The Use Of Ball Bearings

Ball bearings are designed to fix the relative position of two mechanical components (typically a shaft and a bearing housing), ensure flexible free rotation, and transmit operational loads between mating parts. Under high-speed operating conditions, such as gyro ball bearing applications, ball bearings can achieve low-wear stable rotation. This superior performance relies on an elastohydrodynamic lubrication film, a continuous adhesive fluid layer that isolates the internal mating surfaces of the bearing.

Denhard (1966) demonstrated that structural elasticity can be consistently maintained both under shaft load and bearing preload states. This enables the shaft to maintain ultra-high positioning accuracy and operational stability, with deviation controlled within 1 microinch to 1 nanoinch via the effective hydrodynamic lubrication film.

Ball bearings are widely applied in diverse machinery and equipment equipped with rotating components. Mechanical designers frequently evaluate and select between ball bearings and fluid film bearings according to actual application scenarios. Compared with fluid film bearings, ball bearings possess prominent advantages in most working conditions, which are summarized as follows:

1. Low starting friction and stable operating friction performance; 2. Excellent bearing capacity for combined radial and axial loads; 3. Strong tolerance to temporary lubrication interruption; 4. Free from self-excited operational instability; 5. Reliable and easy startup performance at low temperatures.

Within the standard operating range, variations in load, rotational speed and working temperature exert negligible impacts on the comprehensive performance of ball bearings.

Meanwhile, ball bearings also have certain limitations relative to fluid film bearings: 1. Discrete and unstable finite fatigue life with large performance differences; 2. Larger radial installation space occupation; 3. Relatively weak vibration damping capacity; 4. Higher operational noise level; 5. Stricter installation and application requirements; 6. Higher comprehensive application cost.

Due to the above performance differences, fluid film bearings are commonly adopted in piston engines, while jet engines predominantly apply ball bearings. Each type of bearing has exclusive performance advantages and applicable scenarios, so bearing selection must be optimized according to specific working conditions. The Engineering Sciences Data Unit (ESDU, 1965, 1967) of the UK has formulated systematic and practical guidelines for scientific bearing selection.

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