The Use Of Ball Bearings
Jul 02, 2022| The purpose of a ball bearing is to determine the relative position of two parts (usually a shaft and a housing) and to ensure their free rotation, while transferring the load between them. At high rotational speeds (eg in gyro ball bearings) this use can be extended to include free rotation with little wear in the bearing. To achieve this state, the two parts of the bearing are separated by an adherent fluid film called an elastohydrodynamic lubricant film. Denhard (1966) pointed out that elasticity is maintained not only when the bearing is subjected to a load on the shaft, but also when the bearing is preloaded so that the positioning accuracy and stability of the shaft does not exceed 1 microinch or 1 nanoinch Hydrodynamic lubricating film.
Ball bearings are used in various machines and equipment with rotating parts. Designers often have to decide whether a ball bearing or a fluid film bearing should be used in a particular application. The following characteristics make ball bearings more desirable than fluid film bearings in many applications,
1. Low starting friction and suitable working friction.
2. Can withstand combined radial and axial loads.
8. Not sensitive to interruption of lubrication.
4. No self-excited instability.
5. Low temperature starting is easy.
Within a reasonable range, changing load, speed and operating temperature has only a small effect on the good performance of a ball bearing.
The following characteristics make ball bearings less desirable than fluid film bearings.
1. The finite fatigue life varies greatly.
2. The required radial space is large.
3. Damping capacity is low.
4. Noise levels are high.
5. The requirements are more stringent.
6. Higher cost.
According to the above characteristics, piston engines usually use fluid film bearings, while jet engines almost only use ball bearings. Various types of bearings have their own unique advantages, and the most appropriate bearing type should be carefully selected for a given application. The UK Engineering Science Data Organization (ESDU 1965, 1967) has provided useful guidelines for the important issue of bearing selection.