Premature failure of a spiral bevel pinion in a turbine condenser gear reducer

Within several months of service, a spiral bevel pinion inside a gear reducer failed resulting from serious pitting and associated tooth breakage. The failure was investigated using metallographic, scanning electronic microscopic techniques, and microhardness testing. The study indicates that the pinion suffered surface contact fatigue initially due to the repeated contact stresses, and later normal fatigue under the repeated bending stresses. Misalignment (or spiral angle error) of the pinion with the mating gear could cause the premature failure of the spiral bevel pinion, not due to materials deficiencies and/or poor mechanical properties. The alignment of the pinion should be checked carefully after assembly. This could be done by applying “engineering blue” to the gear teeth and manually rotating the gears to check the contact pattern.