Numerical Calculation Of Processing Temperature And Foaming Behavior Of Polyolefin Materials

With the rapid development of the plastics industry,foamed polyolefin composites have been widely noticed because of their advantages such as light weight and heat insulation.Foaming temperature plays a vital role in the processing of foamed polyolefin composites.However,the processing temperatures studied are tested with the help of equipment such as temperature sensors and other instruments,and the processing temperature is generally set by default to the temperature set on the instrument regardless of the molding method.Due to the characteristics of the molding instruments and the complexity of the mold cavity design,the temperature of each micro-region inside the foamed polyolefin composites varies,but the study of processing temperature usually focuses on the local area of the melt,resulting in the presentation of the results of a point-by-point study.In this paper,the temperature distribution of polypropylene composites is numerically calculated to explore the relationship between the internal temperature distribution of polymers and the internal pore structure of actual foamed polypropylene composites,so as to predict and regulate the foaming quality of foamed polypropylene composites and open up new ways for the development and application of foamed polypropylene composites.The main results of this thesis study are as follows:（1）The heat conduction equation and Fourier’s law of heat transfer are used as the basic formulas,and the formulas are derived and simplified by combining the actual boundary conditions of the processing and molding process to obtain the empirical formulas for the one-dimensional steady-state heat transfer process.The empirical equation in the one-dimensional steady-state heat transfer process is given by = ₁- ₁ ¹2+ ₂ ¹2.After calculation,it can be obtained that the temperature of different isothermal surfaces S-1 to S-4in the molding process decreases from 437.30 K to 349.00 K;the temperature of different isothermal surfaces M-1 to M-4 in the molding process decreases from 393.56 K to 324.04 K.（2）Detailed numerical discretization formulas for the imaginary boundary meshless Galliakin method applicable to the calculation of foamed materials are obtained in the two-dimensional steady-state process heat transfer,which provides a convenience for other scholars to use the method to study foamed materials.By substituting the boundary conditions of the injection molding process and the molding process into the two-dimensional steady-state heat transfer numerical analysis formula,the temperature from the a region to the d region in different regions of the same isothermal surface of the injection molding process is reduced from 406.35 K to 311.63 K.The temperature from the Ma region to the Md region in the molding process is reduced from 326.35 K to 309.14 K.（3）The calculated results were used to investigate the effect of temperature distribution on the internal foaming quality of foamed polypropylene composites.During the injection molding process,the cell size decreases and then increases,while the cell density increases and then decreases,and the number of cells increases and then decreases in different isothermal surfaces from S-1 to S-4,among which the foaming quality is more satisfactory in S-2 isothermal surface,with the average diameter of cells and the density of cells being 28.14μm and 3.7×10⁹cells·cm^-3,respectively.In different regions of the same isothermal surface,the cell size decreases and then increases,while the cell density increases and then decreases,and the number of cells increases and then decreases,among which the foaming quality in region c is more satisfactory,with the average diameter and density of cells being 26.5μm and 2.43×10⁹cells·cm^-3,respectively.（4）During the molding process,the cell size gradually decreases,the cell density gradually increases and the number of cells gradually increases in different isothermal surfaces from M-1 to M-4,which indicates that the foaming quality in M-4 isothermal surface is more satisfactory,and the average diameter and density of cells are 160μm and6.33×10⁴cells·cm^-3,respectively;the cell size gradually decreases and the cell density gradually increases in different areas of the same isothermal surface from Ma to Md.The size of vesicles gradually decreased,the density of vesicles gradually increased and the number of vesicles gradually increased in different regions of the same isothermal surface,which indicated that the foaming quality in the Md region was more satisfactory,and the average diameter and density of vesicles were131.2μm and 6.3×10⁴cells·cm^-3,respectively.