Failure Analysis of Flakes Fell from Small Gear Surface in Wind Power Gearbox postprint

Abstract: Flakes fell from the tooth surface of the small gear in the gearbox of a 1.5 MW wind turbine in service. The design lifetime of the gear is 20 a. However, it failed 5 a later since it was installed into the gearbox. The material is 20CrNiMo and the gear was carburized and quenched during the manufacturing process. Macro- and micro- observation of the fracture surface as well as some necessary physical and chemical analysis were applied to analyze the cause for the failure of the small gear. Besides, results from the macro-observation showed that only two teeth failed, on the one of which flakes fell from the tooth surface only left some pits, and on the other tooth surface some cracks can be observed obviously. The results also showed that pits and cracks could be attributed to the same reason. Tool marks on the tooth surface increases the risk of cracking. In addition, the abnormal load introduced by emergency braking led to cracks occurred along the machining marks on the tooth surface. Then, fatigue cracks nucleated at the tip of the crack and extend slowly driven by the working load. Finally, the hardened layer fell from the tooth surface and left some pits. It was suggested that the machining quality and the braking technology should be improved in order to avoid the cracking of the teeth surface under the abnormal impact load.