Melt Redistribution Element for Injection Molding Shear Stress
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Solution Overview
Problem
Conventional injection molding hot runner systems experience flow imbalance due to shear stress-induced variations in temperature, viscosity, and velocity along melt channels, leading to inconsistent molded parts across cavities and batches.
Innovation Solution
A melt redistribution element with a helical melt pathway is integrated into the injection manifold to redistribute the melt stream, providing a non-invasive pressure increase and mixing of the melt stream to achieve a more symmetrical shear stress profile, reducing flow imbalances and preventing the formation of flow lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional circular melt channels are used in the hot runner manifold, then the structure is simple and easy to manufacture, but the shear stress-induced flow imbalance causes inconsistent temperature, viscosity, and velocity distribution across the melt stream
Solution Approach 1:
The melt redistribution element divides the melt stream into multiple segments using vanes that create separate flow paths. This segmentation allows different portions of the melt stream to be redistributed independently, improving homogeneity by addressing local variations in temperature, viscosity, and velocity distribution across the cross-section of the melt stream.
Solution Approach 2:
The invention transitions from a simple axial flow configuration to a three-dimensional flow redistribution system using helical vanes and radial flow paths. This dimensional change enables the melt stream to be redistributed not only axially but also radially and circumferentially, creating a more uniform flow profile that addresses the limitations of conventional circular channels.
2Temperature
If melt material flows through conventional circular channels, then the flow path is simple, but the material in the center has higher velocity than material along the sides, causing temperature and viscosity imbalance
Solution Approach 1:
The melt redistribution element applies different flow redistribution characteristics to different regions of the melt stream. Vanes positioned at specific radial locations create localized flow modification zones that address temperature and velocity imbalances in specific areas of the cross-section, allowing the center and periphery of the melt stream to be optimized independently for uniform temperature distribution.
3Manufacturing precision
If shear stress is reduced in the melt channels, then temperature and viscosity distribution becomes more uniform, but the flow rate and productivity of the injection molding system decreases
Solution Approach 1:
The melt redistribution element acts as an intermediary device positioned between the conventional circular channels and the mold cavities. It receives the imbalanced melt stream from the channels and actively redistributes it to achieve uniform temperature, viscosity, and velocity distribution before delivering the melt to the cavities, thereby decoupling the flow rate requirements from the homogeneity requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in a more uniform shear stress, temperature, and viscosity profile across manifold outlets, enhancing the homogeneity of the melt material and improving the quality of molded parts by reducing inconsistencies between cavities and batches.
Implementation Method 1
The helical melt pathway changes the direction of flow of the outer portion of the melt stream to reorient the shear stress and to mix some of the outer portion of the melt stream with some of the adjacent central portion of the melt stream
Implementation Method 2
an inlet tapered section that increases the melt's pressure and generates a pressure increase, or what is known in the injection molding trade as a pressure drop
Implementation Method 3
melt material against the sides of a channel are further heated and stressed (i.e., sheared) by the friction generated as the melt moves against the side channels
Implementation Method 4
The helical melt pathway changes the direction of flow of the outer portion of the melt stream to reorient the shear stress and to mix some of the outer portion of the melt stream with some of the adjacent central portion of the melt stream
Data Source
AI summary
An injection molding apparatus having a manifold and several manifold melt channels communicating with several hot runner nozzles includes a melt redistribution element. The melt redistribution element is placed at specific locations along the melt channels to balance the uneven shear stress profile accumulated during the flow of a melt along the manifold channels. The melt redistribution element has an unobstructed central melt bore having at its inlet a narrowing tapered channel portion. The melt redistribution element also includes a helical melt pathway portion that surrounds the central melt bore. The incoming melt is first subjected to a pressure increase by the tapered portion that causes the melt to flow at a higher velocity through the central melt bore. The outer portion of the melt is forced to flow along the helical path and thus it changes direction multiple times and partially mixes with the melt flowing through the central melt bore. Accordingly, at the outlet of the melt redistribution element the shear stress profile is more evenly distributed than at the inlet of the redistribution element.