Different types of mining and construction machines, such as excavators, wheel loaders, hydraulic mining shovels, cable shovels, bucket wheels, and draglines commonly employ track systems, as opposed to wheels. In large mining shovels, for example, the undercarriage tracks include a plurality of track pads connected to one another by pins, thereby creating pivoting joints between the adjacent track pads. The track pads are typically cast components, and so are formed as a single, integral cast piece. The track pad includes a ground-engaging portion having a relatively large surface area, which is designed to distribute the weight and forces of the mining shovel or other heavy equipment. The track pad may further include a pair of laterally spaced rail surfaces designed to engage a track roller. Conventional designs of track pads create high hertzian stress, which can cause spalling along the edges of the rail surface, particularly when the machine is inclined and the track pad is angled relative to the roller. The track roller path of machines used in heavy-duty applications are particularly susceptible to wear and spall under relatively modest angles of articulation due to hertzian stresses developed in mating surfaces.
Wear along the surfaces of the links and rollers of track systems may also result from highly abrasive materials encountered during operation. Continued operation of the moving undercarriage structure produces wear along the entire contacting surfaces of the links and rollers. Replacement of the track pads and/or rollers in the track systems of mining and construction machinery can be very costly and labor intensive. Moreover, work stoppages waiting for replacement parts and/or for replacement of the parts themselves may have a direct effect on machine efficiency, and, by extension, related operations.
Attempts have been made to extend the wear life of the undercarriage structure through modification of the roller and/or pad structures. U.S. Pat. No. 5,752,574 to Oertley, for example, discloses an arrangement wherein first and second track guiding rollers are connected to respective parallel roller frame assemblies with axes of rotation of each guide roller in a substantially non-perpendicular relationship to the longitudinally extending centerline, producing a “toe-out” or “toe-in” of the guide rollers. While some improvements have been made in extending the life of guide rollers and track pads, further improvements are desirable, particularly with regard to relatively large machines.