One area of a manufacturing plant had a high rate of motor replacements. Despite a great deal of expense and effort, the cause eluded discovery for years. Two different motor maintenance shops had done post-mortems on some of these motors. Bearing failure was almost always the failure mode, and both shops recommended laser alignment and vibration testing.
Subsequent alignments performed on deceased motors before removal seldom showed any significant error. Vibration testing was performed quarterly, and the vibration was always within acceptable limits. The motor shops confirmed failures weren’t due to current through the bearings. The cause was ultimately discovered. What might it be?
One afternoon, the mechanical maintenance foreman heard “a heck of a racket”. The plant made large appliances; a unit on a conveyor had just flipped on its side due to operator error. The foreman observed vibration ringing all the way to the drive motor.
The operators e-stopped the line, righted the appliance, and restarted the line (short restart interval). There were additional vibrations during each of these actions. This circus happened about twice a week.
Had these lines been equipped with vibration monitoring, this problem would have been discovered years earlier. But they weren’t. It was pure luck the maintenance foreman was standing in that particular spot when this incident occurred.