Hydrodynamic Lubrication :- In hydrodynamic lubrication hydro means (liquid) and dynamic means (relative motion) it is the combination of both liquid and relative motion to reduce the friction. In hydrodynamic lubricated bearings, a thick film of lubricant is formed between the journal and the bearing. According to Reynolds their are some essential factors for the formation of a thick film of oil in hydrodynamic lubrication. They are
- A continuous supply of oil is required.
- A relative motion between the two surfaces in a direction approximately tangential to the surface.
- The ability of one of the surfaces to take up a small inclination to the other surface in the direction of the relative motion.
- The line of action of resultant oil pressure must coincide with the line of action of the external load between the surface.
These factors are essential for the formation of thick film between journal and the bearing. In hydrodynamic lubricated bearing the bearing is supplied with sufficient lubricant, a pressure is build up in the clearance space when the journal is rotating about an axis that is eccentric with the bearing axis. The load can be supported by this fluid pressure without any actual contact between the journal and bearing.
The load carrying ability of a hydrodynamic bearing arises simply because a viscous fluid resists being pushed around.Under the proper conditions, this resistance to motion will develop a pressure distribution in the lubrication film that can support a useful load.
The load supporting in hydrodynamic bearings arises from either
- The flow of a viscous fluid in a converging channel(known as wedge film lubrication).
- The resistance of a viscous fluid to begin squeezed out from between approaching surfaces surfaces (know as squeeze film lubrication)