Date

2019

Document Type

Thesis

Degree

Master of Science

Department

Mechanical Engineering

First Adviser

Coulter, John P.

Abstract

There are great challenges in industries when injection molding thin walled parts using hot runner systems. One of the main challenges is processing thermally sensitive materials such as Liquid Crystalline Polymers LCPs. In hot runner systems, cold slug formation problems occur between injection molding cycles at the nozzle tip due to high viscosity associated with lower temperatures.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 potential solution to overcome the issue of cold slug formation in hot runner systems while processing thermal sensitive polymers is presented. Basically, instead of increasing the processing temperature that may cause polymer degradation, reducing the viscosity by applying shear rate to the molten polymer is explored.Analytical and experimental investigations were performed to validate the developed “Rheo drop” 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 was able to produce a sufficient amount of shear to significantly reduce the dynamic viscosity between injection molding cycles. Experimentally, most of the previous and current issues and complications regarding a prototype hot runner mold were resolved. Three samples of ABS were molded without using the rheo drop concept, with all samples produced with defects. The experimental investigation could not be completed as planned due to sprue heater problems that could not be resolved within the timeframe of the thesis research. The work will continue, however, with a full experimental validation of the concept expected once the remaining heater problems are addressed.

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