Study On The Thermo-mechanical Coupling Behavior And The Flatness Problem During Twin-roll Casting Of Aluminum Strip

Along with the development of roll-casting process in the fast ultrathin direction, roll-casting flatness problem will be prominent day by day. To promulgate the special roll-casting flatness phenomenon and its production mechanism and to control it effectively, have already become a key technical problem which is urgently awaited to be solved. At the same time, such are also urgent need for realizing the industrialization of roll-casting process. In this paper, the research object is twin-roll casting system of Aluminum. Aimed at flatness problem and through the computer numerical simulation and the scene industry test, the thorough research and the simulation analysis are made on such problem as heat transfer companied with the flowing and solidification of the metal in the roll-casting zone, three dimensional temperature field of the roll shell, thermo-mechanical coupling deformation behavior of three-dimensional multi-body contact system consisting of workpiece, roll shell and roll core. In order to enhance flatness control precision, the random harmful noise is removed from flatness detection signal, and the attached disturbance is compensated.In view of heat transfer problem companied with the flowing and solidification of metal, this paper looks on the metal with different state as generalized fluid, and uniformly describes the process including the metal flowing, solidification and heat transfer in the roll-casting zone. The equivalent thickness geometry model and the finite element model of the roll casting zone are established. A supposition which states the heat flow density decreases linearly along the roll direction is proposed. Through the coupling solution to the above models at different process condition, the distribution law of temperature field in the roll-casting zone is promulgated, the most front solidification position and the lowest temperature of the exit strip are obtained, the roll speed limit is verified for the given cooling condition of conventional roll casting, the relationship between liquid cave depth and casting velocity is cleared off.A typical heat transfer problem with periodic motive contact boundary, which includes microscopic heat conduction and macroscopic mass-moving heat transfer, is studied in this paper. According to the equivalence of heat transfer process, the circumvolving of roll shell is regarded as the ordinal circumfluence of generalized fluid in the round tube. Based on the analysis method of fluid flow and heat transfer, a new heat transfer model of roll shell is established, and the motive contact boundary between the workpiece and the roll shell is treated as non-motive boundary. Through the mathematic simulation research of heat transfer process of roll shell at many kinds of work states for the normal casting and the fast ultra-thin gauge casting, the corresponding temperature field of roll shell is obtained separately. It is known about the influence rule of some main heat transfer factor, such as casting velocity, inner heat transfer coefficient and conduction coefficient of roll shell material, etc. on the temperature field of roll shell. At the same time, some primary data conditions are provided for the solution of the thermo-mechanical coupling deformation of casting roller.In order to verify the production mechanism of roll-casting flatness, for the first time, strip/roll system is regarded as three-dimensional multi-body contact problem, which consists of workpiece, rol shell and roll core. The mathematical model and finite element model are built for solving the thermo-mechanical coupling deformation of strip/roll system. After expounding the basic theory of mixed finite element method in detail, the solution condition of contact surface and the determination condition of contact state are given, the general finite element equation is derived for the internal force distribution in the contact interface, the methods to deal with boundary condition are analyzed. In addition, the roll-casting force model and equivalent node load model resulted from variable temperature are established, which is suit for finite element analysis of contact system. With mixed finite element method for contact problem, the numerical simulation is done for the thermo-mechanical coupling behavior of strip/roll contact system at various roll-casting conditions. Simulation results open out the relationship between the thermo-mechanical coupling deform of casting roller and main process factors such as casting velocity, inner heat transfer coefficient and roll shell material, etc.Flatness detection is an essential condition to automatically control flatness defect, its precision is the most important factor to decide control effect. In this paper, flatness detection signal is looked on as dynamic time series. With the theory of adaptive filtering, a general method is established to remove the harmful noise from the flatness detection signal, and a filtering program is developed. Exemplifications and simulation results prove that the above method can be used in the real time control with good effect. In order to remove the inherent additional disturbance from the flatness detection signal, the temperature deviation compensating model is established. The compensating means studied in this paper can be directly taken to amend the flatness detection signal, which can effectively avoid misoperation of control mechanism and improve control precision and have the important practical value for the scene control of roll-casting flatness.As for the experiment, a certain domestic casterΦ1020×1600mm is by way of its research object. Some industry measuring plans are drew up for temperature field of roll shell and strip surface, thermal deformation of casting roller, on-line and off-line crosswise thickness difference of rolled strip. At the same time, the scene measuring has been carried on. The experimental values of the above parameters are very consistent with the simulation values, which proves that the models established in this paper are correct, the corresponding numerical solution is feasible, and the simulation results are reliable.