Lubrication:

Process of applying a substance to moving parts of machine which reduces friction between the surfaces and thereby minimizes their wear and tear.

A lubricant is a substance introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move.

• Boundary Lubrication or Thin Film Lubrication

Boundary lubrication exists when the operating condition are such that it is not possible to establish a full fluid condition, particularly at low relative speeds between the moving or sliding surfaces.

The oil film thickness may be reduced to such a degree that metal to metal contact occurs between the moving surfaces. The oil film thickness is so small that oiliness becomes predominant for boundary lubrication.

Boundary lubrication happens when

• A shaft starts moving from rest.

• The speed is very low.

• The load is very high.

• Viscosity of the lubricant is too low.

Examples for boundary lubrication:

• Guide and guide shoe in two stroke engine.

• Lubrication of the journal bearing in diesel engines (mainly during starting and stopping of engine).

• Piston rings and when cylinder liner is at TDC and BDC position when the piston direction changes and if the relative speed is very slow.

• Boundary Lubrication