Heat Transfer In Injection Molding Of Crystalline Plastics

Heat transfer is one of the most important stages in injection molding process, because the material physical properties, surface quality and also the demolding time are largely dependent on thermal change in the mold. Not many exact solutions can be found for these heat transfer problems due to the inherent nonlinearities present. It is very necessary to find a mathematical model for the injection molding of crystalline plastics. This mathematical model could help us to know the cooling process of plastics product in injection molding, optimize the technology of injection molding CAD (computer aided design) and establish feasible processing conditions.A review of polymer blends and the research on cooling process of injection molding is presented. Some equations of line are found to be sufficiently adaptable to the thermodynamic parameters. The thermodynamic parameters included thermal conductivity, heat capacity, density, latent heat of crystallization and crystallization temperature. High-density polyethylene (HDPE) and polypropylene (PP) were melt-blended in the following percentages of HDPE by weight: 25, 50, 75 and the thermodynamic parameters (density, latent heat of crystallization and crystallization temperature ) of polymer blends is measured by hydrostatic weighing method and the DSC (differential scanning calorimetry) crystallization experiment. The relationship between the percentages of PE by weight and the values of the thermodynamic parameters is concluded in the article.A theoretical mathematical model is presented to describe the temperature distribution and the rate of phase change in injection molding process of pure crystalline plastics (HDPE and PP). Under some assumptions, an exact closed form is solved by use of an internal technique. The model was tested by measuring the temperature profile in a slab mold instrumented with thermocouples. The model prediction fitted well to the measurements.The existing finite-difference approach is used to simulate the numerical performance of blend crystalline plastics (HDPE-PP blend) in injection molding process. An enthalpy E and parameter T~* are employed to convert the energy equation into a non-linear equation successfully. Under some assumptions, an exact closed form is solved by use with the mathematical software language MATLAB and the numerical analysis method. The results fitted well to the measurements. The results of investigations as well as statistical analyses may find their application as a help in optimization activities for injection molding process.