Properties Of Lubricants

The following are important properties of lubricants :

Viscosity

It is the most significant property of lubricants. The behaviour of lubricants is finding out by its viscosity.

Viscosity of a fluid is the property which resists its flow or shear. The quantitative measure of this property is dynamic or absolute viscosity that is defined as the force needed shearing a layer of unit thickness at unit velocity. Its units in CGS are "Poise" and in SI it is Pa. S. In practice a smaller CGS unit of centi poise (cp) is utilized. The ratio of absolute viscosity to density of oil is known as kinetic viscosity.

The SAE oil classification utilized absolute viscosity while ISO classification is depend upon kinematic viscosity. As both absolute viscosity & density are affected by temperature, each value should be described for a temperature only.