Deep groove ball bearings are the first choice for most standard three-phase induction motors. They can handle the radial loads commonly found in motor applications. When a motor operates under heavy axial loads, high radial loads, or conditions involving shaft misalignment, other bearing types may be required. Depending on the application, these include angular contact ball bearings, cylindrical roller bearings, and spherical roller bearings.
Bearing selection for general operating conditions
More than 90% of standard enclosed three-phase induction motors in China's common Y, YX3, and YE2 series use deep groove ball bearings. The commonly used bearing series are 60, 62, and 63.
For example, motors with frame sizes from Y80 to Y132 commonly use bearings such as 6204, 6205, and 6305. Motors with frame sizes of Y160 and above often use 6306 and 6307 bearings. The actual bearing model depends on the motor frame dimensions and original design configuration.
Deep groove ball bearings are suitable for general industrial applications where radial loads predominate and the operating speed is close to the rated frequency-related speed of the motor. Common speeds at standard mains frequency are 1,500 r/min and 3,000 r/min. These applications generally do not involve additional axial impact loads, allowing deep groove ball bearings to provide the required support and positioning.
Bearing shielding and sealing arrangements must also match the operating environment. Common options include double shields (ZZ type) and double contact rubber seals (2RS type). ZZ bearings generally use metal shields, while 2RS bearings use contact rubber seals. The bearing sealing arrangement alone does not determine whether the complete motor meets the IP54 protection rating. This rating depends on the enclosure design of the entire motor.
Bearing selection for special operating conditions
Motors subjected to axial loads
When a motor must withstand significant axial loads, a standard deep groove ball bearing may not provide sufficient capacity for the application. Examples include drive motors connected to pulleys or sprockets, as well as fan motors subjected to substantial axial thrust during operation.
Angular contact ball bearings are an option for these applications. A single-row angular contact ball bearing primarily carries axial loads in one direction. Two bearings are commonly mounted as a pair, using either a back-to-back or face-to-face arrangement. This configuration can accommodate combined radial loads and axial loads in both directions.
Some heavy-duty Y-series motors use 73 series angular contact ball bearings.
Motors subjected to heavy radial loads
Motors used in equipment such as crushers may experience high radial loads and impact loading during operation. When the radial load exceeds 20% of the rated load capacity of a deep groove ball bearing, cylindrical roller bearings can be considered.
Cylindrical roller bearings have a higher radial load capacity and are suitable for motors operating under heavy radial loads. However, their permissible operating speed must be checked against the specific bearing model, dimensions, and lubrication conditions. It is not accurate to assume that all cylindrical roller bearings have higher limiting speeds than deep groove ball bearings.
Their axial load capacity also depends on the flange design. Some common configurations are intended primarily for radial loads and require additional bearing support for axial positioning. The bearing arrangement should therefore be selected according to the specific design.
Motors with shaft alignment deviations
When a motor has some shaft alignment deviation after installation, or its bearing housing has undergone slight deformation, self-aligning ball bearings or spherical roller bearings may be considered.
Both types can accommodate a certain degree of shaft misalignment within their allowable limits. Spherical roller bearings have a higher load capacity and are suitable for large, low-speed, heavy-duty motors, such as those used in high-power rolling mills.
However, the self-aligning capability of a bearing does not eliminate the need for proper installation alignment. The permissible misalignment must still be checked against the bearing specifications and equipment requirements.
Bearing selection considerations for three-phase induction motors
Check the motor frame size and rated speed
Bearing selection must match the motor frame size, shaft diameter, and rated speed. For high-speed motors operating above 3,000 r/min, the appropriate radial internal clearance must be determined according to the bearing model, shaft and housing fits, operating temperature, and lubrication conditions. A smaller clearance should not be selected solely because of higher rotational speed. Insufficient clearance can increase friction and operating temperature.
Select the sealing arrangement according to the environment
Outdoor, dusty, and humid environments require appropriate protection against dust and moisture. ZZ shields and 2RS contact seals have different designs and sealing performance. The choice should account for dust, moisture, and operating speed. Open bearings can be considered for clean and dry workshop environments.
Check the original bearing specification before replacement
When replacing motor bearings, give priority to the original bearing model specified by the motor manufacturer. Bearings with the same bore and outside diameters may still have different internal designs and specifications, which can affect load capacity and operating performance. Substituting bearings based only on mounting dimensions may result in an unsuitable bearing arrangement.
Custom machining of motor and transmission components
Motor bearing selection and installation also involve dimensional requirements for shaft diameters, shaft shoulders, bearing housings, and related transmission components. When standard parts cannot meet specific structural or dimensional requirements, we provide precision machining based on customer-supplied drawings. Both single-piece and small-batch orders are supported.
Hansheng Automation machines shafts, bearing support components, and other non-standard mechanical parts according to customer drawings. Our machining services also cover several other industries, including yacht structural components, RC racing car parts, tobacco packaging machinery components, and filling machinery parts. We manufacture these components according to the design requirements of different equipment applications.
