| Rapid Heating Cycle Molding (RHCM) technology is a dynamic mold temperature controlling method. Making use of this technology, the mold is heated to a high temperature before the injection, and then injection molding is performed in this high temperature condition, which helps the melt to flow and fill in the mold successfully. At the later stage of the packing, the plastic product temperature is cooled rapidly using cooling medium to raise the molding efficiency.The injection molding products of the fiber reinforced composites (FRP) possess better and thermal properties than those of individual polymers, so that they obtain more and more attention. Many defects always appear in the parts produced by the traditional injection method, like fiber orientation unevenness, superficial fiber emerging and anisotropism, all which restrain the development and their applications. Short glass fiber reinforced composites (GFRP) can be transformed to high quality plastic products, by RHCM technology. However, the problems concerned the fiber orientation, weld mark and superficial emerged fiber, are not deeply researched. For this purpose, the RHCM technologies used in the short GFRP are studied profoundly and systematically in this thesis. This study can provide a theoretical foundation to apply this technology in the industrial production.In this thesis, the electric heated RHCM production line designed by our research team, is presented detailedly, as well as the principles of every part (including the heating system, cooling system, mold temperature controller, air compressing system, monitoring system and injection molding machine) and signal transforming system among them. Designing methods of some key parts in this technology are introduced, such as the gate types and the positions of the temperature sensor. A mold type in which electric heating elements and cooling channels coexist in the cavity plate, and another type in which electric heating elements are positioned in the cavity plate and the cooling channels are installed in an individual cooling plate, are presented in detail.The experimental samples for the tensile, bending and the impact tests are molded simultaneously in one injection product. Aiming at investigate the fusion splicing status when two wet flows encounter, two different injection molds, with one or two gates respectively, are designed. Two sets of standard samples, of short glass fiber reinforced ABS and short glass fiber reinforced PP respectively, are produced by RHCM method in different heating conditions.The injection molding CAE software Moldflow is used to simulate the RHCM processes of the short GFRP in different mold temperatures. The analysis of the interior fiber orientation leads to a skin-shear layer-core-shear layer-skin model in the thickness direction and the causes of the layers formation are interpreted. Quantitative analysis of the fiber orientation in different mold temperatures result in that the fiber orientation degree will be decreased obviously when the temperature is high enough. The thickness of each layer exist differences among those samples molded in different mold temperatures and these differences are explained reasonably. The RHCM samples molded in different mold temperatures are brittle-fractured in the liquid nitrogen condition. And the fiber orientations at the cross-section observed from the Scanning Electron Microscope can verify the validity of the simulation results.The standard tests of the short GFRP products produced by the RHCM in different mold temperatures, reveal the influence of the mold temperature on the tensile, bending and impact performances. The surface qualities of these products can be observed with the help of the white-light interferometer, and we can find that the best surface qualities can be gained when the mold temperature is115℃. |
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