K. Alqosaibi, C. Thakur, H. Noor, A. Almalki, A. Duhduh, J. Coulter
Lehigh University,
United States
Keywords: injection molding, hot runner system, incomplete filling, rheodrop
Summary:
A novel technology “Rheodrop” was developed to advance the process of hot runner based injection molding. The technology utilizes the application of shear rate to the polymer melt during the injection molding process. The application method involves rotating the valve pins inside the hot drops. The intensity of the applied shear rate is controlled by adjusting the rotational speed. The shearing process reduces the viscosity of molten pseudo plastics inside the hot drops. Viscous polymer melts are more prone to produce incompletely filled products due to higher flow resistance. Hence, Rheodrop technology overcomes incomplete filling defect as well as enhances the quality of the molded parts by reducing the viscosity of the processed polymer. In addition, this technology enables processing materials at lower temperatures, which can eliminate/reduce thermal degradation for temperature sensitive materials. Analytical and experimental analysis were performed to investigate the effect of applying Rheodrop technology to the molded parts. Numerical simulations were performed using ANSYS to study the applied shear and viscosity in the hot drops during valve pin rotation. Also, a four cavity hot runner mold was modified to retrofit the technology for experimental investigation. The experimental results showed that this technology was able to enhance the quality of molded parts as well as prevent incomplete filling defects. Experiments were performed for both Rheodrop and conventional moldings at different levels of polymer melt temperature that are within the range of the selected polymer’s melt temperature. The experimental results showed that the quality of molded parts was enhanced using this technology with minimal incomplete filling defects. At lower levels of processing temperature of conventional molding, the molded parts were defected as the cavities were incompletely filled. However, when applying Rheodrop, the molded parts were perfectly filled throughout the considered melt temperature range.