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BE1370 Drag Drum Case Study
Background
The 2 drag drum bearings are grease lubricated double race spherical roller bearings with an approximate outside diameter of 1000mm (36 inch). The bearing application is a reversing, variable speed (0-20 rpm), variable load application. The bearings were monitored utilizing Wear Debris Analysis grease samples were taken every 2 months. The dragline operates approximately 7,200 hour per year, with a downtime cost of approximately $1,200 per hour The expected bearing life was 35,000 hours. |
Detection
The Wear Debris Analysis detected an increase in the ferrous wear within the L/H drag drum bearing, initially in June 1998, approximately 6 months prior to the bearings removal. This early detection allowed the bearing to be replaced in conjunction with other maintenance work. The survey prior to removal showed a heavy density of ferrous wear with particles up 2mm in size. |
Strip Down Inspection
The visual inspection of the L/H drag drum bearing confirmed the bearing was failing. The attached picture shows the deterioration of one of the rolling elements. This rolling element was damaged across approximately 30% of the circumference at one end to 5% of the circumference at the other end. Within this damaged area the rolling element had lost most of the original surface material and the damage in places was up to 3mm deep. The remaining bearing components, rolling elements, cage and inner/outer races showed some signs of surface bruising but were in good serviceable condition the outer race shown is typical of these components. Thus the damage was confined to one rolling element. |
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| Cost Benefit Analysis |
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Production Downtime Saving |
Repair Cost Saving |
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The planned change-out without any secondary damage is typically 24 hours. Unplanned change-out typically 36 to 120 hours dependent on the secondary damage. Thus saving between $14,400 and $129,600 |
In service failure would have resulted in shaft damage and/or bearing housing damage. Typically adding between $30,000 to $80,000 to the repair cost. |
| Mid Range Savings |
$USD 72,000 |
$USD 55,000 |
| ROI |
6000% (based on 1 event per 5 year period) |
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