The Design of Rolling Bearing Mountings

110 Straightening rolls of a rail straightenerRails for railway track systems or for craneways are hotrolled in rolling mills. After rolling the rails cool downon cooling beds but not uniformly, resulting in warping.Afterwards they have to be straightened in railstraighteners between horizontal and vertical rolls.The straightening plant consists of two machines oneinstalled behind the other. In the first machine the railsrun through horizontally arranged rolls, in the secondmachine through vertically arranged rolls. Thus therails are straightened in both planes after having passedthrough the two machines.Each machine features nine straightening rolls, four ofwhich are being driven. The straightening rolls withdiameters of 600...1,200 mm form an overhung arrangementin order to allow easy replacement.Demands on the bearing assemblyThe mounting space for the bearings is dictated by thedistance of the straightening rolls. In this mountingspace bearings are accommodated which have such ahigh load carrying capacity as to allow for reasonablerunning times.The bearing assembly for the straightening rolls musthave maximum rigidity since this determines the accuracyof the rolled stock.The roll position must be adjustable to the position ofthe rolled stock. For this reason the bearing assemblyhad to be designed such as to allow for a change of theposition of the straightening rolls by ±50 mm in theaxial direction.Horizontal straightening rollsThe maximum rolling force at the horizontal rolls is4,200 kN. Depending on the type of rolled stock,thrust loads of up to 2,000 kN have to be accommodated.Speeds range from two to 60 min –1 .Double-row cylindrical roller bearings have been providedto accommodate the radial forces and because oftheir high load carrying capacity. The higher loadedcylindrical roller bearing, which is situated directlybeside the roll, was especially developed for supportingthe straightening rolls (dimensions 530 x 780 x 285/475 mm). The less loaded cylindrical roller bearing hasthe dimensions 300 x 460 x 180 mm.The cylindrical roller bearings are fitted with boredrollers which are evenly spaced by pins and cage sidewashers.As this design allows the distance between the rollersto be indefinitely small, the largest possible number ofrollers can be fitted and, adapted to the mountingspace, the highest possible load carrying capacity canbe obtained for the bearing.The thrust loads are accommodated by two sphericalroller thrust bearings FAG 29448E.MB (dimensions240 x 440 x 122 mm). They are spring-adjusted.When positioning the straightening rolls, the bearingsmust be able to compensate for axial displacements byup to ±50 mm. This is made possible by providing anextended inner ring for the cylindrical roller bearinglocated beside the straightening roll. The inner ringwidth is such that the lips of the two seals always slidesafely on the inner ring even with maximum axial displacement.The second cylindrical roller bearing is seated, togetherwith the two spherical roller thrust bearings, in asleeve which is axially displaceable within the hollowcylinder. The position of the straightening rolls relativeto the rolled stock is adjusted by means of a ball screw.Vertical straightening rollsThe vertical straightening roll bearing arrangement isin principle identical to that of the horizontal straighteningrolls. Due to the lower straightening loads, however,smaller bearings can be mounted.Radial bearings: one axially displaceable double-rowcylindrical roller bearing (dimensions 340 x 520x 200/305 mm) and one single-row cylindrical rollerbearing FAG NU2244M.C3 (dimensions 220 x 400x 108 mm).Thrust bearings: two spherical roller thrust bearingsFAG 29432E (dimensions 160 x 320 x 95 mm).FAG 156