Date

2017

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Mechanical Engineering

First Adviser

Coulter, John P.

Other advisers/committee members

Pearson, Raymond A.; Webb, Edmund; Angstadt, David C.

Abstract

Runner-based shear imbalances is a common feature in injection molding of polymers. Its effect on the melt flow is a main concern, causing problems even in cases where the mold cavities are naturally balanced and the geometry is traditionally defined. Melt rotation technology has been applied to address this issue, as well as that of shrinkage and warpage.In the present study, this technology is taken several steps further with the goal of exploring and solving product quality variations that is attributed to the imbalanced polymer melt flow problem. Molding trials were conducted with and without melt rotation using several types of polymers, and the resultant effects on the physical, thermal, and mechanical properties of the molded products were explored. The study found that important product quality parameters such as crystallinity and tensile modulus vary significantly throughout conventionally molded products, and that these can be dramatically altered by implementation of the melt rotation technology. For semi-crystalline materials, specimens taken from product regions associated with higher melt flow shear levels exhibited higher crystallinity levels as well as higher tensile moduli due to the localized shear rate variation.This work also includes visual analysis of how shearing of the polymer through the runner system affects mold filling in real-time. Multi-cavity molding is widely used to increase manufacturing efficiency by primarily reducing time and cost. It is mainly generally accepted that the optimal runner design is one that is geometrically balanced. However, is now also understood that imbalances are also due to the shearing of the polymer melt as it is pushed through the runner system. To gain a deeper understanding on how this occurs, a custom-built mold with transparent mold inserts and runner system was utilized. Cavity filling of polymers into different cavity designs was captured using a high-speed camera. Analysis of this visual data would provide aid in finding methods to mitigate the non-uniform behavior of molten polymers undergoing shear-thinning. Molding trials were implemented and experimental results have been found to support the effectiveness of the melt rotation technology.The results in this work also show the potential of adopting the technology for a broader range of applications that require a homogeneous polymer melt flow for ensuring efficient manufacturing and desired quality products.

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