Fixed Bearing in Motor Bearing Systems
For the selection of the fixed-end bearing in motor bearing support (referred to as the motor fixed end), the following factors should be considered: (1) the precision control requirements of the driven equipment; (2) the nature of the load driven by the motor; and (3) the bearing or bearing assembly must be able to withstand a certain amount of axial force. Considering these three design elements, deep groove ball bearings are more commonly chosen as the preferred fixed-end bearing for small- and medium-sized motors.
Deep groove ball bearings are the most widely used type of rolling bearing. When using deep groove ball bearings, the structure of the motor bearing support system is very simple, and maintenance is also convenient. Deep groove ball bearings are mainly used to bear radial loads, but when the bearing's radial clearance is increased, they exhibit characteristics similar to angular contact ball bearings and can bear combined radial and axial loads. When the speed is relatively high and thrust ball bearings are not suitable, deep groove ball bearings can also be used to bear pure axial loads. Compared with other types of bearings of the same size specifications, this type of bearing has advantages such as a low coefficient of friction and high limiting speed, but it also has disadvantages such as being less resistant to impact and unsuitable for heavy loads.
After deep groove ball bearings are mounted on the shaft, within the range of the bearing's axial clearance, they can restrict the shaft or housing in both directions for radial fit. Radially, the bearing and the shaft adopt an interference fit, and the bearing and the end cap bearing chamber or housing adopt a small interference fit. The ultimate goal of selecting this fit is to ensure that during motor operation, the working clearance of the bearing is zero or slightly negative, resulting in better bearing performance. Axially, the fit between the locating bearing and related components should be determined based on the specific situation of the floating-end bearing system. The inner ring of the bearing is positioned by the limiting step on the shaft (shaft shoulder) and the bearing retaining ring, while the outer ring is controlled by the fit tolerance between the bearing and bearing housing, the height of the inner and outer covers, and the length of the bearing housing.
(1) When a separable bearing is selected for the floating end, both bearing outer rings adopt an interference-free axial fit.
(2) When a non-separable bearing is selected for the floating end, an appropriate length of axial clearance should be left between the bearing outer ring and the bearing cap, and the fit between the outer ring and the bearing housing should not be overly tight.
(3) When there is no clear fixed end and floating end for the motor, deep groove ball bearings are generally used at both ends, with the outer ring of the locating bearing being fixed axially against the inner cover while leaving a gap against the outer cover, or both outer rings having no axial clearance against the outer cover while leaving a gap against the inner cover.
The above fit relationships are theoretically relatively reasonable. However, the actual bearing configuration should match the motor's operating conditions, including specific parameters such as bearing clearance, heat resistance, precision, and the radial fit between the bearing and bearing housing.
It should be noted that the above analysis is only applicable to horizontally mounted motors. For vertically mounted motors, both the bearing selection and the corresponding fit relationships must have specific requirements.