| Polymer PVT property plays an improtant role in the application research of injection molding,which can provide the necessary parameters for the mold design, process optimization and control and product precision analysis. However, the evolution of spcific volume has a largely dependence on the experienced thermo mechanical process. The complex process conditions in the injection molding process, such as high temperature and pressure, high shear flow and fast non-isothermal cooling, have greater impact on the PVT property. In order to solve this problem, a PVT tester with fast cooling and shear functions was developed which could be used to study the influence of cooling rate and shear rate on the polymer PVT property under specific pressure condition. Then the appropriate measurement method for the PVT tester was put forward to get the polymer PVT property which was more close to the actual value of injection molding. So the prediction accuracy of simulation analysis and the quality of the products could be improved. The content and conclusions of this study are as follows:After analysing of the functions and advantages of foreign advanced instruments, basing on the Piston-cylinder technology with annular cavity and sample, a PVT tester with fast cooling and shearing functions was developed as a function of pressure (1 to 100MPa), temperature (30 to 300℃), cooling rate (up to 25℃/s), and shear rate (0 to 320s-1). But the upper limit of pressure was 20MPa when the shear rate was applied. The good measuring accuracy of this instrument was verified by contrasting the measurement results with those of other precision instruments.Taking the semi crystalline polymer as the research object, the cooling rate and shear rate as the main variables, and considering the pressure and the temperature variable as well, the influence of cooling rate, shear rate and the coupling influence of cooling rate and pressure, shear rate and pressure, shear rate and shear applied temperature, shear rate and cooling rate on the PVT property were studied experimentally. Basing on the effect laws summarized from the above experiments, the effect of the applied measuring conditions on PVT property were furthest similar to the the actual situation of injection molding. The PVT property of PP6331 was measured in this way. And the dates were fitted by Tait equation, to establish the connection between PVT property and CAE simulation analysis for injection molding.Basing on measuring other necessary parameters for analysis of PP6331 and optimizing the injection molding process parameters, the shrinkage and warpage of product were analysed in Moldflow by using four kinds of PVT properties which were mearsured with natrual cooling method, cooling rate method, shear rate method, cooling rate and shear rate coupled method. Then their effect laws on the simulation results were summarized. Comparing with the actual products and considering the obtained effect laws, it can be found that the PVT property measured with cooling rate and shear rate coupled method could improve the prediction accuracy of the simulation analysis, which also further proved that the PVT tester have a good measuring accuracy and the correlated measurement methods were practical and accurate on some level. |
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