How Motor Speed Control Impacts Bearing Heat Generation

The heating of motor bearings is somewhat related to the motor’s rotational speed. During the selection of motor bearings, engineering technicians verify the maximum and minimum rotational speeds of the bearings.

The verification of rotational speed takes into account factors such as the contact stress between the bearing rollers and raceways, the centrifugal force under rotational speed, and lubrication considerations. In these considerations, an inappropriate choice can lead to phenomena like motor bearing overheating and excessively high temperatures.

It’s important to note that when considering the upper and lower limits of the motor bearing speed (maximum and minimum speeds), the impact of changing speeds on bearing heating also needs to be taken into account.

The mentioned changing speed conditions include start-up, stop, and acceleration/deceleration. In actual operating conditions, this includes both slow and rapid speed changes, as well as changes in the direction of rotation.

Typically, when a motor changes speed slowly in the same direction, the impact on the bearings is not significant.

First, the condition of frequent startups may involve unidirectional speed changes and rapid shifts in speed.

Second, it encompasses situations where the direction of rotation changes (back-and-forth motion).

The main reason for the speed change of motor bearings affecting their heat generation is due to the impact of speed changes on the formation of the oil film. We know that the formation of the speed within the motor bearing lubricating oil or grease is fundamentally dependent on the speed.

When the speed changes, there might be sliding friction between the bearing rollers and the raceway. Simultaneously, due to rapid fluctuations in speed or changes in direction, the internal lubrication film may fail to form effectively, resulting in direct contact between metal surfaces, leading to heat generation or wear in the bearing.

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In the condition of unidirectional speed change (speed change and frequent startup), if motor bearing overheating occurs, one can check whether the bearing selection is suitable for this condition.

For the case of speed changes, it is recommended to choose bearings with good cage strength, preferably using lighter, softer material cages. This way, during bearing speed changes, the collision between the cage and the bearing rollers can be mitigated, consequently reducing additional damage and heat generation caused by this.

On one hand, anti-wear additives can be selected for the lubricant to reduce friction, heat, and wear caused by sliding friction between the various components inside the bearing when the rotational speed changes.

For oscillating conditions, the bearing type needs to go through an additional verification process. Factors such as the static load of the bearing are considered, not just the rated fatigue life of the bearing.

For oscillating motion bearings, it is essential to select a lubricant with extreme pressure additives to protect the friction surface when the rotation speed changes direction at low speeds.

Upon examining the above, it’s evident that the focus is on lubrication considerations and improvements under unfavorable oil film formation conditions. The primary goal is to form an oil film as much as possible or, in cases where it is truly impossible to form an oil film, to use other measures (such as extreme pressure additives) to prevent direct contact and friction between bearing metals.

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