Volume 1 Issue 1 - Lubrication

Article Index
Lube Notes: Intro to Lubrication
Surface Furnish: Asperities
Boundary Lubrication
All Pages

Surface Furnish: Asperities

Viewing the surface of metal with a microscope reveals extremely small jagged peaks called asperities (Figure One). There are continuous peaks and valleys of metal almost like microscopic mountain rages. It is impossible to machine the metal surface fine enough to remove these asperities. Obviously, separating these asperities is paramount to reducing friction and resulting wear. Reviewing the factors listed that affect friction, it is apparent that lubrication is the factor most useful for limiting friction. The motion is set by application and the load and speed will be related to the work application. Temperature is usually a range determined again by the application. Now since lubrication is our vehicle for limiting friction and wear, it is important to identify the types, or regimes as they are called, of lubrication that are available and in which applications each regime comes into play.


lubrication-asperities

A microscopic look at two metal surfaces as they contact one another: the white spots represent gaps in contact between the two objects. Where asperities contact each other, friction and wear occur.


Hydrodynamic Lubrication

Hydrodynamic (HD), or full fluid film, conditions occur where the fluid film of oil completely separates the moving surfaces preventing any contact between asperities (Figure Two). In this lubrication regime, friction between the surfaces is, for practical purposes, non-existent (having been prevented by the lubricant). Internal fluid friction exists but we will save that for another discussion. Under light loads, main bearings on the crankshaft of internal combustion engines will operate in this regime.


hydrodynamic-lubrication

Hydrodynamic Lubrication occurs in conditions where the fluid film of oil completely separates the moving surfaces, preventing any contact between asperities.


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