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BE1570W Dragline Lower Swing Bearing Case Study

Background
The Lower Swing Bearing is located approximately 6 feet below the swing gearcase adjacent to the swing pinion which engages the swing rack. The bearing reacts the radial loads associated with the swinging of the dragline. The bearing is mounted on a sleeve to ensure no vertical loads are reacted out by the bearing and the surface between the sleeve and swing shaft is lubricated so the sleeve can rotate independently of the shaft. The Lower Swing Bearing is surveyed on an 8-week cycle utilizing WDA Grease Analysis as the monitoring method. The Lower Swing Bearing is a low speed bearing and WDA Grease Analysis is the most cost effective method of monitoring the bearing condition. The cost of production downtime on this dragline is $3,600 per hour and the dragline operates 7000 hours per year.
Detection

Grease was obtained from the bearing and the analysis revealed an extreme density of large ferrous abnormal wear, mainly comprising laminar wear particles, and a medium density of abnormal brass laminar wear particles evident. The figure on the right shows the grease sample at 100 times magnification and illustrates the extent and appearance of the ferrous wear within the grease sample. The largest wear particle within the grease sample is 4000 microns with an average size of 400 microns.

Change-out of the bearing was recommended.
Strip Down Inspection
The bearing was replaced 2 months after sampling and severe spalling of all bearing surfaces was confirmed by inspection. The rolling elements from the bearing are shown in the figure on the right. When the rolling elements are in this condition, the motion of the element against the brass cage results in the generation of brass particles, hence the reason for the cupric particles evident in the grease sample.
Cost Benefit Analysis
  Production Downtime Saving Repair Cost Saving
  The planned change out without any secondary damage is typically 24 hours and an unplanned change out is 48 to 60 hours depending on the secondary damage. Thus savings in the range $86,400 to $172,800. In service failure could have resulted in a combination of swing pinion, swing rack and/or swing bearing housing structural damage.
Mid Range Savings $USD 129,600 $USD 40,000
ROI 7,455% (based on 1 incident every 6 years)