How should we determine whether the motor bearing temperature is abnormal under actual working conditions?
I . Bearing Temperature Standards
Typically, most motor engineers will make judgments according to some corresponding national standards. Some common engine temperature patterns are as follows:
1. GB3215-82 4.4.1: During pump operation, the maximum bearing temperature should not exceed 80°C.
2. JB/T5294-91 3.2.9.3: The increase in bearing temperature shall not exceed the ambient temperature by 40°C, the maximum temperature shall not exceed 80°C.
3. JB/T6439-92 4.3.3: When the pump is operating under specified conditions, the temperature of the outer surface of the inner bearing shall not be more than 20°C above the temperature of the conveyed medium, and the maximum temperature shall not exceed 80°C. The temperature of the outer surface of the outer bearing must not rise more than 40°C above the ambient temperature. The maximum temperature must not exceed 80°C.
4. JB/T7255-94 5.15.3: Bearing operating temperature. The increase in bearing temperature must not exceed the ambient temperature by 35°C, and the maximum temperature must not exceed 75°C.
5. JB/T7743-95 7.16.4: The increase in bearing temperature shall not exceed the ambient temperature by 40°C, and the maximum temperature shall not exceed 80°C.
6. JB/T8644-1997 4.14: The increase in bearing temperature should not exceed the ambient temperature by 35°C, and the maximum temperature should not exceed 80°C.
II. How to determine abnormal bearing temperatures
However, in engineering practice, can we rely solely on these national standards to determine whether they are completely in line with actual conditions?
For example, we often encounter the following issues in practice:
The standards mention 75℃ and 80℃, which one should I choose?
Is it correct to declare a problem as soon as the engine operating temperature exceeds the standard? For example, if the standard is 80℃ and the motor bearing temperature is consistently at 82℃, should we necessarily conclude that there is a problem?
I've seen many articles that directly apply national standards, literally. Many perspectives use a single temperature “red line” as a reference to determine whether bearing temperatures are abnormal. Based on many years of engineering practice, I believe such rigid application is inappropriate.
Firstly, national standards come with certain environmental prerequisites. The actual requirements of the engineering environment differ from those stipulated by national standards.
Second, national standards provide guidance for common situations. Bearing voltage and heat dissipation vary under different circumstances. Add potential bearing design, installation and usage issues to the mix and a number of complications arise in applying these standards.
This is why when I discuss bearing temperatures, I don't directly address the judging criteria. Instead, I start with the basics of bearing temperatures and temperature distribution. Understanding these basic concepts allows for more rational and practical judgments about whether a bearing temperature is abnormal or not.
III. Anomalous bearing temperature is a comprehensive judgment
Therefore, I generally recommend using national standards to evaluate engine bearing temperatures, but it is crucial to make an integrated judgment by considering the temperature difference between the bearing and adjacent components, as well as the temperature distribution of the bearing itself. This approach can help avoid or explain the following problems:
The engine bearing temperature has not exceeded the limit, but a sudden drastic change in temperature causes the bearing to burn out.
The engine bearing temperature has not exceeded the limit, but localized high temperatures lead to bearing burnout.
The motor bearing temperature has exceeded the limit, but the bearing runs stably and smoothly.
In a high temperature environment, the temperature of the engine bearings exceeds the limit, triggering frequent alarms.
The engine is severely overheating, the bearing temperature consistently exceeds the limit, and changing the bearings does not help.
Of course, so far we have only discussed how to identify anomalies. The reasons causing these anomalies will be gradually revealed in the future!
4. Conclusion
In summary, the assessment of engine bearing temperature anomalies should not rigidly adhere to certain national standards. It requires a comprehensive understanding of the basic knowledge of bearing temperature and making decisions based on the surrounding circumstances. At the same time, it is important not to ignore national standards.
