Abstract
The process stability of finishing mill is significantly influenced by the clearance between the chocks and housing in mill stands. The on-site data of a finishing mill had shown that the clearances in the finishing mill stands were clearly associated with the incidence of strip end flip. The aim of this work was to establish a numerical model to analyze the effect of the clearances on the deviation of the centerline of the strip and on the incidence of strip end flip. By adopting conditions from a particular strip, the numerical model not only predicted the strip end shape, but also visualized strip end flip, which would be otherwise invisible. Four different degrees of asymmetry regarding work rolls and backup rolls were postulated. It was found that the degradation of the work rolls’ clearance level was the most significant influence on the centerline deviation of the strip. Strip end flip was most susceptible to the degradation of the horizontal clearance of the work roll. The simultaneous degradation of the work rolls’ and backup rolls’ level of clearance led to larger reactions and enhanced the asymmetric wear on the liners. The superimposed axial clearances at the roll end provided an axial constraint to the work roll, and were able to reverse the trend of centerline deviation. The numerical results provided a guideline for designing a suitable maintenance strategy for clearances.
Highlights
The rapid growing demands on high strength and ultra-thin steel strips have driven the development of finish milling technology to achieve superior strip quality and productivity
The superimposed axial clearances at the roll end provided an axial constraint to the work roll, and were able to reverse the trend of centerline deviation
In a four-high mill assembly, work roll chocks and backup roll chocks are mounted in the windows of mill housing
Summary
The rapid growing demands on high strength and ultra-thin steel strips have driven the development of finish milling technology to achieve superior strip quality and productivity. The high-speed steel strip generates a disturbing load and causes the chattering of the roll chocks in the housing [1]. Strip end flip is the most serious dynamic instability that can occur during the finishing process It often happens at the instance when the strip end is escaping from the work roll bite of a mill stand. The statistics show that the regular maintenance of the liners was effective in suppressing the incidence of the strip end flip. No literature or research was found that focused on the effect of the clearances in the finishing mill stand on the finishing stability, or more precisely, on the strip end behavior during the finishing process. The aim of this work is to establish a finite element numerical model to analyze the collective effect of the clearances on the deviation of centerline of the strip and on the incidence of the strip end flip
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