The Occurrence of Flow Marks during Injection Molding of Linear Polyethylene
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M. C. Heuzey
Abstract
Injection molded parts often show several types of surface defect. It has been hypothesized that wall slip is associated with some of these defects. Wall slip of molten plastics has been observed above a certain critical shear stress in rheological measurements. The objectives of the proposed research were to analyze the occurrence of flow marks during the injection molding of linear polyethylene and evaluate its possible relation to wall slip. Various variables were studied in terms of their influence on flow mark formation: mold thickness, mold temperature, melt temperature, gate, injection speed and TeflonTM and silicone oil coatings. It was found that injection speed is the controlling factor for the generation of flow marks during injection molding of the linear polyethylenes studied. Since one of the resin studied had shown no tendency to slip in capillary flow experiments, and since a Teflon TM coating on the mold walls did not affect the occurrence of flow marks, we conclude that there is no relationship between wall slip and the generation of flow marks. Microscopic observation of molded surfaces suggests instead that flow marks result from the filamentaton and stretching of semi-solidified material in the neighborhood of the three-phase contact line.
© 1997, Carl Hanser Verlag, Munich
Articles in the same Issue
- Contents
- Contents
- Editorial
- Editorial
- Screw Extrusion/Mixing
- Melt Temperatures and Residence Times in an Extruder by Infrared Spectroscopy
- Continuous Mixing of Low Viscosity and High Viscosity Polymer Melts in a Modular Co-Rotating Twin Screw Extruder
- Flow Field Analysis of Both the Trilobal Element and Mixing Disc Zones within a Closely Intermeshing, Co-Rotating Twin-Screw Extruder
- A Composite Model for Solid Conveying, Melting, Pressure and Fill Factor Profiles in Modular Co -Rotating Twin Screw Extruders
- Temperature Rise in the Extrusion of Highly Viscous Composite Materials
- Simulation of Free Surface Flow in Partially Filled Internal Mixers
- Die Extrusion
- Processing of Sheath-Core and Matrix-Fibril Fibers Composed of PP and a TLCP
- Fibers and Films
- Experimental and Theoretical Study of Rectangular Fiber Melt Spinning
- Distributed Crystallinity Control during Cast Film Extrusion
- Application of Neural Networks to Analyze the Drawing Process of PET Films
- Molding
- Physically-Based Adaptive Control of Cavity Pressure in Injection Molding: Filling Phase
- In-Mould Shrinkage Measurements of PS Samples with Strain Gages
- The Occurrence of Flow Marks during Injection Molding of Linear Polyethylene
Articles in the same Issue
- Contents
- Contents
- Editorial
- Editorial
- Screw Extrusion/Mixing
- Melt Temperatures and Residence Times in an Extruder by Infrared Spectroscopy
- Continuous Mixing of Low Viscosity and High Viscosity Polymer Melts in a Modular Co-Rotating Twin Screw Extruder
- Flow Field Analysis of Both the Trilobal Element and Mixing Disc Zones within a Closely Intermeshing, Co-Rotating Twin-Screw Extruder
- A Composite Model for Solid Conveying, Melting, Pressure and Fill Factor Profiles in Modular Co -Rotating Twin Screw Extruders
- Temperature Rise in the Extrusion of Highly Viscous Composite Materials
- Simulation of Free Surface Flow in Partially Filled Internal Mixers
- Die Extrusion
- Processing of Sheath-Core and Matrix-Fibril Fibers Composed of PP and a TLCP
- Fibers and Films
- Experimental and Theoretical Study of Rectangular Fiber Melt Spinning
- Distributed Crystallinity Control during Cast Film Extrusion
- Application of Neural Networks to Analyze the Drawing Process of PET Films
- Molding
- Physically-Based Adaptive Control of Cavity Pressure in Injection Molding: Filling Phase
- In-Mould Shrinkage Measurements of PS Samples with Strain Gages
- The Occurrence of Flow Marks during Injection Molding of Linear Polyethylene
