Abstract
Flatness is an important quality characteristic for rolled products. Modern hot rolling mills are equipped with actuators that can modify the uneven thickness distribution across the width of the strip (crown), taking into account online measurements of various process parameters such as temperature, force and exit strip profile, either automatically or manually by the operator. However, the crown is also influenced by many parameters that cannot easily be measured during production, such as work roll temperature evolution through thickness and roll geometric variation due to thermal expansion (thermal camber). These have an impact on the strip flatness. In this paper, a thermo-mechanical finite element model on LS-DYNA™ software was utilized to predict the influence of process parameters, and more specifically strip temperature, cooling strategy (application of cooling on the entry or entry and exit side simultaneously) and roll core temperature, on the evolution of roll temperature and thermal camber. The model was initially validated with industrial data. The results indicate that the application of both entry and exit cooling is ~30% more efficient compared to the entry cooling only, thus the thermal camber will be reduced by 2 μm. A hotter roll (380 K) is more stable compared to the cold roll (340 K), showing also an improvement of 2 μm. The hotter roll will also reach a thermal steady state on the surface faster compared to the colder one, without making a significant difference on the steady state temperature. Strip temperature plays a roll in the thermal camber evolution, but it is a less important parameter compared to cooling strategy and roll temperature.
Highlights
Aluminum alloys are constantly increasing in terms of their consumption and spectrum of industrial use, with emphasis, amongst others, on the transportation sector, the food industry and construction
Strip temperature plays a roll in the thermal camber evolution, but it is a less important parameter compared to cooling strategy and roll temperature
The strip profile is significantly influenced by the temperature profile on the roll and the camber evolution caused by thermal expansion
Summary
Aluminum alloys are constantly increasing in terms of their consumption and spectrum of industrial use, with emphasis, amongst others, on the transportation sector, the food industry and construction. Shigaki et al [7] predicted roll stack deflection by coupling a commercial FEM model with a multi-slab model for strip deformation Such approaches have shown good results and are adapted in the real industrial environment in order to either define set points or counteract the effects of variations induced in the process. When these variations become significant, predictive models have reduced accuracy and the adaptive bending system sometimes either cannot completely correct the crown or it can introduce inhomogeneities in the material.
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