A study of bearing and its types conference Paper

II. TYPES OF BEARINGS 
The sliding contact bearings, according to the thickness of layer of the lubricant between the sliding surfaces are 
classified as follows:
 
2.1 Thick Film Bearings

The thick film bearings are those in which the working surfaces are completely separated from each other by the 

lubricant. Such type of bearings is also called as 
hydrodynamic lubricated bearings.
 
2.2 Thin Film Bearings 
The thin film bearings are those in which, although lubricant is present; the working surfaces partially contact 
each other at least part of the time. Such type of bearings is also called 
boundary lubricated bearings.
 
2.3. Zero Film Bearings

The zero film bearings are those which operate without any lubricant present.

 
2.4. Hydrostatic or Externally Pressurized Lubricated Bearings
 
The hydrostatic bearings are those which can support steady loads without any relative motion between the 
journal and the bearing. This is achieved by forcing externally pressurized lubricant between the members.
III. HYDRODYNAMIC LUBRICATED BEARINGS 
In hydrodynamic lubricated bearings, there is a thick film of lubricant between the sliding surfaces. A little 
consideration will show that when the bearing is supplied with sufficient lubricant, a pressure is build up in the 
clearance space when the runner is rotating. The load can be supported by this fluid pressure without any actual 
contact between the sliding surfaces. 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 lubricant film that can support a useful load. The load supporting pressure in 
hydrodynamic bearings arises from either
1. The flow of a viscous fluid in a converging channel (known as wedge film lubrication), or 
2. The resistance of a viscous fluid to being squeezed out from between approaching surfaces (known as 
squeeze film lubrication).