Stress wave analysis increases service life of critical mining equipment
A major UK mining company was understandably concerned when a vital piece of capital equipment – the roadheader cutter gear case – appeared to be failing at less than half its predicted life span.
Whilst failure was detectable at the input to the second motion shaft of the gear case, it was not apparent where the root cause of the problem was located. PCMS were asked to mount an investigation and report back to senior management with a solution.
The ChallengeDirect access to the gearbox was impractical as during operations the gearbox was covered with a cutting mat that is used to extract the roadway mineral.
The SolutionPCMS undertook a programme of stress wave analysis to detect component fatigue and wear. Accelerometers were embedded onto the second motion shaft and cabled back to a position where data could be safely collected whilst in operation. The following diagram shows the position of the embedded sensors.
A bearing problem on the left hand side of the second motion shaft support bearing was identified. There was also indication of an alignment issue between the first and second motion shafts. The unit was removed from service and stripped down to display spalling on the second motion support bearing, caused by uneven loading. Investigation into the gear alignment revealed that the casing bores, which supported the second motion shaft, were slightly offset.
The ResultsOn the basis of these findings, the gearbox housing was redesigned from a single gearbox unit to three separate units – which enabled the bore alignment machining to be undertaken using specialised equipment, ensuring a perfect alignment finish. Since the newly designed gear cases were put back into service, premature failures have been eliminated and units are already achieving service lives well in excess of the original predictions, therefor reducing costly downtime and postponing capital expenditure on replacements.
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