Issues regarding the axial vibration of centrifugal fans
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Hello, experts. I have a question I’d like to ask you. To make it short, my company has 3 coal powder boilers, equipped with fans from well-known manufacturer. The supply fans worked fine during the testing phase in May this year, but after 2 months of operation, they began to exhibit intermittent axial vibration – the vibration started in the afternoon and would improve at some point during the day the following day. The maximum vibration speed reached 9.3 mm/S. We took the following measures: 1. Tightened all bolts. 2. Stop the fan and check the coupling; alignment is fine. 3. The bearing that causes vibration at the drive end was replaced, but vibration persisted after the replacement. 4. Check the impeller for dust accumulation; no dust accumulation was found. 5. A spectral analysis was performed on the vibrating end bearing, which showed vibration peaks at the 1st harmonic, 2nd harmonic, and higher harmonics in the axial direction. The rated speed of the fan is 1480, while the actual maximum speed is 1100. The bearing model is 23034/SKF.
Was the axial alignment of the coupling checked?
Is the fan drive motor constant speed or variable speed? Is the drive motor connected directly to the fan, or is a speed controller used?
My suggestion is to check the levelness of the equipment and open the bearings to see if there is any wear. My vision is blurred; I can’t see the structure clearly. It seems to be a roller bearing structure. Check carefully for any damage. During use after installation, the equipment may experience uneven settlement of the foundation, loose anchor bolts, and issues regarding the strength of the secondary grouting. There are also issues related to the process itself; it is necessary to check whether the inlet and outlet pressures during operation fall within the specified range and whether surge phenomena may occur. Oh, and the clearance of the coupling also needs to be checked according to the instructions. For reference.
For general mechanical equipment vibration, if it is caused by internal issues, it will not improve on its own. Therefore, other causes also need to be checked, such as changes in the medium composition, flow rate, and inlet and outlet pressures, etc. It also includes whether the dampers are automatically controlled, whether the control signals change, and so on.
The fan drive is an inverter-driven motor, with the drive being directly connected to the fan!
Consider the possibility of resonance at a certain rotational speed frequency
Was there any fluctuation in the current during vibration?