薄膜流延成型数值模拟关键技术研究及其工艺分析

发布时间：2018-06-14 23:26

本文选题：薄膜流延 + 有限元方法　；参考：《山东大学》2017年硕士论文

【摘要】：流延成型是聚合物薄膜重要成型工艺方法,该工艺过程影响因素多,控制难度大。本文针对聚合物薄膜流延成型工艺进行系统性分析,建立了描述挤出、流延、换热各工艺过程的数值模型,采用有限元方法求解控制方程并研究了相关关键技术,通过对薄膜流延成型工艺过程进行数值模拟,探究各工艺参数对流延膜成型质量的影响,以指导实际成型工艺控制。针对流延膜挤出过程,依据理论经验公式,设计衣架型挤出流道以提高流动均匀性。基于计算流体力学理论,建立了描述熔体挤出流动过程的三维非等温数学模型,针对压力—速度耦合问题采用罚函数有限元方法进行解耦求解,采用线性化交替迭代法实现稳定数值求解。将出口流速模拟结果与工艺实验结果进行比较,验证了数学模型和数值计算方法的可靠性,并具体分析了模具温度、挤出速度等工艺因素对出口流速分布的影响。针对聚合物熔体通过口模后的流延过程建立数学模型,考虑到三维模型中薄膜厚度方向尺度小,网格划分困难等问题,将厚度作为变量进行求解,推导得到二维模型。以一维模型的解析解作为初始场,采用有限元方法进行数值分析,通过Newton-Raphson方法迭代求解速度场、厚度场、自由边界。考虑空气强制对流换热作用,以及非牛顿流体的粘性作用,对非等温条件下薄膜流延过程进行数值仿真,通过与工艺实验结果对比验证模拟方法的合理性。分析流延比、模辊间隙等工艺条件对薄膜成型质量的影响,探究颈缩、哑铃边等成型缺陷形成的原因以及改进措施,分析了材料弹性因素对薄膜宽度、厚度的影响规律。针对薄膜冷却定型过程,设计平行流道换热系统,考虑冷却水湍流对薄膜冷却带来的影响,建立聚合物熔体、流延辊以及冷却水之间热量传递的数学模型。根据换热边界条件的不同,对上述热传递过程进行耦合数值求解,并分析了薄膜在轴向和径向的温度分布;通过调节冷却工艺参数分析其影响规律,统计薄膜两侧热交换量,同时探讨了流延辊转速所造成的薄膜温度差异性。本文通过数值仿真与工艺实验,系统研究了薄膜流延成型过程各工艺参数影响规律,有助于提高薄膜生产质量与工艺控制水平。
[Abstract]:Casting is an important process for polymer film forming, which has many influencing factors and is difficult to control. Based on the systematic analysis of polymer film casting process, a numerical model describing the extrusion, casting and heat transfer processes is established. The control equations are solved by finite element method and the relevant key technologies are studied. Through the numerical simulation of the casting process of thin film, the influence of various process parameters on the forming quality of the film is explored to guide the actual process control. In order to improve the flow uniformity, a garment rack extrusion channel was designed according to the theoretical empirical formula for the extrusion process of ductile film. Based on the theory of computational fluid dynamics, a three-dimensional non-isothermal mathematical model was established to describe the melt extrusion flow process. The penalty function finite element method was used to solve the pressure velocity coupling problem. The linear alternating iteration method is used to realize the stable numerical solution. The reliability of the mathematical model and the numerical calculation method are verified by comparing the simulation results of the exit velocity with the experimental results, and the effects of die temperature and extrusion speed on the velocity distribution of the outlet are analyzed in detail. In view of the mathematical model of polymer melt flow through the die, considering the small dimension of film thickness and the difficulty of mesh division in the three-dimensional model, the thickness is taken as a variable to solve and the two-dimensional model is derived. The analytical solution of one-dimensional model is taken as the initial field, the finite element method is used to carry out numerical analysis, and the Newton-Raphson method is used to iteratively solve the velocity field, thickness field and free boundary. Considering the forced convection heat transfer of air and the viscous effect of non-Newtonian fluid, the numerical simulation of thin film flow under non-isothermal conditions is carried out. The rationality of the simulation method is verified by comparing the results with the experimental results. The influence of casting ratio and die roll clearance on the film forming quality is analyzed. The forming reasons of forming defects such as necking and dumbbell edge and the improving measures are discussed. The influence of material elastic factors on the film width and thickness is analyzed. Considering the influence of cooling water turbulence on film cooling, a mathematical model of heat transfer between polymer melt, roll and cooling water was established. According to the difference of heat transfer boundary conditions, the coupled numerical solution of the heat transfer process is carried out, and the temperature distribution of the film in axial and radial direction is analyzed, and the influence law of the film is analyzed by adjusting the cooling process parameters, and the heat exchange amount on both sides of the film is calculated. At the same time, the film temperature difference caused by roll speed is discussed. In this paper, through numerical simulation and process experiment, the influence of process parameters on film casting process is systematically studied, which is helpful to improve the film production quality and process control level.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.2

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