Fracture Cause of Correction Roller in Hot-dip Galvanizing Line

A correction roller in a hot-dip galvanizing line fractured at the transition fillet of its shaft head during operation. The fracture cause of the correction roller was analyzed by chemical composition analysis, tensile property testing, microstructure observation, micro-area composition analysis, non destructive testing and stress analysis. The results show that the failure mode of the correction roller was multi-source fatigue failure caused by complex loads including bending load and torsion. The pits on the outer surface of the transition fillet of the correction roller shaft head and the stress concentration here promoted the initiation of multiple fatigue cracks on the surface. The fatigue cracks propagated under high loads, and finally the fracture of the correction roller occurred. In order to avoid the reoccurrence of such failure, it was recommended to use the larger radius of the transition fillet to reduce the stress concentration degree at the transition fillet, improve the surface quality and strengthen nondestructive testing before putting into operation.