Fluid film or hydrodynamic or thick film lubrication
- Low load
- Uniform temperature
- Moderated speed
In this type of lubrication, the sliding metals surfaces or rotating metal surfaces are completely separated from each other by applying a film of liquid lubricant between them.
The liquid lubricant does not have any chemical affinity to the metal surface and it sticks to it only due to viscosity or stickiness. So it is also known as fluid film lubrication.
The pressure developed is sufficient to keep the moving surfaces apart under such condition (as per hydrodynamic theory), so it is also called hydrodynamic lubrication.
The thickness of the fluid film is effective up to 1000A so that there is no direct contact between the metal surfaces.
The coefficient of friction (force required to cause motion divided by the applied load) for well-lubricated surfaces ranges from 0.001 to 0.03.
The lubricant chosen should have the minimum viscosity under working conditions since the only resistance is due to internal resistance of lubricant.
In case of the shaft running at a fair speed, hydrodynamic friction and a film of lubricating oil cover the irregularities of the shaft that of bearing surfaces.
Hydrocarbon oils (viscosity the s independent of the season) are used
Certain additives like antioxidants, viscosity index improvers, and oregano-metallic detergents are added to improve the quality of the oil.
In case of delicate instruments and light machines like watches, clocks, guns, sewing machines and scientific instruments