubricate …   New Collegiate Dictionary


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