Hydrodynamic lubrication

﻿
Hydrodynamic lubrication

Hydrodynamic (HD) lubrication (or fluid film lubrication) has essential elements:

#A lubricant, which must be a viscous fluid.
#Hydrodynamic flow behavior of fluid between bearing and journal.
#The surfaces between which the fluid films move must be convergent.

Hyrdrodynamic (Full Film) Lubrication is obtained when two mating surfaces are completely separated by a cohesive film of lubricant.

The thickness of the film thus exceeds the combined roughness of the surfaces. The coefficient of friction is lower than with boundary-layer lubrication. Hydrodynamic lubrication prevents wear in moving parts, and metal to metal contact is prevented.

Hydrodynamic lubrication requires thin, converging fluid films. These fluids can be liquid or gas, so long as they exhibit viscosity. In computer components, like a hard disk, heads are supported by hydrodynamic lubrication in which the fluid film is the atmosphere.

The scale of these films are on the order of micrometers. Their convergence creates pressures normal to the surfaces they contact, forcing them apart.

3 Types of bearings include:

*Self-acting: Film exists due to relative motion.
*Squeeze film: Film exists due to relative normal motion.
*Externally pressurized: Film exists due to external pressurization.

Conceptually the bearings can be thought of as two major geometric classes: bearing-journal(Anti Friction), and plane-slider(Friction).

The Reynolds equations can be used to derive the governing principles for the fluids. Note that when gases are used, their derivation is much more involved.

The thin films can be thought to have pressure and viscous forces acting on them. Because there is a difference in velocity there will be a difference in the surface traction vectors. Because of mass conservation we can also assume an increase in pressure, making the body forces different.

Wikimedia Foundation. 2010.

Look at other dictionaries:

• hydrodynamic lubrication system — A type of lubrication system in which the surfaces to be lubricated are separated by a substantial quantity of oil. The oil has the effect of keeping the two surfaces apart. Also called fluid film lubrication. Hydrometer measuring density of a… …   Aviation dictionary

• 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… …   Wikipedia

• Boundary lubrication — Brief description of lubricationLubrication is the process, or technique employed to reduce wear of one or both surfaces in relative motion to one another by interposing a substance called lubricant between the surfaces to carry or to help carry… …   Wikipedia

• fluid film lubrication — A type of lubrication in which the surfaces to be lubricated are separated by a substantial quantity of oil. The oil has the effect of keeping the two surfaces apart. Also called hydrodynamic lubrication …   Aviation dictionary

• Plain bearing — Crankshaft plain bearing shells A plain bearing, also known as a plane bearing[1] or a friction bearing[2] is the simplest type of bearing, comprising just a bearing surface and no rolling elem …   Wikipedia

• Lubricant — A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat. The property of reducing friction is known as lubricity. A good lubricant… …   Wikipedia

• Gordon Higginson — Nationality British Education Leeds University Work Engineering discipline Hydrodynamic Lubrication, Tribology and Bio engineering Institution memberships …   Wikipedia

• Beauchamp Tower — Infobox Engineer image size = 165px caption = name = Beauchamp Tower nationality = British birth date = January 13 1845 birth place = Moreton, Essex death date = December 31 1904 death place = education = spouse = parents = children = discipline …   Wikipedia

• PETROV N P — RUSSIA (see also List of Individuals) 25.5.1836 Orlov/RU 15.1.1920 Tuapse/RU Nikolai Pavlovich Petrov graduated from the Saint Petersburg military college in 1855 to continue engineering studies until 1862 at the Saint Petersburg Academy. In 1867 …   Hydraulicians in Europe 1800-2000

• SWIFT — UNITED KINGDOM (see also List of Individuals) 15.12.1894 Romney/UK 14.10.1960 Keswick/UK Herbert Walker Swift was educated at St. John s College, Cambridge and then was commissioned for active service from 1915 in World War I. He was then from… …   Hydraulicians in Europe 1800-2000

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.