Selection of bearing type is made after the general design concept of the machine has been established and the magnitude of the loads and speeds estimated. Special conditions can directly affect bearing operation and must be considered.

These include ambient or localized temperatures, shock or vibration, dirt or abrasive contamination, difficulty in obtaining accurate alignment, space limitations, need for shaft rigidity, and reliability of lubrication.

Selection of the proper type of bearing is not an exact science.The fields of application for many types of bearings overlap, and the value of experience in bearing applications cannot be overemphasized.

Each type of bearing, however, has inherent features, which determine its relative suitability for a specific application. Careful analysis of these features and familiarization with the fundamental characteristics of each type of bearing will help in selecting the proper bearing.

Ball Bearings versus Roller Bearings. Using balls as the rolling elements in bearings offers certain performance advantages. Most of the advantages of ball bearings are derived from the small areas of contact between the ball and raceways.

Ball bearings may be operated at higher speeds, with less internal friction and less heat generation.They have a greater inherent ability to accommodate slight misalignment. Under certain conditions of combined loading, ball bearings occupy less space than required for roller bearings of the same bore size.

Rollers are not limited to a single geometric shape.There are several types, such as tapered rollers, spherical rollers, and cylindrical rollers. For a given load and diameter of rolling element, rollers transmit load through a larger contact area than do balls.

This allows roller bearings to support greater loads and accommodate far more shock than ball bearings of equivalent size. For a given applied load, contact area stresses for roller bearings are lower than for ball bearings, and, therefore, they produce lower elastic deformation.

Since the larger contact areas create more friction, permissible operating speeds for roller bearings are lower than those for ball bearings.

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