As part of a larger study to identify factors influencing the practical operating life of wire rope used on large draglines in surface coal mining, field trips to operating surface coal mines were made during late 1975. Wire rope performance information was obtained from personnel at thirteen mine sites west of the Appalachians.
During the field visits, mine operators provided rope life information about their machines. Some of the rope life data consisted of gross averages; other data was in the form of detailed records, including rope construction and manufacturer, cutoff and resocketing periods, end-for-end switching, and downtime for rope change-out.
Some form of data normalizing, however, was considered desirable. One apparently useful factor was the amount of cross-sectional wire performing the hoist or the drag function. A simple expedient was to sum the squares of the nominal rope diameters used in each function and divide that number into the total yards handled until retirement. The performance of draglines with different bucket sizes could then be crudely compared, since the normalizing factor is approximately proportional to the actual cross-sectional area of the wires in the rope (and hence the weight per unit length of rope, or, roughly, the cost