Failure analysis of a high-speed offset bearing

There are presented the consequences of the events during the operation of two variants of sliding bearings (offset type) within two gearboxes of similar construction and way of loading. Both assemblies have suffered serious damages of the gear transmission (gear teeth breaking, active flanks scoring, etc.), accidents that occurred after a longer or shorter period of use. During operation, each gearbox was monitored and the parameters values were recorded: gas turbine speed, driving power, important temperatures (oil input, bearing surface, etc.), vibrations (proximity sensor on the input shaft, accelerometer on the gearbox housing). For each type of bearing, the geometric characteristics are presented, the antifriction material is described by its mechanical properties, and the dynamic characteristics of the bearing surface are used to estimate the critical mass which establishes the boundary between stable and unstable operation. Relying on the operating parameters, the behaviours of two HS bearings (HS Sun pinion bearings), which have been analyzed are compared mainly during instability occurrences and especially in the last period before their removal from service. The conclusion is that the stability of the undamaged fluid film bearing is proved both from the computational model and by the dynamic response of bearing to external loading.