The purpose of the ball is to determine the relative position of two parts (usually axes and housings) and to ensure their free rotation while passing the load between them. At high speeds (for example in a gyro ball bearing), this use can be extended to include free rotation and almost no wear in the bearing. In order to achieve this state, a viscous fluid film, called an elastic hydrodynamic lubrication film, is used to separate two parts of the bearing. HUD (1966) points out that the elastic hydrodynamic lubrication film can be maintained not only when the bearing bears the load on the shaft, but also when the bearing is preloaded so that the positioning accuracy and stability of the shaft are not more than 1 micro inches or 1 cents in.
Ball is used in various machines and equipment with rotating parts. Designers often decide whether to use ball bearings or fluid film bearings in specific applications. The following features make ball bearings more desirable than fluid film bearings on many occasions,
1. The starting friction is small and the work friction is suitable.
2. can withstand radial and axial joint load.
8. Insensitive to the interruption of lubrication.
4. No self-excited instability.
5. It is easy to start at low temperature.
In a reasonable range, changing the load, rotational speed and working temperature have only a small effect on the good performance of the ball bearings.
The following features make the ball bearings less desirable than the fluid film bearings.
1. The change of finite fatigue life is large.
2. The required radial space is larger.
3. Low damping capacity.
I. High noise level. ·
6. Strict in the requirements.
6. Higher cost.
According to the above characteristics, the piston engine usually uses a fluid film bearing, while the jet engine almost only uses the ball bearing. Various types of bearings have their own unique advantages, in a given application situation, should carefully select the most suitable type of bearing. The British Engineering Science Data Organization (ESDU 1965, 1967) has provided useful guidelines for selecting bearings as an important issue.