Failure analysis of drive spindle sleeve of Finishing Mill of Hot Strip Mill

Abstract This paper analyses the failure of a bottom spindle head sleeve in a finishing mill stand. The sleeve, manufactured by Mill OEM and installed in 2022 (after overhauling), exhibited fatigue cracking after approximately 2.9 years of service. Metallurgical analysis revealed lower hardness and microstructural changes in the interphase weld zone, stemming from multiple previous refurbishments involving hard facing. Repetitive welding during these overhauls induced thermal cycles, leading to softening of the parent material and ultimately, fatigue failure. Finite Element Analysis (FEA) showed that stress levels at the failure location remained within the acceptable range at rated load but exceeded the safe limit at peak loads (150% of rated current). Recommendations include improved supplier oversight, enhanced quality assurance procedures for overhauling, and a more robust maintenance protocol to prevent recurrence.