What Is Lubrication?

Lubrication is the process or method used for the reduction of friction and wear of the moving surfaces by applying an additional substance between the surfaces. This substance is called as Lubricant. While the study of this lubrication science, friction, and wear is called as Tribology.

Lubrication is necessary for the correct operations of the mechanical operations works on the contacting- rubbing phenomena, like pumps, pistons, turbines, bearings etc. so that the pressure generated by the contact between the surfaces can be minimized, and so is the risk of wear- tear as well as friction losses.

Regimes Of Lubrication

There are several distinct regimes which are commonly used to describe the fundamental principles of lubrication. When the load increases on the surfaces in contact, usually following distinct regimes are observed, with respect to the lubrication modes. These regimes are called as regimes of lubrication.

• Fluid film lubrication

In fluid film lubrication regime, the moving surfaces have a liquid or gaseous lubricant film between them, so that the contact between the surfaces can be avoided. So both the frictional power loss, as well as the pressure is the functions of lubricant viscosity, as well as the shear rate and geometry of the contacting surfaces. This regime is common in electric motors, and generators.

• Boundary lubrication

Boundary lubrication regime is used for the worse conditions, where the fluid film lubrication is not enough to cover the applied load severity. I.e. when the bodies come in contact, heat generated by the by the load causes stick-slip conditions, which can lead to breakage. At high pressure and temperature conditions, the reactive particles of the lubricant reacts with the contacting surfaces forming a layer on the moving surfaces, this layer is highly resistive and can support the load, so can avoid the breakage. This lubrication layer is often considered as the boundary film lubrication. The most common example of boundary film lubrication is Hypoid gears in automobiles.

• Elastohydrodynamic lubrication (EHL)

This regime of lubrication is the lubrication between the non-conformal surfaces contact, i.e. the contact between those surfaces, which do not fit each other, such as bearings (ball and roller), cams, gear teeth, or other friction drivers. By understanding EHL, it can be predicted that how thick lubricant films should be formed on the basis of the contacting pressure magnitudes and the surface stresses. 

It is not enough to know about the lubrication regimes, as there are several different lubricants, which are used in any of the lubrication regime. So a detailed study of tribology is needed to understand any friction-lubrication case.  

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