Current Practice in Temperature Monitoring for Bearing Maintenance
Bearing temperature monitoring is a prevalent method of bearing health monitoring. Typically, temperature sensors are installed to collect the bearing’s temperature data.
During actual monitoring, a threshold value for bearing temperature is set according to relevant standards or regulations. An alert is issued and an inspection ensues when the bearing temperature reaches this alarm value, indicating an “overheating” state to the engineer.
The most common response to bearing overheating by onsite engineering technicians is to “add oil”. Sometimes this lowers the bearing temperature, sometimes it doesn’t. Occasionally, further cooling measures such as installing fans are implemented for the bearing.
It’s not difficult to see that this approach is a somewhat rough method of managing bearing health. Nevertheless, many details still demand attention.
Issues with Fixed Thresholds in Bearing Temperature Monitoring
Setting an alarm value for bearing temperature seems straightforward, but fundamentally, it’s a bit complex. For instance, general alarm values are often fixed thresholds, or a few segmented thresholds, but the actual temperature variation of the motor may not be uniform.
For starting and stopping the motor, the bearing temperature is typically a dynamic process.
The image illustrates the temperature data for a motor over the course of a month. It is clear from the graph that the bearing temperature is not linear, but rather fluctuates with the motor’s start and stop cycles.
In such a scenario, if we were to manage the system using a fixed threshold warning method, the bearing temperatures would all appear normal. It’s fair to say that monitoring the motor bearing with a fixed threshold approach is a relatively rough method. It only provides a general sense of the bearing temperature.
For instance, a bearing temperature of 60℃ in a given situation may appear normal when looked at in isolation. We might deem it an acceptable temperature just using a threshold for comparison.
However, if we consider that the temperature rose from 20℃ to 60℃ within ten minutes, the conclusion might not be consistent with the previous one. It’s easy to see that a standalone threshold method cannot monitor whether the trend of the motor bearing temperature is normal.
Upon closer inspection of the graph, one can see that both the upper and lower limits of the motor bearing temperature are not linear.
If the upper limit of the motor bearing temperature is observed, motor engineers can easily conclude that this upper limit is related to the motor current. But why does the lower limit fluctuate after the motor stops? In fact, this is influenced by room temperature. These features cannot be found for reference in a fixed threshold system.
Those who frequently perform daily maintenance on motor bearings can observe that each time new lubricating grease is added to the motor bearings, a temperature fluctuation occurs. Experienced engineers pay attention to this temperature fluctuation after grease is added. However, it’s hard to find a basis for this fluctuation within a fixed threshold temperature detection method.
To summarize, a fixed threshold warning method for motor bearing temperature cannot accommodate the following factors:
1. Changes in the trend of motor bearing temperature
2. Variations in the working environment of the motor bearing
3. Changes in the relationship between the motor bearing and the motor load
4. Temperature fluctuations after the addition of grease.
The factors mentioned above may all be indicative of some abnormality in the bearings. Thus, the monitoring of motor bearing temperatures not only involves setting thresholds for alarms and management, but also requires attention to changes and fluctuations in motor bearing temperatures due to other influences.
With the advancement of data technology, more comprehensive temperature monitoring data analysis methods can be employed, taking into account all the factors mentioned above to yield more accurate motor bearing temperature monitoring results.
However, in environments without data analysis tools, engineers need to investigate the possibilities of these factors in the current state of motor bearing temperature, aiding in the troubleshooting of abnormal motor bearing temperature issues.
