Options to increase the permissible stress of press-fit and bearing seats of wheelset axles by surface layer treatments

摘要

A characteristic feature of wheelsets on rail vehicles are the various axle/hub joints linking the axles to wheels, bearings, brake discs, etc. In this respect the applicable EN standards on wheelset design include, beside the technical design requirements, among others also definitions of the fatigue strength values to be achieved and the resulting permissible stresses of the standard axle material employed. Current investigations, however, show that these stresses for the press-fit and bearing seats might possibly not be reached with small diameter relations between the press-fit or bearing seat, respectively, and the adjacent shaft. By coating the press-fit and bearing seats with molybdenum it is possible to avoid such fatigue stress drop. A remarkable increase of the permissible stresses as compared with the standard values, even with unfavourable diameter conditions, can, however, be achieved by application of the newly developed BVV surface layer process. For this process the axles are first subjected to a chemo-thermal surface treatment to improve their strength and then the press-fit and bearing seat surfaces are additionally protected against the reactions resulting from the unavoidable sliding movements in the axle/hub joints by applying a thin molybdenum layer.