Failure analysis of coal pulveriser gear box

The premature failure of coal pulveriser gear box has been studied in this investigation. Complete breakage as well as cracking in a number of gear teeth were noticed in which the cracking initiated from the middle of the root-fillet of the teeth and propagated beneath the root region. Studies were conducted using microstructural studies, hardness measurements, fracture surface studies, etc. The failure was found to be initiated by bending fatigue from the root fillet region of teeth which mainly constituted coarse ferrite–carbide aggregate resulting in a relatively low hardness level. The life of gear box could be improved by local hardening of the fillet root to provide a fine martensitic structure with hardness in the range of 55RC.