Fracture failure analysis of internal teeth of ring gear used in reducer of coal mining machine

A failure investigation has been conducted on a ring gear of cutting gear reducer used in coal mining. The fracture failure of this ring gear occurred in a trial run state after it was put into service within only 8 h. Detailed examinations on the fracture part of this ring gear were conducted. The results indicated that no-metallic inclusions, machining tracks, network nitride and over brittle microstructures are combined acting as reasons for the cracks initiation under unstable load of using process. Typical characteristics of brittle fracture, such as the cleavage and quasi cleavage micro-morphology combined with river pattern and the fan pattern, were observed on the fracture surface. The fracture morphology reveals the fracture is resulted from rapid propagation of cracks due to the brittleness of material.