bluuebunny/crossref_metadata_2025 huggingface dataset:
An Integrated Approach for Numerical Analysis of Coupled Flow and Heat Transfer in Co-rotating Twin Screw Extruders
Authors: Kalyon D. M. , Malik M.
Published: December 2013

The co-rotating twin screw extrusion process is widely employed in chemical industries for the processing of complex fluids including various polymers, suspensions, emulsions and gels. Here we propose a new integrated modeling strategy that is based on the numerical analysis of pressure-generating extrusion elements concomitantly with the pressure-losing extrusion elements of the co-rotating twin screw extrusion process for non-Newtonian fluids under nonisothermal conditions. The numerical analysis undertakes three-dimensional (3-D) finite element simulations of any multiple combinations of forwarding and reversing fully-flighted screw elements with other types of elements including kneading discs staggered in the forward or reverse configurations and the die. The abilities of the methodologies in simulating the coupled flow and heat transfer in industrially-relevant mixing sections or pressurization/die shaping are demonstrated with predictions of the degree of fill and typical velocity, deformation rate, stress magnitude, pressure distributions as functions of various operating parameters and basic twin screw extrusion geometries for a viscoplastic type generalized Newtonian fluid.
Relationship Between Structure and Spinning Processing of As-Spun PP Fibres
Authors: Yang R. D. , Mather R. R. , Fotheringham A. F.
Published: December 2013

As-spun polypropylene (PP) fibres, obtained under a one-step statistical experimental design using orthogonal arrays and involving all the common spinning parameters were studied with wide angle X-ray scattering (WAXS). The WAXS results revealed that the micro-structure of PP fibres can be altered progressively from less-ordered para-crystalline states to highly-ordered crystalline states with an α-monoclinic lattice. The degree of structural order has been evaluated quantitatively in terms of (W½)−1, the reciprocal of the half-height width of the first WAXS reflection peak. On the basis of such quantitative evaluation, which is shown to be consistent with the conclusions derived from “traditional” qualitative assessment, comprehensive quantitative analysis of the effects of processing parameters and their interactions on the degree of structural order is accomplished, using systematic but simple statistical methods. Parameters significantly affecting structure, including types of raw materials, winding speed, spinning temperature, application speed of spin finish and metering pump speed are identified, and correlation between structure and parameter setting is established in a concise statistical model. The model indicates clearly the combination of parameter levels for increasing or reducing the degree of structural order over the whole range from essentially amorphous to highly crystalline forms. Comparisons with the “conventional” approach of “one factor at a time” demonstrated the validity of the new approach and its significant advantages. The latter includes the economy in experiment scale, efficiency in result analysis and a comprehensive overview of the process being studied, which covers effects arising from synergistic interactions as well as from individual parameters.
Wave Behavior in the Coating Process of Multilayer Polymeric Materials
Authors: Su Y.-Y.
Published: December 2013

A mathematical analysis model of multilayer viscoelastic fluids flowing down an inclined plane for any arbitrary wave numbers has been established to improve multilayer product quality in the coating processes. In the stability study of the free surface with small elastic force, Reynolds number is the primary parameter to induce surface instability for long and intermediate waves. When the elastic force in either layer is large, elasticity can affect the stability of long and intermediate waves. In addition, viscosity stratification across the interface can also affect the stability of the free surface. For the interfacial stability of two-layer flow system, it is found that purely elastic instability occurs in most depth ratios for the whole spectrum of waves when the fluid with elasticity is placed as the inner layer next to the solid wall. In the study of stability for viscoelastic fluids it demonstrates that arranging the more elastic and less viscous fluid as the outer layer leads to interfacial stability. In the more than three-layers investigation we found that placing the most viscous and least elastic liquid as the innermost layer next to the solid wall and the least viscous and most elastic liquid as the outermost layer next to the passive air can ensure the stability for the whole spectrum of waves.
Analysis of Shrinkage Development of Injection Moulded PS Samples
Authors: Pantani R. , Titomanlio G.
Published: December 2013

Modern approaches to the phenomenon of dimensional accuracy in injection moulding link the evolution of shrinkage from the moment of first solidification to a force balance between restraining and constraining forces which sets in inside the mould before ejection. Such an approach needs a complete understanding of what happens inside the cavity during the moulding cycle. In a recent paper [9], a new technique has been presented, by which it is possible to follow the shrinkage development of an injection moulded sample from the moment it starts solidifying to soon after ejection.

In this work, with reference to a simple rectangular cavity, shrinkage curves measured by strain gages in different moulding conditions are analysed by means of a simple thermomechanical model recently proposed. Results show that the model satisfactorily predicts the moment shrinkage starts inside the mould and reveal the existence of a restraining force not due to pressure, which builds in gradually in a few seconds from the instant of first solidification. Knowing the value of this force—which can be drawn by Hooke's law from the strain jump at mould opening—the model gives a good description of both shrinkage development inside the mould and ejection shrinkage.
Chrome Nitride Coatings for Applications in Plastics Processing
Authors: Berg G. , Friedrich C. , Broszeit E. , Cremer M.
Published: December 2013

Coated moulds, especially cavity surfaces and ejection parts are state of the art in plastics processing. Regarding the plastification unit i.e. screws and barrels coatings are not well established. Wear in processing remains a problem, especially when no abrasion is permitted e.g. in manufacturing optical elements. The surfaces must resist the abrasion of hard glas fibres as well as the corrosive attack of the polymers. Electroplated chrome is one of the answers to these demands, because of its hardness and corrosion resistance. Another solution are thin hard coatings which are not yet well established. Titanium nitride produced by PVD technique was found to show excellent abrasion resistance but often not sufficient corrosion properties. Chrome nitride was found to have great hardness like TiN, corrosion resistance behaviour similar to electroplated chrome and in contrast to electroplated coatings no tensile internal stress.

The present study deals with the spectrum of characteristic properties of CrxN coatings like hardness, adhesion, internal stress, chemical composition and phases produced by PVD magnetron sputtering. The coatings were deposited on steel, described in characteristics and tested in a model wear test with plasticized moulding material (PA 66-GF50 and others) simulating the tribological situation between screw and barrel of extruders or injection moulds. The tribological behaviour was studied after the complex test procedure. The high temperature of the plasticized material, high abrasion by glas fibres and corrosive influence could only change the coatings properties of CrxN slightly.
Simulation of Flow in an Intermeshing Modular Counter-rotating Twin Screw Extruder: Non-Newtonian and Non-Isothermal Behavior
Authors: Hong M. H. , White J. L.
Published: December 2013

An analysis of flow fields, pressure fields and screw pumping characteristics is presented for non-Newtonian fluids in various types of screw elements of an intermeshing counter-rotating twin screw extruder. These elements are in turn considered modules of a modular intermeshing counter-rotating twin screw extruder and an analysis of non-isothermal starved low in such a machine is presented. Pressure profiles, fill factor profiles and temperature profiles have been calculated for various modular screw designs of a Leistritz GG modular intermeshing counter-rotating twin screw extruder.
Injection Moulding of a Commercial β-Nucleated Polypropylene
Authors: Varga J. , Breining A. , Ehrenstein G. W. , Bodor G.
Published: December 2013

In a recent paper [1], the preparation techniques, structural features, crystallization, melting characteristics, and certain properties of the β-modification of isotactic polypropylene (β-IPP) were reviewed. Possible uses of β-IPP were demonstrated through example applications. The problems involved with the processing of β-nucleated polypropylene were analyzed and the conditions of the processing technology of β-IPP end-products were discussed. In the present paper, the results of the studies on the injection moulding technology of a commercial β-nucleated polypropylene are addressed.
Modeling the Distributive Mixing in an Internal Batch Mixer
Authors: Hutchinson B. C. , Rios A. C. , Osswald T. A.
Published: December 2013

Mixing has been the focal point of many experimental studies in recent years, but advances in modeling and simulation now allow for fast, accurate and useful simulation analysis. Numerous mixing indices have been developed but the majority are tailored to experimental studies. In this study, a new mixing index is developed to analyze the particle position history of the mixer. Due to its simplicity when dealing with moving boundary problems, the boundary element method is employed to model the fluid flow and track particles.

Numerous geometries can be modeled and compared on a basic workstation. First the mixing index is applied to Couette flow. Analytical and boundary element simulation results compare well. Next the method is used to analyze the mixing capabilities of a Banbury mixer with different speed ratios. Further the mixing index is used to compare the mixing capabilities of triangular mixing lobes versus typical Banbury type.
Profile Die Design Based on Flow Balancing
Authors: Švábík J. , Plaček L. , Sáha P.
Published: December 2013

This paper presents a methodology for the design of profile dies based on the Cross Flow Minimization Method. The flow balancing is described for cases where the flows are balanced by varying the die land length combined with the flow separation. Three different approaches were utilized in the die analysis. First, the flow in two proposed profile dies was calculated by substituting the flow domain by a set of simple geometries. The second approach applied the Cross-Sectional Calculation method, while the last method is a fully 3D FEM non-isothermal calculation. The results are verified by comparison with experimental data. It is shown that each of the calculation procedures may be the choice of preference depending on the geometrical complexity.
Comparative Study of Ziegler-Natta and Metallocene Based Polypropylenes in Injection Molding
Authors: Isayev A. I. , Churdpunt Y. , Guo X.
Published: December 2013

Injection molding of the isotactic polypropylenes polymerized using metallocene and Ziegler-Natta catalysts and having the same molecular weights was performed. Rheological properties and shear-induced crystallization kinetics were measured and their comparative analysis is made. These data are fitted to the equations necessary for simulation of the injection molding process. Numerous injection molding runs were carried out and pressure measurements during molding were performed. The gapwise distribution of crystallinity, spherulite size and thickness of flow-induced crystallized layer in moldings were measured. The effect of various processing conditions on these values was determined. The measured values were compared with the results obtained from the simulation of injection molding process using unified theory of crystallization proposed earlier. Comparative analysis is made between flow conditions and crystallization behavior of these polymers and their effect on the pressure development and structural characteristics of the moldings.
Non-Isothermal Transient Startup of A Starved Flow Modular Co-Rotating Twin Screw Extruder
Authors: Kim E. K. , White J. L.
Published: December 2013

A model for non-isothermal Newtonian flow startup in an initially empty modular self-wiping co-rotating twin screw extruder is developed. A viscous Newtonian fluid is considered to gradually fill a modular co-rotating twin screw extruder with viscous heating and heat transfer to the barrel (and screw). The build up of the axial cup mixing temperature profiles with time was calculated for various modular screw configurations.
Polymer Flow Velocity in the Helical Channel in Dependence of a Coordinate System
Authors: Sikora R. , Sasimowski E.
Published: December 2013

Taking into consideration the extensive literature we conducted our own studies of polymer flow velocity in the helical channel of the plasticating system. They included the following subjects: studies conditions in rectangular and helical coordinate systems—a model with a rotating barrel and a model with a rotating screw (theoretical principles); computational verification on the concrete example for different screw channel depths; comparison of the models with regard to drag flow velocity, pressure flow velocity, longitudinal flow velocity (resultant), shear rate and polymer viscosity.

The thesis that both models of a screw-based plasticating system with a rotating barrel or a rotating screw differ fundamentally was confirmed in the same conditions in two coordinate systems—rectangular and helical. In connection with this theoretical investigations at a rotating barrel and next their experimental verification at a rotating screw, which is a common practice, are unsuitable.
Polymer Melt Rheology at High Shear Rates
Authors: Haddout A. , Villoutreix G.
Published: December 2013

The importance of polymer flow properties during processing has required the development of new on line measurement systems, able to work under rates encountered during industrial processes. This paper will describe a rheometer which is able to study the thermorheological behavior of polymers within industrial injection or extrusion machines. Its main feature is to work at high shear rates which are experimented during production processes; it is equipped with dies of different diameters and lengths, allowing shear rates between 102 to 107 s−1. Some results concerning viscosity and first normal stress differences are presented for high density polyethylene (HDPE), polypropylene (PP) and polypropylene/polyarylamide blends (PP/PA). The plot of viscosity and first normal difference against shear rate for these materials are not linear. Two non Newtonian regions and a third one similar to Newtonian behavior were observed in the wide range of shear rates up to 8.106 s−1.
Dynamic Analysis of Melting in Injection Extruder
Authors: Yung K. L. , Xu Y. , Lau F.
Published: December 2013

Melting is one of the most important process in plastics processing. Admit the extensive use of plastic injection moulding machine in industry, most studies were on extruders which were simpler to model. This paper studies the melting process and derives its transient (dynamic) model for predicting the characteristics of melting in feeding stage of injection extruder. Based on this transient model, factors affecting the melting speed in injection extruders are exposed. Simulation results agree with the results from experiments.
A New Approach in Offline-Optimization of the Injection Molding Process
Authors: Kuhmann K. , Meckbach S. , Zhao G. , Ehrenstein G. W. , Jeltsch-Fricker R.
Published: December 2013

For the purpose of process optimization of the injection-molding process a robust processing point is determined, at which specified characteristics of the parts are met and the process is insensitive to disturbances. The idea of the new optimization concept is to ensure that also around the robust processing point, within the so-called robust processing window, the part geometry is in tolerance and a low standard deviation respectively a high SN-ratio is achieved. Instead of reducing the optimization task to a one-dimensional problem by combining the target functions, in this approach one defines lower and upper bounds for the characteristics to be optimized. These bounds must be fulfilled in the range of the robust processing window and, if necessary, might be sharpened or relaxed during the optimization procedure. The corresponding response surfaces are generated by means of new Scattered Data Interpolation-methods.
Radially Dependent Stress and Modeling of Solidi cation in ilament Melt Spinning
Authors: Henson G.M. , Bechtel S.E.
Published: December 2013

When polymer fibers are manufactured by melt spinning, axial velocity is nearly uniform across any cross section but temperature and stress vary significantly across the fiber radius. Thus, the fiber solidifies from the outside in, with the fiber being solid on the outside but molten on the inside for some distance before complete solidification, and stress near solidification, the controller of mechanical properties of the spun fiber, has radial variation. We present a computationally 1D melt spinning model which recognizes the radially inhomogeneous solidification region, and computes axial and radial dependence of stress in the spinline. With this radial resolution, stress near solidification is now the stress evaluated on a surface near the solidification boundary. In simulations of melt spinning processes, we investigate features of the solidification boundary and stress near solidification, and examine how these change as material properties and process conditions change. As part of this study, we propose and investigate a solidification criterion that is a function of both stress and temperature.
Numerical Study of Internal Bubble Cooling (IBC) in Film Blowing
Authors: Sidiropoulos V. , Vlachopoulos J.
Published: December 2013

Numerical simulation of turbulent airflow emerging from an Internal Bubble Cooling (IBC) stack and directly impinging on the internal surface of a blown film bubble has been carried out. The streamline pattern and heat flux are determined through a finite volume numerical technique using a version of k-∊ turbulence modeling. It is shown that balancing the airflow between the multiple slits of the stack is useful to increase the internal cooling rates, but may require more elaborate designs of the inlet pipe. As the air flows towards the internal bubble surface there is significant deceleration which diminishes the effectiveness of the heat removal mechanisms. Depending on the flow rates and geometrical configurations the airflow may induce compressibility effects at the exhaust pipe. The numerical results suggest that Internal Bubble Cooling (IBC) equipment introduces distinctive design and operation challenges.
Comparison Studies of Anionic Polymerization of Caprolactam in Different Twin Screw Extruders
Authors: Lee B. H. , White J. L.
Published: December 2013

There is a study on the comparison of twin screw extruders and a batch mixer in the polymerization of caproiactam. A sodium metal initiator and 4–4'-diphenylmethane diisocyanate (MDI) as the activator were used. Our attention is given to (i) a modular intermeshing co-rotating twin screw extruder, (ii) a modular intermeshing counter-rotating twin screw extruder and (Hi) a modular tangential counter-rotating twin screw extruder. We consider the variables of screw configuration, temperature profile, screw speed, and throughput on polymer characteristics. It was found that the conversion of twin screw extruders with proper mixing segments is much higher than the internal mixer at low mixing times. This was seen as higher conversion in twin screw extruders than an internal mixer for the same mean residence time considered.
Microstructure and Prediction of Stress-strain Behaviour of Cold-rolled PP Sheets
Authors: Wu S. Z. , Lee W. B.
Published: December 2013

A constitutive equation for cold-rolled polypropylene is presented based on a modified two-phase model for semicrystalline polymer, which combines the crystalline network that obeys the Langevin based theory and the entangled network with slip-linked character. The microstructure of the rolled semicrystalline polymer consists of packed crystalline inclusions which are separated by adjacent amorphous regions. A theoretical description of the stress strain behavior is obtained by the sum of the stress effects from crystalline and entangled networks. The microstructural observations by scanning electron microscopy X-ray pole figures and differential scanning calorimetry show that polymer chains are aligned along the rolling direction. The stress-strain equation can be obtained from the modified two-phase model and verified by experimental results.
Effects of Process Conditions on the Dissolution of Carbon Dioxide in PS in Foaming Extruders
Authors: Zhang Q. , Xanthos M. , Dey S. K.
Published: December 2013

The effects of the main processing conditions on the dissolution behavior of CO2 in polystyrene melt were studied using a novel in-line method in connection with both single and twin-screw foaming extruders. Apparent solubility data obtained from the twin-screw extrusion experiments showed better consistency compared with those obtained from the single screw experiments, indicating the importance of enhanced mixing in affecting the gas dissolution and solubility behavior during an extrusion foaming process. Gas dissolution inside a twin-screw foaming extruder was further studied for CO2 in the polystyrene melt. The measured gas up-take was compared with the values calculated assuming equilibrium conditions in the gas injection zone in an effort to elucidate possible mechanisms for gas dissolution inside a foaming extruder during the actual foaming process.
An Empirical Study of the Surface Blush in Gas-Assisted Injection Molded Parts
Authors: Liu S.-J. , Lin I.-H.
Published: December 2013

Gas-assisted injection molding of thermoplastic materials has become an important process in industry, because of its capability of producing parts that have thick and thin sections with a good structured rigidity. However, there are some unsolved problems that confound the overall success of this technique. Surface blush of the molded parts caused by glossy difference of the materials is one of them. An L'18 experimental matrix design based on the Taguchi method was conducted to investigate the surface blush of gas-assisted injection molded thermoplastics. The material used was black-pigmented polypropylene. Experiments were carried out on a 4.1 oz reciprocating injection-molding machine equipped with a high-pressure nitrogen-gas injection unit. A plate cavity with gas channels of different geometry was used to mold the parts. After molding, the surface quality of the parts was characterized by a gloss-meter. For the factors selected in the main experiments, mold temperature and gas pressure were found to be the principal factors affecting the surface quality of gas-assisted injection molded parts. The surface glossy difference increases with the content of the pigment in the materials. In addition, a trapezoidal gas channel of small width was found to mold the parts with the least glossy difference. An aluminum mold helps reducing the surface blush in molded parts.
Estimation of Residence Time Distribution in two Elements of a Ko-Kneader
Authors: Mehranpour M. , Nazokdast H. , Dabir B.
Published: December 2013

An attempt has been made to estimate the resident time distribution (RTD) in the KE and EZ elements of the Buss Ko-Kneader. The effects of both rotating and reciprocating motions of the screw were taken in to account in the flow analysis as well as in a simplified mathematical model developed for the RTD estimations. The basic function employed in the present work was F(t) = ∫ f(t) dt, where f(t) dt defined as dq/q was evaluated as a function of the channel depth. Due to the periodic nature of the system averages of minimum resident time was considered as tmin in the above equation. The computation of the model was carried out to evaluated the F(t) as a function of time for both KE and EZ elements. These results demonstrate that the residence time distribution in KE element is slightly narrower than that in EZ element.
Direct Measurement of Fiber Temperature in the Continuous Drawing Process of PET Fiber Heated by CO2 Laser Radiation
Authors: Okumura W. , Yamaguchi T. , Ohkoshi Y. , Gotoh Y. , Nagura M.
Published: December 2013

Poly(ethylene terephthalate) (PET) fiber was heated by carbon dioxide laser radiation during the continuous drawing process. Numerical calculation shows that the PET fiber can be heated much more rapidly and uniformly by heat radiation than by convective heat transfer through the fiber surface. During CO2 laser heated drawing, temperature in the vicinity of a neck-like deformation can be measured on-line with high precision, because the neck-like deformation is located within a range of 0.5 mm. We measured the fiber temperature profiles on the drawing process by IR thermometer that has a range resolution of 0.355 mm. The temperature at which neck-like deformation of the fiber initiates is higher than Tg when draw ratio is less than 4.5, but lower than Tg when draw ratio is more than 5.5. The maximum fiber temperature in the drawing process increases with draw ratio, up to 208°C for a draw ratio of 6.0. The rate of orientation-induced crystallization in the drawing process was estimated by comparison of measured temperature profiles with calculated temperature profiles.
A New Method for Simulating the Conveying of Solid Pellets
Authors: Yung K. L. , Xu Y. , Lau K. H.
Published: December 2013

A new method for simulating the solid conveying process in plasticating machine is proposed in this paper. The new simulation method is superior to previous ones by having the ability in modeling the movements, in any direction, of solid pellets of any geometry or whether it is densely or sparsely packed. New normal and tangential contact force models are introduced. With the new method the solid conveying process are simulated more realistically. In the simulation, the effects of velocity of the barrel, the sliding frictions of the pellets against the barrel and the screw walls with respect to the solid conveying speed are studied, which coincide with empirical results.
Tensile Strength Characteristics of Polymer Melts
Authors: Zatloukal M. , Štach P. , Liu P. , Sáha P.
Published: December 2013

Two different methodologies were employed to determine tensile strength properties of two LDPEs and two metallocene LLDPE resins through capillary and Haul-off (Rheotens-like) measurements. It has been shown that the tensile strength properties obtained by both methods yield almost the same values. Moreover, these values can be correlated to the drawability in tubular film blowing for corresponding materials.
Residual Stress and Warpage Models for Complex Injection Molded Parts
Authors: Young W.-B. , Wang J.
Published: December 2013

In the postfilling stage of an injection molding process, thermal induced residual stress usually develops during the solidification of the melt with non-uniform through thickness temperature distribution. Furthermore, the packing pressure is applied through the gate, and will be different in different locations. Since the local melt pressure varies with time due to the change of melt viscosity, the material solidifies under different frozen-in pressure. The stress relaxation behavior of the plastic materials also complicates the stress field. This study uses a simple thermoviscoelastic model to calculate the residual stress developed in the postfilling stage and a elastic model to determine the warpage after demolding for three dimensional complex parts. Based on the calculation of the injection molding process, the temperature and pressure histories in the postfilling stage can be determined, and used to calculate the developed stress field. The model divides the thickness into two regions, liquid and solid phases. Residual stress calculation is applied in the solid region, while the liquid region is kept at the melt pressure without any strain. The resulted in-mold stress fields are used to calculate the part warpage after demolding.
Crystallization and Orientation Development in Melt Spinning Isotactic PP of Varying Tacticity
Authors: Choi D. , White J. L.
Published: December 2013

We investigated the effects of tacticity on crystallization and orientation development in melt spinning isotactic polypropylene (iPP) through air. Melt-spun fibers were characterized by wide-angle X-ray diffraction (WAXD), birefringence and differential scanning calorimetry (DSC). The melt-spun fibers usually exhibited the monoclinic α-crystalline form, but the mesomorphic form was found under certain processing conditions. The mesomorphic structure was formed more readily in low tacticity fibers. We found certain amounts of hexagonal β-crystalline form in all of the α-form fiber samples. The amouns were generally negligibly small, but the low tacticity fibers spun at high draw-down ratios exhibited significant amounts of β-form crystals. At low spinline stress levels, some low tacticity fibers exhibited lower birefringence and chain orientation than high tacticity fibers due to a less perfect crystal structure. At certain high spinline stress levels, low tacticity fibers exhibited much higher birefringence and chain-axis orientation levels than expected. This was attributed to a reduction in epitaxial lamellar branching (a*-axis oriented group in bimodal orientation). However, the extent of lamellar branching in low tacticity fibers appeared to increase again at higher stress levels. This led to a significant decrease in birefringence and crystalline orientation.
A New Style Single Screw Extruder with Improved Plastification and Output Power
Authors: Grünschloβ E.
Published: December 2013

A single-screw-extruder is presented, consisting of a barrel with grooved feed zone (helical grooves), a grooved melting zone (axial or helical grooves) and a barrier-screw with mixing and shearing elements. Compared with extruders with a smooth melting zone, significant process improvements are achieved regarding mass throughput, pressure build up, melt temperature, melt homogeneity, feed-zone cooling, processing wall-slipping polymers, abrasive wear, residence time, total degree of efficiency and economy. The processing principles of the new extruder are explained. Experimental results confirm the theoretical predictions. The system has proven to be very worthwile in more than 100 extrusion blow molding machines since 3 years.
Investigation of Bubble Instabilities in Film Blowing Process
Authors: Laffargue J. , Parent L. , Lafleur P. G. , Carreau P. J. , Demay Y. , Agassant J. F.
Published: December 2013

This paper describes an original on-line video device developed in order to study bubble instabilities occurring in the film blowing process, taking into account their three-dimensional behavior. For a linear low-density polyethylene, two forms of instabilities and combination have been observed: draw resonance and helical instability. These instabilities could be quantitatively described and differences in behavior could be assessed using real objective measurements and criteria. The influence of key processing conditions was investigated and the results showed that the instabilities are enhanced by increasing the draw ratio, blow up ratio and frost line height. These first results are in agreement with the majority of the results reported in the literature, but allow for a more accurate analysis of the phenomena.
PP-based Model Compounds as Tools for the Development of High-impact-ethylene-propylene Copolymers
Authors: Gahleitner M. , Hauer A. , Bernreitner K. , Ingolic E.
Published: December 2013

The development of heterophasic PP-copolymers, which are necessary in many applications because of their specific property profile, requires large capacities in pilot plants (or at least in bench-scale reactors) for a systematic variation of the matrix and elastomer properties. A possible alternative are model compounds, where the different components are blended in an extruder. The possibility to evaluate three main influence factors on mechanics of such systems, namely the viscosity ratio between matrix and elastomer phase, the phase compatibility and the composition of the elastomer phase, is demonstrated in a series of investigations. Morphology investigations based on transmission electron micrographs have proven to be an indispensable tool for obtaining systematic information about such blend systems, which can be further used for the development of reactor-based systems.
Free-radical Reactions and Thermal Effects in PE during Pipe Extrusion
Authors: Özcanli Y. Lenger , Mamedov Sh. V. , Aktaş B. , Yalçinyuva T. , Alekperov V. A. , Yilgin R. , Durmus A. , Öksüz S.
Published: December 2013

In this study, various effects on the properties of the material, such as free-radical (FR) processes, oxygen induction time (OIT), melting temperature and melting heat are examined during several stages of the polyethylene (PE) pipe extrusion process. The spectra in the Electron Spin Resonance (ESR) are researched between 77–293 K and in a wide range of magnetic fields. At 77 K a triplet signal in ESR is observed. The parameters of the signal are ΔHm1 ≅ 1:4 – 1:6 mT; ΔHm2 ≅ 1 – 1:2 mT; ΔHm3 ≅ 0:6 – 0:8 mT and g1 ≅ 2:020; g2 ≅ 2:011; g3 ≅ 1:99 and Hyper Fine Structure constant ΔH12 ≅ 2:1 mT; ΔH23 ≅ 5:3 mT. As the temperature increase from 77 K up to 293 K, the signal for g4 ≅ 2:02 (ΔHm4 ≅ 0:7 – 0:8 mT) appears and intensity of signals increase. It is also thought that the triplet observed at 77 K belongs to macroradicals of alkyl (–CH2–CH–CH2), alyl(~CH2 C HCH = CHCH2~), carboanions and the acyl (H C O) radicals of the fourth signal. At room temperature, all the FR's transform into peroxide radicals. The total concentration of the FR's is minimum at 463 K and increases at the outlet of the extruder and the pipe sample.

It is observed that the OIT (Oxygen Induction Time) values decrease as one approaches the outlet of the extruder (from 20–30 to 10–15 minutes), while they increase for the processes of 433 K to 463 K. This event proves that the peroxide radicals form as one passes to room temperature. These results support those of the effects of the extrusion stage on the dynamic-mechanical characteristics [2].

Finally, FR's appear as a result of the breaking of the C-C bonds in the main polymer chains starting from the first step in the extrusion process (433 K) and in the later stages, due to the oxygen in the polymer structure, oxidation processes take place.
Modeling Filler Dispersion along a Twin-Screw Extruder
Authors: Lozano T. , Lafleur P. G. , Grmela M. , Vergnes B.
Published: December 2013

Particle size distribution strongly affects physical and mechanical properties of filled polymers. A new model has been developed to predict agglomerate size distribution in a twin-screw extruder (TSE). The model considers the break-up and erosion processes and it uses agglomerate size population balance in its mathematical formulation. The model parameters were evaluated in simple field flow. This paper shows the validation of the model along the extruder using different screw configurations of a short twin screw extruder. Flow parameters along of the TSE necessaries to apply the new dispersion model have been calculated with ©Ludovic software. Calcium carbonate filled polypropylene system was used as model compound. The agglomerate size distribution was evaluated from micrographs of polished samples at different locations along the extruder obtained by reflected light microscopy in conjunction with-semiautomatic image analysis.
Characterisation of Finite Length Composites
Authors: Gleissle W. , Curry J.
Published: December 2013

This paper is a technical report about the structure and the rheological behaviour of processed polypropylene-glass fibre composites. The present studies has been carried out as a part of the international project on the Characterization of Finite Length Composites initiated and organized by the IUPAC Working Party: Structure and Properties of Commercial Polymers. Seven industrial and university laboratories in Europe and in USA worked together in a common project to investigate the influence of the processing conditions on the rheology and manufacturing behaviour of polymer-glass composites preprocessed in a twin screw extruder. All investigations presented concern the influence of the processing procedure on the structure of the composites such as fiber length destribution, fiber orientation, destribution of the fibre concentration in the sample and the rheology of the composites. The flow behaviour dependent on the processing conditions has been measured using capillary rheometers to investigate the viscosity functions, the entrance and outlet pressures losses as well as for observations of the shape and internal structure of extruded composites. Torsional rheometers for low shear rate, oscillatory and transient viscosity behaviour and for the quantification of fibre orientation with ongoing shear process. Additionaly queeze flow experiments are made.

Most laboratories used analogous recording sytems to documente the primary experimental results. So results are partially given here as direct copies from the original data readings. The different data handling and the transfer of data from laboratory to laboratory for comparison of results leads sometimes to unavoidable inhomogeneous (due to the style and possibilities of the different laboratories) presentation of the results. The present report is a result of data collecting, data comparison and documentation of results over a period of nearly ten years.
Measurement and Prediction of Temperature Distribution in an Injection Molding Cavity
Authors: Manero F. , Kamal M. R. , Lai-Fook R. A. , Varela A. E. , Patterson W. I.
Published: December 2013

A method to measure the melt temperature distribution in an injection mold cavity is developed. A thermocouple is used in the construction of a sensor with a tip that can be adjusted at different depths of a mold cavity, to measure temperature profiles at different positions in the mold. Polymer temperature distributions are measured and factors affecting temperatures and the key variables that influence distributions are determined. Measurements are compared with temperatures obtained from numerical simulation of the injection molding process using a three-dimensional heat transfer analysis. Although showing lower values and generally higher cooling rates, temperature data measured from the mold cavity indicate similar behavior to predicted transient temperature distributions.
Montmorillonite Co-intercalated with Octadecylamine and Stearic Acid by Low Temperature Melting and its Influence on PP Nanocomposites
Authors: Merinska D. , Chmielová M. , Kalendova A. , Weiss Z. , Capkova P. , Šimoník J.
Published: December 2013

Organically modified Na-montmorillonite (MMT) samples were prepared by co-intercalation of octadecylamine (ODA) and stearic acid (STA) using a low-temperature melting procedure A blend of MMT and ODA (with the ratio 1: 0.5) was stirred for one minute at 80°C in a laboratory mixer and then different amount of STA (weight ratios of MMT + ODA: STA = 1 : 0.3 and 1 : 1) were added and stirred for another five minutes. The resulting mixture was annealed at the same temperature for one hour. X-ray diffraction (XRD) powder patterns of two co-intercalated samples contain a non-regular set of d spacings of basal diffractions. The first basal diffraction with d = 4.8 nm probably gives evidence for prevalent bilayer molecular arrangement in the interlayer and the non-regular set of d spacings of basal diffractions indicates possible mixed-layer interstratification and/or disorder in the bilayer arrangement of the interlayer space. The set of basal diffractions in the XRD patterns of co-intercalated samples significantly differs from the set of basal diffractions in the patterns of the samples intercalated by only ODA or STA. XRD patterns of Na-montmorillonite sample intercalated with ODA (in the ratio of MMT: ODA = 1:0.5) and with STA (in the ratio of MMT: STA = 1: 1) contain broadening peaks. Polypropylene (PP) nanocomposite samples were prepared by mixing MMT modified in the described mode into the PP matrix. To improve the PP affinity to intercalated MMT, maleic anhydride modified PP as a compatibilizer was used. The level of PP nanocomposites exfoliation was evaluated by XRD technique. The influence of the nanofiller on mechanical properties was measured by tensile tests, and an improvement of mechanical properties was noticed.
A Study of Processing Conditions on the Properties of Diffraction Optical Elements by Injection/Compression Molding Process
Authors: Tseng S. C. , Liao C. L.
Published: December 2013

The purpose of this work is to develop manufacturing techniques of diffraction optical elements (DOE) and compare the performance of micro injection (/compression) molded products. The DOE mold was fabricated by LIGA-like lithography technique. The optical performance of molded products strongly depends on the replication degree of micro patterns on the surface of DOE. Because of the complex micro patterns on the surface of the DOE, it is very difficult to measure the degree of duplication by traditional microscope measurement like SEM or AFM etc. In this work, a laser computer imaging system was developed to evaluate optical performance of molded parts directly. To achieve better duplication degree and properties of molded DOE, Taguchi's method was employed in the experiments to examine the effects of processing conditions on the performance of molded DOE. Residual stresses of different molded products were measured by a photo-elasticity system. Experimental results reveals that residual stresses of micro injection compression molded elements are much less than those of the micro injection molded ones. This is because compression process provides a higher and more uniform pressure distribution inside the cavity and it can help reduce the unbalanced shrinkage and residual stresses. Compression speed dominates the cavity pressure distribution and becomes the most important factor of final DOE's optical properties.
Radiant Heating of Plastics: Application to Film Blowing Processes
Authors: Benkreira H. , Talford M. C.
Published: December 2013

This paper presents experimental data and a mathematical model for the radiant heat transfer operation used in the production of biaxially oriented polypropylene (BOPP) films by the Double Bubble process. The data was obtained from an industrial pilot plant fully instrumented for the purpose of the study. In the mathematical model the effect of the view factor is considered, along with the effects of natural and forced convection on the heat transfer coefficients. Experiments were also conducted in a laboratory radiant heater to determine the range of heat transfer coefficients experienced under different heating conditions, and analytical methods to determine these are discussed.
Modeling and Analysis of Helicoidal Flow in a Conical Extruder
Authors: Sarioglu A. , Månson J.-A. E.
Published: December 2013

The present paper discusses the unique flow behavior in a new type of extruder. The extruder design is based on a hollow conical assembly of static (stators) and rotating (rotor) parts. Extrusion is achieved from each side of the rotor to provide a two-layer annular product. Flow is helicoidal in the vicinity of the rotor tip and die entry where the polymer layers merge. However, it becomes fully parallel to the main extrusion direction after a certain distance downstream from the rotor tip. Numerical simulations based on the resolution of Navier-Stokes equations using a Generalized-Newtonian viscosity showed that the length of the helicoidal flow depends on die design, viscosity and flow rate ratios between adjacent polymer layers. Analysis of flow variables along the interface showed that the helicoidal flow distance can be increased using a die design inducing lower interfacial shear rate and velocity. When the viscosity ratio and the flow rate of the most viscous polymer are increased, the helicoidal flow can be maintained over a longer distance in the die. Finally, experiments have shown that the advantage of the helicoidal flow is for short fiber orientation in pipes. The fibers are oriented along the streamlines in the hoop direction in the mid-gap of the die; however, they are parallel to extrusion direction in the vicinity of the stators.
Computational Study of Velocity Field in the KE Element of a Modular Ko-Kneader with CFD Method
Authors: Mehranpour M. , Nazokdast H. , Dabir B.
Published: December 2013

Attempts were made to predict the velocity field and shear rate distribution of a Newtonian type fluid in the KE element of the Buss Ko-Kneader by means of CFD method. The role of both rotating and reciprocating motion have been considered in three dimensional flow field. The computed results showed appreciable changes in the velocity counters during a period of reciprocating motion, and these changes were greater for the transverse flow compared to the down channel flow.

The predicted results also showed pronounced variations in the velocity profile of the transverse flow regarding both with direction and extent of drag and pressure flow as a result of reciprocating action, while the down channel velocity profile was found to be almost unaffected.

The extent of shear rate and hence shear rate distribution were found to be dominantly control by the down channel flow while transverse flow has a greater influence in determining the residence time distribution.
Quality Aspects on the Power Cable Core Insulation Extrusion and Thermal Curing Process
Authors: Harlin A. , Huotari P.
Published: December 2013

The insulated core quality of power cables is directly linked to the performance of the cable in its end-use. The high voltage distribution installations at 10 to 500 kV range are large, expensive, and essential for community. Consequently, the most important quality properties are therefore the expected service life of the cable and its manufacturing costs. Standard cable constructions, with the exception of the extra high voltage (EHV) construction for over 385 kV, have substantial overdimensioning in the insulation layer thickness. Medium voltage cables in the range 10 to 35 kV (MV) are increasingly becoming commodity items and the cost function has become critical to the economic viability of cable production. Insulated core quality depends on the raw materials quality, e. g. the purity of the peroxide cross-linkable PE-LD. The extrusion process and insulation curing process should be considered as the major quality aspects. The total quality of the cable can be assured only if manufacturing is made correct at once. In the following is reviewed the good practice and related aspects based on marked field experience.