There will be various faults in the process of testing and using the motor. As an electrical engineer, it is often necessary to deal with and resolve these faults. This is a delicate and complicated job, which involves a very wide range of mechanical and electrical knowledge, and is a severe test for electrical engineers.

 A large proportion of motor failures are bearing related. However, there are also motor failures that appear to be bearing-related, but are actually less relevant. The bearing only acts as a carrier to present this fault.

Motor failures often show up in bearings because the bearing is the only part of the motor that both carries load and rotates on its own. This point is destined that the bearing has a special position in the various parts of the motor. Take the internal rotation ordinary motor as an example:

And the operation and relative motion of the bearing are carried out inside itself. Compared with other components, the volume of the bearing is very small, so the bearing is a very fragile and sensitive part of the motor structure in general.

It is also because of this characteristic of the bearing that many problems with other parts of the motor will also be reflected in the bearing. In this case, various "symptoms" will appear in the bearing, such as vibration, noise, heat generation, etc. These "symptoms" of the bearings are warnings issued by the bearings to the outside world in the early stage. If the electrical engineer notices this warning message and eliminates it, some problems will be dealt with in the early stage.

Please note that the troubleshooting of this fault is not simply replacing the bearing. To give an inappropriate example: doctors should treat symptomatic people, not simply kill patients. Engineers need to find the cause of this symptom. Otherwise, simply replacing the bearing will not solve the fundamental problem.

The simple expression of this situation is "the symptoms are bearing, but the cause is not".

Here are a few examples to illustrate this situation:

Contaminants enter the bearing

In this case, the bearing will generate heat initially, and then poor lubrication will cause surface fatigue. If it continues to develop, the bearing will burn out. Therefore, the method of exclusion should be to find the source of pollutants and eliminate them.

Misalignment

In this case, it will be manifested as poor vibration and noise of the bearing. The bearing itself will not tell the engineer that there is a misalignment, it will only exhibit the above symptoms. Engineers need to find out the misalignment and eliminate it, instead of simply judging that there is a problem with the bearing itself.

Motor parts tolerance out of tolerance

The most typical is the running circle and the fracture of the bearing ring. These are two extreme cases, the first case is a fit that is too loose, the second case is a fit that is too tight. This kind of symptom can only solve the problem of parts matching. The bearing is used as a standard part, and the general accuracy is more reliable (not excluding unqualified bearings). Therefore, this problem should be ruled out for the root cause.

Improper bearing arrangement

When designing the motor, the configuration of the bearings is not appropriate, resulting in the selection of inappropriate bearings. In this case, the bearing will reflect the problem of heat and noise. Therefore, I personally used to inquire about the working conditions as the first step when analyzing motor faults, and then look at the drawings to compare whether the design meets the requirements of the working conditions. In this case, if there is a deviation in design considerations, no matter how to replace the bearing, it will not work.

There are many similar examples. For example, improper lubrication selection, damage in bearing installation, preload problems, shaft current problems...

Of course, some bearing quality problems cannot be ruled out. However, electrical engineers must be aware that bearings, as a symptom response component, are not necessarily the root cause of the disease. They should pay more attention to surrounding factors while checking the quality of bearings. Only by prescribing the right medicine can the disease be cured.

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