Reasons for excessive vibration of the motor shaft in axial flow fans
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It has been two years since we started preparing to install this equipment; the motor has been here for two years without being used, nor has it been rotated. Currently, whenever the motor is tested individually, vibration causes an interlock shutdown based on a four-out-of-two principle. Checked now: there’s no problem with the instruments. There is no problem with the gap between the rotor and stator. The bearing is fine. The motor has not yet been grouted. Now, shaft vibration always causes the machine to shut down. Could someone experienced please advise what might be the cause? Could it be due to the following reasons: 1. Excessive shaft vibration caused by lack of grouting? 2. Did the shaft bend due to the motor not having been turned for a long time? 3. Is there a problem with dynamic balance? Or for other reasons, I hope experts can give some advice.
It’s definitely the first one that has a significant impact
The second reason is that, generally, motors without grouting do not exceed the vibration limits even when tested individually. Check in which direction the vibration levels are excessive, whether it’s at one end or both ends, to determine if there is a problem with the tightening force of the footings.
It is necessary to first check the rotor’s dynamic balance. Check the factory documents to see the dynamic balance data.
Without grouting of the foundation, vibration will definitely be high; it’s as if there are no foot bolts to secure everything. I’m not sure what size your axial flow fans are, but generally speaking, a single-stage design should suffice. If it is left in place for too long, the rotor should be rotated periodically to prevent bending of the rotor and jamming of the bearings. Based on your description, the rotor should be dynamically balanced and aligned.
1. Does lack of grouting cause excessive shaft vibration? There are also reasons for the lack of grouting; check the factory data from that time. 2. Could the shaft have bent due to the motor not having been rotated for a long period of time? If the bearing has not been rotated for a long time, there is a high likelihood of bending; it is recommended to conduct a dynamic balance check before making a judgment.
The cause has now been identified; it was a problem with the dynamic balance, and this has been resolved by adding counterweights. By the way, does water cooling on large motors have an impact on vibration?
The quality of water cooling affects the performance of the lubricant, which in turn has an impact on the vibration of the unit!