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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Critical Factors Affecting the Use of Finite Element Analysis for Rotomolded Parts
Computer aided engineering (CAE) technologies, such as finite element analysis (FEA) of stresses offers the capability to optimize and validate engineering designs within a virtual environment, enabling potential problems to be highlighted and development time to be decreased. FEA has been used widely in the rotomolding industry, although it does not always appear to give an accurate prediction of behavior in the field. This paper examines several aspects with the aim of ensuring better correlation between FEA and actual part performance. Aspects considered include: Is Young’s Modulus representative of real stiffness? How important is Poisson’s Ratio? What is the effect of wall thickness variation in moldings?
4 Case Studies to Discover the Possible Automotive Applications of Glass Beads
Solid glass beads can be used in a lot of different thermoplastics in order to improve the following properties : scratch and abrasion résistances, dimensional stability, processing, ... The goal of this presentation is to show, with 4 case studies in automotive, the advantages given by the introduction of solid glass beads in different resins. The 4 case studies are : Mix of glass in Nylon compound in order to improve surface properties. Filler Pp compound with glass beads to improve scratch resistance Advantages to use glass beads in styrenic resins New solid glass bead grade to improve PC properties General conclusion will finish this presentation.
Limitations & Level of Accuracy of Tests for Rotomolding Powders
The rotomolding industry commonly uses two connected tests to assess the quality of plastic powders: Dry Flow and Bulk Density. Industry-specific test methods are available for both parameters. Repeated measurements were carried out on five different rotomolding powders, in order to assess the influence of the various equipment and environmental parameters that are thought to affect the test. This enabled estimates to be made of the limits for the accuracy and repeatability that are achievable practically. The results obtained from the Dry Flow test suffer from significantly higher variance than those obtained from the Bulk Density test.
Effects of Temperature and Viscoelasticity on Film Die Flow Uniformity
This study shows the effect of die temperature distribution and resin viscoelacticity on the flow uniformity in a film die. The magnitude of the thermal affects can be significant enough to mask other rheological effects. Computational Fluid Dynamics (CFD) simulations predictions using temperature-dependent viscosity models and gradients in the die wall temperature boundary conditions agreed well with the experimental measurements of flow uniformity. When the die wall is more uniformly heated, the flow uniformity is improved in both the measurements and simulations, although the simulations showed more deviation from the experimental results as the elasticity and shear thinning of the resins increased.
Unique Rheological Properties of Polymer Melts with Flexible Nanofibers
Rheological response under elongational flow is studied using polymer melts with polymeric fine fibers composed of poly(butylene terephthalate) PBT and poly(4-methyl-1-pentene) PMP. Both fibers are prepared by hot-stretching of the blends with isotactic polypropylene PP or poly(L-lactic acid) PLA. The samples with 1 wt% of PBT fibers whose diameters are smaller than 1 µm show marked strain-hardening in elongational stress. On the contrary, the sample with PMP fibers with a diameter of approximately 2 ?m shows no strain-hardening, although the measured elongational stress is significantly higher than that calculated from the linear viscoelastic properties.
A Study on Void Formation in the Residual Wall Thickness of a Curved Area during Fluid-Assisted Injection Molding
We analyzed the different effects on the formation of void in a residual’s wall thickness during fluid-assisted injection molding where water and silicone oil that had different thermal properties were used. For this, we conducted heat transfer analysis and injection molding analysis. We confirmed that void formation occurred due to the distribution of the temperature and volumetric shrinkage in the direction of the residual wall thickness in a curved area with a hollow section. We also found that void formation in the curved area decreased in case of using silicone oil compared to using water from simulation and experiment.
Viscoelastic Models with Logarithmic Strains
Analysis of 3-D viscoelastic flows is of a particular interest in polymer processing. Classical approaches rely on the Finger tensor and its inverse for strain evaluation. In this paper, we present a general Maxwell model with a logarithmic tensor for strain determination. Since the logarithmic strain provides a better representation of the state of straining of the material, the resulting constitutive model is expected to have a number of advantages including more uniform straining in different directions and extended linear behavior towards moderate deformations. Model testing on simple shear with only two material constants demonstrated simultaneous prediction of shear thinning and first and second normal stress differences.
Nucleation Efficiency of Talc in the Foaming Behavior and Cellular Structure of Polyolefin-Based Foams: New Perspectives for Optimized Lightweight Materials
The research consisted in evaluating the nucleation efficiency of different types of talc (with different particle size distributions, morphologies and even surface modifications) in the foaming behavior and cellular structure of polypropylene-based materials, with the objective of developing lightweight materials with improved stiffness at lower densities. Nucleation efficiency was first evaluated in talc filled PP foamed with a physical blowing agent inside a high pressure vessel. Depending on different talc characteristics, such as particle size distribution, surface area and morphology, cell density as much as doubled. Optimized foamed PP-talc composites prepared by injection-molding using the MuCell® process displayed further weight reductions for similar stiffness values. There was some work done on polystyrene foams
Cooling Simulation for the Prediction of Quality Properties and Production Costs of Semi-Finished Extruded Products like Pipes
When producing extruded products like pipes, the cooling process has a decisive effect on the quality and the production costs. The high potential for optimization of cooling processes is shown by a cooling simulation software that replicates the cooling stage in a virtual model, named chillWARE. Using the recommended settings for specific processes can reduce residual stresses and eliminates the need for follow-up processes like a subsequent tempering. It is possible to link the cooling process settings to the demanded product quality properties. In many cases, a positive side effect is the resulting reduction in operating costs for the cooling process.
Micromechanical Modeling of Thermally Conductive Polymer Matrix Composite Foams
A micromechanical model has been developed to study the effect of polymer matrix composite (PMC) foams’ morphology on its effective thermal conductivity (keff). Polymeric foams are commonly used for thermal insulation. This paper reveals that it is possible to fabricate light-weight thermally conductive PMC foams by tailoring their cellular structures. Their keff are governed by both the foams’ volume expansion ratios as well as the foaming-assisted alignment of thermally conductive filler. Moreover, the PMC foams’ keff would further be promoted by tailoring the aspect ratio of the cellular structures through constrained foaming. The exciting results have led to new research directions to develop novel polymeric material systems for thermal management applications.
Composites of Multi-Walled Carbon Nanotubes and Ethylene-Tetrafluoroethylene Copolymers
Multi-walled carbon nanotubes (MWCNTs) were added to random copolymers of ethylene and tetrafluoroethylene. Surprisingly, the electrical percolation threshold of the resultant composites was quite low; approximately 0.9 wt. %; the same nanotubes with the same mixing procedures in polyamide 6,6 yielded a percolation threshold of 1.5%. This low percolation threshold occurred even though the polymer surface energy is quite low which should make tubes more difficult to disperse. The effect on crystallization kinetics was quite small; suggesting perhaps that a lack of transcrystallinity might explain the low percolation threshold. The dispersion was measured via optical microscopy and seemed to be excellent.
Polypropylene Block Copolymers Flame Retarded with the Blends of Poly(Pentabromobenzyl Acrylate) and Magnesium Hydroxide
Flame retardant systems for polypropylene block copolymers based on combinations of poly(pentabromobenzyl acrylate) and synthetic magnesium hydroxide are reported in this paper. This combination of flame retardants allows a significant decrease of use of antimony trioxide synergist. It also helps to maintain good physical properties and significantly reduces smoke evolution. The addition of ethylene/1-octene copolymers to this combination improves Izod impact strength. Since poly(pentabromobenzyl acrylate) is a high molecular weight polymer, it will not migrate from the plastic parts and cannot penetrate through the cell membranes of living organisms and therefore it is believed to be safe in use. The high thermal stability of poly(pentabromobenzyl acrylate) and synthetic magnesium hydroxide indicates good recyclability of the flame retardant polypropylene copolymer.
Predicting the Flow Behavior of Powders, with Particular Reference to Rotomolding Materials
The rotomoulding industry uses a simple but crude measure to assess the flowability of powders, which involves timing the discharge of powder through a funnel with a circular bottom orifice. The flow of granular materials through orifices has been the subject of considerable research elsewhere and equations exist that relate flow to the various parameters involved. The most well accepted formula was assessed for its suitability to typical rotomoulding materials, as well as a variety of other powders and granulates. The characteristics of many materials (including rotograde micropellets) showed good correlation to theoretical predictions. Polyethylene and polypropylene rotograde powders showed behaviour that could be described by a modified version of the existing equation.
Modeling of Moisture Effects on the Rheological Behavior of Polymers and Influences on the Injection Molding Process
By processing technical polymers like polyamide or polybuthylene terephthalate, possible causes for process variations are residual moisture of the material or different conditions with respect to time and temperature. To show influences on the quality of an injection molding process, the changes have to be measured and described by a rheological model. The material behavior is measured by a rotational rheometer and a high-pressure capillary rheometer at different conditions. Effects like thermal and hydrolytic degradation or viscosity reduction by residual moisture are examined during this investigation. Combining measurements to a rheological model allows the simulation of influences on the processing and compensations. Therefore a new extension of the Carreau-model is presented. Parameters describing the material behavior are completed by a thermodynamic and calorimetric analysis of the material.
Quality Improvement by Enhanced Pressure Controlled Injection Molding
Today’s machine capability in injection molding is at a high standard and the variation of material properties are within a small range. Nevertheless variation in material properties and conditions influence the process- and product-quality. Examples are residual moisture or drying conditions by varying material handling. With respect to surface properties especially the injection-phase has a large influence on the part quality. By a recently developed process adapted pressure control during the injection phase a compensation of variations in the rheological behavior of the material is possible within the processing. Combined with a control of the switch-over point and packing-pressure, the quality of the process can be improved. Process variations by, for example, varying residual moisture content of the material are compensated by this new control strategy.
Two Dimensional Predictive Functional Control for Injection Molding Process
A batch process can be viewed as a 2-dimensional (2D) system with a time dimension within each batch and a batch dimension from batch to batch. In this paper, a 2D control algorithm that combines the iterative learning with the predictive functional control (PFC) which is the third-generation of model predictive control (MPC) is proposed based on the characteristics of batch processes. The proposed control scheme is tested experimentally through the implementation to an injection molding which is a typical batch process. The result shows the good performance of the proposed control algorithm.
Enhancement of Injection Molding Appearance Quality with Exterior Gas-Assisted Holding Pressure
Ghost marks is an appearance defect that appears in injection molding parts. Particularly, ghost mark presents an uncertain visual darkness depending on watching angles. This tiny defect is often omitted conventionally but couldn’t be ignored nowadays when considering a high quality appearance. The paper presents the causes of ghost marks through experimental study of injection molding a tensile-testing-sample and improves them with exterior gas-assisted holding pressure. The injection mold is peculiarly designed to enable executing exterior holding pressure on the in-molded part surface. Additionally, the surface qualities of testing samples are digitized through a proposed image processing approach in this research. Experimental results depict that a setting of high mold/melt temperatures as well as high injection speed/pressure enables to reduce the defect. Moreover, employing exterior gas-assisted holding pressure above 30 kgf/cm2 has a significant effect on reducing ghost marks.
Simulation as a Tool for Troubleshooting and Improving Twin-Screw Extrusion Processes
A variety of average, or “bulk”, flow models have been developed to simulate twin-screw extrusion performance [1-6]. While these models cannot accurately predict all critical process variables for many polymers, blends or alloys over a wide range of operating conditions, they do provide important insights into compounding operations. Following an approach described for troubleshooting single screw extrusion processes , this paper illustrates how such models can be used to diagnose problems and provide options for making design or operational improvements on co-rotating, intermeshing twin-screw machines. Three examples are presented to illustrate the value of employing flow simulations in process development and troubleshooting activities. Polyolefin/TiO2 masterbatch compounding was studied to validate the flow model on a laboratory extruder. The effects of throughput and screw wear on pumping efficiency were examined to diagnose vent port flooding. The flow model was used in the investigation of a reactive extrusion safety incident in order to determine the physical state in a critical process region and to identify factors contributing to a catastrophic failure.
Aqueous Colloidal Suspensions of Polymers for Conformal Coatings
In this work, a mini-emulsion technique is used to prepare aqueous surfactant-stabilized suspensions of bio-based and optoelectronic polymers. Doctor blade coating is used to prepare films of controlled thickness. The relationship between colloidal suspension properties, processing parameters and film morphology is determined. This versatile wet coating process is appropriate for a large variety of applications, and the use of water instead of organic solvents improves the environmental profile of coating preparation. The required coating procedures and resulting properties are studied for two polymers: poly(3-hexylthiophene) and poly(butylene succinate), which find applications in polymer electronics and degradable packaging, respectively.
Studying the Effect of Powder Geometry on the Selective Laser Sintering Process
This paper presents an effort to use physics based simulation techniques to model the Selective Laser Sintering (SLS) layering process. SLS is an additive manufacturing process that melts thin layers of extremely fine powder; we use powder with an average diameter of 58 microns. In the numerical model, each powder particle is a discrete object with 632,000 objects used for the SLS layering simulation. We first performed an experiment to measure the angle of repose for the polyamide 12 (PA 650) powder used in the SLS process. This measurement was used to determine the correct friction parameters and calibrate the numerical model. Once calibrated, initial simulations for the SLS layering process were performed to measure the changes in the surface profile of the powder. Future work will study the effect that different powders and roller speeds have on the surface roughness of a newly deposited powder layer along with determining the changes to density and porosity in the final part.
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