bluuebunny/crossref_metadata_2025_split huggingface dataset:
The ABC's of extruder screw design
Authors: Rauwendaal Chris 
Published: April 2003

AbstractScrew design for single screw extruders is a subject often surrounded by a certain degree of mysticism; in fact, by many people it is considered to be a black art. Others approach screw design from a mathematical point of view and determine the screw geometry from mathematical simulation of the extrusion process. Neither approach works very well. Our understanding of the extrusion process has improved considerably over the last 40 years. As a result, screw design certainly cannot and should not be considered a black art, because doing so would basically ignore all the progress made in the development of improved understanding of the extrusion process. On the other hand, relying only on mathematical modeling to achieve the desired extruder performance is not entirely appropriate, simply because the extrusion theory has not developed to the point that extruder performances can be predicted with 100 percent accuracy. The correct way to approach screw design is to combine extrusion theory and practical experience. As long as the extrusion theory is not fully developed, there is no substitute for practical experience. In this paper a practical approach to screw design is developed, with a minimal use of extrusion theory, to facilitate wider implementation of this approach. The design of the solids conveying, plasticating, melt conveying, and mixing zones of the extruder will be described based on a discussion on what physically happens to the material as it progresses along the extruder screw. It will be shown that the appropriate screw design is strongly dependent on the flow properties of the material to be extruded as well as the amount of pressure that has to be developed by the screw. This means that the screw design cannot be analyzed without consideration of the die that will be used at the end of the extruder. The design of the die, the melt flow properties of the polymer, the throughput rate, the melt temperatures, and the screen pack determine the amount of pressure that has to be developed by the screw. Therefore, the screw design that is appropriate in a regular extrusion operation is usually not optimum when a melt pump is used, because in the latter case the screw only has to develop a small amount of pressure.
Modeling plug‐assist thermoforming
Authors: Throne James L. 
Published: April 2003

AbstractPlugs are sometimes used to prestretch thermoplastic sheet prior to drawdown into thermoform mold cavities. The amount of force required to stretch the sheet depends upon the material constants in the stress‐strain equation, the sheet thickness, the extent of stretching, and the geometry of the plug. Two decades ago, Williams proposed simplifying the general thin membrane large strain theory to obtain a tractable force‐deflection model. In this paper, it is shown that for plug forming, the general theory reduces to a relatively simple, transcendental relationship. Experimental force‐deflection data obtained on two thicknesses of natural rubber sheet agree reasonably well with the general theory but not at all with the Williams large strain model.
A finite element study of viscoelastic effects in double‐layer coextrusion of polymer melts
Authors: Luo X.‐L. , Mitsoulis E. 
Published: April 2003

AbstractA finite element simulation of viscoelastic flows in double‐layer coextrusion of polymer melts has been performed. The constitutive equation used is a realistic integral model of the K‐BKZ type which can describe the viscoelastic memory characteristics of polymer melts. Viscosity and first normal stress data of typical PS and HDPE melts at 200°C are employed along with a feed ratio used in actual experiments found in the literature. Our results reveal important viscoelastic effects that could not be predicted by previous inelastic simulations. In particular, when the outer layer is more elastic than the inner layer, an enhanced extrudate swell is observed relative to the opposite configuration at the same flow rate, even if the outer layer is less viscous than the inner layer. In terms of a dimensionless stress ratio SR measured on the die wall, the more elastic material at the outer layer results in a higher SR value than that of the opposite configuration at the same flow rate. On the other hand, when the outer layer is less elastic than the inner layer, a reduced extrudate swell is observed relative to the opposite configuration at the same flow rate even if the outer layer is more viscous than the inner layer. When compared at the same SR value, however, our results show that the inelastic swell mechanism proposed by Tanner still applies qualitatively, i.e., a more viscous outer layer will result in larger extrudate swell than the opposite configuration.
Knit lines in reaction injection moldings
Authors: Maier Christian , Hrymak Andrew N. , Wood Philip E. 
Published: April 2003

AbstractKnit lines in reaction injection molding (RIM) are formed when a fluid flow front passes through the mold cavity and must pass around objects in its path. Factors were ordered in importance of their effects on the deterioration in mechanical strength associated with knit lines. In order of decreasing importance, reactant temperature, mold temperature, and relative location (from the product) of the knit line sample were found to affect the knit line strength.
An experimental evaluation of flow distribution models for spiral mandrel dies
Authors: Perdikoulias John , Vlcek Jiri , Vlachopoulos John 
Published: April 2003

AbstractThree recent mathematical models, developed to simulate the flow of polymer melts through spiral mandrel dies were analyzed. The models were compared against each other and with experimental data. The experimental data were obtained from processing several polymers through a 100 mm diameter spiral mandrel die attached to a 38 mm extruder. The die had no post‐spiral sections to ensure that only the effect of the spiral distribution system would be measured. The model developed by Vlcek et al. (Int. Polym. Process., 2, 174–181, 1988) was found to be the most accurate in predicting both the magnitude of the flow variation and the pressure drop.
Development of recycling technology for plastic fishing gear—a materials evaluation
Authors: Dagli S. S. , Kelleher P. G. , Monroy M. , Patel A. , Xanthos M. 
Published: April 2003

AbstractThe recycling potential of used plastic fishing gear by melt reprocessing is examined from a materials standpoint, as part of broader efforts to combat marine pollution caused by plastic debris. The present paper focuses on the identification of plastics and contaminants in a large variety of collected fibrous fishing gear, and the characterization of plastics in terms of possible degradation in the marine environment and their expected thermal stability during reprocessing. None of the major plastics involved (nylons and HDPE) was found to be significantly altered after exposure; accelerated thermal stability tests also indicate that these plastics could be reprocessed to acceptable products. Strong evidence suggests, however, that PP found in minor quantities would further degrade during extrusion. The presence of asphaltic and alkyd‐type coatings on the nylon fibers was shown to complicate the characterization and melt flow behavior. Preliminary data on extrusion conditions and the effects of coatings and additives on the mechanical properties of injection molded compounds are presented. General technical and economic aspects of complete recycling facilities are also discussed.
Measuring spatial fiber orientation—A method for quality control of fiber reinforced plastics
Authors: Fischer G. , Schwarz P. , Mueller U. , Fritz U. 
Published: April 2003

AbstractProperties of short and especially long fiber reinforced thermoplastics highly depend on fiber length distribution in the processed material and local fiber orientation in the processed part. Good mechanical performance is achieved, if overall mean fiber length is high and fiber orientation is well adapted to the external stress situation. If non optimized processing parameters are applied, a decay in mean fiber length and unfavorably orientated fibers in areas of high stress may result. Knowledge of morphological parameters provides quantitative information about the injection molding process and the design of the cavity. Recent advances in automated methods of measuring fiber length and spatial fiber orientation, which are based on image processing systems, reveal even small differences in morphology. Measuring spatial fiber orientation on polished cross‐sections by means of an image processor is a newer concept, that allows fast and quantitative description and optimization of the mold filling process. Some examples show the performance of the method; the measured fiber orientation is used to model thermal expansion and Young's modulus.
Peroxide modified polyolefin blends: Part I. Effects on ldpe/pp blends with components of similar initial viscosities
Authors: Yu D. W. , Xanthos M. , Gogos C. G. 
Published: April 2003

AbstractAs part of a broader research effort to prepare polyolefin blends with controlled rheological and mechanical behavior, LDPE/PP blends were peroxide modified through reactive processing in intensive batch mixers. Polymers with similar initial viscosities and elasticities were first melt mixed and then simultaneously reacted and mixed to produce blends whose reaction‐modified components had very different molecular weights and molecular weight distributions. The rheological behavior of the blends in both shear and elongational flow were found to depend on composition, peroxide concentration, and, possibly, on the relative response rate of the individual components to peroxide attack. In general, the rheological properties of the reacted blends differed significantly from those of blends compounded in the absence of peroxide, and they were influenced by the presence of two components with vastly different structural and rheological characteristics: the degraded PP of low viscosity and elasticity, and a branched or crosslinked LDPE with increased viscosity and increased melt elasticity. Data from the batch experiments of this work are useful in defining process requirements for continuous reactive extrusion compounding, such as component characteristics, length of mixing/reaction zones, screw geometry, and sequence of feeding, as they relate to product characteristics.
Applications for thermotropic liquid crystal polymer blends,
Authors: Williams David J. 
Published: April 2003

AbstractThermotropic liquid crystal polymers (TLCPs) are being widely investigated for their potential as “blend additives” in the 5 to 30% composition range for thermoplastic resins. Motivation for this activity stems from the desire to impart some of the remarkable qualities of TLCPs to the host resin, including enhanced processing and self reinforcement. The barriers inhibiting this technology include high TLCP resin costs, absence of specialized processing equipment, and blend brittleness. These and other barriers are expected to decline as the technology evolves. In the meantime, TLCP blends are expected to find usage in high value added niche applications, where current barriers are not controlling and where their prices can be justified on the basis of performance. The market potential for several TLCP/thermoplastic polymer blends in film and fiber applications are explored. Film and fiber blends are believed to have high potential for near term technical and commercial success. The incentives for development appear to lie primarily with host resin suppliers and device fabricators, and not with TLCP suppliers. The former are expected to benefit from improved consumption and sales resulting from improved resin system and device performance.
Morphology and property control via phase separation or phase dissolution during cure in multiphase systems
Authors: Hsich Henry S.‐Y. 
Published: April 2003

AbstractThe morphology and properties of polymer alloys and blends can be controlled via phase separation or phase dissolution during cure. The morphology and properties control by phase separation was achieved by simultaneously manipulating miscibility, kinetics of phase separation, and cure reaction of polymer systems. Using phase diagrams consisting of binodal and spinodal curves, the morphology of epoxy/CTBN (carboxyl‐terminated butadiene acrylonitrile copolymer) systems can be controlled by the mechanism of nucleation and growth or by spinodal decomposition. We have found that the particle size of the rubber reinforcement in epoxies is affected by the mechanisms of phase separation. Phase separation by nucleation and growth gives larger rubber particles than the corresponding phase separation by spinodal decomposition. This contrast in the morphology development is the consequence of controlling phase separation through chemorheological behavior. Modification of the phase separation kinetics in epoxy/CTBN systems was extremely effective at altering both morphology and properties of these alloys. This technique offers a mean to shift the glass transition temperature of the rubber‐rich phase while leaving the glass transition temperature of the epoxy‐rich phase intact. Such control over morphology is the key to ultimately controlling material properties. The morphology and properties can also be controlled by phase dissolution during cure via invoking anion–cation interactions or intrachain repulsion forces. Phase dissolution in elastomer blending is the key for achieving optimal morphology having a synergistic effect in the polymer blends. The morphology and properties of NR (natural rubber)/EPDM blends were controlled through compatibilization and co‐vulcanization to promote phase dissolution during cure. A synergistic result in the blends was achieved by having an interconnected phase morphology. The domain sizes of the blends are 3–5 μm before cure and 1–2 μm after cure. These blends showed superior mechanical properties to those of the individual NR or EPDM, after a long term of high temperature aging.
Impact behavior of modified PVC for outdoor applications
Authors: Tseng A. A. , Borrosky M. A. , O'Connor S. M. , Knotts J. J. 
Published: April 2003

AbstractA systematic study was conducted to determine the optimum polyvinylchloride (PVC) molecular weight and impact modifier concentration blend for the construction or outdoor application. This application called for a material with superior impact and weathering properties as well as cost efficiency. Three different molecular weights of PVC have been used in the present study. Impact modifier was blended with the PVC at various concentrations to improve its impact properties. The blends were extruded, pelletized, and injection molded for testing. Three types of impact tests, including the lzod, the Gardner, and the Dynatup impact tests, were conducted, all of which followed the ASTM Standards. A cost analysis was also conducted based on the relationship of the blend impact properties and their respective cost. The optimum blend developed has a molecular weight of 61,000 with an impact modifier concentration of six parts per hundred.
Report on the state of the art: Injection molding of fiber reinforced thermoplastics. Part I. materials and processes
Authors: Kelleher Paul G. 
Published: April 2003

AbstractThis is part of a survey of recent developments in injection molding of fiber reinforced thermoplastics. Topics discussed include materials and properties, the injection molding process with emphasis on fiber orientation and fiber lenght, advances in injection molding, as well as alternative methods for processing reinforced polymers.
PS–PMMA Block copolymer system as compatibilizer for PS–PVC blends
Authors: Caneba Gerard T. , Kandiraju Srinivasarao 
Published: April 2003

AbstractWe are studying the use of PS–PMMA block copolymer systems to improve the mechanical properties of immiscible PS–PVC blends. For a particular PS–PMMA block copolymer system, we found that effective compatibilization occurs at compatibilizer levels of 1–5 wt % in a 50/50 PS–PVC blend. In the samples, storage and stress relaxation moduli were at least midway between those of pure PS and PVC. On the other hand, the equivalent uncompatibilized blend exhibited storage and stress relaxation moduli that are much lower than those of the soft PVC component. Stress relaxation moduli of pure PS remained fairly constant with time, while a 25% drop was observed for pure PVC after 120 sec. Also after 120 s, stress relaxation moduli for the uncompatibilized blend exhibited a 20% drop, while a less than 10% drop was observed for the compatibilized PS–PVC blends.
Mathematical modeling of the pultrusion of epoxy based composites
Authors: Trivisano A. , Maffezzoli A. , Kenny J. M. , Nicolais L. 
Published: April 2003

AbstractThe thermokinetic and rheological behavior of epoxy based composites during the pultrusion of carbon fiber composites is analyzed using a mathematical model accounting for the heat transfer and the heat generation characteristics of polymerizable systems. An energy balance and a kinetic expression for the chemical reaction are simultaneously solved to calculate the temperature and degree of reaction profiles. Afterwards the viscosity as a function of the degree of reaction is computed applying a theoretical model. The dimensionless mathematical model is applied to the description and optimization of the process variables. General optimization criteria are identified and applied to compute, through a tailored numerical simulation, the optimum set of processing conditions for different case studies corresponding to different die temperatures, pulling speeds, and composite thicknesses.
Output computation in the grooved‐barrel extruder with regard to various conveyance techniques
Authors: Potente H. , Stenzel H. , Bergedieck J. 
Published: April 2003

AbstractToday the design of extruder screws for grooved barrel extruders is often still based on the known values of the designing engineers or on empirical methods. For some years theoretical approaches for the design of grooved‐barrel extruders have existed1–5 which are, however, not yet satisfactory in computing the output performance, especially in the pressure gradient dependent range. The article presented here introduces a technique for the computation of the output performance in grooved‐barrel extruders in the transport stiff as well as in the pressure gradient dependent range. This also allows the computation of optional multisection screws with shear and mixing sections. The equations are based on a physical–theoretical model that permits a precise statement about output performance and the relevant material‐, geometry‐, and process‐parameters.
Design and optimization of extrusion dies using computer based simulations
Authors: Rakos Ronald , Sebastian Donald 
Published: April 2003

AbstractComputer based simulations can be used to design and optimize commonly used industrial dies thereby reducing the need for costly modifications of a poorly designed die. Strategies are presented for the design and optimization of three types of extrusion dies, a mandrel pipe die, a spiral blown film die, and a coat‐hanger sheet die. The development of the computer model for each of the dies is presented. The assumptions made in the model and the numerical techniques employed in each of the simulations are outlined. Numerous examples are given to illustrate how each of the design simulations is used.
Melting theory for temperature‐dependent fluids, exact analytical solution for power‐law fluids
Authors: Rauwendaal Chris 
Published: April 2003

AbstractThe first quantitative description of melting in single‐screw extruders was given by Tadmor around 1965. A simple analytical theory was developed for Newtonian fluids assuming the fluid viscosity to be unaffected by changes in temperature. Also, an approximate analytical theory was developed for a power‐law fluid assuming the power‐law constants to be independent of temperature and viscous dissipation to be negligible. Later workers extended the theory; however, most of these extensions did not allow closed‐form analytical solutions, thus requiring numerical techniques to obtain solutions. One of the most crucial assumptions in the analytical melting theory is the assumption that the viscosity of the polymer melt in the melt film is not affected by temperature differences in the melt film. This assumption has been eliminated in the improved melting theory by deriving and exact solution of the temperature and velocity profile in pure drag flow of a temperature‐dependent power‐law fluid between two parallel plates. It will be shown that the inclusion of the temperature dependence of the viscosity dramatically affects the predictions of the melting rate. It will further be shown how the new theory can be used to predict the optimum barrel temperature for melting.
Structure development in powder processing of polyphenylene sulfide
Authors: Jog Jyoti P. , Lodha Anjali , Nadakarni Vikas M. 
Published: April 2003

AbstractThe thermal and crystallization behavior of polyphenylene sulfide (PPS) in the context of its structure development in solid‐state processing is reported. The solid‐state processing of polymers involves cold compaction of the powder, followed by sintering. Since this process comprises of heat treatment at high temperatures for extended periods, the structure of PPS would be expected to be affected. An attempt has been made to elucidate the effect of compaction and sintering process parameters on the physical and chemical structures of the polymer. The changes in the structure of the polymer were monitored by characterizing its melting and crystallization behavior. It was observed that compaction resulted in changes only in the physical structure, leading to destruction of the smaller/less stable crystallities. The thermal treatment at high temperatures led not only to physical changes involving crystal growth and perfection but also to chemical changes in the structure, resulting in modification of crystallization behavior. The extent of change was found to be different for PPS in the powder form and in the pellet form, which is explained on the basis of the restricted diffusion of air in pellet form as compared to the powder. Such changes observed in the samples were also dependent on the type of sintering medium. The sintering in presence of nitrogen did not show significant changes in the crystallization or melting behavior. Thus, the structure development in solid‐state processing of PPS was influenced by the sintering time, temperature, and sintering medium, leading to physical and/or chemical changes.
Postmolding and load‐induced deformation analysis of plastic parts in the injection molding process
Authors: Santhanam N. , Chiang H. H. , Himasekhar K. , Tuschak Peter , Wang K. K. 
Published: April 2003

AbstractTo assess warpage and shrinkage of an injection‐molded plastic part, an integrated computer‐aided engineering (CAE) system has been developed. This integrated system employs a simultaneous analysis of the compressible fluid flow, heat transfer, and residual stresses in the polymer during the filling and postfilling stages of the injection molding process and of mold cooling/heating that occurs throughout the entire process. Using the polymer temperature and pressure distributions as a function of time, an analysis has been performed to predict the residual stresses, treating the polymer as a viscoelastic material. The resultant loading is interfaced with the structural analysis program ABAQUSTM to predict the postmolding shape of the plastic part. Analysis has also been performed to evaluate the load‐deflection behavior of a molded part and the effects of different degrees of material anisotropy.