Root cause and fatigue analysis of traction winch failures

This paper describes the investigation, analysis and proposed solutions to the problem of a regularly failing traction winch that resulted in significant and unacceptable downtime of crucial production machines. The winch's wire ropes fail on average about once a month. The reliability of the machine investigated is critical to the success of the business. A Root Cause Analysis (RCA) of the failing machine was conducted which identified the physical, human and latent root causes of the traction winch failures. The average number of cycles to failure for the wire ropes was only 1088 cycles (equating to approximately 24 days of service). Physical root causes were identified through theoretical fatigue analysis and visual inspection and scanning electron microscopy (SEM) to examine the fracture surface of the failed wire ropes. The analysis indicated that there were extensive bending fatigue cracks leading to total rope failure. It was concluded that the leading physical root cause of the premature failure of the traction winch was the bending fatigue failure in the wire rope caused by the specification of an undersized sheave and drum in the traction winch design