Analysis of production line motor failure. CRADA final report for CRADA number Y-1293-0215

The Oak Ridge National Laboratory (ORNL) was approached by a Food Products Manufacturer (FPM) to investigate the rapid failure of motors in a manufacturing facility. It was reported that some motors or their bearings were being replaced after as little as four months of service. The deciding symptom for replacement was always high motor vibration. To protect against unscheduled downtime in the middle of a process run, the FPM`s maintenance team removes a motor from service when its vibration level reaches a conservative threshold of approximately 0.4 inches per second. In their experience, motors left in service after reaching this vibration threshold can fail at any time within the time span of the next process run causing significant losses of raw material and production capacity. A peculiar finding of vibration level trend analysis was that at least one motor exhibited cyclic variations with 24-hour periodicity. The vibration level reached a maximum at about 4:00 a.m., ramped down during the day, and then rose again during the night. Another peculiarity was that most of the vibration energy in the affected motors was at the 120 Hz frequency. Since this is twice the 60 Hz line frequency the FPM suspected the vibration was electrically induced. The electric loads at the FPMs plant remain constant during the five days of a continuous production run. Thus, the periodicity of the vibration observed, with its daily peaking at about four am, suggested the possibility of being driven by changes in the electrical power grid external to the plant