Maintenance and reworking
Backing bearings in the middle of the roll are subjected to heavier loads than those at the ends of the roll. As the middle bearings wear more than the others, they should be replaced more often.
Because of the design, the shafts of cluster mills at the entry and exit sides are much more heavily loaded than the other shafts. This also leads to increased wear on the backing bearings on the entry and exit shafts. It is therefore recommended that the backing bearings on a heavily loaded shaft should be moved regularly to a less heavily loaded shaft. This strategy pays off as the service life of all the backing bearings will be considerably extended.
As the bearings are subjected to a stationary inner ring load, SKF recommends that the inner ring be turned by 90° after each bearing inspection so that another part of the raceway becomes the loaded zone. The arrows marked on the side faces of the rings (fig. 1) provide a useful indication of the position of the loaded zone.
Unavoidable production disturbances (e.g. rupture of the rolled material), the overrolling of foreign matter or uneven wear will sooner or later result in damage to the outside cylindrical surface of the backing bearings, including indentations, flattened areas and irregularities resulting from cold welding. To prevent such damage from causing premature backing bearing failure, the outside diameter must be reground. For additional information, refer to Remanufacturing and maintenance services.
After reworking, the outer rings must be cleaned, remeasured, marked and reassembled with the appropriate roller complements or roller and cage assemblies and inner rings to form complete backing bearings. It is also necessary to regrade into cross-sectional height groups.
Suitable intervals for bearing exchange, turning the inner rings and regrinding the outer ring outside diameters depend on the operating conditions and must be determined during the mill commissioning phase. Guideline values for appropriate intervals are listed in table 1.