Study On Distribution Of SCF Bubble Nucleation In The Process Of Microcellular Injection Molding

bubble nucleation is the crucial factor to control the foam quality, which has decisive effect on cell density and cell distribution directly. This paper studies the influence of injection pressure and melt temperature on bubble density and bubble distribution when using supercritical CO2 fluid as a physical foaming agent in the injection molding process of microcellular PS foams, which is based on classical nucleation theory of microcellular plastics.In the process of microcellular injection molding, it can make use of homogeneous nucleation of classical nucleation theory to illustrate the form of bubble nucleation in the molding process. In the case of constant concentration of supercritical CO2 fluid, whether the prediction of the interfacial tension is right or wrong is the key factor to calculate bubble nucleation velocity according to the formula of homogeneous nucleation velocity. So this paper develops different models of interfacial tension which include polymer PVT model and LGT theory model.The polymer PVT model is applied so early to solve the interfacial tension of the mixture and improved mainly from the following two aspects in this paper.(1). The Tait experience equation of state is taken for the solution of the physical state parameters of PVT of Polymer melt, which changes the melt density that is constant in practice and makes the melt density vary with the variation of the pressure and the temperature.(2). The S_L equation of state is taken for the solution of the mixture density containing polymer melt and supercritical fluid, which doesn't use the method of the density addition by every component any longer and provide more accurate prediction of the mixture density under different pressures and temperatures.The LGT theory model to predict the interfacial tension of the mixture mustcombine the S_L equation of state.Though its form is very complicated,it can accurately predict the trends of interfacial tension under different pressures and temperatures.Contrasting the two above models with the experimental data in other literatures, it is found that the interfacial tension calculated by the polymer PVT model contrary to the experimental data while the LGT theory model is in accordance as the pressure varies. Therefore, the later model is applied to calculate nucleation velocity in the process of microcellular injection molding in this paper.Due to the restriction of domestic experimental conditions, it is impossible to verify the correctness of the nucleation density model. The calculation results show that the impact of injection pressure on the number of bubble nucleation is larger than that of the melt temperature in the process of microcellular injection molding and the number creases when the pressure is increasing, and it reduces with the increasing of the temperature.In the end, the flow behavior of the uniform phases solutions containing Polymer melt and supercritical fluid presents great complexity, which makes the distribution of bubble nucleation uncertainty. So this paper achieves random distribution of supercritical fluid nucleation by adopting the random seed function in Visual C++and the system's time as the seeds, which is helpful to improve the accuracy of the computer simulation. On this basis, it makes use of the programming method of date sharing between Visual C++and Matlab and achieves visualization of random distribution. The date visualization can help researchers to be more intuitive understanding to the distribution of dates and characteristic of tendency.