Lubrication

Lubrication of the ship steam engine crankshaft. The two bottles of lubricant are attached to the piston and move while the engine is operating.

Lubrication is the process or technique employed to reduce friction between, and wear of one or both, surfaces in proximity and moving relative to each other, by interposing a substance called a lubricant in between them. The lubricant can be a solid, (e.g. Molybdenum disulfide MoS2)[1] a solid/liquid dispersion, a liquid such as oil or water, a liquid-liquid dispersion (a grease) or a gas.

With fluid lubricants the applied load is either carried by pressure generated within the liquid due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces, or by the liquid being pumped under pressure between the surfaces.

Lubrication can also describe the phenomenon where reduction of friction occurs unintentionally, which can be hazardous such as hydroplaning on a road.

The science of friction, lubrication and wear is called tribology.

Adequate lubrication allows smooth continuous operation of equipment, 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.

The regimes of lubrication

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

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 pistons, pumps, cams, bearings, turbines, 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.

See also

References

  1. http://www.engineersedge.com/lubrication/applications_solid_lubrication.htm – 14k
  2. San Andrés. L. "Introduction to pump rotordynamics, Part i. Introduction to hydrodynamic lubrication". ("MEEN626 Lubrication Theory Class:Syllabus FALL2006"). (11 Dec 2007)
  3. 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.
  4. 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.
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