The Essential Guide to Lubricating Motor Bearings: Best Practices and Tips

Two key considerations when lubricating motor bearings are:

  • Aim not to mix different greases when adding oil to motor bearings.
  • It’s preferable to lubricate the bearings at lower speeds, or ensure adequate grease distribution after applying the lubricant.

In addition to these, there are several other factors to pay attention to:

Amount of Lubricant Added for Motor Bearing Replenishment

Generally, the grease volume added for lubrication replenishment in a horizontal internal rotor motor should be:

For bearings without an intermediate oil hole:

G = 0.005BD

Here, D is the outer diameter of the bearing, B is the width of the bearing, and the units are in millimeters. These two pieces of data can be obtained from the bearing catalog. The unit for G is grams.

For bearings with an intermediate oil hole:

G = 0.002BD

The units in this formula are the same as the previous one.

For continuous grease injection equipment, it is often necessary to set the appropriate grease injection rate. Generally, this information can be obtained from the lubrication equipment manufacturer.

If this data cannot be acquired, you can refer to the results calculated from the formulas above to get the lubrication replenishment volume, and then set the grease injection rate to add this volume of lubricant to the bearing within the lubrication replenishment time interval.

Injecting grease too quickly can lead to an excess of lubricant inside the bearing, potentially causing high temperature issues among others. Injecting grease too slowly can result in inadequate lubrication. Therefore, it’s important to choose an appropriate injection rate.

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“Same-Temperature” Operation During Lubrication

The term “same-temperature” operation is something I coined myself and is especially necessary in the Northern winters for reasons outlined below:

When a motor is operating, the temperature of its bearings should be close to that of the motor end cover, influenced by the motor’s heat source, which makes this temperature higher than the ambient temperature.

In the North, during winter, the ambient temperature can often drop to zero or even lower. If the lubricant is stored at room temperature, its temperature will be the same as that of the room. At this time, the grease in the motor bearings operates at working temperature.

From what we know about grease, even the same type can have different viscosities at different temperatures. If two greases with different viscosities are mixed, it will undoubtedly affect the lubrication performance. (To make an imperfect analogy, the lubrication properties of the two temperatures of grease are different, akin to mixing two lubricants with different lubrication performances, which is obviously unreasonable.)

Therefore, when supplementing the lubrication of motor bearings in the North during winter, the grease can be placed indoors for a while. Doing so ensures that the temperature of the new grease is as close as possible to that of the working grease, and adding it at this point will not affect the lubrication performance of the grease inside the bearing.

On another note, I do not recommend manually heating the grease in the factory. This is because heating grease carries certain risks: uneven heating can cause the grease to denature and also introduce safety risks. Hence, simply storing the grease at room temperature can greatly alleviate the issues caused by differing temperatures.

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Readers can check their own lubrication records to see if, after adding grease in the winter, the bearing temperature unreasonably rises and then drops a few hours later, returning to normal afterward?

This situation becomes more frequent as the temperature drops.

If such problems do occur, it’s time to pay attention to the “same-temperature” operation.

Other Points to Consider

When perusing general resources, at least the following points will be raised during the lubrication process:

1. Pay attention to environmental cleanliness.

2. Ensure the cleanliness and hygiene of the lubrication equipment.

Hygiene is the most crucial aspect of lubrication. The reason I’ve placed this most critical point last is that it has been mentioned in many articles and is now a universally acknowledged point of caution.

The application of bearings is all about the details; any minor misstep in the process can potentially lead to premature bearing failure.

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