How to choose the fixed end bearing of the motor?

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:

1. The precision control requirements of the driven equipment;

2. The load properties of the motor towing;

3. 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 two directions can be limited. Under normal circumstances, 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 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 fit tolerance of the bearing and the bearing chamber, the height of the inner and outer cover stop of the bearing, and the length of the bearing chamber.

(1) When the floating end selects a separable inner and outer ring bearing, the outer rings of the bearings at both ends adopt an axial clearance-free fit.

(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 is not easy to 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 outer ring of the limit bearing is locked with the inner cover and there is a gap between the outer cover and the outer cover in the axial direction; or the outer ring of the bearing at both ends has no gap between the outer cover and the bearing in the axial direction, and there is a gap between the inner cover and the outer cover in the axial direction.

The above matching relationships are 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 matching relationship between the bearing and the bearing chamber.

Note: The above analysis is only for horizontally installed motors. For vertically installed motors, there must be specific requirements for both the selection of bearings and related matching relationships.