There are three main types of bearings commonly used in electric motors : rolling bearings, sliding bearings, and oil-impregnated bearings, which support the rotation of the motor's rotating parts. Micro or small motors generally use oil-impregnated bearings, which require fewer accessories and are maintenance-free, simplifying the structure. Sliding bearings are mainly used in medium and large motors, suitable for heavy-duty and impact-resistant applications . Rolling bearings are the most widely used, and the topics discussed below primarily focus on this type of bearing.
How to identify bearings
The designation of a rolling bearing consists of a prefix, a basic designation, and a suffix designation. The prefix is represented by a letter and means a component of a complete bearing set. The basic designation indicates the bearing's type and dimensions, as well as other main characteristics. The suffix designation indicates the bearing's precision and material characteristics.
Bearing suffixes and their meanings
●Examples of the meanings of commonly used internal structure symbols
B – Angular contact ball bearing with a contact angle of 40°
C – Angular contact ball bearing with a contact angle of 15°
AC – Angular contact ball bearing with a contact angle of 25°
E – Enhanced Design
●Examples of codes and meanings for sealing, dustproofing, and external shape changes
●Tolerance grade code
P0 – Dimensional accuracy is P0 grade.
P6 – Dimensional accuracy is P6 grade.
P5 – Dimensional accuracy is P5 grade.
P4 – Dimensional accuracy is P4 level.
P2 – Dimensional accuracy is P2 level.
The precision of rolling bearings increases sequentially from grade 0.
Bearing sealing structure
2Z – Bearings with dust covers are used in bearing configurations where contamination is not severe and there is no risk of moisture, vapor, or other substances coming into contact with the bearing. Dust covers are also used in applications where reducing friction is important due to speed or operating temperature considerations.
2RZ – Bearings with non-contact seals are often used in applications where contamination is not severe. Their application is similar to that of dust covers, but they offer slightly better sealing performance.
2RS – Bearings with contact seals (referred to as seals) are often used in bearing configurations where moderate contamination, moisture or water splashes are unavoidable, or where a long service life without maintenance is required.
Regarding motor bearing clearance
● The radial (axial) clearance of a bearing is the radial (axial) distance that one race moves from one radial (axial) limit position to the opposite limit position relative to another race when the bearing is not under external load. In reality, due to the shape errors of the races and the inconsistencies of the rolling elements, it should be the average value of the radial (axial) displacement in different directions of the races and in different relative positions of the races and rolling elements.
● Clearance is an important technical parameter of bearings, which directly affects the bearing's load distribution, vibration, noise, friction, temperature rise, service life, and the operating accuracy of the machinery.
a) Excessive clearance reduces the bearing's internal load-bearing area, increases contact surface stress, and thus shortens its service life. Excessive clearance also reduces bearing operating accuracy and increases vibration and noise.
b) If the clearance is too small, negative clearance (interference) may occur in actual operation, which will increase frictional heat generation and temperature rise, and then make the effective clearance even smaller or the interference even larger. This vicious cycle will lead to the bearing seizing.
