- Hydrodynamically lubricated bearings or slider bearings.
Generally these bearing works on the principle of hydrodynamic lubricating film. If a lubricant film is enclosed in a wedge or tapered gap between the stationary and moving members, the oil films is drawn into the wedge shape generating a pressure that can support a load.
It has been shown experimentally that the coefficient varies as shown in fig. (a) in which a curve of (f ) verse ( ) is plotted. It is found that in the operation of a bearing to the left of point B, lubricated is not stable and is called boundary lubrication.
However, if operating in the region BC, the lubrication is stable and is called thick film or hydrodynamic lubrication.
When a journal starts rotating in a bearing as shown in the figure (b), the lubricant is forced into a wedge shaped (strictly a curved wedge) space by a pumping type of action and the pressure built up in the wedge supports the load on the journal.
As a result of the lubricant pressure, a minimum film thickness (ho) occurs, not at the bottom of the journal but displaced in the direction of rotation, as shown in the figure. This is because the lubricant pressure in converging gap reaches maximum at a point to the left of the bearing centre.
- Rolling contact bearings.
Types of rolling contact bearings :
- Ball bearings : In ball bearing, the rolling element is a spherical ball.
- Roller bearings : In roller bearing, the rolling element is a roller, which might be cylindrical, spherical or conical.
- These have greater capacity for radial loads for a given overall size, due to greater area of contact.
- These are more easily adopted to high speeds.
- These are costlier.
- These are more sensitive to misalignment and dirt.
- These have considerably smaller axial thrust capacity.
Material for rolling elements bearings:
High quality steel
E.g. special alloy steels with N; and either Cr or Mo.