Root cause analysis of an abnormal groove-clogging failure on sink rolls in continuous hot-dip galvanizing line

Abstract

In this study, the root cause of an abnormal premature groove-clogging failure on a sink roll in a hot-dip galvanizing line was investigated. Cross-sectional metallurgical characterization was performed on samples obtained from both the groove-clogged and groove-clear sink rolls. Process investigations focused on the Al and Fe concentrations in zinc bath, bath temperature (Tbath), and strip entry temperature (Tstrip). It was found that groove-clogging failure on the sink roll was caused by a large amount of Fe2Al5Znx dross buildup in the grooves, and Tstrip control was the key factor. When Tstrip was consistently lower than Tbath for a long time period during operation, the Fe2Al5Znx intermetallic compounds preferentially precipitated and grew in the locally cooled zinc bath because of the decreased Fe solubility at lower Tbath. When Tstrip was controlled at least 5 ℃ higher than Tbath, the groove-clogging failure was successfully solved.