Date

2016

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Mechanical Engineering

First Adviser

Coulter, John P.

Other advisers/committee members

Nied, Herman; Pearson, Raymond A.; Angelov, Aleksandar; Webb III, Edmund

Abstract

Valve gate systems were originally introduced to control melt flow during the injection molding cycle of hot runner injection molding machines. One of the problems that can arise with such systems is cold slug formation during the injection molding cycle. Systems currently being used in industry cannot resolve the issue of the cold slug formation while processing semi crystalline polymers using direct gated hot runner system. Moreover, these hot runner systems with valve gating systems exist in the presence of shear imbalance issues as well which lead to poor part quality. There are two main ways to reduce the viscosity of a polymer during an injection molding cycle (1) providing heat and (2) introducing shear. Current hot runner systems consist of heating bands around the runner system which keeps the polymer in the molten stage throughout the injection molding cycle. The solution family focused on during the present study is primarily a shear based technology that introduces rotatory motion of a valve pin which helps to provide shear and reduce the viscosity of the material. The main objective of this research was to solve the cold slug formation as well as coloration issues by applying a scientific approach to develop and implement localized shear rate control technology for hot-runner injection molding systems. The subject technology was developed to solve these issues and thus enable high quality precision controlled hot runner injection molding success with an expanded range of materials. This technology was developed to control the part quality throughout the injection molding process. There are several advantages of this technology listed as follows Removal of Cold SlugsHigh quality productsLess cycle timeReduction in shear imbalancesLow material waste Precision moldingReduction in coloration mixture challenges This technology is primarily suited for shear thinning materials. In order to validate the concept, three different categories of materials including a crystalline, semi crystalline and amorphous were studied. Numerical simulations and experimental results of common polymers, such as Ultramid A3EG7 (35% glass filled) (Crystalline), Vectra E130i (Semi-crystalline) and ABS CMold Estimates (Amorphous) were considered. This research focused on reducing the viscosity, within the shear limits of a polymer, by increasing the shear rate. Therefore, a valve pin located in a nozzle of a hot runner system was rotated at different angular velocities. Behavior of the polymer in the lower region of the nozzle was studied at different RPMs and temperature. In depth analysis was performed by developing a scientific idea, re-designing the molding mechanism and running analytical simulations using Autodesk Moldflow, MoldEx3D and Ansys Fluent.The concept was successfully designed and build and also proved using different analytical software. After the proposed changes were implemented in a hot runner system, the technology was successfully generated. Analytical simulations was performed using different software packages such as Autodesk Moldflow, Moldex3D and Ansys Fluent. The analytical simulation revealed that the viscosity was reduced by, on average, 60% at 5000 RPM. The work included in this dissertation advanced science and technology in the field of injection molding process. This dissertation includes the development of a new scientific approach, the design and implementation of a novel new technology and the analytical and to a lesser extent physical validation of the related scientific base.

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