The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Broad Shear Rate Viscosity Measurements via Reconstruction of Fluid Velocity Profiles in Contaminant Melts
A method of building velocity profiles from through the thickness, in situ, optical observations in polymer melts is discussed. It is shown that it is not necessary to know particle position across the thickness of the slit to allow for accurate shear rate determination. Coupled with a pressure drop measurement, the accurate velocity profile is transformed in a broad band viscosity vs. shear rate curve. Controversial resolution limitations are discussed along with experimental data.
Comparison of Experimental and Predicted Data for Conventional Single Screw Extruders
Single screw extrusion is widely used in the processing of thermoplastic materials. Good understanding of the extrusion process can save time and capital investments. Simulation programs capture the solids conveying, melting and pumping behavior to help us study the process and eventually to fit the screw design to a particular thermoplastic material. From such a study, the best processing conditions may be determined. There is still a considerable lack of understanding of the physical process in an extruder particularly with regards to the solids conveying. Our objective is to contribute to the understanding of this process, which should lead us to an improvement of the solids conveying model. In this paper we present a set of experimental data measured on various screw designs, for varying properties of different PE resins. Further more, the comparison of measured and predicted data is presented. This comparison is used to evaluate the physical model used during simulation of the extrusion process.
Simulation of the Micro Injection Molding Process
To predict the filling process of micro injection moldings, a dedicated 3 dimensional software is under development. The algorithm is based on automatic re-meshing of the varying flow domain. Currently, viscous flow calculations are performed, while visco-elastic effects will be addressed at a later stage. To verify the results, micro injection molding trials with different polymers were carried out. Therefore, new test structures, realized by means of the LIGA technique, were designed. Visco-elastic effects like unique shapes of the frozen flow fronts have been observed, which leads to a new interpretation of micro mold filling.
Vacuum Stamping of a Refrigerator: Identifying Problems through Numerical Simulation, Solving Them and Validating the Solution on the Production Line
Thermoforming is gaining more and more applications because of its comparatively easy and fast process. With thermoforming either small (yoghurt pots) or large (refrigerator panels) flat parts can be moulded and a complete description of the process can be found. On the other hand, to simulate the thermoforming process is a real challenge, as various factors have to be investigated and taken under consideration if we want to achieve a realistic simulation. At the present paper, a very complicated thermoforming process is simulated using finite element and other numerical tools and the results are compared to the real process. Moreover, problems occurred in the real process are solved using the simulation tool.
Extrusion of Polystyrene Microcellular Foam with Supercritical CO2
The continuous production of polystyrene foam with supercritical CO2 is achieved by injection of CO2 into the extruder barrel at a certain pressure and rapid pressure release in the die. The effects of temperature, pressure, and die shape, are analyzed in detail. Fundamental work related to the foaming process is accomplished by modeling the phase equilibrium with the Sanchez-Lacombe equation of state and combining the equations of motion, the energy balance and the Carreau viscosity model to characterize the flow behavior. The experimental parameters were selected according to the Tg and phase equilibrium. The position of nucleation in the die was studied according to the simulation results via a computational fluid dynamics code (FLUENT).
Processing Glass-Filled Polyethylene on a Twin-Screw Injection Molding Extruder
The mechanical properties of glass-fiber reinforced thermoplastics depends largely on the post-processing fiber length distribution. The traditional method of compounding in an extruder followed by injection molding causes considerable fiber attrition. In this study, the benefits of using a novel type of machine -the Twin-screw Injection Molding Machine (T.I.M.E.) - is investigated. The effects of operating conditions such as screw speed, glass-fiber content and extent of screw fill, on the final fiber lengths and distribution are studied. Optical microscopy and image analysis methods were used to analyze the processed parts.
Developing Animations and Simulators for Plastics Education
Instructional technology, computer-based training, and multimedia are a few of the modern words associated with the wave of technological advancement in educational methods. The plastics industry is not only riding this wave, but has been a contributor in leading these advancements. This paper describes the development of several projects that expand the body of technology-based plastics education. These projects include animations used to describe machinery or present difficult polymeric concepts and simulators used to teach operational techniques. Hardware, software, and methods used in these projects are discussed.
Cover Part as an Application Example for Gas-Assisted Injection Molded Parts
The gas-assisted injection molding process is in use now for several years offering new technical and creative possibilities for injection molding. After a brief survey of the principle sequence of the process and basic process physics this paper comments on an application example for a cover part and provides solutions for the problem s found during the process of fixing existing issues on this tool.
Magnetic Resonance Imaging of Polymer Melt Flows
A tubular rheometry that is based on obtaining velocity profiles by nuclear magnetic resonance imaging (NMRI) and measuring pressure drop of the flow is used for the polymer melts. This technique allows one to get viscosity data potentially over many decades of shear rate region in a single measurement. In this study, we examined polyethylene melt as the flow medium. Despite the low shear rates attained, our results reveal that this non-invasive and non-destructive method is promising for constructing an on-line polymer melt rheometer.
Relaxation Model for FE Analysis of Plastic Product Behavior
The non-linear creep-based models cause numerical instabilities during FEA calculations because of the necessary inversion of stress-strain relations. From this point of view, the relaxation-based models are preferable for use within FEA. On the other hand, engineers avoid such models, due to complicated tests. Therefore, the goal was to develop the non-linear relaxation model, which uses the data of creep-recovery tests. In this way the model would be comparatively inexpensive and unconditionally stable in FE calculations.
Vibration Assisted Resin Transfer Moulding (VIARTM): A New Alternative Technique to Improve RTM Performance and Part Quality
At the present paper a new system with the aim to improve the RTM process has been developed and presented. The system is based on the assistance of the resin flow with mould-inducing mechanical vibrations. Potential advantages of the proposed method are the improvement of the quality of the composite part (reduction of voids and reach areas), decrease of the filling time and/ or the maximum applied flow pressure. A test apparatus has been set up at NTUA to study the various mechanisms that relate the resin flow through the preform mat, the curing and the external vibrations. The project is progressing well and initial results are very promising and will be presented at the conference.
A Novel Ionomer for Nylon Modification
A new family of Surlyn® ionomers containing reactive functional groups is being developed for polymer modification, e.g., modifying nylon for blow-molding applications. Compared to existing ionomers, the new ionomers exhibit a higher degree of compatibility with nylon. One of the unique features of the new modifier is that the new ionomers can be dispersed in nylon in an extremely fine particle size and narrow size distribution. This has a profound effect on both the melt rheology and the mechanical properties of the modified nylon. Most significantly, the new ionomer imparts a truly shear thinning melt viscosity of the modified nylon 6. The paper discusses the dispersion of the new ionomer in nylon 6 as analyzed by SAXS and TEM and the melt rheology behavior of the modified nylon 6 and briefly highlights the effectiveness of the new ionomer to modify nylon 6 for the demanding blow-molding applications.
The Creep Behavior of Poly(ethylene terephthalate) Bottles
Room temperature viscoelastic behavior of PET beverage containers was studied. Internal pressures result in an increase of the container volume. By assuming a cylindrical geometry, stresses can be computed and linear strains can be estimated from the volumetric changes. A time-dependent creep compliance was determined for 2-L freestanding containers under various internal pressure loads. These values match favorably with uniaxial creep measurements. From isochronous plots, the viscoelastic behavior is shown to be linear over a limited range of pressures. The creep curves show all the characteristics of simple linear viscoelastic models such as instantaneous elastic response, retarded elastic response and permanent deformation.
Measurement of Layer Deformation in Coextrusion Using Unique Feedblock Technology
Multilayer coextrusion is a process in which two or more polymers are extruded and joined together in a feedblock or die to form a single structure with multiple layers. These layers should be uniform in thickness across the structure for best performance. However, layer thickness non-uniformities have been observed in many coextruded products. Previous work has shown these layer thickness variations can occur due to viscosity differences between the polymers in the layers and/or elastic effects that introduce secondary flows. The objective of this work was to experimentally measure the secondary flow velocities in a square channel using a unique coextrusion feedblock that produces annular rings instead of planar layers.
Enhanced Performance via Ester Lubrication of Rigid PVC Formulations Modified with Chlorinated Polyethylene
In traditional calcium stearate/paraffin wax systems, higher levels of wax leads to lower melt temperatures, higher gloss, and higher impact properties of the extruded sheet or profile. Unfortunately, higher levels of wax also leads to longer PVC fusion times, and an increased tendency to develop die plate out. However, recent work with ester lubricant systems, in PVC formulations using chlorinated polyethylene, have shown that lower extrusion temperatures, pressures and torque can be achieved without sacrificing fusion time or increasing the risk of die plate out. All while maintaining or enhancing gloss and impact properties.
A Study on the Poly(ethylene naphthalate)/Poly(ethylene terephthalate)-Poly(ethylene naphthalate) Copolymer Blends
Poly (ethylene naphthalate)/Poly (ethylene naphthalate)-poly (ethylene terephthalate) copolymer [PEN/(PEN-PET)] blends were investigated. It was found that introducing PEN-PET copolymer to PEN/PET blending system instead of using PET caused the lowering of transesterification reaction in melt mixing as compared to PEN/PET blends. As the duration of mixing gets longer, the transesterification difference between PEN/PET blends and PEN/(PEN-PET) blends becomes more evident. The increase of transesterification in PEN/(PEN-PET) blends with increasing mixing time resulted in the decrease of melting temperature, while glass transition temperature increased. In addition, our time resolved light scattering data shows that slower crystallization could be obtained in PEN/(PEN-PET) blends as compared to PEN/PET blends.
Warpage Analysis of Solid Geometry
The requirement to create a shell model on the midplane of the part for warpage analysis is at odds with the trend toward solid modeling. A method is introduced that enables warpage analysis without the midplane model. This ensures that the user interacts only with the solid geometry. In this paper we present results obtained with the new technique and compare them to those obtained on a midplane model.
Assessment of Opportunities to Produce Distributed Multilayer Film Microstructures in Thermoplastic Blends by Chaotic Mixing
Chaotic mixing of binary components has been recently used to produce and distribute fibers, multi-layer films, and fragmented sheets in melts. Formation mechanisms and means to promote one type over the other remain uncertain. In this study, in situ film formation and breakup in PS/LDPE blends was examined for differing extents of mixing. Results demonstrate new opportunities to develop distributed multi-layer films during blending processes.
A Novel Additive for PP Fiber
The purpose of this paper is to present the data on UV stabilization of flame retarded polypropylene fiber. The evaluation was conducted by exposure in the xenon arc weatherometer @ 63°C under dry conditions. Proprietary additives provided unique physical property retention for flame retarded polypropylene fiber.
Thermal Analysis during Epoxy Casting Process for Joint Units of High Voltage Cable
The temperature distribution and the degree of cure in an epoxy system during the casting process, which is used in the connecting unit of high voltage cable, have been simulated using the FE solver of MARC including the programmed routines. The curing kinetics of the epoxy system used in the casting process was determined by DSC test, which was used as material input data of the developed program. To verify the developed simulation program, we have compared the simulated results for the simple model problem with those simulated by C-MOLD. The simulation results of real epoxy system for the connecting unit of the 400 kV cable, which is currently under development, are also presented for various processing conditions.
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