Motor bearings play an integral role in the operation of any electric motor. These elements are often underestimated, yet they are the backbone of motor efficiency and longevity. In short, a motor bearing is a device that allows rotational or linear motion while reducing friction and supporting loads. NSAR manufacture a variety of bearings for electric motors, so speak with our technical experts.

Which bearings are used in electric motors?

Roller bearings, also known as antifriction bearings, are integral to most electric motors. They allow shafts and axles to rotate at incredible speeds while minimizing power loss, and they do this by drastically reducing friction by replacing sliding motion with rolling motion.
Cylindrical roller bearings are an ideal choice for electric motors, especially for applications where there is a possibility of thermal expansion of the main shaft. Since the rings can move freely in the axial direction and have a high load capacity, cylindrical roller bearings are often used in larger motors.

What is the purpose of bearings in electric motors?

Bearings provide support for the weight and forces generated during rotation, preventing components from being subjected to excessive stress. Bearings help maintain precise shaft alignment, ensuring accurate operation in a variety of applications.

Factors to consider for bearings in motor design

During the motor design stage, choosing the right bearing is one of the key factors to ensure motor performance and reliability. The choice of motor bearings not only affects the motor’s operating efficiency, but is also directly related to the motor’s service life and maintenance cost.
First, it is necessary to evaluate the load conditions of the motor under working conditions, including radial load, axial load, and dynamic load. Different types of bearings have different load-bearing capacities and characteristics, which should be matched with the actual load. Different types of bearings have different load-bearing capacities and characteristics, and bearings that match the actual load should be selected.
For example, tapered roller bearings are suitable for larger combined loads, while angular contact ball bearings are mainly used for axial loads.
The operating speed of the motor is another important consideration. Higher speeds place higher demands on the thermal stability and lubrication performance of the bearing. Needle roller bearings and angular contact ball bearings usually have good high-speed performance and are suitable for high-speed motors. For low-speed large motors, more attention should be paid to the load-bearing capacity.
The working environment of the motor in actual applications also has a great impact on the selection of bearings.
If it is a harsh environment such as high temperature, dustproof, and corrosion-resistant, special materials or specially designed bearings are required to ensure good adaptability. Sealed bearings protect from contaminants, while ceramic bearings offer excellent resistance to high temperatures.
The size and internal layout of the motor must also be considered to avoid interference and restrictions between the bearing selection and the motor.
Compact needle roller bearings and deep groove ball bearings offer certain advantages in this regard. At the same time, the bearing assembly tolerances must be met to ensure that the bearing can be accurately installed.
Noise and vibration are important factors that affect motor performance and operating experience. The impact of bearings on motor vibration and operating noise should be fully considered during design, and targeted optimization should be carried out. Generally, the noise of ball bearings is less than that of roller bearings.
Finally, the convenience of bearing maintenance and replacement should also be considered. A removable outer ring or inner ring design is used to facilitate maintenance. At the same time, the lubrication of the bearing should be considered to ensure the overall maintainability of the motor.

Why do motor bearings fail

When bearings operate under repeated load cycles, the material will gradually damage and eventually crack. This damage usually occurs on the rolling elements or inner and outer rings of the bearing. The speed of fatigue damage depends on the size of the load, the material properties of the bearing, and whether there is sufficient lubrication. Over time, these small cracks will expand and eventually lead to bearing failure.
Insufficient lubrication will increase the wear of the bearing and reduce its load-bearing capacity; while excessive lubrication may cause leakage, heat and other problems. In addition, the aging and contamination of the grease will also affect the lubrication effect. Without effective lubrication, the bearing will soon lose its ability to work.
Improper bearing installation will also affect performance. If there are errors or deviations, it will cause problems such as uneven bearing force and excessive preload, accelerating wear and even damage.
If there is severe vibration or impact load during motor operation, it will also pose a great threat to the service life of the bearing. Vibration will cause increased sliding wear inside the bearing, while impact load will directly damage the rolling element and the inner and outer ring raceways.
If there are pollutants such as dust, moisture, and chemical media in the working environment of the motor, once they enter the bearing, they will cause erosion and contamination, quickly reduce its performance and cause failure.
In addition, for some special-purpose motors, if the bearing temperature exceeds the design temperature range, it will also cause various problems. High temperature will cause oxidation and aging of grease, softening and deformation of metal materials, etc., which will reduce the performance of the bearing until it fails.

How bearing size affects motor performance

The bearing size not only determines its load-bearing capacity, but is also closely related to the maximum allowable speed of the motor. Choosing the right size of bearing is crucial to maximize the performance of the motor.
First of all, the bearing size determines its load-bearing capacity. Generally speaking, the larger the diameter and the wider the width of the bearing, the stronger its load-bearing capacity. Because the larger the size, the larger the rolling element raceway curvature radius and the more rolling element action area can be provided.
For example, the basic static load rating of a deep groove ball bearing with a diameter of 55mm is 13.9kN, while that of a deep groove ball bearing with a diameter of 100mm is 44.3kN. Sufficient load-bearing capacity ensures that the bearing will not be overloaded when the motor is running, avoiding premature wear.
Secondly, for the same type of bearing, the larger the size, the lower the maximum allowable speed. This is because the increase in size leads to an increase in the centrifugal force and nonlinear vibration of the rolling element, thereby limiting the maximum speed. Taking the 623 type deep groove ball bearing as an example, when the size is 17×40×12mm, the limit speed is 33000rpm, and when the size increases to 40×90×23mm, the limit speed is reduced to 18000rpm. Moderate size is conducive to bearings meeting the needs of high-speed motors.
Therefore, in the motor design stage, it is particularly important to choose a reasonable bearing size. On the one hand, it is necessary to provide sufficient load-bearing capacity for the bearing according to the actual load of the motor; on the other hand, the working speed of the motor should also be considered, and the size should not be too large to avoid affecting the high-speed performance.