Numerical Simulation Key Technology Research And Process Analysis On Film Casting

Film casting is an important polymer film forming process.The process has many influencing factors and is difficult to control.Through systematic analysis for polymer film casting process,the numerical model which describes the process of extrusion,casting and heat transfer has been established.The finite element method was used to solve the control equations and the related key technologies were also studied.Meantime,numerical simulation of the forming process was adopted to study various factors affecting the quality of casting film.Firstly,according to the empirical formula,the coat-hanger channel which has a better flow uniformity was designed for extrusion die of casting film.Based on the theory of the computational fluid dynamics,a three-dimensional non-isothermal mathematical model was established to describe the melt extrusion flow and the pressure-velocity coupling problem was solved by the penalty function finite element method.Considering the non-linearity of the viscosity,the asymmetric weight function was introduced by SUPG method,which overcomes the numerical oscillation problem caused by the convection dominance of the energy equation and then the linearized iterative method was used to realize stable solving.The influence of the mold temperature and the inlet velocity on the outlet uniformity has been analyzed as well.Secondly,the mathematical model was established for the casting process after the extrusion section.In order to solve the problem that meshing is difficult in the thickness direction caused by small thickness for the three-dimensional model,the two-dimensional model was got by some simplified method and the thickness can be solved as a variable.The numerical solution of the one-dimensional model was used as the initial field with the numerical analysis was carried out by the finite element method.The velocity field,the thickness and the free surface were solved by the Newton-Raphson method.Under non-isothermal condition,the heat transfer effect of the forced convection as well as the viscous effect of the non-Newton fluid had been taken into account,numerical simulation of the film casting was carried out and its simulation results were compared with the experimental results to verify the rationality of the simulation method.Then effect of the processing conditions such as casting ratio and gap between rollers on the film quality was analyzed.The cause of the defects such as necking and edge-bead and the improvements methods have been researched.Finally by considering the viscoelastic fluid model,the influence of the elastic element and its ratio on width and thickness of film was analyzed.Thirdly,for the film cooling process,the casting roll with parallel channel was designed for heat transfer.Considering the influence of cooling water turbulence flow on the film,the mathematical model of the heat transfer within the polymer melt,casting roll and cooling water was established.According to the difference of heat transfer boundary conditions between each of them,the numerical calculation was carried out by coupling method,with analysis of temperature distribution of the films in the axial and radial directions.The influence of cooling water was analyzed by adjusting its parameters and then the heat exchange capacity on both sides of the film was calculated.Besides the temperature difference caused by casting roll speed was also researched.In this paper,the influence of each process parameter was studied systematically by simulations and experiments,which is helpful to improve the film production quality and process controlling level.