In the testing and operation of motors, a variety of failures can occur. As a motor engineer, it’s often necessary to address and resolve these issues.
This intricate and complex task involves a broad spectrum of knowledge in mechanics, electrics, and other areas, posing a significant challenge to motor engineers.
A significant portion of motor failures is related to bearings. However, some sensorially bearing-related motor failures are in fact not particularly related. Bearings merely serve as carriers presenting these failures.
Motor failures commonly manifest in bearings because bearings are the only components in a motor that both bear load and rotate themselves. This fact inherently assigns a unique status to bearings among the various components of a motor.
Take the example of an internal rotating general-purpose motor:
| Load-bearing Conditions | Motion Status | |
| Stator | Load-bearing | Non-rotating |
| Rotor | Bearing Load | Whole Rotation, No Internal Relative Movement |
| Bearing | Carrying Load | Internal Relative Movement |
| Carbon Brush | Non-load-bearing | Non-rotating, but in Contact Friction with Rotating Parts |
| Seal | Unburdened | Static, but Experiencing Friction with Rotating Components |
The operation and relative motion of the bearings occur within themselves. Compared to other components, bearings are quite small in size, making them very fragile and sensitive within the structure of the motor.
This characteristic of bearings often results in them exhibiting issues from other components of the motor. In such situations, various “symptoms” like vibrations, noise, and heat can emerge from the bearings.
These “symptoms” serve as an early warning launched by the bearings. If motor engineers heed these warning signs and eliminate them, they can address some issues early on.
Note that resolving these faults is not merely about replacing the bearings. To draw an imperfect analogy: a doctor treats a symptomatic patient rather than simply ending the patient’s life.
Engineers need to identify the root cause of these symptoms. Simply replacing the bearings will not solve the fundamental issue.
This situation can be succinctly expressed as “the symptoms appear in the bearings, but the cause is not within them.”
Here are a few examples to illustrate this situation:
Contaminants Entering Bearings
In such cases, the bearing initially exhibits overheating, which subsequently leads to poor lubrication and surface fatigue. If this continues, the bearing will burn out. Therefore, the method of elimination should be to identify the source of the contaminants and remove them.
Misalignment
This condition results in poor bearing vibration and noise. The bearing itself will not alert the engineer of a misalignment issue; instead, it will only exhibit the aforementioned symptoms. The engineer needs to identify and rectify the misalignment rather than simply assuming that the bearing itself has a problem.
Motor Component Tolerance Exceeding Limits
The most typical signs are spinning and bearing race fracture. These are two extreme conditions; the first implies too loose of a fit, the second too tight. This situation can only be resolved by addressing the fit of the components.
Since bearings are standard parts, their precision is generally more reliable (though substandard bearings are not ruled out). Therefore, this problem must be addressed at its root.
Improper Bearing Configuration
If the bearing configuration is not appropriate when designing the motor, an unsuitable bearing may be selected. In such cases, the bearing will demonstrate issues such as overheating and noise.
Therefore, when I personally conduct motor fault analysis, my first step is always to inquire about the working conditions, then examine the schematic to assess whether the design meets the operational requirements. In this scenario, no matter how often the bearing is replaced, if there is a design discrepancy, it won’t help.
There are many similar examples. For instance, improper lubrication selection, damage during bearing installation, preload issues, shaft current issues…
Of course, some bearing quality issues are not ruled out. However, it’s crucial for motor engineers to understand that while bearings serve as symptom indicators, they are not necessarily the root of the problem.
In addition to inspecting bearing quality, more attention should be paid to surrounding factors. It is only by treating the symptoms appropriately that the problem can be completely eliminated.
