Failure Analysis of Worm Gear in Worm Transmission

Abstract

The failure cause of the worm drive in the NMRV reducer of the grounding knife-switch mechanism of State Grid was analyzed in this paper. The macroscopic analysis, chemical composition inspection, microscopic metallographic observation, hardness test, SEM analysis were carried out to evaluate the worm gear failure mechanism. The stress distributions of the tooth flank using dynamic contact finite element simulation were obtained based on ANSYS Workbench software. The results showed that an initial crack at the root position of softer worm gear was caused by excessively high impact at the initial stage of meshing in the worm drive, whose value was 308MPa higher than the allowable contact stress of 220MPa. The main reason for the hardness of the worm gear decreasing was that the amount of (α+δ) eutectoids fell and distributed unevenly.