Advantages and Disadvantages of Rolling Contact Bearings Over Sliding Contact Bearings

Introduction:

In rolling contact bearings, the contact between the bearing surfaces is rolling instead of sliding as in sliding contact bearings. The ordinary sliding bearing starts from rest with practically metal-to-metal contact and has a high coefficient of friction. It is an outstanding advantage of a rolling contact bearing over a sliding bearing that it has a low starting friction.

The ball and roller bearings consist of an inner race which is mounted on the shaft or journal and an outer race which is carried by the
housing or casing. In between the inner and outer race, there are balls or rollers as shown in Fig. A number of balls or rollers are used
and these are held at proper distances by retainers so that they do not touch each other. The retainers are thin strips and is usually in two parts which are assembled after the balls have been properly spaced. The ball bearings are used for light loads and the roller bearings are used for heavier loads. The rolling contact bearings, depending upon the load to be carried, are classified as :

(a) Radial bearings, and

(b) Thrust bearings.

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Rolling Element Bearing :

In rolling element bearings, friction and wear are low, so we require lesser quantity of lubricant. These bearings work with elastohydrodynamic mechanism. Low friction & moderate lubricant requirements are two important advantages of rolling bearings. Additionally, these bearings are mass produced therefore, are cost effective. These bearings are purchased in standard sizes instead of being customized by individual designer. The bearings are selected from catalogues of bearing. But very large size bearings, which are specially designed, are often very costly; so selection of bearing is important for proper life of bearing. One of the important bearing selection criterions is retainer (Fig), which is required to maintain constant angular distance between rolling elements. But due to retainer, sliding (friction) increases and lesser number of rolling elements (means lesser load carrying 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. Accuracy of shaft alignment.

4.Low cost of maintenance, as no lubrication is required while in service.

5. Small overall dimensions.

6. Reliability of service.

7. Easy to mount and erect.

8. Cleanliness.

Disadvantages

1. More noisy at very high speeds.

2. Low resistance to shock loading.

3. More initial cost.

4. Design of bearing housing complicated.

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