Research On Numerical Simulation Of Heat Transfer And Thermal Crowning Of Roll Shell During Twin-Roll Casting

The rolls are very important in a twin-roll casting process as they provide both the cooling needed for solidification of melted aluminum and the rolling necessary for plastic flow and deformation. Heat transfer is one of the two basic physics phenomena in aluminum alloy twin-roll casting process. To research and master the heat transfer mechanism of roll shell is a basic need for designing roll casting environment and establishing process parameters and controlling the quality of cast strip. With rising of market requirement standard and intensifying of the process, the shape and profile of cast strip is becoming a problem in practice. Because the mechanism and process of roll casting are different from hot or cold rolling, thermal crowning of the roll has greater effect on the shape and profile of cast strip. To research and master the development of thermal crowning of roll is the base to solve the problem of shape and profile of cast strip.Based on the analysis of mathematical models of twin-roll casting process at home and abroad, combined experience with mechanism research, mathematical models of heat transfer in roll casting process are built with numerical computation methods in this dissertation. So mathematical models of roll shell and boundary thermal load are built, FDE's based on balancing method are derived, methods to deal with the boundary conditions are given. Three finite difference models are used to simulate the cross-section temperature field of roll shell, including a two-dimensional steady state analysis based on a Eulerian coordinate system, a two-dimensional transient analysis based on a Lagrangian coordinate system, and a one-dimensional transient analysis. So the influence of heat conduction in the circumferential direction of roll shell are compared, which is the base for using an axisymmetric model to simulate the roll shell temperature field. The influence of various casting speed, roll shell material thermal conductivity and the heat transfer coefficient between roll shell and inner cooling water are also studied. Part roll shell and roll casting region are simulated together with coupling heat transfer, while solidification is dealt with a enthalpy model, and a constant strip/roll interfacial heat transfer coefficient is evaluated by optimization methods. The temperature fields resulted from different heat input distribution in roll casting region, while the total heat input are the same, are compared. The transient analysis shows that the roll shell reaches heat balance in several revolutions, it is different from hot or cold rolling. The heat transfer of roll shell is studied with an axisymmetric model and then thermal crowning of rollshell is obtained. The surface temperature of strip and roll shell with other process parameters are measured on a conventional commercial aluminum twin-roll caster. The thin-gauge high-speed strip casting trials performed on a pilot caster are analyzed by numerical simulation too. And some regularity understanding has been obtained. All of the numerical results are visualized and various figures of temperature field and thermal expansion are presented.With all the achievements mentioned above, an integrated numerical simulation system suitable for personal computers is developed for analyzing heat transfer and thermal crowning of roll shell, which is convenient and practical in caster roll design and roll casting process design.