| View attachment (13) Hello everyone, I need assistance with a problem involving a radial fan experiencing high vibrations at 7.6 orders and its harmonics, with 17 mm/sec on the axial side. The fan has 11 vanes, and the 7.6 orders seem to match with the bearing outer race. However, upon inspection, the bearing outer races appear to be normal, with inner race clearances at 0.3 mm. I am struggling to pinpoint the issue, so any help would be greatly appreciated. Please see the attached New Text Document for more details.
"Upon inspection, 7.6 orders were found to match with the bearing outer race, indicating a potential fault. Even though the outer races appeared normal, there was a fault frequency with 1xSS sidebands, suggesting an outer race fault. But how was the outer race actually checked? Keep in mind that many bearings require destructive disassembly to fully assess the race surface. To avoid getting overwhelmed by data, it's important to focus on the key indicators. - Walt"
Have these spectra been taken both before and after conducting "bearing checks"? Were the bearings replaced or reinstalled during the inspection process? It appears that there may be a defect in the bearings. Best regards, Ali M. Al-Shurafa
Upon inspecting the bearings and alignment, we discovered proper inner clearances without any physical defects on the outer race. These spectrums provide valuable information for ensuring optimal performance and longevity.
We measure bearing clearances using a feeler gauge for both inner and outer components.
After disassembling both the DE and NDE bearings and conducting a thorough physical inspection, we found no defects in the outer race.
Hi there, it's indeed strange that the high vibrations seem to line up with the bearing outer race despite a clean bill of health. From the additional data you provided, one possible culprit might be resonance. It’s known that various system components can resonate at certain speeds. If the rotational speed is closely linked to any of these resonant frequencies, this might be causing the excessive vibration. Try conducting a Modal Analysis to identify any natural frequencies that line up with this 7.6 order frequency; if there's a match, that might just be your culprit. Also, cross-check for misalignment as that could be another potential reason. Good luck!
You aren't too far off with the initial bearing assumption, especially with the vibrations matching 7.6 orders. However, considering the bearing inspections turned out normal, the high vibrations could also be due to Fan Blade Pass Frequency (FBPF). You've mentioned there are 11 fan blades; sometimes the interplay between the spinning blades can lead to such high vibrations. Excessive vibrations could also be a result of aerodynamic interferences or non-uniform air gaps in your fan. One approach could be to try rotation balancing and alignment to manage it. If that doesn't cut, perhaps a structural resonance analysis could shine light on any potential issues. Also, it would be interesting to know the condition of the damper and if it's well tuned or not, as dampers have been known to cause similar symptoms.
It sounds like you're dealing with quite a conundrum. Just to clarify, have you also checked the conditions of your fan's mounting and foundation? Sometimes a high level of vibration can be caused by resonance from inadequate mounting rigidity or foundation. More importantly, the problem could also be due to an imbalance in the fan wheel or a misalignment issue between the fan and the driving motor. If these checks come out clear, I would recommend troubleshooting further on the aerodynamic side including investigating the flow rate and pressure. It might be worth doing a thorough vibration analysis if possible to detect any abnormalities.
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Answer: - The high vibrations could be attributed to issues such as imbalance, misalignment, bearing defects, or resonance within the system.
Answer: - The 7.6 orders matching with the bearing outer race could indicate potential faults in the bearing elements such as inner race clearances or ball defects that are not visually apparent.
Answer: - Troubleshooting steps may involve conducting further analyses such as vibration spectrum analysis, checking for misalignment, inspecting the fan blades for damage, and examining the bearing elements more closely to identify any hidden defects.
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