The following factors should be considered when selecting the fixed end of the motor bearing support (referred to as the motor fixed end): (1) the precision control requirements of the driven equipment; (2) the nature of the load driven by the motor; (3) the bearing or bearing combination must be able to withstand a certain axial force. Based on the above three design factors, deep groove ball bearings are more often used as the first choice for the motor fixed end bearing in small and medium-sized motors.
Deep groove ball bearings are the most commonly used rolling bearings. When deep groove ball bearings are used, the motor bearing support system structure is very simple and easy to maintain. Deep groove ball bearings are mainly used to bear radial loads, but when the radial clearance of the bearing is increased, they have the characteristics of angular contact ball bearings and can bear combined radial and axial loads; when the speed is high and thrust ball bearings are not suitable, they can also be used to bear pure axial loads. Compared with other types of bearings with the same specifications and dimensions as deep groove ball bearings, this type of bearing has the advantages of low friction coefficient and high limit speed, but the disadvantages are that it is not impact-resistant and not suitable for bearing heavy loads.
After the deep groove ball bearing is installed on the shaft, the radial fit of the shaft or housing in both directions can be limited within the axial clearance range of the bearing. In the radial direction, the bearing and the shaft adopt an interference fit, and the bearing and the end cover bearing chamber or housing adopt a small interference fit. The ultimate goal of selecting this fit is to ensure that the working clearance of the bearing is zero or slightly negative during the operation of the motor, so that the operating performance of the bearing is better. In the axial direction, the axial fit of the locating bearing and the related parts should be determined in combination with the specific conditions of the floating end bearing system. The inner ring of the bearing is limited by the bearing position limit step (shoulder) on the shaft and the bearing retaining ring, and the outer ring of the bearing is controlled by the fit tolerance of the bearing and the bearing chamber, the height of the stop of the inner and outer covers of the bearing, and the length of the bearing chamber.
(1) When the floating end selects a separable bearing with inner and outer rings, the outer rings of the bearings at both ends are matched with no axial clearance.
(2) When the floating end selects a non-separable bearing, a certain length of axial clearance is left between the outer ring of the bearing and the stop of the bearing cover, and the fit between the outer ring and the bearing chamber should not be too tight.
(3) When the motor does not have a clear positioning end and floating end, deep groove ball bearings are generally used at both ends, and the fit relationship is that the outer ring of the limited bearing is locked with the inner cover and there is a gap between the outer ring and the outer cover in the axial direction; or the outer ring of the bearings at both ends is matched with no axial clearance between the outer ring of the bearing and the bearing cover, and there is a gap between the outer ring and the inner cover in the axial direction.
The above matching relationships are all relatively reasonable relationships analyzed theoretically. The actual bearing configuration should match the operating conditions of the motor, including specific parameters such as clearance, heat resistance, precision, etc. in the motor bearing selection, as well as the radial matching relationship between the bearing and the bearing chamber.
It should be noted that the above analysis is only for horizontally installed motors, while for vertically installed motors, both the selection of bearings and related matching relationships must have specific requirements.