Some Studies on the Damages of the War-time Standard Turbines and their Reduction Gears

Abstract

Many damages have been reported on moving blades, high speed pinions and wheels as well as flexible couplings of the war-time standard turbines and their reduction gears of the propulsion use.It is generally understood that these damages were caused by the use of materials of inferior quality and the poor workmanship during the war time. However, the author's careful investigations on several damaged parts has disclosed that the fault of the so called“racked train”type gearings in its mechanism is another important cause of these damages.Since the high speed pinion of the single helical“rocked train”type, having thrust collar between fore side pinion bearing and flexible coupling, has long dimension in overhang length, the pinion itself tends to be put into the unstable condition, such as the whirling motion in the journal bearings. The load fluctuation on the gear teeth caused by the whirling motion results the irregular distribution of the pitting, which is clearly observed on the gear teeth.It is noted that the frequency of this load fluctuation which is observed as the irregular distribution of the pitting on gear teeth is ten or twelve cycles per revolution of pinion, and that it coincides with the mumber of coupling teeth.From the above mentioned phenomena, the author concludes that the shock load caused by the whirling motion of the high speed pinion introduces all sorts of unusual damages above-mentioned and he also gives the follwing recommendations for the design of the reduction gear: -(1) The advantage of so called“rocked train”type gearings in which the transmitting load is reduced to half, is cancelled by the demerits that the severe shock load induced by the whirling motion is added to transmitting load and, that the adjustment of the ununiform distribution of teeth loads is very difficult. From this point of view, the employment of this type of gearings is to be avoided as practicable as possible.(2) When the employment of this type of gearings is obliged, the ball or roller bearings are to be used in high speed pinion in order to prevent the whirling motion of the pinion as small as possible.(3) As the gear coupling having insufficicient flexibility may introduce the damage on turbine blades, high speed pinions and gears as well as couplings themselves, some devices are necessary to be considered to increase the flexibility and improve the lubrication.