Why were two of the rear bearings of a multi-stage blower burned out simultaneously?
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Our company has a multi-stage blower of model D90-71; recently, another one was added because the airflow output of one of the blowers was insufficient. Less than two hours after it was started, the bearing began to smoke; an emergency shutdown was carried out and it was found that the bearing had burned out. This bearing had been replaced not long ago, so it hadn’t been in use for very long. It was lubricated with bearing grease, there was no lack of oil, and the cooling water was also flowing properly, with no interruptions. Inspection revealed that one impeller and one balance drum were damaged. After replacing the impeller, balance drum, and bearings, a trial run was conducted; it was operated at a load that did not meet the requirements for 2 hours, during which the temperature and vibration levels were normal, after which it was shut down. The next day, just 1 hour after being put into operation under load, the motor stopped running. Upon inspection, it was found that the rear bearing had burned out again; the loss this time was significant – the entire rotor set was essentially ruined. Please help analyze the reasons
1. Check whether the installation quality of the blower is satisfactory, including its levelness as well as the coaxiality between the motor and the blower； 2. Has the rotor been subjected to dynamic balance testing, and is there a test report? ； 3. Is the motor power compatible with that of the blower? 4. From a design perspective, is the design reasonable?
Are the two fans operated simultaneously? If it is necessary to adjust the operating conditions of the two fans to be the same, any difference will lead to changes in axial thrust, which in turn can cause the bearings to overheat and get damaged
Why burn the bearings? The rear bearing does not bear axial forces
This analysis requires a lot of data. First, what is the clearance between the bearing and the shaft? What are the top clearance and side clearance between the bearing cover and the bearing? If it’s not a newly installed machine, besides the installation data, what should be the bearing clearance setting? Are there other data such as vibration levels and temperature during the machine’s operation? These days, installation is often done based on experience, but it’s hard to say whether that experience meets the standards or not. If there were no problems in the past, it might be because attention was paid to all the details of the installation; those gaps are usually just a few dozen microns, or even just a few microns! Bearings can burn out, and there are differences between the inner ring, outer ring, and cage
Is the bearing installation in compliance with standards? Is the axial play of the shaft within the standard range of 0.1–0.2 mm? It must not be too large
You can check the rotor; there should be no problem with the motor. I think the issue lies in your manufacturing process during filling, as there are probably no problems with the unit itself. A sudden shutdown of the machine should not cause wear to the main bearings. Your oil pump should not stop working either; you should check the changes in vibration and displacement of the main unit when it is under full load.
There should be no problem with the fan itself; it works fine when not under load. It’s possible that changes occur when both fans operate simultaneously, so it’s advisable to test it while it is under load