Failure of a coal transportation conveyor belt pulley

摘要

A conveyor belt pulley was investigated, due to premature failure. The failure had occurred on the pulley shaft. The surface of the shaft had signs of rough machining on the radius near the fracture surface. Microstructural investigation revealed subsurface closed cracking and most importantly signs of surface welding. The surface welding on the outer radius caused additional internal stresses in the shaft. The cause for surface welding was unknown. Metallographic analysis revealed that the base material (42CrMo4) was inappropriately heat treated. This reflected on the mechanical properties, especially on the low impact toughness. The combination of poor material heat treatment, surface welding and dynamic loads resulted in inevitable cracking and consequent failure.