Bending Fatigue Failure of a Helical Pinion Bevel Gear
The analysis of pinion gear damage operated in a tube coiler machine gearbox was investigated. Visual inspection, SEM fractographic analysis, and metallographic evaluation are employed as the principal analytical techniques for the investigation. Fractographic observations indicated the occurrence of bending fatigue started at the maximum load surface of the gear teeth, known as active flank, and propagated to the opposite area resulting in catastrophic tooth fracture. Unbalanced stress conditions led to the consecutive damage and fracture of adjacent teeth resulting in machine interruption and immediate replacement of the gear system. The multiple fatigue crack initiation sites suggest significant stress concentration probably caused likely by gear misalignment. Metallographic evaluation revealed an entirely heat-treated gear microstructure consisted of tempered martensite free from microstructural abnormality that could be associated to the failure. Regular gear inspection and system alignment checks together with the consideration of increasing surface hardness, through selected surface strengthening procedures, are suggested as further corrective actions to minimize similar failures and machine downtime in the future.
KeywordsBending fatigue Fractography Pinion gear Failure analysis
The author wishes to express special thanks to Mr. A. Vazdirvanidis for the constructive technical discussion, Mr. A. Toulfatzis for technical assistance, and Mr. A. Rikos for metallographic preparation and hardness tests of sample section. Special thanks are also addressed to Plant Maintenance team for their assistance in background information and fruitful discussions.
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