Thermally-induced failures in railroad tapered roller bearings

摘要

An Association of American Railroads (AAR) class F (6 1/2 X 12) tapered-roller bearing assembly is modeled, using finite elements, to examine thermally-induced failures observed in the laboratory when the bearing is operating at relatively highspeeds. It is hypothesized that this failure is caused by an unstable thermal expansion/internal bearing load feedback process. Sequentially-coupled, transient thermal and static structural models are used to obtain the thermal-mechanical transient timeresponse as a junction of speed, seal type, and lubricant starvation at the rib contact. The model assumes no external loads and zero initial preload (zero end-play). Therefore, the loads developed in the bearing are thermally-induced andself-equilibrated. Two train speeds, viz. 80 and 100 mph, are considered. Simulation results indicate that at axle rotational speeds equivalent to a train speed of 100 mph, a combination of grease starvation and heat flux from the contact seals cause high rib temperature and subsequent unstable load growth which will lead to failure. At rotational speeds equivalent to train speeds of 80 mph or for bearing assemblies that utilize special design seals, the rib temperature is relatively low and no operational instabilities were observed for the model used.