Abstract: The service life of electric motor bearings is closely related to the selected bearing configuration. Reasonable selection of bearing configuration can improve the service life of bearings and thus enhance the service life of electric motors. Use examples of electric motors in the current market to illustrate how to choose and use rolling bearings correctly.

Keywords: Rolling bearings; Bearing configuration; choice

Introduction

The bearings of an electric motor (hereinafter referred to as rolling bearings) are important supporting components between the stator and rotor, used to ensure uniform air gap and load transmission in the motor. The correct selection and application of bearings is an important part of electric motor design. According to the different characteristics of electric motors, such as their own structure, load type, working speed, bearing life, etc., the selection of bearings for electric motors also varies. Only by selecting bearings appropriately and reasonably can the inherent characteristics of bearings be fully utilized to ensure the reliable operation of the motor.

1. Bearing configuration

In order to better choose bearing configurations, it is necessary to understand the inherent characteristics of the bearings. There are many types of bearings, and here we will provide a detailed explanation of the two commonly used types of bearings: deep groove ball bearings and cylindrical roller bearings. If certain special bearings need to be applied, relevant information must be searched to understand their characteristics.

The rolling element of a deep groove ball bearing is in point contact with the inner and outer rings of the bearing. It has the advantages of quiet operation, low cost, being able to bear a certain range of radial and axial loads, low friction, low heat generation, and high-speed operation; Its disadvantage is that it cannot withstand impact loads or radial and axial heavy loads.

The rolling element of a cylindrical roller bearing is in line contact with the inner and outer rings of the bearing. It has the advantage of being able to withstand radial heavy loads and is widely used in large and medium-sized electric motors as well as large, medium, and small electric motors with belt conveyors as the load; Its disadvantages are lower rated speed and higher noise compared to deep groove ball bearings.

1.1 Typical Bearing Configuration

The bearing configuration of the electric motor is mainly related to the installation method and load size of the motor itself. Here, only some typical bearing configurations of the horizontal IMB3 will be analyzed and explained.

(1) Deep groove ball bearing+deep groove ball bearing configuration:

Both the driving end and non driving end of the electric motor use deep groove ball bearings, with the driving end being the positioning end and the non driving end bearing having elastic preloading, as shown in Figure 1. The advantages are high speed, low noise, and stable operation; The disadvantage is that it cannot withstand radial heavy loads, such as belt conveyors. This configuration is suitable for light load of small and medium-sized motors.

Figure 1 Configuration of Deep Groove Ball Bearings and Deep Groove Ball Bearings

(2) Deep groove ball bearing+cylindrical roller bearing configuration:

The motor drive end adopts cylindrical roller bearings, and the non drive end adopts deep groove ball bearings for positioning, as shown in Figure 2. The advantage is that the shaft extension end can withstand heavy loads, and the motor does not require axial preloading or reserved axial thermal expansion clearance of the rotor; The disadvantage is that the noise is slightly higher and the allowable speed is slightly lower than that of two deep groove ball bearings, and the load must accept axial expansion. This configuration is suitable for large and medium-sized motors, with heavy loads at the drive end.

Figure 2 Configuration of deep groove ball bearings and cylindrical roller bearings

(3) Deep groove ball bearing+cylindrical roller bearing+cylindrical roller bearing configuration:

The motor drive end adopts deep groove ball bearings and cylindrical roller bearings. The deep groove ball bearings are in radial clearance fit with the bearing chamber, and an O-ring is used to prevent the outer ring of the bearing from rotating. The non drive end adopts cylindrical roller bearings, as shown in Figure 3. The advantage is that the shaft extension end can withstand certain axial and radial heavy loads, without the need for preloading in the axial direction, and the non driving end can accept the thermal expansion of the motor rotor. The disadvantage is that the motor has high noise and a higher probability of bearing damage (compared to the two bearing configuration). This configuration is mostly used for large motors.

Figure 3 Configuration of deep groove ball bearing+cylindrical roller bearing+cylindrical roller bearing

1.2 Current bearing configuration of electric motors on the market

(1) Siemens high and low voltage motor bearing configuration: The high voltage motor adopts a three bearing configuration (with light series bearings), as shown in Figure 4. The low-voltage motor adopts a two bearing configuration, as shown in Figure 5.

(a) Drive end (b) Non drive end

Figure 4 Siemens High Voltage Motor Bearing Configuration

(a) Drive end (b) Non drive end

Figure 5 Siemens Low Voltage Motor Bearing Configuration

(2) ABB's motor bearing configuration: Low voltage frame numbers H355 to H500 all adopt a two bearing configuration (2 medium series deep groove ball bearings), as shown in Figure 6. The high-voltage large motor adopts a three bearing configuration, as shown in Figure 7.

(a) Drive end (b) Non drive end

Figure 6 ABB High Voltage H355~H500 Bearing Configuration

(a) Drive end (b) Non drive end

Figure 7 Bearing Configuration for High Voltage Large Motors

(3) Some high-voltage motors in domestic motor factories adopt a three bearing configuration, and the deep groove ball bearing at the shaft extension end is a light series bearing, the same as Siemens, as shown in Figure 8.

(a) Drive end (b) Non drive end

Figure 8: Bearing configuration of high-voltage motors in some domestic motor factories

2. Conclusion

In summary, when selecting a bearing configuration for an electric motor, the combination of deep groove ball bearings and deep groove ball bearings should be given priority when all loads permit. If the configuration of deep groove ball bearing and cylindrical roller bearing cannot meet the radial load at the driving end, the preferred configuration should be deep groove ball bearing and cylindrical roller bearing, followed by deep groove ball bearing+cylindrical roller bearing+cylindrical roller bearing configuration or other bearing configurations.

2024 May 4th Week JFZ Product Recommendation:

Deep groove ball bearing 6200 Series:

6200 series bearing is deep groove ball bearing, mainly used in centrifuges, half-shaft bolts, CNC punches, cylindrical gear reducers, electric vehicle motors, pressure reducing valves, CNC cutting, electrodialysis equipment, electrical instruments, and automotive lights etc.

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