Introduction:
In rolling contact bearings, the contact between the bearing surfaces is rolling rather than sliding, as in sliding contact bearings. The common sliding bearing starts from rest with practically metal-to-metal contact and has a high coefficient of friction. It is a notable advantage of a rolling contact bearing over a sliding bearing that it has low initial friction.
Ball and roller bearings consist of an inner race mounted on the shaft or journal and an outer race that is supported by the
carcass or casing. Between the inner and outer race, there are balls or rollers as shown in Fig. Multiple balls or rollers are used
and these are kept at suitable distances by retainers so that they do not touch each other. Retainers are thin strips and usually consist of two parts that are assembled after the balls have been properly spaced. Ball bearings are used for light loads and roller bearings are used for heavier loads. Contact bearings, depending on the load to be transported, are classified as:
(a) Radial bearings, and
(b) Thrust bearings.
Read more: Magnetic Bearing – Functioning, Advantages and Applications
Rolling Element Bearing:
In rolling element bearings, friction and wear are low, which is why we need less lubricant. These bearings work with an elastohydrodynamic mechanism . Low friction and moderate lubricant requirements are two important advantages of bearings. Furthermore, these bearings are mass-produced, so they are cost-effective. These bearings are purchased in standard sizes rather than being customized by an individual designer. Bearings are selected from bearing catalogs. But specially designed, very large size bearings are often very expensive; therefore, bearing selection is important for proper bearing life. One of the important bearing selection criteria is the retainer (Fig.), necessary to maintain a constant angular distance between the rolling elements. But due to the retainer, the sliding (friction) increases and fewer number of rolling elements (means lower load capacity) can be arranged.
Advantages of Rolling Contact Bearings
1. Low starting and running friction, except at very high speeds.
2. Ability to withstand momentary shock loads.
3. Shaft alignment accuracy.
4. Low maintenance cost as no lubrication is required during service.
5. Small overall dimensions.
6. Service reliability.
7. Easy to assemble and erect.
8. Cleaning.
Disadvantages
1. Noisier at very high speeds.
2. Low resistance to shock loads.
3. More initial cost.
4. Complicated bearing housing design.
