Accumulation of dust and dirt on all rotor blades lead to a 1x vibration peak in the velocity spectrum. The sine waveform and phase analysis confirmed the results. A static unbalance was the reason for the increased vibration.
The balancing procedure was successfully performed on-site during the next shutdown phase of the plant. VIBXPERT II and OMNITREND software were used for the balancing runs. The static unbalance requires only a one-plane balancing procedure which was ideal for those fans. The accelerometers were attached to the non-drive end (NDE) bearing in horizontal direction. VIBXPERT offers a “second plane control feature” where the second accelerometer contorls any negative influence on the NDE bearing during trim runs. This ensures that the vibration on both bearing will be equally reduced and balanced. The target quality grade of 6.3 according DIN ISO 1940 was easily reached.
The plant went back online a few days later and the customer was extremely satisfied with the result of this service, who later stated:
“In the last 6 years, I have never seen those fans run so smooth.”
Special thanks to PRUEFTECHNIK Canada for sharing this successful story with us.