All material surfaces, hard or soft, have many irregularities in the form of asperities known as peaks and valleys. When two solid surfaces pass over each other, the asperities of both surfaces come in contact with each other and cause a deformation on the metal surface. This deformation happens due to friction, which is the force that acts on two moving surfaces and resists the motion. A substance known as a lubricant is introduced between the two surfaces to reduce the friction. This process of reducing frictional resistance between moving surfaces by the application of lubricants is termed as lubrication.
This handbook discusses various types of lubricants along with their properties.
There are three types of lubrication mechanisms:
Fluid film or hydrodynamic lubrication
Thin film or boundary lubrication
Extreme pressure lubrication
In this type of lubrication, a thick film of lubricating oil separates two moving surfaces from each other, preventing the direct contact of the two rubbing surfaces. The lubricating oil covers the irregularities of the sliding surfaces and forms a thick layer in between them so that there is no direct contact between the surfaces.
This type of lubrication is used when a thick fluid film cannot be maintained between two moving surfaces and direct metal-to-metal contact is possible. Direct metal-to-metal contact occurs in the following cases:
When the viscosity of oil is low
When the speed of movement is very low
When the load...
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