Hot runner systems are prevalent in the manufacturing of thin walled polymers parts. There are great challenges in industries associated with the quality of the molded parts when utilizing a hot runner system. One of the main challenges is processing thermally sensitive materials such as Liquid Crystalline Polymers LCPs. In hot runner systems, the viscosity increases between injection molding cycles at the nozzle tip due to lower temperatures. This might cause serious problems such as incomplete filling defects. Mainly, there are two ways to reduce the dynamic viscosity of shear thinning thermoplastics (1) increasing temperature and (2) applying shear. In this research, a novel “rheodrop” concept is developed to control the shear rate during injection molding process. Applying a shear at the nozzle will decrease the viscosity of the molten polymer. This innovative idea is suitable for temperature sensitive polymers as they might degrade when subjected to excessive heat for longer periods of time. An analytical investigation was performed to validate the developed “rheodrop” concept which applies shear to the polymer in between filling cycles by rotating the valve pin inside the hot drop. Simulations were performed using ANSYS fluent and the results confirmed that the concept is able to produce a sufficient amount of shear to significantly reduce the dynamic viscosity between injection molding cycles.
Journal: TechConnect Briefs
Volume: TechConnect Briefs 2019
Published: June 17, 2019
Pages: 119 - 122
Industry sector: Advanced Materials & Manufacturing
Topics: 3D Printing, Advanced Manufacturing