Melt Flow Characteristics Research Articles

Influence of die geometric structure on flow balance in complex hollow plastic profile extrusion

The unbalanced flow problem often occurs at die exit in the extrusion process of plastic profile, which directly influences the performance of final products. For the lack of corresponding theoretical basis, reasonable extrusion die design is still a difficult task, especially for the complex hollow profile. With the development of computational fluid dynamics theory, numerical method becomes an effective way to investigate the complex material forming problems. In the present study, a design strategy for complex hollow profile extrusion die was proposed based on the principles of flow balance. The mathematical model for three-dimensional non-isothermal polymer melt flow within complex extrusion die runner was developed based on the computational fluid dynamics (CFD) theory. The governing equations were deduced based on the finite volume method, and the pressure-velocity coupling problem was solved by using the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. The Arrhenius equation was employed to involve the temperature dependence of material parameters. The flow characteristics of PVC polymer melts in the extrusion process of complex hollow profile were investigated. The distributions of principal field variables including flow velocity, melt temperature, and pressure drop were obtained. The effects of die geometric parameters on the velocity distribution uniformity were further analyzed, and a design strategy was proposed to achieve the flow balance in complex plastic profile extrusion process.

Morphological Evolution of Polystyrene/Poly­ethylene Blend Induced by Strong Second Melt Penetration

Recently, a melt penetration process in which one kind of polymer melt severely penetrated by a second polymer melt is achieved in our home‐made multimelt multi‐injection molding instrument. The morphologies of polystyrene (PS)/polyethylene blends are observed to study the characteristics of melt flow during melt penetration. For comparison, the morphologies of dispersed phase in injection molded samples with only the “first” melt injection process (FIM) and only the “second” melt (SIM) are also examined. In the penetrated layer, the dispersed phases PS deforms much more in comparison to those in the molding parts by FIM and SIM processes, which can be ascribed to a larger deformation induced by the second flow via melt penetration. In the penetrating layer, the deformity degree of PS is less than those in the molding parts during SIM processes, owing to the resistance of the “first” melt. image

Three-Dimensional Viscoelastic Simulation for Injection/Compression Molding Based on Arbitrary Lagrangian Eulerian Description

Different from conventional injection molding (CIM), injection/compression molding (ICM) evolves boundary variation in gapwise direction. In order to describe melt flow characteristics in ICM correctly, a new material derivative based on arbitrary Lagrangian Eulerian (ALE) description was introduced to modify the material derivatives in the governing and constitutive equations. To avoid large amount of calculation and weak stability of integral numerical method, an iterative approach employing twofold iterations was proposed to decouple the interdependence between velocity, stress, and temperature. The initial values of material parameters in constitutive equations were obtained or fitted by rheological experiments. The ICM experiments for an iso-thick and a var-thick rectangular panel were carried out to validate the proposed method and find the special characteristics of ICM. In addition, the photoelastic tests on a quarter of spherical part processed by ICM were conducted to identify the relationship between residual flow-induced stress distributions and flow fields. Both simulations and experiments show that the pressure profile displays a plateau during compression, temperature decreases with time according to exponential law, large flow-induced stress originates in thick transitional region, flow start, and flow end areas, and gravity has significant effect on meltfront for thick part ICM. The good agreement between experiments and simulations indicates that the current method can properly describe the flow characteristics of ICM.

Infrared welding of cross-linkable polyamide 66

Radiation cross-linking of polyamide 66 with electron beams alters the material's characteristics. This leads to a varied relationship amongst the process, structure, and properties for infrared welding cross-linked polyamide 66. A three- dimensional network of covalent bonds results in an impeded melt flow and altered welding characteristics. Compared to non-cross linked polyamide, a changed energy input in the weld during infrared heating and a reduced meltdown can be ob- served. Such thermal developments and a reduced meltdown affect the resulting weld strengths. Welding factors of almost 60% of base material strengths can be achieved. A clear influence of the heating time on the weld strength can be observed. The scope of this article is to investigate the influence of radiation cross-linking on the material characteristics and, by ex- tension, the resulting processing and welding characteristics. Mechanical and optical investigations serve to highlight the influence of radiation cross-linking on the infrared welding process of polyamide 66.

Morphology and toughness enhancements in recycled high‐density polyethylene (rHDPE) via solid‐state shear pulverization (SSSP) and solid‐state/melt extrusion (SSME)

ABSTRACTSolid‐state, mechanochemical polymer processing techniques are explored as an effective and sustainable solution to appearance and performance issues commonly associated with recycled plastic products. Post‐consumer high‐density polyethylene (HDPE) from milk jugs is processed via conventional twin screw extrusion (TSE), solid‐state shear pulverization (SSSP), and solid‐state/melt extrusion (SSME), and compared to the as‐received and virgin forms regarding output attributes and mechanical properties, as well as morphology. Solid‐state processing methods, particularly SSME with a harsh screw configuration, produce samples with consistent appearance and melt flow characteristics. Tensile ductility/toughness and impact toughness are enhanced by up to 11‐fold as compared to the as‐received sample, to a level near and above those of an equivalent virgin HDPE. Calorimetry, optical microscopy, X‐ray scattering, and rheology characterization reveal that the mechanical improvements result from a favorable combination of physical and molecular changes in rHDPE, such as impurity size reduction, spherulite size enlargement, and chain branching. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43070.

Shape Optimization for Weight Reduction of Polymer Extrusion Die

Polymer extrusion is one of the most widely utilized manufacturing processes across many industries including automotive, architecture, aerospace etc. However, in order to maintain normal operations, polymer extrusion dies are conventionally designed with large dimensions and thick walls which results in the overweight of them. In this paper, a shape optimization method is proposed to reduce the weight of polymer extrusion dies without sacrificing the required performances of extrudate. Firstly, Finite element simulation of the extrusion process is conducted using the commercial software HyperXtrude to study both the essential flow characteristics of polymer melts and the deformation and stress distribution of extrusion die. Secondly, shape optimization is conducted to find the minimum weight of extrusion die while satisfying the required properties and productivity of polymer product. The extrusion die is then redesigned according to the result of shape optimization and compared with the original one. A Medium-sized polymer profile extrusion die is selected as case study, the result of which shows that the weight of the extrusion die is reduced by 31.6%,though the maximal deformation and stress of the die are increased by 1.7% and 16.1% respectively. The proposed approach is demonstrated to be effective for the lightweight design of polymer extrusion die.

Rheological and dynamic mechanical characteristics of rotationally moldable linear low‐density polyethylene fumed silica nanocomposites

In rotational molding process, polymer powders undergo a cycle of heating, melting, cooling, and subsequent solidification in the mold. Resins, like linear low‐density polyethylene (LLDPE), are used in this process on a large scale mainly because of its good mechanical properties and excellent thermal stability. Yet, incorporation of additives is necessary to further improve the visco‐elastic, thermal as well as melt flow properties of the resin. This study investigates the effects of nanocomposites of fumed silica (FS) with rotationally moldable LLDPE. Thermal transitions in the LLDPE‐FS nanocomposites were investigated and correlated with their melt flow characteristics. The effect on melt processing during rotational molding and compounding, were analyzed by melt flow index and torque rheometry studies. A suitable blend of FS in LLDPE has been recommended for rotational molding based on rheological studies and dynamic mechanical analysis. POLYM. COMPOS., 37:2995–3002, 2016. © 2015 Society of Plastics Engineers

粘弾性流動計算による平行平板型レオメータ用カップ型ジグの評価

In order to measure the flow characteristics of polymer melt with high melt index, e.g. polyester and polyethylene terephtalate (PET) used for fiber processing, we discuss the utility of the cup-type jig for measurement of the steady-state shear flow characteristics in the rotational-type rheometer, especially parallel plate rheometer, by using the viscoelastic flow simulation. The multiple mode Phan-Thien Tanner (PTT) model was employed as the constitutive equation. We considered the deviation between the rheological data from the parallel plate rheometer with cup-type jig and the data from the normal parallel plate rheometer with the same disk diameter. As a result, the deviation of shear viscosity increased with the distance between the disk and the cup-type jig. The average value of the deviation of shear viscosity increased linearly with this distance. Then, the absolute value of the deviation of the first normal stress difference also seems to increase with this distance. On the other hand, the deviations of shear viscosity and the first normal stress difference are almost independent of the cup-type radius in the region over about 1.2 times of jig diameter divided by the disk radius. These results imply that large radius of cup-type jig and narrow distance between the disk and the cup-type jig would be suitable for measurement of polymer melt flow characteristics using the parallel plate rheometer with the cup-type jig. In addition, these obtained results would imply that to use the cup-type jig is valid for measurement of rheological data.

Preparation of Nano-Filled Polypropylene Microfibers

The effects of carbon nanotubes (CNT) and CNT-compatibilizer additives on the flow characteristics of melts of polypropylene—copolyamide (PP—CPA) mixtures were studied. It was shown that the elasticity of the melts and the longitudinal deformation increased in the nano-filled mixtures. It was found that combining CNT with a compatibilizer improved PP fiber formation in a CPA matrix by decreasing the surface tension at the interface of the components. This stabilized the PP liquid streams. Nano-filled PP microfibers with increased specific surface area and hygroscopicity were obtained.

Synergetic effects of radiolytically degraded PTFE microparticles and organoclay in PTFE-reinforced ethylene vinyl acetate composites

This article reports exceptional synergistic effects observed in organic–inorganic dual filler containing ethylene vinyl acetate (EVA) composites. Polytetrafluoroethylene microparticles (PTFEMP) were produced by mechanically grinding radiolytically degraded PTFE; composites of EVA containing PTFEMP and organoclay were prepared in different proportions by melt compounding and their mechanical, melt flow, morphological and crystallographic characteristics were examined. Mechanical properties of ternary composites demonstrated high synergy between fillers, leading to manifold increase in the modulus of dual filler filled composites in comparison to single filler systems. Nielsen model fitted well with EVA/PTFEMP system; however it predicted remarkably low values for EVA/PTFEMP/organoclay system, confirming exceptional synergy between two fillers. Melt viscosity of EVA increased substantially on the addition of either of the fillers. X-ray diffraction studies revealed around 10% intergallery expansion in organoclay, in the composites having high loading of PTFEMP; though the crystallinity of EVA did not change.

NUMERICAL INVESTIGATION OF THE SPREADING AND HEAT TRANSFER CHARACTERISTICS OF EX-VESSEL CORE MELT

The flow and heat transfer characteristics of the ex-vessel core melt (corium) were investigated using a commercial CFD code along with the experimental data on the spreading of corium available in the literature (VULCANO VE-U7 test). In the numerical simulation of the unsteady two-phase flow, the volume-of-fluid model was applied for the spreading and interfacial surface formation of corium with the surrounding air. The effects of the key parameters were evaluated for the corium spreading, including the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The results showed a reasonable trend of corium progression influenced by the changes in the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The modeling of the viscosity appropriate for corium and the radiative heat transfer was critical, since the front progression and temperature profiles were strongly dependent on the models. Further development is required for the code to consider the formation of crust on the surfaces of corium and the interaction with the substrate.

Computational Modeling of the Effects of Viscous Dissipation on Polymer Melt Flow Behavior During Injection Molding Process in Plane Channels

The present finite volume method based fluid flow solutions investigate the boundary-layer flow and heat transfer characteristics of polymer melt flow in a rectangular plane channel in the presence of the effect of viscous dissipation and heat transfer by considering the viscosity and density variations in the flow. For different inflow velocity boundary conditions and the injection polymer melt temperatures, the viscous dissipation effects on the velocity and temperature distributions are studied extensively to analyze the degree of interactions of thermal flow field dominated by the viscous heating and momentum diffusion mechanism with varying boundary conditions. The modified forms of Cross constitutive equation and Tait equation of state are adopted for the representation of viscosity variations and density change, respectively, in the polymer melt flow. These models together with the viscous dissipation terms are successfully incorporated into the finite volume method based fluid flow solutions to realistically represent the heat effects in the plane channel. The numerical results presented for two different commercial polymer melt flows, namely, polymer Polyacetal POM-M90-44 and polypropylene (PP), demonstrate that proposed mathematical formulations for viscosity and density variations including viscous heating terms into the energy equations, which are fully coupled with momentum equations, lead to more accurate representation of the fluid flow and heat transfer phenomena for the polymer melt flows in plane channels.

Modeling and simulation of polymer melts flow in the extrusion process of plastic profile with metal insert

The extrusion technology of plastic profile with metal insert is recently an advanced plastic processing method whose products keeps rising today for their excellent performance. However, the related fundamental research on polymer forming mechanism in the extrusion process of plastic profile with metal insert is lagging behind. With the development of computational fluid dynamics (CFD) theory, numerical method becomes an effective way to investigate such complex material forming problems as in the polymer extrusion process. In the present study, the mathematical model for three-dimensional non-isothermal viscous flow of the polymer melts obeying a Carreau model is developed based on the CFD theory. The Williams–Landel–Ferry equation is employed to involve the temperature dependence of material parameters. A decoupled numerical algorithm based on the penalty finite element method is conducted to predict the rheological behaviors of polymer melts within the complex flow channel. The streamline upwind/Petrov–Galerkin scheme is employed to improve the computational stability for the calculation of temperature field. Based on the theoretical model, the essential flow characteristics of polymer melts in the extrusion process of plastic profile with metal insert is investigated. The distributions of principal field variables like flow velocity, melt temperature, flow stress and pressure drop are predicted. The effects of die structure parameters including the intake angle and the distribution section length upon the melts flow patterns are further discussed. The variations of melt rheological properties versus different processing conditions like the volume flow rate and the metal insert moving velocity are also investigated. Some advice on practical processing operations of the extrusion process of plastic profile with metal insert is accordingly put forward based on the numerical results.

Finite Element Analysis of Flow Field in Nano-Laminated Coextrusion Die

FEM analysis of flow field in nano-laminated coextrusion die is introduced. Nano-laminated coextrusion die is a new type of laminated composite generator which is based on the principle of the melt calculus. The distributions of pressure field and velocity vectors are obtained and analyzed. The result using finite element simulation software Polyflow shows an improvement in structure of die as well as better quality for melt flow characteristics. The paper is helpful in design and optimization of coextrusion die and process.

The Characteristics of Melt Flow in Composite Spinning Micropore

From the rheological theory, the combination of the rheological characteristic of melt spinning and principle of spinning, the paper researches the mathematical model of the velocity distribution and shear rate distribution when the melt flow in composite spinning sheath-core orifices. According to the mathematical model, the melt flow velocity and pressure characteristic of the composite spinning micropore are researched with the software of CFD-Fluent. The results for the design of composite spinning technology and components provide a good theoretical basis.

Effects of Liquid Contaminants on Heat Seal Strength of low‐density polyethylene Film

Heat sealing is commonly applied for making form‐fill‐seal packages fabricated from thermoplastic films. One of the challenges frequently faced by the industry is inadvertent contamination of film–film interface by the product during filling, which can compromise package seal strength. In this study, the effects of dwell time (0.5–1.5 s), jaw pressure (28–1860 kPa), jaw configuration (narrow versus wide contact area) and jaw temperature (150°C–180°C) on the interface temperature and seal strength of a linear low‐density polyethylene (LLDPE) film were investigated. Three different film–film interface conditions were studied: (1) no contaminant; (2) with water contaminant; and (3) with vegetable oil contaminant. In the presence of liquid contaminant, jaw pressure played an important role in displacing the liquid from the seal area to form intact seals. Short dwell time (0.3 s) and low jaw temperature (150°C) was not favourable for forming intact seals in both water‐contaminated and vegetable oil‐contaminated films. The optimum jaw temperature and dwell time required to produce intact seals for oil contaminated films was 180°C and 0.3 s, respectively, whereas a combination of 165°C jaw temperature and 1 s dwell time was required to form intact seals for water‐contaminated films. Within the experimental conditions investigated, interface temperatures of 130°C–140°C resulted in the most optimum seal strength for both water‐contaminated and clean film specimens. Above 140°C, a weakening of seal strength was observed, presumably because of the change in melt flow characteristics and possible initiation of thermal degradation of the polymer. Copyright © 2011 John Wiley & Sons, Ltd.

Study on Effect of Vibration Parameters in Filling Process of the Dynamic Injection Molding

As an application of vibration technique, dynamic molding technology has been applied to the injection molding field due to its effectiveness in practice. In order to simulate this technique in numerical analysis field of the injection molding, a Visual Basic procedure was successfully developed on the basis of the Moldflow Plastics Insight Application Programming Interface. This procedure has been used to simulate filling process of dynamic injection molding of a disk-shaped mould. The results show that dynamic injection molding technology can effectively improve the melt flow characteristics, reducing energy consumption.

Measurement and simulation of low‐density polyethylene extrudate swell through a circular die

AbstractBACKGROUND: Extrudate swell is a common phenomenon in polymer processing. The investigation of its mechanism is of both scientific and industrial interest.RESULTS: The rheological parameters of a material described by the viscoelastic PTT (Phan‐Thien–Tanner) constitutive model are obtained by fitting the distributions of material functions detected with a strain‐controlled rheometer. The swelling ratios of low‐density polyethylene (LDPE) under different volume flow rates are indirectly obtained using a photographic technique. A mathematical model of extrudate swell is established and its finite element model is derived. A penalty method is employed to solve the extrudate swell problem with a decoupled algorithm. Computation stability is improved by using the discrete elastic‐viscous split stress algorithm incorporating the inconsistent streamline‐upwind scheme.CONCLUSION: The swell phenomenon of LDPE through a circular die is investigated using both experimental measurement and numerical simulation. The swelling ratios obtained from the simulation are compared with those measured: they agree well with each other. The essential flow characteristics of polymer melts are predicted and the mechanism of the swell phenomenon is further discussed. Copyright © 2009 Society of Chemical Industry

Surface Energy of Modified Nanoclays and Its Effect on Polymer/Clay Nanocomposites

Surface properties of thermally stable phosphonium-modified montmorillonite were investigated at both room temperature and 220°C. These properties were compared with those of pristine and ammonium-modified montmorillonite. Surface properties at room temperature were calculated from contact angles measured using sessile drops. Several liquids with known polar and dispersion components of surface tension were used. Surface energy of nanofillers at 220°C was calculated from contact angles, using sessile drops of polymer melts. Two commercial polystyrene (PS) resins, with different melt flow characteristics, and high-density polyethylene (HDPE) were used. Isothermal TGA experiments were used to determine the thermal stability of the resins and nanofillers. The dispersion behavior and mechanical properties of the nanocomposites are correlated with the values of the Hamaker constant and thermodynamic work of adhesion for these polymer–nanoclay systems.

Numerical study of nonisothermal polymer extrusion flow with a differential viscoelastic model

AbstractA numerical study of nonisothermal viscoelastic flow is conducted to investigate the complex flow characteristics of polymer melts in the extrusion process. A general thermodynamic model for the energy conversion related to viscoelastic fluid flow is introduced. The mathematical model for three‐dimensional nonisothermal viscoelastic flow of the polymer melts obeying a differential constitutive equation (Phan‐Thien and Tanner model) is established. A decoupled algorithm based on the penalty finite element method is performed on the calculation. The discrete elastic‐viscous split stress (DEVSS) algorithm, incorporating the streamline‐upwind Petrov‐Galerkin (SUPG) scheme is employed to improve the computation stability. Essential flow characteristics of polymer melts in the extrusion die for hollow square plastic profile is investigated based on the proposed numerical scheme with ignoring the outer thermal resource. The energy partitioning, which quantified the conversion of mechanical energy into thermal energy, is discussed. The effects of volume flow rate and die contraction angle upon the flow patterns are further investigated. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers