Improvement of rolled strip surface and geometry by advanced automatic diagnosis of surface defects and optimisation of friction in the roll gap

Modelling of some aspects of defect formation through different passes in a hot strip mill was conducted, but further work required characterisation of friction in the roll gap. Hot plane strain compression testing gave mean friction results of limited applicability. Tests using an experimental hot friction test rig allowed derivation of a variable friction relationship used in a model of the first finishing pass. A comprehensive advanced concept for an automatic online diagnosis system was developed for hot strip. A new system for surface inspection that combines shape measurement and surface inspection was developed and successfully tested in a hot strip mill. Laboratory trials were carried out to investigate primary and secondary scale growth, and to determine the effects of descaling and work roll lubrication on rolled strip surface. Findings from a literature study on tertiary scale were proven by mill trials. Strip chemistry was also found to have a big influence. A Parsytec surface inspection system was used to investigate the effect of finishing temperature and inter-stand cooling in reducing scale defects, and ways to inhibit tertiary scale were found that do not adversely affect the rollability of certain products. An automatic system was installed in the finishing stands of a hot strip mill to measure changes in back-up roll bearing oil film thickness. Models were developed and implemented to allow initial comparisons with results obtained from automatic oil film tests. These show quite good agreement when the test data are consistent. Improvements are still required in the data capture system and data pre-processing software.