bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixing in Non-intermeshing Twin Screw Extruders
Authors: Bigio D. , Baim W. , Wigginton M.
Published: December 2013

Twin Screw extruders are operated typically in the starve-fed mode, with regions of channels partially-filled with polymeric materials. Although much has been done to understand and characterize the process of devolitalization and polymerization, many of the models have been based on simple mixers like batch mixers or continuous stirred reactors, not on the complex flow patterns found in twin screw extruders. Accurate models of the entire process requires appropriate modelling of the nature of mixing in a partially-filled channel. This paper presents results of a visual study of the counterrotating, non-intermeshing twin screw extruder operated with partially-filled channels. The experiments characterize the nature of mixing and the effect due to screw flight stagger and fluid viscosity.
Simultaneous Diameter and Thickness Control in Tube Extrusion
Authors: Defaye G. , Caralp L. , Delfanne B. , Labaig J. J.
Published: December 2013

In recent years, many applications of process control to extruders have concentrated on the control of temperature and pressure in the die. This study investigates the simultaneous control of the two-dimensional characteristics of a tubing. An identification and control package is used. The system is shown to be non-interacting.
Processing and Properties of Polycarbonate/Liquid Crystal Polymer Blends
Authors: Valenza A. , La Mantia F. P. , Paci M. , Magagnini P. L.
Published: December 2013

Rheological and mechanical properties, structural characteristics, extrusion and injection molding behavior of blends of polycarbonate (PC) with a thermotropic, wholly aromatic copolyesteramide have been investigated. The processability of polycarbonate is remarkably improved by addition of small contents of liquid crystal polymer. All the flow curves of the blends lie between those of the pure components. In the processing conditions adopted, the LCP particles are easily elongated in the flow direction. In this direction the elastic modulus rises remarkably with LCP content. The modulus-composition curve is, however, lower than that expected on the basis of an additive rule due to the incompatibility and poor adhesion between the two phases. Finally, injection molding of this extrusion grade PC has been easily performed by adding small contents of LCP. The impact strength values of the injection molding samples of these blends are only slightly lower than that of the pure PC.
Scale-up Effect in Internal Mixers
Authors: Kawanishi K. , Yagii K. , Obata Y. , Kimura S.
Published: December 2013

In the development of a new polymer and a new compound, mixing equipment plays an important role. However, the properties of a compound tend to vary depending on the size and shape of the equipment used and a means to obtain the same compound by a small scale laboratory mixer as the one obtained by a large scale mixer has been longed for a long time.

As a rubber compound is characterized by the physical properties, they are affected both by the dimensions and shape of the equipment and the mixing conditions. Recently, we developed a laboratory mixer generally following the designs of FH Banbury with exchangeable rotors and mixing chamber blocks which enable us to investigate the influences of the shape of equipment as well as the mixing conditions.

In analysing rubber mixing, we found that the following factors should be taken into account, that is, unit-work which is the applied energy to the unit volume of the material during mixing, Mooney viscosity of the compound, bound rubber which is the amount of polymer unextractable from the compound by a solvent, and weight average molecular weight of polymer extractable by a solvent. If the values of the four factors are close enough for the two compounds obtained by different mixers of different size and shape, one may regard them as the same compounds. Furthermore, we experimentally measured the four factors for the compounds of typical formulations of three species of commercially available rubbers, that is, styrene butadiene rubber, ethylene propylene rubber and butadiene, and expressed the values of the factors as functions of mixing conditions and the parameters of rotor shapes by means of multiple regression analysis. Among the rotor parameters, the following showed significant effects: tip clearance, tip width, total bulkiness and wing overlap ratio. As for the mixing conditions, mixing time, rotor speed and mixing temperature were dominant.

Using the functions obtained by the above mentioned method for the laboratory scale mixer, we tried to find the combinations of rotor shapes and mixing conditions that reproduced the compound mixed by large scale mixers. The optimum parameters of a laboratory mixer for the reproduction of the mixing of an industrial mixer were found to be larger rotor tip clearance, larger rotor tip width, larger wing overlap ratio, higher mixing temperature, and higher rotor speed than those of proportionally reduced dimensions and comparable conditions.
Mixing and Extrusion of High Silica and all Silica-natural Rubber Compounds
Authors: Nakajima N. , Shieh W. J. , Wang Z. G.
Published: December 2013

This work is an investigation on causes of extrusion problem of a high silica- and all silica-filled natural rubber compounds containing a coupling agent. The 67% silica and 33% carbon black, N110 compound (Compound 3) gave a wavy surface of extrudate from a profile die. The 100% silica-filled compound (Compound 4) was too stiff to be extruded. Reference compounds, 100% carbon black (Compound 1) and 33% silica with 67% carbon black (Compound 2), gave smooth extrudates. The amplitude dependence of storage modulus measurements indicated Compound 4 had a poorer dispersion of the filler. Scanning electron microscopy also showed a poorer dispersion for this compound. However, Compound 3 could not be distinguished from Compounds 1 and 2 in the above investigation. Transient shear measurements at very low deformation rate indicated a reaction between natural rubber and the coupling agent, resulting in gel and long-branch formation. Differential scanning calorimetry indicated the coupling reaction was completed at 140°C within the mixing time. By holding the maximum temperature of mixing as low as possible, the extrudate of Compound 3 became smooth, but Compound 4 still did not perform well. Improvement of dispersion is necessary to make Compound 4 extrudable.
An Analytical Model of Partial and Thorough Melting in Single-screw Extruders
Authors: Potente H.
Published: December 2013

Based on the classic Tadmor model, a number of mathematical models have been developed for calculating the melting profile in single-screw machines. The most comprehensive of these is the five-zone model from Lindt. All these models can only be solved by numerical methods. Parallel to this, attempts have been made to find analytical solutions which describe the melting profile with sufficient accuracy. In this report a comprehensive analytical solution for the whole premelting- and melting process on barrel and screw with respect to the power law will be given.
Extrusion of Rubber Compounds and Highly Filled Thermoplastics through Coathanger Dies
Authors: Wang Y.
Published: December 2013

The isothermal flow of plastic fluids in coathanger dies is studied. A general three-dimensional finite element code is developed for the flow analysis purpose. The pressure distribution, the velocity distribution and the transverse flow rate distribution are calculated. The yield value of filled compounds gives rise to a mobile plug in the flow channel. The development of plug zone along the flow direction is also shown by the finite element analysis. The effect of the die geometry on the transverse flow rate distribution is critically discussed. It is found that the cross sections of the flow channel in a coathanger die has the shape of a dog bone or a dumbell which make a nearly even transverse flow rate distribution possible.
Conveying and Melting in Screw Extruders with Axial Screw Movement
Authors: Rauwendaal C.
Published: December 2013

Reciprocating extruders are used in injection molding. The number of reciprocating extruders used in the plastics processing industry is larger than conventional extruders. Therefore it is surprising that only few studies have been made of the conveying and melting process in reciprocating extruders.
Melt Strength Behavior of Polyethylene Blends**
Authors: Ghijsels A. , Ente J. J. S. M. , Raadsen J.
Published: December 2013

Melt strength data are presented on different types of binary polyethylene blends as linear low density polyethylene/low density polyethylene (LLDPE/LDPE), linear low density polyethylene/high density polyethylene (LLDPE/HDPE) and LDPE/LDPE. Melt strength was assessed from uniaxial tensile experiments with a Rheotens apparatus. In addition, the blends were characterised in terms of a few other rheological properties such as the zero-shear viscosity and the extrudate swell in capillary extrusion. For the LLDPE/LDPE blend pairs synergistic effects were observed for the melt strength and some other properties. No melt strength synergism was observed for the LLDPE/HDPE and the LDPE/ LDPE blends. The results are discussed in terms of the Bersted model on the effects of long chain branching on the low-shear melt viscosity of polyethylenes.
Thermoviscoelastic Calculation of Residual Stresses and Residual Shapes of Injection Molded Parts**
Authors: Kabanemi K. K. , Crochet M. J.
Published: December 2013

The present paper describes a three-dimensional finite element method for calculating thermoviscoelastic stresses generated during cooling of injection molded parts. The initial temperature field corresponds to the end of the filling stage. The fully time-dependent algorithm is based on the calculation of the elastic response at every time step. The time-temperature equivalence is assumed for the non-isothermal behavior. At the end of the calculation, one obtains the residual stresses and the shape of molded parts at room temperature. The method is illustrated by means of four examples.
Analysis and Simulation of Structural Reaction Injection Molding (SRIM)
Authors: Aoyagi H. , Uenoyama M. , Güçeri S. I.
Published: December 2013

A numerical approach is taken to the analysis and simulation of structural reaction injection molding (SRIM). Formulation is based on anisotropic Darcy flow through a porous medium. Governing equations are developed for thin gap mold cavities with no gapwise flow. The reaction of the resin and its effect on the local viscosity are accounted for by using constitutive models. A numerical grid generation method is employed to handle irregularly shaped flow domains during the filling stage. A new finite difference mesh is generated at each time step to cover the flow domain as described by the mold boundaries and the moving resin front. The technique is shown to be capable of handling a wide range of irregularly shaped planar geometries in monitoring the instantaneous state of the cure along with the temperature and the flow fields in a detailed form. The results indicate a highly pronounced disturbance of the temperature field due to the exothermic nature of the chemical reaction. It is also shown that this temperature field and the state of cure significantly influence the flow field through fluid viscosity. The method reduces to the simulation of resin transfer molding (RTM) processes by dropping the reaction terms. The comparisons with limited experimental data for isothermal flows indicate high accuracy in both predicting the resin front locations and the fill pressures.
Starve-fed Flow in Co-Rotating Twin Screw Extruders
Authors: Bigio D. , Cassidy K. , Dellapa M. , Baim W.
Published: December 2013

A visual study was performed to determine the mixing abilities in simple conveying sections of the partially-filled, corotating, twin screw extruders (PFCoTSE). The amount of mixing that occurs in the PFCoTSE is heavily dependent on the degree to which the channels are filled. A quasi-quantitative method of measuring the growth of an injected tracer is used in determining mixing. It was determined that the PFCoTSE's mixing sections are linear mixers as can be seen from the fact that an injection of tracer quickly transforms into a line and stays as a line throughout the machine and does not break apart while going through the nip (i.e., no reorientation).
Modelling Twin Rotor Mixers and Extruders
Authors: David B. , Sapir T. , Nir A. , Tadmor Z.
Published: December 2013

An improved flow model for simulating flow in batch and continuous twin rotor mixers and extruders is presented. The model adopts an Eulerian point of view from the stationary barrel surface. It incorporates Couette flow analysis, which accounts for the curvature effects in the non-intermeshing region, and correction factors for treatment of flow near the bounding sidewalls of a batch mixer. A method for tracking the motion of fluid particles is presented.
Real Time Video Techniques in the Analysis of Blown Film Instability
Authors: Sweeney P. A. , Campbell G. A. , Feeney F. A.
Published: December 2013

This paper describes a device which was developed to measure the degree of instability during blown film processing. Two types of data analysis are developed which can be used to analyze the instability data and the relative merits of each are discussed. The paper also describes how the device was used to measure the effect of adding two stabilizers (2 MI LDPE and 0.25 MI LDPE) at different concentrations to a 1 MI LLDPE during blown film processing. The process stability improved with higher concentrations of either LDPE with the 0.25 MI LDPE having the stronger effect. These results are consistent with the belief that long chain branching in polyethylenes plays a major role in stabilizing the blown film processing of polyethylenes.
Injection Molding of iPP
Authors: Saiu M. , Brucato V. , Piccarolo S. , Titomanlio G.
Published: December 2013

An experimental study of iPP injection molding is carried out. Pressure distribution during both filling and post filling stages, mass entering the mold during each stage of the process, morphology and crystallinity distribution of the final object are analysed. Interesting features are evidenced and discussed in relation to gate geometry and filling flow rate. Evidence of flow crystallization inside the cavity is also reported.
The Challenges of Waste Toward the 21st Century
Authors: Saeki Y.
Published: December 2013

The problems of waste disposal have become major issues in Japan. Japan must deal directly with these issues. In early 1970s, “KOGAI” or environmental pollution already loomed as major problems. A number of technical innovations and systems were proposed to recycle various waste products. Based on those experiences, current situation of urban refuse, waste plastics, scrapped tires and scrapped automobiles in Japan and their challenges toward 21st century are discussed.
Effect of Surface Coatings on Wall Slip of LLDPE
Authors: Hatzikiriakos S. G. , Stewart C. W. , Dealy J. M.
Published: December 2013

The polymer-metal interface in a sliding plate rheometer was modified by applying three fluoropolymer coatings to the plates in order to examine their effect on the wall slip behavior of a linear low density polyethylene. All three coating materials increased the slip velocity markedly. Furthermore, it was found that the critical shear stress for the onset of slip scales well with the work of adhesion of the interface, suggesting that slip is the result of adhesive failure at the interface.
Effects of Interfacial Conditions on Wall Slip and Sharkskin Melt Fracture of HDPE
Authors: Hatzikiriakos S. G. , Dealy J. M.
Published: December 2013

Experiments were performed in capillary and slit rheometers to determine the effects of the presence of fluoropolymers at the polymer-wall interface on wall slip and extrudate distortion of a molten high density polyethylene. Two fluoropolymers were used to modify the interface. It was found that one of these decreased slip compared to the clean interface while the other increased slip. However, both were found to improve extrudate appearance, thus indicating that both adhesion promoters and slip promoters may improve extrudate appearance. The mechanism underlying this rather surprising conclusion is also discussed.
Modeling of Non-isothermal Film Blowing with Integral Constitutive Equations
Authors: Alaie S. M. , Papanastasiou T. C.
Published: December 2013

Non-isothermal, melt film-blowing is analysed by means of a nonlinear integral constitutive equation that incorporates shear history effects, spectrum of relaxation times, shear thinning and extension thinning or thickening. The temperature history, as predicted by the simultaneously solved energy equation, is introduced into the constitutive equation by means of the appropriate shift factor incorporated in the linear modulus of the constitutive equation. The resulting system of integrodifferential equations is solved by finite element discretization and Newton iteration. Bubble shape, velocity, temperature, stress and thickness profiles are predicted simultaneously. Predicted film thickness, temperature and stress profiles of blowing of polystyrene are compared with experimental data taken from the literature.
Processing-Structure-Properties Relationships in Blends with Thermotropic Liquid Crystalline Polymers
Authors: Incarnato L. , Nobile M. R. , Frigione M. , Motta O. , Acierno D.
Published: December 2013

In this paper the effect of the inclusion of thermotropic liquid crystalline polymers (TLCP) in thermoplastic polymers is analyzed, with due attention to similar studies reported in the literature. Numerous results relative to TLCP containing blends are considered in terms of structure development in typical processing operations like extrusion and fiber spinning. Several systems have been studied in order to emphasize that different effects can be obtained as regards processing and mechanical properties of the host matrices. As for rheological aspects, it has been verified that TLCP can be considered as effective flow aids, even at low concentrations. The addition of a low percentage (5 to 10 %) of a TLCP with a viscosity lower than that of the matrix produces a significant reduction (25 to 40 %) in the blend viscosity. Moreover, mechanical results have shown that an improvement of the matrix rigidity can be obtained, especially at high percentages of TLCP (30 %), under processing conditions where a highly extensional flow prevails. However, a decrease in the ultimate elongation of the matrices has been found in all systems where a poor adhesion between the two phases exists.
RIM-pultruded Prepreg for the Injection Molding of Long-fiber Epoxy Composites
Authors: Ishida H. , Zimmerman D. A.
Published: December 2013

A long-fiber injection molded phenoxy composite has been developed by using a new processing technique that combines reaction injection molding (RIM) and pultrusion to produce a prepreg pellet. RIM-pultrusion uses a reaction injection system instead of the resin bath typically used in pultrusion. The resin system and process developments are described. The fiber damage during injection molding is minimized by using the RIM-pultruded pellet as prepreg. The resulting long-fiber carbon fiber composite has an average volume aspect ratio that is an order of magnitude higher compared to typical short-fiber injection molding. The fiber length distribution (FLD) is measured for both glass and carbon composites. The extent of bundling has been determined from the moment ratio. The extent of reaction of the diepoxide during processing is measured using Fourier transform infrared spectroscopy (FT-IR). The pultrusion line speed and temperature are determined for secondary processing, namely injection molding, from the epoxide conversion. Also, dynamic mechanical analysis has been performed on the resin, prepreg, and injection molded sample to study the mechanical and thermal properties. Scanning electron microscopy is employed to examine fiber-matrix adhesion, void content, bundling, and fiber pull-out.
Potential Applications for Computer-aided Extruder Design
Authors: Potente H. , Hanhart W. , Schöppner V.
Published: December 2013

The simulation method is able to relieve the engineer of experimental work during the planning of extrusion plant and thus clearly reduces the development time. Sufficiently precise determination of the calculable parameters is possible with the process models developed so far. The empirical knowledge of the engineer is, of course, necessary as well in order to estimate the impact of influencing parameters that are not taken into account in the calculation models. The presented simulation program REX can perform these complex calculations in a comprehensive manner, with its simple and comfortable user interface. The program, however, can be employed as a valuable tool only if it is in the hands of an expert operator who can, and indeed must, be able to interpret the results as well.
Real-time Neutron Radiography of Injection Mold Filling
Authors: Weissenberger M. M. , Giacomin A. J. , Reuscher J. A. , Russell C. M.
Published: December 2013

A new method of flow visualization has been used to film the injection mold filling operation. A study of jetting has been performed using real-time neutron radiography which permits real-time visualization through metal molds. Results of this method for a thermoplastic elastomer filling an end-gated strip mold are reported for a bench-scale injection molder at constant pressure.
Unsteady Flow of Semi-Concentrated Fiber Suspensions in Compression Molding
Authors: Ahmed A. , Alexandrou A. N.
Published: December 2013

This paper deals with the flow behavior and the resulting fiber orientation during compression molding of semi-concentrated fiber suspensions. The suspension is characterized using the Dinh and Armstrong integral constitutive relations, expressed in terms of the finite deformation tensors. The equations of motion are expressed in a convenient Generalized Eulerian-Lagrangian reference frame. The resulting nonlinear system of equations is solved using full Newton-Raphson iteration procedure. An integral boundary condition has been applied at the press wall to represent the constant force condition at that boundary. Results are presented for the isothermal filling of a two-dimensional rectangular cavity for the flow field and the associated fiber orientation. The influence of different parameters such as molding force, fiber concentration, fiber aspect ratio etc. on the compression rate is also presented.
Residual Stresses in Quenched and Injection Moulded Products
Authors: Jansen K. M. B.
Published: December 2013

The differences between residual stress formation mechanisms are studied for several important polymer processes. The most important cases are free quenching (e.g. in extrusion), constrained quenching and constrained quenching with varying applied pressure (injection moulding). A simple, but physically relevant, elastic solid model is assumed (viscous melt and purely elastic solid) yielding Struik's cooling stress model for the free quenching case. In the constrained quenching case, however, the residual stresses are found to vanish. This allowed us to derive a simple analytical expression for the residual stresses in injection moulded products. These stresses were found to be proportional to the maximum melt pressure and are tensile near the surfaces. The predictions compared well with the measured stress distribution. Finally the effects of residual stresses with respect to warpage and environmental stress cracking are discussed.
Influence of the Thermomechanical Parameters on the Morphology of a Polyamide (PA 6) and Polypropylene Blend
Authors: Knobel B. , Villemaire J. P. , Agassant J. F.
Published: December 2013

The morphology of a polypropylene and polyamide blend has been investigated with the Rheoplast rheometer which allows us to apply a well defined thermomechanical history before the capillary flow. The polymer flow in the Rheoplast has been modeled using a homogenization hypothesis for the rheology. Correlations between the different observed morphologies and shear rates, elongational rates as well as dissipated energies are discussed.
Finite Element Simulation of Thick Tube Expansions
Authors: Sun J. , Luo X.-L. , Tanner R. I.
Published: December 2013

We consider the numerical simulation of the combined drawing and radial expansion of a thick tube, which is a possible model for continuous tube-making. Both Newtonian and visco-elastic cases are considered. Mesh refinement studies show convergence; to stabilize the computations we have introduced relaxation factors. The main difficulty here is in finding the region of contact with the sizing die, as well as the form of the free surface. It was found that the extra stress component, τθθ, is most helpful in considering the characteristics of tube expansion. The maximum value of τθθ occurs near the outer wall of the exit of the annular die for Newtonian flow and near the interface for K-BKZ liquids. Both for Newtonian and K-BKZ liquids the extra stress component τθθ in the expansion region, not including the vicinity of the exit of the die, develops from the inner free surface toward the outer free surface. The pressure value needed for tube expansion increases and then decreases as the expansion ratio R0/RW increases.
Flexural Modulus of Compression Molded Glass Fiber Reinforced Thermoplastics
Authors: Xia M. , Hamada H. , Maekawa Z.
Published: December 2013

The flexural properties of compression molded stampable glass fiber reinforced polypropylene are examined. Fibers flowing with the polymeric matrix are found to be oriented close to the edge of the die. The fiber orientation distribution is characterized by a fiber orientation index using an image processing system. The flexural elastic modulus of the plaque estimated from laminated-plate theory is found to be in good agreement with the experimental results.
Multilayer Injection Moulding
Authors: Peters G. W. M. , van der Velden P. J. L. , Meijer H. E. H. , Schoone P.
Published: December 2013

The modelling of multilayer reactive injection moulding is studied. After presenting the equations describing the process, two important aspects are dealt with in more detail. These are particle tracking and the modelling of the flow front. First results demonstrate the possibilities of the modelling and show satisfactory agreement between predictions of numerical simulations and experimental results, concerning particle tracking in the whole flow domain and the break-through of layers in sequential two component moulding.
Modeling and Simulation of High Reynolds' Number Flows During Reaction Injection Mold Filling
Authors: Mohammed Rahima K. , Osswald Tim A. , Spiegelhoff Timothy J. , Sun Esther M.
Published: December 2013

Reaction injection molding (RIM) involves the injection of low viscosity polymers into mold cavities at relatively high injection speeds. The short cycle times, coupled with low injection pressures and clamping forces make RIM well suited for the rapid production of complex parts. High injection speeds, low viscosities and narrow cavities lead to high Reynolds' number flows during mold filling. The presence of high Reynolds' number flows is a notable difference between RIM and conventional thermoplastic injection molding (TIM). Unfortunately, this type of flow with significant inertia effects can lead to reduced part quality. The material properties and characteristics of RIM parts are influenced by flow patterns, weld lines, air entrapment as bubbles or pockets, especially as the material flows around inserts. These defects and characteristics, coupled with a growing demand for high quality RIM parts, is responsible for the increased interest in the flow during mold filling. This paper presents the development and test of a model to stimulate high Reynolds' number flows in thin cavities present during reaction injection mold filling.
Analysis of Mixing Performance in a VIC Mixer
Authors: Yang Haur-Horng , Manas-Zloczower Ica
Published: December 2013

The VIC mixer is an intermeshing internal mixer, whose unique feature is its ability to vary the clearance between the two rotors. The flow field in the chamber of an internal mixer is difficult to analyze due to the complex geometry and transient character of the flow. Here, a fluid dynamics analysis package – FIDAP, using the finite element method was employed to simulate the flow patterns in a VIC 1.9 mixer. A 3D flow analysis was carried out for the whole mixing chamber. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries to represent a complete mixing cycle. The flow field was characterized in terms of velocity profiles, pressure contours, shear stresses generated and a parameter λ quantifying the elongational flow components. The last two parameters are the most important ones in analyzing dispersive mixing efficiency. Distributive mixing was studied numerically by means of tracking the evolution of particles originally gathered as clusters. The pairwise correlation function and the particle concentration were used to quantify the degree of mixing. The dynamic average flow field characteristics based on the particle tracking were also calculated. The effect of changing gap size on dispersive and distributive mixing was investigated.
Compatibilization and Dynamic Vulcanization of PA 6/Isobutylene Methylstyrene Elastomer
Authors: Kuwamoto K.
Published: December 2013

The effect of reactive polymer blending on the rheological properties and the deformation of dispersed phase in extruded films is described. Three types of polymer blends are studied: (1) a non-reactive blend of nylon 6 (PA 6)/isobutylene-co-para-methylstyrene elastomer; (2) a compatibilized blend of PA 6/brominated (isobutylene-co-para-methylstyrene) elastomer (XP-50); (3) a compatibilized, dynamically vulcanized blend of PA 6/XP-50 plus curatives. Mixing is performed with a Brabender mixer and a twin screw extruder. Rheological measurements were performed at 240 °C which is above melting temperature of PA 6. The storage moduli and complex viscosities of type (3) are the highest, those of type (2) are the next and those of the mechanically mixed non-reactive components are the lowest. The dispersed phases in extruded films show that the deformation of the dispersed elastomer in type (3) is the smallest. The sizes of the dispersed-elastomer domains in type (2) and type (3) are much smaller than those of type (1). There are large and highly deformed dispersed phases in the film of type (1). Also the interfacial bonding is poor.
Integral Constitutive Model (K-BKZ) to Describe Viscoelastic Flow in Injection Molding
Authors: Chang Rong-Yeu , Chiou Shiaw-Yuh
Published: December 2013

A novel theory which employs the K-BKZ viscoelastic integral constitutive model was developed in this study for simulating the non-isothermal injection molding filling process and the frozen stresses of a three-dimensional thin part. The simulation of viscoelastic model in such a problem has not yet been discussed in most previous works as a result of the complexity of this problem. A quasi-steady approximation concept was developed in the present investigation for solving the non-isothermal filling process via K-BKZ viscoelastic integral constitutive model. Additionally, the numerical method of flow field was based on the control volume finite element method. The flow field of generalized Newtonian fluid was used as the initial guess of flow kinematics. The quasi-steady state approximation was introduced for each element to calculate the flow kinematics and stress profile from the K-BKZ integral constitutive model. The finite difference method with streamline upwind characteristic was adopted here for calculating the temperature field of process. When the cavity is fully filled, the subsequent non-isothermal stresses would relax after cessation of flow. Thereby, the frozen stresses (or frozen birefringence) could be obtained.
Mechanical Effects in Extrusion: Slit Dies
Authors: Pittman J. F. T. , Sander R. , Schuler W. , Pick H. , Martin G. , Stannek W.
Published: December 2013

Simulations of the elastic deflection of a 1.2 m slit die under load during the extrusion process have been performed, using the commercial finite element package MARC. The melt pressure distribution needed to assign the loads to the MARC package was previously obtained by a Hele-Shaw based finite element program, and was thus not coupled with the deflection analysis. Existing analytical calculation methods for deflection are also examined. Experiments using production scale machinery have been conducted to record the die deformations under different melt pressures and compared with the computed data. Analytic deflection predictions are shown to be inadequate. The numerical results are fair, but it is clear that coupling of flow and deflection analyses is essential.
Structures and Properties of Injection Moldings of β-Crystal Nucleator-Added Polypropylenes
Authors: Fujiyama M.
Published: December 2013

An isotactic polypropylene homopolymer (PP) was added with 0 to 10000 ppm of γ-quinacridone, a β-crystal nucleator of PP. Flexural test specimens were injection-molded from the PP at cylinder temperatures of 200 to 320 °C and the structures and properties have been studied. The results can be summarized as follows: The crystallization temperature increases with γ-quinacridone content. The β-crystal content decreases with increasing cylinder temperature and shows a maximum at a γ-quinacridone content of about 100 ppm. The thickness of the skin layer scarcely depends on γ-quinacridone content. The orientation of β-crystals decreases with increasing cylinder temperature. It is high at the surface regions and decreases toward the interior. The Izod impact strength increases with γ-quinacridone content. The degree of the increase is higher as the β-crystal content is higher and reaches more than threefold in the highest case. The flexural modulus and strength decrease by about 10 % in the highest case. The heat distortion temperature increases with γ-quinacridone content. The mold shrinkage increases with γ-quinacridone content. From these results, it is concluded that the injection moldings of PPs containing γ-quinacridone are superior in impact strength and heat resistance.
Analysis of Polymer Flow through Coathanger Melt Distributors
Authors: Schläfli D.
Published: December 2013

Coathanger melt distributors are generally designed on the basis of one-dimensional flow models. These do not always have the desired performance, wherefore a 2-D flow analysis tool was developed based on lubrication approximation theory. This tool uses a contour adapted calculation grid and accounts for manifold side walls. Good agreement is observed for a variety of distributor designs. The integration of this tool into the design process permits to evaluate distributor geometries at design stage, reducing empirical corrections and adjustments.
Elastic Calculation of Residual Stresses in Injection Molding
Authors: Boitout F. , Agassant J. F. , Vincent M.
Published: December 2013

A calculation of residual stresses in injection molding using a 2-D description of the geometry is presented. The polymer follows an elastic behavior law. The thermal shrinkage and the frozen-in pressure when a layer solidifies are taken into account. A calculation of the pressure in the liquid areas after the gate is frozen is presented. A simplified mold deformation model is introduced and its influence on residual stresses is shown. Results are presented for a polystyrene injected in a square plaque.
Structure and Properties of Injection Moldings of β-Crystal Nucleator-Added Polypropylene
Authors: Fujiyama M.
Published: December 2013

Isotactic polypropylene (PP) with MFIs of 0.43 to 44.5 g/10 min were added with 0 to 10 ppm of γ-quinacridone, a β-crystal nucleator of PP. Flexural test specimens were injection-molded from the PPs at constant molding conditions and the structures and properties have been studied. 1) The crystallization temperature increases with γ-quinacridone content and MFI of the base resin. 2) The β-crystal content increases with γ-quinacridone content and MFI. 3) The thickness of the skin layer decreases with MFI and scarcely depends on γ-quinacridone content. 4) The orientation of β-crystals decreases with MFI. 5) The Izod impact strength increases with γ-quinacridone content for PP with MFI < 40 g/10 min, and decreases with MFI. However, little improving effect of γ-quinacridone is observed for MFI > 40 g/10 min. 6) The flexural modulus and strength decreased by about 10 to 20 % by the addition of γ-quinacri-done and the decrease is more significant for PP with higher MFI. 7) The heat distortion temperature increases with γ-quinacridone content and the increase becomes more prominent with increasing MFI. 8) The mold shrinkage increases with γ-quinacridone content and decreases with MFI.
Study on the Performance of Cooling Systems in Precision Injection Molds
Authors: Yang S. Y. , Chang H. C.
Published: December 2013

Mold temperature is one of the most important factors regarding the quality and production rate in injection molding. Enhancing the performance of mold as heat exchanger is expecially critical to precision molding. In this study, mold temperatures measured at four selected points are used to assess the effects of cooling channel layout and core material on the cooling performance of injection molds for precision molding. Measured data indicate that mold temperature is a complex function of space and time (in-cycle and cycle-to-cycle). Three performance indices based on the measured data are first established for comparing the cooling performance between molds with various design parameters. They are the response to reach equilibrium, the thermal uniformity, and the average mold temperature. Molds implemented with three typical cooling channel configurations and inserted with three core materials are constructed. Their cooling performances during injection molding of disks with steps have been compared. Information from computer-aided simulation of the mold cooling process further facilitates the evaluation of mold cooling performance. General guidelines for planning of cooling channel layouts and selection of core materials are drawn from this study. Experimental and theoretical results suggest that high thermal conductivity of the cores enhances the thermal uniformity, while high heat capacity retards the response of the system to reach thermal equilibrium. High convective area to mold volume improves the overall performance of mold as heat exchanger.
Modeling of Polymer Devolatilization in a Multi-vent Screw Extruder
Authors: Wang N. H. , Sakai T. , Hashimoto N.
Published: December 2013

A model for representing polymer devolatilization behavior in a screw extruder with multi-vent sections has been proposed. In this model, an overall film-interface geometry factor (OFIGF) comprised of several local film-interface geometry factors (LFIGF) is used as a measure for the devolatilizing performance of a screw extruder. Moreover, the OFIGF is related to screw geometries and open angles of open areas in vent sections, and dependent on the degree of filling or the flowrate of the fluid and the screw speed. An intermeshing co-rotation twin-screw extruder popularly used was taken as an example to discuss the effect of the OFIGF on its devolatilizing performance. For this purpose, a solution of how to calculate the local film-interface areas and their exposure time in a venthole unfitted zone (VUfZ) and a venthole fitted zone (VFZ) with an open area was presented. Furthermore, several interesting results about how the OFIGF is affected by flowrate, screw speed, lead, and number of tips were predicted and discussed. The results suggested that the devolatilizing performance of the VFZ is lower than that of the VUfZ due to decrease in the surface renewal effect there, and a plot of ln {(wout – w*)/(win – w*)} against (N1/2/Q) in generally used flowrate and screw speed ranges for a given screw geometry does not strictly satisfy a linear relationship due to the filling-degree dependence of the OFIGF.
Models of Flow and Experimental Studies on a Modular List/Buss Kokneter
Authors: Lyu M.-Y. , White J. L.
Published: December 2013

An experimental and theoretical study of the behavior of a List/Buss Kokneter is presented. The experimental study which uses polypropylene considers (i) the interaction of the Kokneter with a crosshead screw extruder, and (ii) distribution of polymer in the modular screw. A modeling study considers the dynamics of flow including the influence of screw oscillation. Calculations are made for various individual Buss elements. A model is developed for the total system including the crosshead screw extruder. It is shown that an oscillating length of fill in the crosshead screw extruder can account for the throughput oscillation stabilization characteristics of the composite machine. Predictions of pressure profiles and positions of starvation in a starved flow machine are made.
Analyses of Bowing Phenomena in Successive Transverse Stretching and Thermosetting Process for Biaxially Oriented Film
Authors: Yamada T. , Nonomura C. , Matsuo T.
Published: December 2013

Bowing distortion phenomena of bi-axially oriented film cause serious problems in practical application. Bowing distortion was conveniently defined to carry out the analysis. Bowing distortion profile throughout a tenter machine was observed. This profile was fairly successfully simulated by FEM using suitable anisotropic and heterogeneous elastic constant distributions, and a suitable initial shape of the elastic body. The mechanism of bowing distortion in relation with TD stretching was estimated by the above results and some experimental data. This leads to the forecast that the insertion of a cooling zone between the TD stretching zone and the thermosetting zone will be an effective way for decreasing bowing distortion of film. This forecast was experimentally verified. Despite the insertion of the cooling zone, a certain level of bowing distortion still remained. It was tried to give an explanation for the mechanism of the remaining distortion in terms of heat-shrinkage force in the thermosetting zone.
Evaluation of the FAN Technique for Profile Die Design
Authors: Huneault M. A. , Lafleur P. G. , Carreau P. J.
Published: December 2013

Die design is a daily concern in the manufacturing of extruded profiles. There are very few available Computer Aided Design (CAD) tools for profile die designers and considerable time and resources must be devoted to trial and error design procedures. This paper examines the applicability of the flow analysis network (FAN) to the design of profile extrusion dies. The FAN method is found to provide useful design information at a fraction of the computing cost required for 2.5 and 3D finite element methods. Experimental flow distribution obtained by extruding PVC compounds and polyethylene through simple profile dies are compared to model predictions. The numerical and experimental results provide evidence about the significant contribution of transverse flow to the flow distribution at die exit.
Devolatilization with Chemical Reaction in Polymer Solutions
Authors: Hu G.-H. , Chen Liqin , Lindt J. T.
Published: December 2013

It has been observed previously [1] that under the specific conditions prevailing in a reflux flask reactor, the overall rate of the transesterification reaction between an ethylene and vinyl acetate copolymer and 3-phenyl 1-propanol can be enhanced appreciably by the introduction of boiling inert hydrocarbon solvents. In the present study, the same reaction carried out under a controlled removal of vapors in a simulator emulating a non-intermeshing counter-rotating devolatilization twin screw extruder, a significant acceleration of the reaction rate has also been observed. In agreement with the previous work [1], the intrinsic reaction mechanism and the chemical equilibrium do not appear to be affected by boiling of the inert hydrocarbon solvents, nor does the additional mechanical agitation due to the rapid bubble growth contribute to the increase of the overall reaction rate. Theoretical analysis of the results confirms that the acceleration of the reaction rate originates from the localized mass transfer effect connected to the presence of the bubble vapor-liquid interface films induced by devolatilization.
Molecular Orientation in Polycarbonate Induced by Cooling Stresses
Authors: Wimberger-Friedl R.
Published: December 2013

The origin of the maximum of the birefringence at the surface of injection-molded polymer products is discussed. By systematic variation of the molding conditions with polycarbonate, it is shown that the maximum at the surface not only depends on the filling, but even more so on the packing conditions. The birefringence at the surface is equal in the flow direction and transverse to it. The height scales with the cavity pressure during compression and packing. This cannot be explained by stresses due to the classical fountain flow at the flow front. Instead, the dominating contribution comes from transient deviatoric stresses induced by the compression of the vitrifying polymer in combination with wall adhesion. The pressure-induced stress history in the vitrifying polymer leads to molecular orientation and residual stresses giving a birefringence maximum at the surface.
Upgrading Recycled HDPE by Rheometer-Controlled Crosslinking
Authors: Pillo A. , Dealy J. M. , Patterson W. I.
Published: December 2013

An in-line rheometer previously described was evaluated for use in the upgrading of post-consumer, recycled HDPE. Feed resin of variable melt index was brought to a preset, uniform viscosity by peroxide induced crosslinking in a twin-screw extruder. Closed loop control was demonstrated using the rheometer as a viscosity sensor. Set-point tracking was achieved using PID-IMC, Dahlin and minimum variance (MV) controllers. The Dahlin controller showed the best load rejection.
On the Simulation of Thermoplastic Injection Moulding Process
Authors: Titomanlio G. , Speranza V. , Brucato V.
Published: December 2013

The relevance of enhancement of crystallisation kinetics by effect of shear flow and rheology during polymer solidification to the phenomena taking place during the injection moulding process has been shown by means of simulations performed on the basis of Lord and Williams [1, 2] model and its recent extensions [3 to 5]. A key point of the simulation was the solidification criterion based on a critical crystallization index; on the basis of simple calorimetric and rheological tests in the limit of zero shear rate, values of a few percent were given to the solidification crystallinity value.

Many experimental features of pressure history both in the runner and in the cavity are recovered by model predictions, if both effects mentioned above are properly accounted for. However, predictions for gate sealing time, although improved, still have a sensitivity to gate thickness lower than that shown by the experiments. Similar conclusions, obviously, regard also the mass entering in the mould during holding.

Another mechanism which sums up to shear stresses to accelerate thin gate solidification has still to be identified.