Fluid-Film or Thick-Film or Hydrodynamic Lubrication

In this the sliding surfaces are separated from each other by a thick-film of fluid (at least 1000 Å thick), therefore that direct surface to surface contact & welding of junctions hardly ever occurs. The lubricant film fills the irregularities of the sliding surfaces and composes a thick layer in among them, so that there is not direct contact among the material surfaces. This consequently reduces wear. The resistance to the movement of sliding parts is just because of the internal resistance among the particles of the lubricant moving over each other. Thus, the lubricant selected must have the minimum viscosity under working conditions and at the same time it must remain in place and separate the surfaces. In such a system the effective coefficient of friction based on thickness of the lubricant, viscosity the relative viscosity & area of sliding surfaces. The coefficient of friction in such cases is as low as 0.001 to 0.05. Hydrodynamic friction takes places in the case of a shaft running at a fare speed as well as in well lubricated bearing with not too high load. Delicate instruments, light machines as, clocks, watches, guns, scientific instruments, sewing machines, etc. are provided with this type of lubrication.

Hydrocarbon oils are let to be satisfactory lubricants for fluid-film lubrication. In order to maintain viscosity of the oil in all of the seasons of years, ordinary hydrocarbon lubricants are blended along with selected long chain polymers.