BACKGROUND/FINDINGS: This fan is part of a Predictive Maintenance Program which utilizes monthly Spectral Vibration Analysis. A trend of the fan outboard bearing was showing a steady increase in vibration amplitude at a frequency which matched the running speed of the fan. This is a sign of fan imbalance.
SOLUTION: A fan balance job was scheduled 2 weeks in advance, on a day when the line was scheduled to be down for other maintenance.
During the inspection of the fan it was found to have a buildup of product and some slight wear. It was decided that the fan wear was acceptable and that the fan should be trim balanced after cleaning.
The fan was balanced and brought back down to below acceptable vibration levels.
CONCLUSION: Catastrophic failure was avoided. The imbalance was identified and eliminated during a scheduled downtime.
Fans will occasionally become out-of-balance. When the imbalance goes undetected it can become the root cause of other failures such as looseness, bearing faults, structural damage, etc.
Trending is the key. Once again the PdM Program was justified.
