Fluid film lubrication

Fluid film lubrication is the lubrication regime in which, through viscous forces, the load is fully supported by the lubricant within the space or gap between the parts in motion relative to one another object (the lubricated conjunction) and solid–solid contact is avoided. 

❖ Viscosity Index: The viscosity of a fluid is a measure of its resistance to deformation at a given rate. Viscosity index (VI) is an arbitrary measure for the change of viscosity with variations in temperature. The lower the VI, the greater the change of viscosity of the oil with temperature and vice versa. It is used to characterize viscosity changes with relation to temperature in lubricating oil.

 ❖ Pour point: The pour point of a liquid is the temperature at which it becomes semi solid and loses its flow characteristics. In crude oil (it is a mixture of hydrocarbons that exists as a liquid in underground geologic formations), a high pour point is generally associated with high paraffin content, typically found in crude deriving from a larger proportion of plant material. 

 ❖ Oxidation stability: Oxidation stability is a chemical reaction that occurs with a combination of the lubricating oil and oxygen. The rate of oxidation is accelerated by high temperatures, water, acids and catalysts such as copper.