Q: How to choose the fixed end bearing of the motor?

A: For the selection of the bearing of the motor support fixed end (referred to as the motor fixed end), the following factors should be considered:

◆Precision control requirements of the driven equipment;

◆The nature of the load driven by the motor;

◆The bearing or bearing combination must be able to withstand a certain axial force.

Combining 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 selected, 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 and bidirectional axial loads. However, when a large radial clearance is selected, deep groove ball bearings also have some characteristics of angular contact ball bearings and can withstand combined radial and axial loads. The advantages of deep groove ball bearings are low friction coefficient, high limit speed, easy installation, and products with a variety of sealing structures. The disadvantages are that they are not impact-resistant and not suitable for bearing heavy loads.

After the deep groove ball bearing is installed on the shaft, the radial position of the shaft or housing in both directions can be limited. Normally, the inner hole of the bearing and the shaft adopt an interference fit, and the outer diameter of the bearing and the end cover bearing chamber or the housing hole adopt a small interference or small clearance fit. The 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. The operating performance of the bearing is better under this zero clearance state. In the axial direction, the axial fit of the locating bearing and the related parts should be determined in combination with the specific situation of the floating end bearing selection. 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 matching 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 axial clearance-free.

(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 stopper 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 stuck with the inner cover and there is a gap with the outer cover in the axial direction; or the outer ring of the bearings at both ends is matched with no axial clearance with the outer cover of the bearing and there is a gap with the inner cover in the axial direction.

The above fit 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, and accuracy in the selection of motor bearings, as well as the radial fit relationship between the bearing and the bearing chamber.

Note: The above analysis is only for horizontally installed motors. For vertically installed motors, specific requirements must be met in terms of bearing selection and related fit relationships.