Ball Mill Gearbox Fault Identified Before Failure

A Wi-care™ wireless condition monitoring system was installed to monitor a Ball Mill gearbox and associated 1MW electrical drive that were suspected to be faulty at a well-established Cement Plant operating at full capacity.

The customer requested technical support after a suspected increase in the vibration level of the equipment. A Wi-care™ wireless condition monitoring system was installed to enable in-depth and concise monitoring and diagnosis of the vibration on the complete assembly.

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SOLUTION

The Wi-care™ system was set up on the gearbox and the electrical drive in minutes using magnetic locators to cover classical vibration directions, vertical, horizontal and axial planes. Note on the right side of the equipment (pictured above) the Wi-care™ speed sensor directly measuring with a key-phasor on the shaft.

Standard spectrum collected via Wi-care™ on the vertical axis. Display in speed units. The dominant frequency appears at 373.9Hz and it's harmonics.

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When zooming in on 373.9Hz appears modulation at 5Hz. The amplitude is close  to 4mm/s RMS.

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Following on from inspection of the drawings and data sheets, we can find the gearbox specifications and calculate theoretical fault frequencies.

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RESULTS

Calculated gear mesh frequency of 373.71Hz and it's harmonics match the measured frequency of 373.9Hz. Detected 5Hz modulation is linked to a ring defect (5.01 calculated). Amplitude trend indicates a 100% growth over a few days.

Based on recommendations via Wi-care™ measurements, the decision was taken by the customer to initiate maintenance inspection. The root cause of the gear defect was excessive looseness in the gear assembly due to structural cracks. The customer was then able to take immediate action to resolve the problem.

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