There are 3 types of lubrication mechanisms
1) Hydrodynamic or Fluid Film or Thick Film Lubrication
2 )Boundary Lubrication or Thin Film Lubrication
3) Extreme Pressure Lubrication
1) Hydrodynamic or Fluid Film or Thick Film Lubrication:-
This type of lubrication is done in those cases where liquid lubricants having minimum viscosity under working conditions are used and at the same time, it should remain in place and separate the moving or sliding parts of the machine.
In the fluid film lubrication, the liquid lubricant fills the grooves or irregularities of the sliding surfaces, and forms a thick layer in between them so that there is no direct contact between the sliding surfaces. In this way, the lubricant reduce the wear and tear by reducing the frictional resistance produced by the movement of sliding parts.
2) Hydrodynamic or Fluid Film or Thick Film Lubrication:-
In the fluid film lubrication, the liquid lubricant fills the grooves or irregularities of the sliding surfaces, and forms a thick layer in between them so that there is no direct contact between the sliding surfaces. In this way, the lubricant reduce the wear and tear by reducing the frictional resistance produced by the movement of sliding parts.
2) Hydrodynamic or Fluid Film or Thick Film Lubrication:-
The frictional resistance to the movement of the sliding parts is only due to the internal resistance between the particles of the lubricant.
The frictional resistance is independent of the load, But depends upon the area and relative velocity of the sliding parts and viscosity, thickness of the lubricants. Due to this reason, the light machines like watches, clocks, guns, scientific instruments etc. and delicate machines are provided with fluid film lubrication's.
3) Boundary Lubrication or Thin Film Lubrication :-
The frictional resistance is independent of the load, But depends upon the area and relative velocity of the sliding parts and viscosity, thickness of the lubricants. Due to this reason, the light machines like watches, clocks, guns, scientific instruments etc. and delicate machines are provided with fluid film lubrication's.
3) Boundary Lubrication or Thin Film Lubrication :-
Where thick film lubrication fails, thin film lubrication is done. Thin film or boundary Lubrication is done for those cases in which the continuous film of lubrication cannot persist and direct metal to metal contact is possible.
This happens when,
A thin lubricant should have high viscosity index, good resistance to heat and oxidation, good oiliness and low pour point.
Vegetable and animal oils and their soaps possess great property of adsorption and are used for thin film lubrication.
Graphite and molybdenum disulphide in oil are also used for boundary lubrication. These lubricants form a thin film on the metallic surfaces, which reduces the friction and can bear compression as well as high temperature.
This happens when,
- a Shaft starts moving from rest
- the speed is very low
- load is very high and
- viscosity of lubricating oil is very low.
A thin lubricant should have high viscosity index, good resistance to heat and oxidation, good oiliness and low pour point.
Vegetable and animal oils and their soaps possess great property of adsorption and are used for thin film lubrication.
Graphite and molybdenum disulphide in oil are also used for boundary lubrication. These lubricants form a thin film on the metallic surfaces, which reduces the friction and can bear compression as well as high temperature.
For the boundary lubrication, the lubricant molecules should possess these properties:-
- They should have long hydrocarbon chains and the lateral attraction between the chains.
- They should have the active polar groups or atoms to promote spreading and to form the linkage with the metallic surfaces at high pressure