An unusual gearbox pinion failure

Two large gearboxes were installed to power a bulk conveyor at a mine site. Upon start-up, failure of the final drive pinion occurred in one gearbox after 43 s when maximum torque was reached. The failure was unusual as fracture in the pinion was approximately at right angles to the pinion axis, in the centre of the pinion. The pinion was forged and integral with its supporting shaft. The initial suspicion was of hydrogen embrittlement, however analysis identified a pattern of inclusions in the centre of the pinion. In consequence, the cause of failure was attributed to improper control of the casting and forging processes used in the manufacture of the pinion blank.