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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Investigation of Heat Transfer in the Plug Assisted Thermoforming Process
A Finite Element model of the plug-assisted thermoforming process has been developed to encompass both 2D axisymmetric and more complex 3D geometry. Initial modelling attempts assumed isothermal conditions, but for further improvement it is necessary to investigate the effects of heat transfer. In this paper the effects of heat transfer on the process are investigated. Heat transfer behavior at the plug and mold interfaces was identified and validated with the use of simple tests. The results were incorporated into the model of the thermoforming process and an improvement in wall thickness prediction has been demonstrated.
The Use of Hot Impact Testing in the Simulation of the Plug-Assisted Thermoforming Process
In mathematical simulations of thermoforming processes, one of the most difficult problems lies in developing realistic models of the behaviour of plastics at forming conditions. This paper investigates the use of a low cost modified impact test to obtain material data. A conventional falling weight impact tester has been modified by inserting an oven and replacing the metal indenter with various plug shapes. This creates loading conditions which are very much similar to the real process and the resulting force-displacement data may be converted to true stress-strain data. A range of thermoplastic materials have been tested using this method and the results are presented in this paper.
Crystallization of Isotactic Polypropylene: Comparison between ? and ? Growth Rates
The influence of a white pigment (White MB PE) and a nucleating agent (Millad 3899) on the spherulite growth rate of isothermally crystallized iPP was investigated by polarizing optical microscopy. Lauritzen and Hoffman analysis was used to determine the kinetic parameters of the growth rate. It was found that the addition of either pigment or the nucleating agent caused a reduction in the spherulite growth rate. This was attributed to the increase of the energies required for the transportation of the macromolecules in the melt. Over the crystallization temperatures used in this study, higher growth rates for ?-spherulites have been obtained in comparison with ?-spherulites. Nucleation densities for the nucleated samples, (FINA4042S and iPP containing 1wt% Millad 3988), were greater than those of either plain iPP or the samples containing the white pigment.
New Rapid Tooling Concepts
Within the scope of Rapid Tooling the IKV is working on the optimization of Soft Tooling techniques and on the development of Hard Tooling techniques. The aim is to get molds with a high mechanical strength and series-like cooling conditions. For that purpose the resin casting process is improved taking advantage of the sedimentation of a steel powder filler. Furthermore the metal injection molding (MIM) is analyzed with respect to its suitability for manufacturing steel molds or prototypes. The mold used in the MIM process is made by stereolithography. The results show the possibility to get steel powder contents as high as the bulk density with the resin casting. It is also feasible to manufacture green parts of steel molds or prototypes with MIM.
Gas-Assisted Reaction Injection Molding (GRIM): Application of the Gas Injection Technology to the Manufacturing of Hollow Polyurethane Parts
The gas injection technology is gaining constantly in importance for thermoplastic polymers and could also offer a great potential of application to the manufacturing of polyurethane parts. Due to the significant differences concerning the material behavior between thermoplastics and reactive PU systems with their coupled chemical and physical processes this molding concept, designated as Gas-assisted Reaction Injection Molding (GRIM), has been investigated. Numerous experimental investigations concerning the most significant process parameters as well as a rheokinetic characterization have been performed. A selection of the results is presented within this paper.
Modelling and Validation of the Blow Moulding of HDPE/Nylon Multilayer Containers
A large growth area for blow molding is in automotive applications. The benefits of plastic for automobiles include (a) lower investment costs for plants and tooling, especially for high production volume, (b) ability to tailor the material to obtain desired barrier and chemical resistance properties and (c) reduced car weight and cost. Recent trends in blow moulding are towards the use of multi-layer sequential material processing. The introduction of multi-layer processing has contributed to increase the number of potential markets for blow molding. This study shows the effect of the processing parameters on the wall thickness distribution of each layer in the final multi-layer blow molded product. Some experimental results are compared to simulation predictions obtained by employing an integral viscoelastic material model (K-BKZ).
Modeling the In-Mold Coating Process of Thermoplastic Substrates
In-mold coating (IMC) is being successfully used as a primer IMC to cover surface defects such as porosity and sinks, for Sheet Molding Compound (SMC) compression molded automotive and truck exterior body panels. A new class of coating materials is being developed [1, 2] for thermoplastic substrates. The potential benefit of using In-mold coating (IMC) as a topcoat for thermoplastics is large. Painting is a very costly and a non-environmentally friendly operation. Key to optimizing the IMC process is to be able to predict the fill pattern, so as to locate the injection nozzle or nozzles, in locations where the potential for trapping air is minimized [3, 4]. CAD software is available  to predict the flow of IMC, when the substrate compressibility can be neglected. However, for SMC parts with large regions parallel to the mold closing direction (most truck parts) and in particular for thermoplastic parts, the substrate compressibility cannot be neglected. Our long-term research aims to develop a simulation package that predicts the flow of IMC when the substrate compressibility cannot be neglected. In this paper, a simple model to predict the pressures needed to inject the coating as a function of the substrate compressibility is presented. We will also show how the clamping force needed to prevent the mold deflection can be estimated.
Biodegradable Plastic Materials in Blends for Cost-Effective Low Temperature Applications
An on-going Pittsburg State University project focuses on the development of biodegradable polymer blends that can be used for low temperature durable and cost-effective bioresorbable castration clips for the farm industry. Clip materials must be non-food contaminants while being functional at the below zero degree polybutylene succinate and polybutylene/adipate copolymer were formulated into injection moldable blends that can withstand down to -20°C (negative 20 degrees Centigrade)."" weather of the North American farm belt winter months. Using the glass transition temperature (Tg) and solubility parameter (?) criteria pre-selected biodegradable materials polycaprolactone
Improving Accuracy of Blow Molding Simulation
Finite element analysis has revolutionized the design of blow molded parts. Using FEA an analyst can predict material distribution in blow molded parts and evaluate part performance prior to prototype molding. However, many finite element analysis procedures make use of shell-element formulations, whereby the parison or preform is modeled as a thin shell. In this paper we present a simulation of blow molding a bellows in which the shell-element formulation results in incorrect calculation of material distribution and offer an improved simulation using continuum elements. The importance of modeling the heat transfer within the melt as it contacts the mold wall is also illustrated.
Predicting Molding Forces in SMC Compression Molding
Much attention is now being given to improving the economy of Sheet Molding Compound (SMC) compression molding by reducing the cycle time required to produce acceptable parts in steady production. The longest stage of the molding cycle is the cure cycle. However, the filling stage does play an important role. The shorter the filling time, the more reactive an SMC can be used and thus the shorter the cure time. In particular for truck parts, due to their large size, being able to predict the press force needed to close the mold at a given speed is extremely important. The long-term goal of our research is to develop a model to predict closing forces as a function of raw material parameters - paste rheology, glass length and concentration - without the need to make the SMC. Here we present a simple model describing our approach and propose a preliminary procedure that can be used to obtain the closing force. This preliminary procedure still requires measurements to be obtained from the already made SMC. The results from this approach are compared to experimental results for a typical automotive grade SMC.
Comparison of DOE Methods on Hot-Plate Welding of Polypropylene
Design of experiments (DOEs) are a valuable tool for optimizing manufacturing processes and ensuring product quality. There are a wide variety of DOEs available, all having their own advantages and disadvantages and unique characteristics. In terms of plastic joining manufacturing processes, hot-plate welding of polypropylene was chosen as a platform for comparing three of the more common DOEs: full-factorial, Box-Behnken, and central composite. A complete analysis of the process was not sought, but within the field of factors studied, hot-plate welding of polypropylene appears to be a robust process. All three DOEs resulted in slightly different model equations, but very similar response surface contour plots.
New Thermoplastic Adhesive and Barrier Resins
BLOX™ Adhesive and Barrier Resins are the first commercialized polymers from a new family of thermoplastics, namely polyhydroxyaminoethers (PHAE). These resins offer a unique property set, including excellent adhesion to a variety of substrates, high gas barrier, superior clarity, and good mechanical strength and toughness. In addition, these resins are amorphous and can be easily processed using conventional thermoplastic processing techniques. Some commercial applications to-date utilizing PHAE resins include barrier packaging, starch-based foam packaging, and powder coatings. contributes to their relatively high selling price (typically between $3.00 - $5.00/lb), thus relegating their use to low volume applications such as resin modifiers and specialty coatings.
Factors Affecting Shot Size Variation in Injection Molding Processes
Many molders transfer from a velocity-controlled fill to a pressure-controlled pack and hold when the part is approximately 95% full. It is commonly known that changes in injection velocity affect the position of the melt front in the cavity at this transfer point. It is less commonly known that many other sources of process variation can have the same effect. This paper investigates the root sources of variation in fill-only part size. Three factors are considered: inertia of the injection unit, check ring leakage, and melt compressibility. While the common explanation in the industry has focused on inertia, deformation of the melt, check ring leakage, and the machine's hydraulic response play even more significant roles.
A Study of the Effects of Process Conditions on the Shrinkage of Plastic Parts in Injection Molding by the Taguchi Method
The shrinkage behavior of a plastic plays a critical role in determining the final dimensions of an injection-molded part. It is well known that process conditions affect many properties of plastic parts including shrinkage. This study applies the Taguchi method to systematically investigate the effects of process conditions on the shrinkage (along and across the flow directions) of three plastics; high-density polyethylene, general-purpose polystyrene, and acrylonitrile-butadiene- styrene. The most important processing variables affecting the shrinkage behavior of each plastic are identified. The optimization conditions to reduce the shrinkage identified by the Taguchi method are experimentally verified.
Modeling of Sink Mark Formation in Cross-Rib-Reinforced Injection-Molded Plastic Parts by Localized Finite Element Shrinkage Analysis
The sink mark formation in cross-rib-reinforced plastic parts has been modeled by a three-dimensional localized finite element shrinkage analysis. Using Abaqus software, sink mark formation is simulated by the localized thermal and structural finite element analyses near a cross-rib base. Initial conditions and boundary conditions for the Abaqus thermal analysis are determined from a molding analysis using C-Mold. Effects of packing pressure and cross-rib thickness on sink mark depth are analyzed. The predicted sink mark depth is compared with the experimental data from the literature.
Viscosity Effects in Rigid PVC
The viscosity of PVC is better understood if it is treated as a fluid which contains filler. Anomalous effects such as die swell increasing with increasing melt temperature and melting history causing changes to the viscosity can be explained if the PVC primary particles are viewed as filler which disappears during melting. The fusion torque peak is well described by this approach. The compaction minimum is a free flowing powder which transitions to a filler-containing viscous liquid. If another viscous liquid is added to a PVC compound then the fusion peak will be at a lower torque because the effective level of filler is reduced. This helps to explain the fusion curve of PVC compounds that contain CPE impact modifier.
TTIR Welding of Aliphatic Polyketone
This paper reviews the evaluation of through transmission infrared (TTIr) welding of aliphatic polyketone (Carilon Polymer). The paper reviews the effects of operating parameters, such as power density, weld time and pressure on weld strength. It was found that with proper operating conditions, parent material strength could be achieved. It was shown that thickness' as high as 6 mm were weldable using power densities in the range of 30 to 40 W/cm. Thickness' above 8 mm will be difficult to weld with TTIr (?=800-900 nm) due to surface heating and high power requirements (45W/cm). A transparent pressure foot may help remove heat and reduce marking.
Poly(phenylene ether) Engineering Thermoplastic Provides Creep Resistance, Toughness and Fire Resistance Required for High Performance Pallets
The first all-plastic pallets to meet high mechanical performance standards, and satisfy Underwriters Laboratories fire requirements have been developed. The foam injection molded top and bottom decks of the assembled pallets are made of a low specific gravity, flame retarded high performance (Poly(2,6 dimethyl 1,4-phenylene ether)/high impact Polystyrene) blend, Noryl® engineering resin. The pallet comer posts are made of injection molded high performance (Polycarbonate/Poly(butylene terephthalate) blend, Xenoy® engineering resin. Both of the resins' intrinsic properties, molding (processing) method, and design geometry meet the requirements for Grocery Market Association pallets. The resulting pallet is an all-plastic pallet with exceptionally high mechanical performance and flame resistance that is rated equal to or better than comparable wooden pallets.
On-Line Viscosity Measurement during Poly(ethylene terephthalate) Extrusion
The effects of various processing parameters (temperature, pressure and drying time) during extrusion of poly(ethylene terephthalate) (PET) were examined using a commercial on-line process control rheometer mounted on a twin-screw extruder. Particular attention was addressed to the effect of the moisture content. Moisture left in the resin pellets due to an incomplete drying reacts with the polyester to break down the molecular weight, which is reflected by a significant decrease of the viscosity. Since the PET resin is highly hygroscopic, off-line melt viscosity characterization may yield erroneous estimates of the rheological behavior. As in-line drying is recommended to achieve optimal properties, on-line viscosity characterization is required to provide an unbiased viscosity measurement and a true estimate of the performance of the drying step.
Nondestructive Study of Temperature-Property Correlations during the Curing of Rubberized Fabric
During the production of waterproof fabric for use as convertible car roofs, fabric and rubber are co-extruded and cured. Temperature control and residence time in the curing oven are key to the final properties. The manufacturer desires a nondestructive instrumented technique to replace the current pressure test used for quality control. Thermal conductivity of these fabrics has been measured nondestructively to relate to the degree of cross-linking. Thermal behaviors and compositions of this material have been evaluated both DSC. Combining thermal analysis techniques with thermal conductivity correlation's, may be an appropriate quality check of such product.
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