Thermal behaviour of work rolls in the hot mill rolling process

This project continues the work of Daniel White which culminated in the thesis, "A Hot Strip Mill Work Roll Temperature Model", submitted to Cardiff University in 2007. The current project presents a combined thermal solution, incorporating a transient, two-dimensional model which predicts changes in the circumferentially averaged temperature profile with time, and a static, three-dimensional model which provides high-resolution results near the surface of the roll and uses the results of the two-dimensional model as boundary conditions. The material properties of both models can now exhibit temperature dependency and boundary conditions at the surface have been improved. The resolution of the static model has been increased dramatically after testing found that the temperature profile was being compromised. The stress models use ABAQUS, a finite element software package, and have been completely redesigned. The stress solution consists of three models, each successive model concentrating more resolution on the roll bite, using the sub-modelling technique. Temperature data is imported from the thermal models, mechanical loads are applied using process data taken from the hot mill database at Port Talbot and residual loads are applied using the best currently available experimental data. Residual and thermal stresses were found to be significant, but the mechanical loads made little difference to the peak or minimum stresses per roll revolution. A brief investigation showed that, for a high-reduction rolling schedule (40% reduction rates), increasing the work roll oxide layer thickness from 3μm to 10μm decreases the cyclic stress range by roughly 100MPa. Taking account of temperature variability in the material properties also made roughly 100MPa difference to the stress range. The radial temperature distribution in the roll was shown to have a strong effect on the stresses at the roll surface, with a cold roll core incurring large peak stresses for the same circumferential temperature profile