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Explain fluid film lubrication.

Marks: 5M, 6M

Year: Dec13, Dec12

In this case the sliding surfaces are separated completely by applying a thin uniform film of liquid lubricants between them.

The thickness of liquid film is at least 1000 Armstrong. The liquid lubricants do not have any chemical affinity to the metal surface and it sticks to it due to viscosity.

The liquid film covers all irregularities in the sliding surface and thus prevents formation of welded junction and hence avoids contact between sliding surface.

The liquid lubricant must have between sliding surface. The liquid lubricant must have sufficient viscosity so as to maintain the fluid film in its place. If viscosity is higher, a large amount of energy is required.

When the load is applied, the pressure developed in the lubricant is sufficient to keep moving surfaces apart and hence it known as hydrodynamic lubrication. It occurs in journal bearing. This type of lubrication is used in watches, clocks, electric motors, turbines etc.