In order to realize the low noise and good speed, usually two hybrid ceramic deep groove ball bearings¡¯ configuration will be axial pre-tightened. A very simple method to axial pre-tightening is to use spring washer, as mentioned in section using spring preload. Recommended axial pre-load can be calculated according to the methods provided in this chapter.
Spring preload
In small motors and similar applications, giving bearings preload can reduce running noise. This kind of bearing configuration is consisted of single row deep groove ball bearings at each end. The simplest method to Exerted preload is through spring or spring "components" (Picture 1). Spring action on one of the two bearing outer ring; The outer ring must be able to axial displacement. Even bearing axial displacement is caused by thermal expansion; preload force should remain almost unchanged. Necessary preload can be calculated by formula.
F = k d
Picture1
According to the design of the motor, the coefficient k value is between 0.005 and 0.01. If the preload is mainly used to prevent damage of bearing vibration when the bearing is static, a larger preload is required, should choose k = 0.02.
Spring load is still a common method for high speed grinding shaft angular contact ball bearing to exert preload. However, this method is not suitable for bearings used in following conditions, high demands to stiffness, load direction changeable or will happen unsure impact load.
Bearing pre-tightening
According to the different application, bearing configuration must have positive or negative clearance. In most cases, work clearance should be positive, namely bearing at run time, leaving certain residual clearance, though they may be very small clearance.
But on the other hand, many applications need to have a negative work clearance - the pre-tightening, in order to improve the stiffness of the bearing configuration or rotating accuracy. For example, the machine tool spindles bearings, the automobile pinion shaft bearings, small motor bearings, or make reciprocating motion bearing configuration, etc. If the bearing work at high speed without or only a small load, preloaded on the bearing configuration should be down. For example By spring, etc. In this case, the bearing pre-tightening is to provide the minimum load, in order to prevent bearing damage due to the sliding roller.