bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Reactive Filling in Complex Cavities***
Authors: Garcia M. A. , Macosko C. W. , Subbiah S. , Güçeri S. I.
Published: December 2013

The flow of reacting monomers into thin planar cavities of irregular geometry is analyzed. The Hele-Shaw approximations are used to simplify the momentum and mass balances. At each time step, the flow domain is mapped onto a rectangular domain using elliptic expressions. The transformed governing equations are solved using finite-differences. The transient three-dimensional energy and species balances are solved using an explicit marching scheme coupled to the flow. Viscosity is modeled as a function of temperature and extent of reaction. Castro's model is used to compare several fountain flow approximations. A simplified algorithm was found to capture the essence of the fountain flow kinematics. The fountain flow approximations described here can also be used in thermoplastic injection molding modeling. Results for a rectangular end gated mold and for an irregular mold geometry are presented.
Dynamic Modelling of Internal Mixers Using System Identification Techniques
Authors: Stoten D. P. , Moore J. M.
Published: December 2013

Dynamical modelling techniques are presented that facilitate the derivation of transfer function models between key inputs and outputs of internal mixing processes. Tests to model the mastication of natural rubber in a Francis Shaw Intermix at two levels of fill-factor are described. The derived models will form the basis for closed-loop control strategies.
Theoretical Principles Governing the Design of Barrier Sections in Extruders
Authors: Potente H. , Stenzel H.
Published: December 2013

Barrier screws used in conjunction with grooved-barrel extruders are gaining increasing importance on account of their high throughput and melting performance as well as their good homogenizing action. Although a number of calculation formulae now exist for the barrier screw, no comprehensive, logical design system for power law melts has been compiled to date. This paper takes a simple melting model and shows how the geometry of the barrier section can be designed (flight depth and screw channel width of the channels for the solid and the molten material and the length of the barrier section). A method of calculating the pressure and temperature profile in the melt channel is also presented. The different variables affecting the melting process are discussed on the basis of parameter studies.
New Ways in the Manufacturing of Finished and Semi-finished Products from Nylon
Authors: Michaeli W. , Berghaus U. , Speuser G.
Published: December 2013

In conventional processing, extruders have been used, mainly, for continuous compounding and processing of polymers. Yet, for a long time they have been serving as chemical reactors. It has been 50 years since first developments were made in the field of extruder application as a reactor. In the following, we will offer the reader a review of research and development activities of the Institut für Kunststoffverarbeitung (IKV) in the field of reactive extrusion.
Flow-Induced Crystallization and Self-Reinforcement During Extrusion
Authors: McHugh A. J. , Tree D. A. , Pornnimit B. , Ehrenstein G. W.
Published: December 2013

Flow-induced crystallization of high-density polyethylene and polypropylene films has been studied in a slit die equipped with optical windows to allow direct visual observation of the process. Mechanical and thermal property measurements and morphological analyses verify the presence of self-reinforced, extended-chain structures in the extrudate. By controlling the location of the crystallization front inside the die but near the exit, continuous extrusion was possible at lower pressures than previously reported. Birefringence measurements of the melt flow indicated the feasibility of an optimal die geometry to maximize oriented structure development during continuous extrusion while minimizing pressure buildup.
Closed Loop Control of Parison Dimension Profiles in Extrusion Blow Molding
Authors: DiRaddo R. W. , Patterson W. I. , Kamal M. R.
Published: December 2013

Extrusion blow molding is utilized in the production of plastic hollow containers. One of the critical steps in the process sequence is the formation of an annular extrudate, called the parison. Extrusion of the parison through an annular die is associated with varying degrees of swell and sag along the length. Moreover, the design of many commercial blow molding products requires variations in wall thickness along the length of the parison. The present work describes the design and operation of an on-line computerized parison thickness profile measurement technique for the purpose of implementing closed loop control of the parison thickness profile.

The proposed thickness measurement technique was evaluated by comparing it to the conventional pinch-off mold technique. The control strategy employed involves a simple on-line adaptive control scheme. Programmed set point profiles, such as constant, linear and oscillatory profiles were implemented to within a 5% error. Moreover, the adaptive controller compensates for system disturbances.
Existing Scale-up Rules for Single-screw Plasticating Extruders
Authors: Potente H.
Published: December 2013

This paper gives a review of existing scale-up rules for single screw plasticating extruders. It is shown that there were and still are rather varied trends. The main three are:

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scale-up rules under the boundary conditions of an invariant shear rate,

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scale-up rules including the power law,

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scale-up rules including the zones of operation.

In Europe, at least, the scale-up rules, which take the power law-flow characteristics into account, seem to have been established in practical terms. For economical reasons conventional extruders are designed in such a way, that the output increases with the square of the diameter. This however, results in the problem that the melting rate does not follow the same scale-up rules as the pumping rate and the solid conveying rate. Thus the discussion continues, to calculate the operating section lengths according to varying scale-up rules. Finally the scale-up problem is discussed once more with respect to the dominant dimensionless numbers, and despite several similarity theoretical difficulties a standardized solution will be attempted to be found.
Mechanical Properties of Thermoplastic Polyurethane Blends and Copolymers of Styrene and Acrylonitrile
Authors: Žerjal B. , Musil V. , Jelčić Ž. , Šmit I. , Malavašić T.
Published: December 2013

Mechanical data obtained on the blends described in a previous paper together with some new data have been correlated with the theory derived for the mechanical properties of polymer composites, to gain insight into the nature of domain interfaces. Thermoplastic polyurethanes are blended in the entire composition range, with styrene-acrylonitrile copolymers. Blending with thermoplastic polyurethanes improves the toughness. Improved toughness is indicated by the increase of elongation at break and by decrease of hardness.
Mixing on Melting in Single Screw Extrusion
Authors: Benkreira H. , Shales R. W. , Edwards M. F.
Published: December 2013

A new approach to assessing mixing in single screw plasticating extruders is proposed. It is based on image analysis of microtomed sections obtained from the polymer helix formed in a suddenly cooled split barrel extruder fed with a mixture of black and white polymer granules. The observations suggest that most of the mixing occurs on melting with little improvement thereafter. A simple laminar mixing model is drawn in the melting zone the results of which compare favourably with experimental data. In particular, it is shown that improved mixing can be achieved with increasing screw speed in complete contradiction with the classical strain theories which consider mixing in the melt conveying zone only.
Simulation of 3-Dimensional Flow in Internal Mixers
Authors: Hu B. , White J. L.
Published: December 2013

The design of internal mixers for the rubber industry has traditionally been based on the basis of intuition rather than a knowledge of the fluid mechanics of motions in the internal mixer. In recent years, efforts have been made to numerically simulate the flow and mixing characteristics in internal mixers. The simulation effort is important for the understanding of mixing mechanisms in the internal mixer, and furthermore, to provide a basis for rational design. In this paper, we develop a new model based on cylindrical coordinate hydrodynamic lubrication theory for internal mixers. This allows full consideration of curvature in an internal mixer. Numerical techniques are used to carry out the calculations of the pressure field and flux field for various rotors described in the patent literature. This is done for a Newtonian fluid in a fully filled mixing chamber. This type of calculation is of key importance in the design of flight arrangements on internal mixer rotors.
Maleation of Polypropylene Melt in Model Reactors
Authors: Polance R. , Jayaraman K.
Published: December 2013

The maleation of polypropylene melt with a peroxide as free radical initiator has been carried out isothermally in a continuous flow reactor and in a batch flow reactor. The continuous flow reactor is designed to provide significant levels of extensional strain in the fluid while the batch flow reactor provides a simple shear flow with uniform residence time. In both reactors, less than 1 part per hundred of dicumyl peroxide (dissolved in xylene) is added to a preblended single phase mixture of polymer melt and dibutyl maleate. The relative extent of maleation is much higher in the continuous flow reactor than in the batch reactor with comparable shear strain rates and mean residence times. As the feed rate and the rotation speed are varied at a fixed temperature in the continuous flow reactor, the highest degree of maleation is obtained under conditions where fluid dynamics computations show the stretching of a fluid element to be the greatest. Hence, increasing shear alone leads to rather limited increases in extent of maleation. These results emphasize the importance of the detailed deformation field for carrying out functionalization reactions on polymer melts.
Melting of Plastics in Kneading Blocks
Authors: Todd D. B.
Published: December 2013

Melting of plastics in intermeshing co-rotating twin screw extruders is known to occur over very short barrel lengths. The melting phenomenon has been studied for both pellets and powder in a readily opened clam shell barrel. The melting mechanism is attributed mainly to the dissipation of the energy imparted in interparticle friction as a consequence of the unique kneading action of this type extruder.
Dynamics and Control of Surface and Mold Temperatures in Injection Molding
Authors: Gao F. , Patterson W. I. , Kamal M. R.
Published: December 2013

Mold temperature control in injection molding is very important for control of production rate and product quality. However, mold temperature is a complex function of machine design, process variables, machine settings and ambient conditions. Data were obtained regarding the variability in both space and time (in-cycle and cycle-to-cycle) of mold metal and mold surface temperatures and heat flux. In view of this variability, it is necessary to define variables which may be useful for control purposes. The following variables were evaluated: cycle average temperature, peak temperature, and partial cooling time. Dynamic models were developed, on the basis of experimental data, to determine the process gains, time constants and time delays for the above variables with regard to coolant temperature, coolant flowrate, and melt temperature as the possible manipulated variables. In view of the dynamic studies, the cycle average surface temperature was selected as the controlled variable for control system design and simulation. The regulating abilities of PI, PID, and Dahlin controllers were evaluated. The results indicate that Dahlin control caused the controlled variable to follow the set-point closely, even when the process parameters vary, thus showing good robustness. However, the Dahlin algorithm achieves this advantage via large variations in the manipulated variable. This may cause difficulty in some circumstances.
Detailed Investigations of Structural Layering Phenomena in Injection Molded Thermotropic LCP
Authors: Hsiung C. M. , Tian J. , Cakmak M.
Published: December 2013

Effects of processing variables on the structural gradients developed in the injection molding of thermotropic wholly aromatic copolyester parts were investigated using optical macro and microscopy combined with image analysis techniques at various sections of the molded LCP parts.

The studies indicate the existence of a multi-layer structure from skin to core of the parts. These include: a skin layer, a transition zone composed of a sub-skin layer, a shear layer and a core region. The effects of processing conditions including injection speed, mold temperature, and mold size on the structural features were evaluated. An interesting buckling phenomenon resembling features observed in jetting at core regions near the end of the cavity after the divergence section was observed for the samples molded at the lowest injection speed and mold temperature.

Digital image analysis of the images of the sectioned parts revealed that there are more layers than one observes macroscopically. In certain instances as many as 15 layers were detected. Orientation behavior and the positional light reflection intensity appear to correlate with each other particularly away from the skin regions. This may be the manifestation of high visible light absorption anisotropy exhibited by these aromatic polymers.
Computer Controlled Rotational Molding of Liquid Silicone Polymer
Authors: Teoh S. H. , Guan K. W. , Lee N. H. , Wong Y. S. , Nee A. Y. C. , Pho R. W. H.
Published: December 2013

Rotational molding in two axes has the advantage of producing hollow products. Previously, the inherent difficulty was in the production of objects with uniform thickness since the speed of the two primary axes are fixed and cannot be varied independently to take into account the changes in material properties such as its density and viscosity. With the advent of computers, it is now possible to control the thickness of the object accurately. This is made possible by creating an intelligent software which takes in the viscosity and density time variation of the polymer and using the flat plate withdrawal theory, computes the new speed for each axis. The relationship between rotational molding parameters and polymeric material properties for a solvent – silicone rubber system to produce a hand prosthesis is illustrated in this paper.
A Unified View of Modeling Flow in Counter-rotating Twin Screw Extruders
Authors: White J. L. , Adewale A. O.
Published: December 2013

Intermeshing counter-rotating twin screw extruders have played an important role in polymer processing technology in the post World War II period. They operate on basically the same principle as low viscosity multiple screw pumps, i.e. they involve forward pumping of fluid contained in C-chambers, which are regions between the screw root and barrel between the interlocked intermeshing regions. Tangential counter-rotating twin screw extruders with open screw channels have also been manufactured in the same period. A new more general model of flow of a Newtonian fluid in a counter-rotating twin screw extruder with partially intermeshing screws is presented. The model allows transition from fully intermeshing to tangential screw machine systems. Calculations are made to show the effect of level of intermesh on pumping capability. Modular counter-rotating twin screw machines are analyzed. The problem of starvation is discussed.
Simulation of Injection Molding and Comparison with Experimental Values
Authors: Potente H. , Schulte H. , Effen N.
Published: December 2013

The outstanding economic importance of injection molding in plastics processing and the steadily growing requirements on the molded parts to be produced are leading to constant further developments in the process engineering for injection molding. Computer simulation is a method that has only recently come to be used to an increasing extent in the field of injection molding, and the use of computers has so far been restricted to simulation of the injection mold. One key prerequisite for the quality of the molded parts, however, is that the melt should have been prepared by the plasticating unit in a manner that comes as close to the ideal as possible.

The article presents a closed basis for calculation for the simulation of the plasticisation process in injection molding. This makes it possible for a large number of screw layout criteria to be estimated and calculated in advance. The computer simulation serves to make the plasticisation process more or less transparent and also clearer and calculable. The validity of the computation model for any size of plasticating units is demonstrated by examining the operating points of large industrial plants.
Two-Dimensional Dynamic Study of the Distributive Mixing in an Internal Mixer
Authors: Wong Tang H. , Manas-Zloczower Ica
Published: December 2013

Distributive mixing in an internal mixer was studied numerically by means of tracking the evolution of the distance between pairs of particles in the mixing chamber. The distributions of these pairwise distances are reported in terms of the probability density function of a pairwise correlation function. In conjunction with this descriptive technique, a dynamic particle-tracking algorithm for two dimensions has been developed to study the dynamics of mixing in the mixer. We also propose a parameter e to monitor the extent of mixing. This general approach represents the first attempt of this kind to address directly the goodness of mixing. A total of five operating modes was considered. Three of them have even speed ratio of 60 rpm and rotors positioned at 90–90, 90–180, 90–270 relative to the horizontal axis, respectively. The remaining two have uneven speed of 60 rpm/40 rpm and rotors positioned at 90–90, 90–270 relative to the horizontal axis, respectively. For each operating mode, a complete period is represented as a sequence of snap shots (72 for even speed and 216 for uneven speed) and the flow field for each snap shot was calculated by means of FIDAP. Based on our proposed framework, we were able to demonstrate clearly that the anti-symmetric configuration (90–270) is the best operating mode among the three even speed cases and the configuration (90–180) is the worst. The performance of the uneven speed cases fell in between the even speed cases.
3-D Flow Simulations of a Cavity Transfer Mixer
Authors: Wang C. , Manas-Zloczower I.
Published: December 2013

The Cavity Transfer Mixer (CTM) was primarily designed as a distributive mixing device to be used as an add-on unit to existing extruders. In determining the CTM overall mixing efficiency as well as its potential use for various applications, the flow patterns/characteristics within this mixer must be well understood. In this work, a fluid dynamics analysis package – FIDAP – using the finite element method was employed to simulate the flow patterns in a CTM with 3 rows and 6 cavities per row. A 3-D, isothermal flow analysis for a Newtonian fluid was carried out. The flow field was characterized in terms of velocity profiles, average shear stresses and a parameter λ quantifying the elongational flow components. The influence of processing variables on the flow characteristics was also discussed. The simulation results show good agreement with the experimental data.
Orientation Evolution in Convergent-Divergent Dies
Authors: Zhao J. , Mascia L.
Published: December 2013

Solid-state extrusion experiments were carried out through constant area convergent-divergent dies using two crystalline polymers, i.e. ultra high molecular weight polyethylene (UHMWPE) and polytetrafluorethylene (PTFE), with the aim of producing extrudates exhibiting biaxial orientation. The evolution of orientation was examined along the extrusion axis by measuring the off-plane birefringence values at various distances from the entry on specimens removed from the dies. Simple analytical expressions relating orientation factor to draw ratio in the three mutually perpendicular directions were derived for crystalline polymers. These generalised relationships were found applicable for all types of deformations, i.e. monoaxial, biaxial and pure shear. On the basis of the data obtained and the predictions from the theoretical analysis, the deformations taking place in dies with small converging angles, known as fish-tail dies, were found to be close to a state of pure shear deformations, while dies with high converging angles initially, then changing to high divergencies in the second section, known as dual-taper dies, were found to give rise to a state of unbalanced biaxial deformations.
Equation of State for Pure Polymeric Fluids Theory Based on An Improved Hole and Cell Model
Authors: Wang N. H. , Sakai T. , Masuoka H.
Published: December 2013

A theoretical equation of state (EOS) for chain molecule fluids is presented based on an improved hole and cell model in which the geometries of both the cells and the mers are defined as the dodecahedrons and reasonably related with the Lennard-Jones potential. Furthermore the number of configurations is treated to contribute to the EOS by means of minimizing the Helmholtz free energy to determine the cell size. This study may be regarded as the improved theories about the hole and cell model proposed by Simha et al. and the hole model by Sanchez and Lacombe. The present EOS has three characteristic parameters per pure fluid, which can lead to a corresponding-state principle for pure polymeric fluids. The validity and applicability of the equation were investigated by correlating the experimental PVT data for some common polymers and predicting the thermal expansion coefficient and isothermal compressibility of PVAc.
Effect of the Cast Film Production Process on the Properties of Oriented Polypropylene Film
Authors: Peiffer H. , Dietz W.
Published: December 2013

To produce highly transparent flat film from polypropylene, the melt must be cooled as quickly as possible to form the cast film. With polypropylene, heat transfer in the cooling unit is associated with crystallization processes. These make it difficult to calculate cooling times and subsequently the geometry of the cooling unit. A mathematical method for designing cooling units for polypropylene melts is described. The calculated results are compared with experimental findings and recommendations for optimized cast film cooling are given.
The Optimisation of Masterbatch Formulations for Use in Single Screw Machines
Authors: Benkreira H. , Britton R. N.
Published: December 2013

Previous work by Benkreira et al. [1] has shown that the critical stage in distribution of additives in single screw extruders is the zone where the polymer melts; the subsequent pumping of the melt makes little difference to the mixture quality. It is suggested that the ideal masterbatch melts before the host polymer and coats each granule, while remaining sufficiently viscous to promote the shear heating and melting of the polymer. In order to test this hypothesis and quantify the requirements in terms of relative melting points and melt viscosities, a set of model masterbatches was produced and used for injection moulding at 1 % addition in a variety of polypropylenes and polyethylenes, but always under the same moulding conditions. Image analysis and “experts” judgement was used to rate the performance of these master-batches. The conclusions drawn from this work are that the designer of a masterbatch must consider the melting ranges of the masterbatch and its host polymer, and their relative viscosities in the temperature range of the forming process, in order to optimise the ease of distribution of the masterbatch.
An In-line Melt Rheometer for Molten Plastics
Authors: Nelson B. I. , Broadhead T. O. , Patterson W. I. , Dealy J. M.
Published: December 2013

An in-line rheometer designed for use as a sensor for closed-loop control of melt processing operations has been previously described. This instrument can measure the true viscosity of a melt stream over a range of shear rates. In order to evaluate its performance in processing applications the rheometer was mounted on a twin-screw extruder. A chemical degradation process was used to introduce changes in the molecular weight distribution, and thus the viscosity of a polypropylene resin, and these changes were monitored using the rheometer. For rapid replacement of melt in the zone of controlled shear in the rheometer, flow simulations indicated that it would be advantageous to operate the rheometer in a cyclic mode. A stochastic process identification technique based on a pseudorandom binary signal was used to determine the parameters of a first-order plus deadtime model of the process. In order to estimate the portion of the system response due to rheometer dynamics, residence time distributions were measured both with and without the rheometer present. It was found that the rheometer has a dead time of about 6's and a first order time constant of less than 15 s. The response of the new instrument is thus significantly faster than than that of melt process rheometers now commercially available.
Miscibility and Mechanical Properties of Poly(ether imide)/Liquid Crystalline Poly(ester imide) Blends
Authors: Ryu Changyeol , Seo Yongsok , Hwang Seung Sang , Hong Soon Man , Park Tae Suk , Kim Kwang Ung
Published: December 2013

As a part of continuous study to search for the high performance in situ composite, this study examines the miscibility of liquid crystalline poly(ester imide) (PEsI) with poly(ether imide) (PEI) and its effect on the mechanical properties and the morphology of the blends of these polymers. Liquid crystalline polymers (LCPs) were synthesized from trimellitic anhydride and α,ω-diaminoalkane with 8, 10, 12 methylene groups. Thermal condensation of these diacids with 4,4′-diacetoxybiphenyl yielded the corresponding imides of thermotropic homopolyesters. Optical polarized micrographs show that the synthesized poly(ester imides) have the smectic structure. Partial miscibility was observed from the shift of the glass transition temperature determined by differential scanning calorimetry. Increasing concentration of the liquid crystalline PEsI in the PEI/PEsI blends shifted the glass transition temperature of the PEI phase to a lower temperature. Mechanical properties of the PEI/PEsI blends were changed with the number of methylene units in PEsI. Morphologies of the partially miscible system were found to be quite different from those of an immiscible system. Strong adhesion between the matrix (PEI) and dispersed phase (LCP) was observed, but fine fibril formation was not possible due to the absence of smectic-nematic transition.
Simulation of Non-isothermal Flow in Twin Screw Extrusion
Authors: Chen Z. , White J. L.
Published: December 2013

Procedures are described for computation of pressure, fill factor and temperature profiles in a molular co-rotating twin screw extruder with multiple feed ports and vents. This is a modification of our earlier Akro Co-Twin Screw software. Sample calculations are given for non-isothermal flow simulation of compounding of thermoplastics with talc. It is shown that the effect of temperature on viscosity plays a significant role in pressure fill factor, and temperature profiles and in overall temperature rise.
On-line Measurement of Residence Time Distribution in a Twin-screw Extruder
Authors: Chen Tong , Patterson W. I. , Dealy J. M.
Published: December 2013

A simple optical on-line residence time distribution (RTD) measurement technique has been developed. Changes in extrudate light transmittance are monitored by a photomultiplier. A He-Ne laser is the light source with carbon black as the tracer. The RTD of a ZSK-30 twin-screw extruder was measured using this technique. The effects of feed rate, screw speed, and melt viscosity on the RTD were studied. Also, the effect of the presence of an in-line rheometer on RTD was examined. The advantages and disadvantages of the technique are discussed.
Simulation of the Screw Bowing Effect in an Intermeshing Counter-Rotating Twin-screw Extruder
Authors: White J. L. , Adewale A. O.
Published: December 2013

The bowing of screws in an intermeshing counter-rotating twin screw extruder due to polymer melt flow induced lubrication pressures between screws is modeled. It is shown that the extent of screw bowing depends upon screw aspect ratio, the modulus of elasticity of the screw, screw design, extent of intermesh, level of shear viscosity and melt throughput.
Solids Conveying and Melting in a Starve Fed Self-wiping Co-rotating Twin Screw Extruder
Authors: Bawiskar S. , White J. L.
Published: December 2013

A flow visualization study of starve fed solids conveying in single screw and a modular self-wiping co-rotating twin screw extruder is observed inflow visualization experiments. Single screw extruders exhibit forward Archimedean transport of material on the undersides of the screw. Self-wiping co-rotating twin screw extruders conveying forward in the intermeshing region and in the region near the apex between the screws. Observations are reported of the melting of solid pellets and possible melting mechanisms are discussed.
Modeling the Residence Time Distribution of a Non-Intermeshing Twin Screw Extruder
Authors: Thompson M. , Puaux J. P. , Hrymak A. N. , Hamielec A. E.
Published: December 2013

The residence time distribution (RTD) of a counter-rotating non-intermeshing twin screw extruder has been studied by a radioactive tracer technique. RTDs were measured at both the die exit and at the first compounding zone of the extruder. The operating parameters investigated were: screw speed, screw flight stagger, and barrel temperature. These parameters have an effect on the mixing efficiency. The mixing efficiency was characterized by fitting measured response data with models comprised of different combinations of ideal reactor elements. The empirical flow models tested were: plug flow and tanks-in-series (with and without recirculation), plug flow and axial dispersion, and the Wolf-Resnick model. The fitted model parameters characterized the observed changes in the RTD due to the variation of the operating parameters.
Modelling and Experiments of Squeezing Flow of Polymer Melts
Authors: Zhang W. , Silvi N. , Vlachopoulos J.
Published: December 2013

A one-dimensional purely-viscous model that includes slip at solid boundaries is proposed to study the flow of polymeric materials when compressed between two approaching parallel surfaces. A squeeze-flow rheometer was designed and built to compress polymer melts under controlled conditions of constant closing speed and constant applied force for different conditions at the polymer-solid interface. One of the purposes of this study was to investigate how the interface conditions influence the flow field during squeezing. The experimental findings revealed that the model can adequately predict the squeezing force for slow squeezing of relatively thin samples. For fast squeezing, however, the experiments appear to suggest the need of including elongational effects in the modelling of the material behavior.
Crystallization Behavior of Carbon Fiber Reinforced Polyamides (I) Dynamic and Isothermal Crystallization
Authors: Zhang Z. , Kitano T. , Hatakeyama T.
Published: December 2013

Polyamide (PA) was compounded with carbon fiber (CF) with various contents (0, 5, 15, 20 vol.-%) using an elastic extruder. The effect of both the carbon fiber contents and the compounding method on thermal behavior and characteristics of crystallization are studied using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and polarizing optical light microscopy (POL). Thermal investigation was carried out under programmed cooling and isothermal conditions. The following results were obtained: (1) The crystallization temperature became higher with the increase of carbon fiber content, while the melting temperature and enthalpy were scarcely affected by the carbon fiber content. (2) The compounding methods affected the thermal behavior of composite systems. The samples that have been extruded twice have higher crystallization and melting temperatures as well as higher melting enthalpy. (3) Isothermal crystallization was observed using DSC. From the rate constant k and Avrami's index n, it was found that crystallization was accelerated by the presence of carbon fiber without changing the type of nucleation. (4) The polarizing micrographs showed that the nucleation of PA occurred on the surface or close to the CF.
Unstable Gas Penetrations in Symmetrical Rib Channels During Gas-assisted Injection Molding
Authors: Yang S. Y. , Huang F. Z.
Published: December 2013

During gas-assisted filling, gas penetrations in symmetrical rib channels are found never symmetrical. The development of this unsymmetry is observed and its cause is analyzed. The system of gas penetrations in melt in symmetrical rib channels is found unstable. Symmetry is upset upon perturbation. Symmetrical gas-channel ribs in gas-assisted injection molded parts should be avoided.
Stress Controlled Simultaneous On-line Measurements of Viscosity, Flow Exponent, and Melt Index
Authors: Gleißle W. , Schulze V.
Published: December 2013

Capillary rheometers have been installed on-line very successfully for real time control of the quality of polymers in production and processing. A substantial extent of the real time information about the state of material and process is reached using an on-line rheometer with a wedge-shaped slit working under pressure controlled conditions. True viscosity, flow exponent and melt flow index can be measured simultaneously and changes in average molecular weight and molecular weight distributions are indicated immediately.
Modeling and Finite Element Analysis of Flow in SMC Compression Molding
Authors: Youn S.-K. , Lee E.-S.
Published: December 2013

A new flow model is developed for the analysis of compression molding of sheet molding compounds (SMC) and a penalty finite element formulation is presented to predict flow front progressions more accurately. In this model SMC is assumed nonisothermal fluid, which has different viscosities in extension and in shear. The flow is allowed to slip at the mold and is resisted by friction force which is proportional to the relative velocity at the mold surface. For the verification of the model, the press force and flow patterns are compared with those of experiments and available results by other works in this field. It is also demonstrated, using the computational procedure described and the proposed model, that optimal initial charge shapes for the filling can be effectively computed.
Melt Strength and Elastic Behaviour of LLDPE/LDPE Blends
Authors: Micic P. , Bhattacharya S. N. , Field G.
Published: December 2013

Differences in processability between linear low denisty polyethylene (LLDPE) and low density polyethylene (LDPE) as well as for their blends subjected to extensional flow were assessed in terms of melt strength and elastic parameters from shear flow such as storage modulus (G′), and first normal stress difference (N11 – N22). The results revealed similar synergistic effects for these parameters in the LDPE rich blends. A DSC test carried out on these LLDPE/LDPE blends when fast cooled disclosed the existence of two phases in the molten blends for the same composition range where the melt strength synergism was observed. The results are discussed in terms of the influence of the different molecular structures of the blend polymers and their miscibility on the measured melt strength. A mechanism is suggested to explain the observed synergistic phenomenon.
Analysis of the Mold Filling Process with Phase Change Considering the Non-steady Effect
Authors: Kim M. S. , Lee W. I. , Lee J. S.
Published: December 2013

Polymer mold filling is a non-Newtonian, non-isothermal, non-steady process with free surface. It is well known that the fountain flow effect in the flow front region and the solidified layer near the cold mold wall have significant effect on the mold filling process and thus the mechanical properties of the molded parts. In this study, a non-isothermal, non-steady mold filling process including the solidified layer as well as the fountain flow effect was analyzed numerically using the finite element method. Shear rate dependency in the viscosity was taken into account by employing the Cross model. Single-step algorithm was used for the numerical integration in time and the flow front was advanced by the explicit scheme. The resulting system of algebraic equations was solved using the Picard iteration technique. In order to verify the validity of the numerical scheme, energy balance and mass conservation were checked. It was found that the energy and mass balances were satisfied within reasonable accuracies. The importance of the non-steady term was assessed by analyses done in a similar manner by assuming that the process is quasi-steady. Two results thus obtained were compared. The quasi-steady assumption was found to be insufficient in describing the inherent non-steady effect during mold filling.
Surface Defect Formation in the Injection Molding of Acrylonitrile-Styrene-Acrylate Polymers
Authors: Chang M. C. O.
Published: December 2013

Surface defects in the injection molding of acrylonitrile-styrene-acrylate (ASA) weatherable polymers, such as “chevrons”, “non-uniform haze” and “step defect “, are examined. A criterion is proposed based on a flow instability mechanism which suggests that recoverable shear strain, shear stress, and coefficient of friction are the key factors controlling the formation of surface defects. The criterion is supported by various experiments.
Theoretical and Experimental Investigations of the Melting of Pellets in Co-Rotating Twin-Screw Extruders
Authors: Potente H. , Melisch U.
Published: December 2013

Knowledge of the plasticizing behavior in tightly intermeshing, co-rotating twin-screw extruders is of crucial importance for assessing the compounding process. Experiments were conducted on a laboratory extruder in order to establish the parameters that influence the melting process. Solidified samples of material were taken from the screw and microtome cuts produced from the plasticizing section. These were then assessed on the basis of image analysis. This visualization of the solid and molten phases which are present simultaneously together with the distribution of the two phases made it possible to quantify the reduction that occurs in the amount of solid material over the length of the screw configuration employed.

A model is additionally presented for the calculation of the melting lengths and the melting profiles. This works on the basis of individual particles which are uniformly dispersed in the polymer melt. Allowance is made for the temperature increase in the solid material conveying section. A comparison of calculated and experimentally determined melting lengths revealed a satisfactory level of agreement.
An Improved Flow Simulation Model for a Tangential Counter-Rotating Twin Screw Extruder
Authors: Bang D.-S. , White J. L.
Published: December 2013

In this paper we simulate the flow of a Newtonian fluid in a tangential counter-rotating twin screw extruder using a cylindrical coordinate lubrication theory model. Special attention is given to the material flows leading to mixing specially to inter-screw and backward leakage between the screws, and how they vary with process conditions.
Modeling and Experimental Study of the Flow in a Simplified Cavity Transfer Mixer
Authors: Wang C. , Manas-Zloczower I.
Published: December 2013

The Cavity Transfer Mixer (CTM) was primarily designed as a distributive mixing device to be used as an add-on unit to existing extruders. Understanding the flow patterns and characteristics within the CTM is of fundamental importance for a proper design and optimum processing. Due to the complex geometry and the transient characteristics of the flow, solving for the flow patterns in the CTM is not an easy task. However, some of the design features of the CTM can be reproduced in a simplified device which will allow more detailed experimental and numerical investigation. In this work such a simplified device was built and used to reveal some of the features of the flow patterns and the influence of one design parameter (cavity shallowness) on the dispersive mixing efficiency.
Simulation of Continuous Polymerization in a Modular Intermeshing Co-rotating Twin Screw Extruder
Authors: Kye H. , White J. L.
Published: December 2013

A method of modeling chemical reactions in a modular inter-meshing co-rotating twin screw extruder is described. This is applied to simulate the anionic polymerization of caprolactam. Calculations are made for specific modular screw configurations. The screw configurations included both screw elements and kneading disc blocks. Reaction conversion and temperature rise were calculated along the screw axis. The results are compared to experiment.
Reactive Blending in a Twin Screw Extruder
Authors: De Loor A. , Cassagnau P. , Michel A. , Delamare L. , Vergnes B.
Published: December 2013

We studied the morphology of a reactive blend, constituted by an EVA/EMA phase dispersed in a polypropylene matrix. The dispersed phase was crosslinked in-situ during the extrusion through a transesterification reaction, catalysed by dibutyltin oxide. Rheological studies allowed to define the changes in rheological behaviour during the crosslinking reaction. Using a flow model developed for twin screw extruders, we computed the reaction extent along the screws and the corresponding blend morphology using a very simple approach. Theoretical results underestimate the extent of the reaction, but explain qualitatively the general tendencies when varying operating parameters.
Structure and Properties of Inflation Films of β-Phase Nucleating Agent-Added Polypropylene
Authors: Fujiyama M.
Published: December 2013

To a homo-isotactic polypropylene (PP) was added 0 to 10 ppm of quinacridonequinone which was a β-phase nucleating agent for PP. The structure and properties have been studied on the inflation films processed from the PPs by the water-cooling or air-cooling methods. The effect of cooling conditions on crystallization has been also studied for reference. Even PPs containing β-phase nucleating agent do not form the β-phase but the smectic or α-phase at low cooling temperature. However, compared with PP without β-phase nucleating agent, they form the α-phase at lower cooling temperature and form the β-phase at high cooling temperature. Even PPs containing β-phase nucleating agent form only the smectic phase in the water-cooled inflation films but form the β-phase in the air-cooled inflation films if β-phase nucleating agent contents are high. Although the film properties are generally not so much affected by the addition of the β-phase nucleating agent, the dart impact strength increases for the air-cooled films which contain the β-phase.
Analytical Study on Flow and Distributive Mixing of a New Type Pin Mixing Section for Screw Extruder
Authors: Yao W. G. , Takahashi K. , Abe Y.
Published: December 2013

A new type of pin to be installed in mixing section of screw extruder is proposed based on the results of numerical calculation of flow field and local mixing efficiency. Two problems presented in general pin mixing section, i.e., the lack of randomization in mixing mechanism and the formation of dead spots, can be solved through diagonally-channeling pins from top to bottom. From the results of numerical analysis of local mixing efficiency it is known that in the cross-section of standard screw (in this study called “cavity”) there are only small regions with high mixing efficiency which is mainly near the two upper corners of the cavity. If two pins are put into the cavity, large high mixing efficiency regions occur in the scope from cavity top to about 1/3 flight height. But, in the case of inserting two holed pins into the cavity, high mixing efficiency regions are distributed in nearly all over the cavity. It is impossible to get such useful information by experiments. Even though the calculation was confined in cross-section of pin mixing section, it has directive significance in designing the practical pin mixing section in the light of theory of distributive mixing.
Development of a Computer Simulation of SCORIM
Authors: Pittman J. F. T. , Aguirre P. , Ding D.
Published: December 2013

SCORIM (shear controlled orientation in injection moulding) is a new technology using pairs of reciprocating pistons connected to the runner system to impose shear in the mould during the holding and packing stages; this provides important control over part properties. A computer simulation is set up, and solved numerically to assist with development and exploitation of this novel process. The one-dimensional transient model considers the cooling and solidification of polymer melt, contained between infinite plane parallel plates, whilst subjected to reciprocating shear flow. A non-Newtonian, temperature-dependent viscosity is used, together with temperature-dependent thermal properties and latent heat of solidification. Two operating modes are considered: (1) flow driven by a fixed pressure gradient; (2) an initially fixed flowrate, which falls after a limiting pressure gradient is reached. Results are shown, based on data for a moulding grade polypropylene; these include details of temperature and velocity fields, pressure and flowrate profiles, and frozen-in material strains, which are related to material alignment. In mode (1) operation, flowrate falls rapidly as solidification proceeds. This is not hindered significantly by viscous heating. Frozen-in strain has its maximum value close to the wall, and falls in a series of oscillations to zero on the central plane. In mode (2), if the limiting pressure gradient is too high, viscous heating can prevent cooling, leading to a dynamic thermal equilibrium. In other cases, where cooling is completed, frozen-in strain can show a complex, oscillatory profile, corresponding to a layered structure in the moulding with alternating regions of higher and lower alignment.
Microstructure Evolution During Moulding of Particulate-Reinforced Thermoplastic Composites
Authors: Papathanasiou T. D.
Published: December 2013

Analysis of injection moulded parts made of polystyrene reinforced with spherical glass particles of various sizes reveals the existence of a number of interesting microstructural features. These include the segregation of particles towards the centre-plane of the cavity, their accumulation close to the free surface and the subsequent occurrence of short-shots, the formation of particle-rich layers adjacent to the perimeter of the moulding and the formation of monolayers of particles attached to the cavity surfaces. Some of these features are consistent with and can he explained by the flow patterns associated with the mould-filling process, namely a Hele-Shaw flow on the plane of the cavity and a fountain flow near the advancing free surface. A mechanism is proposed, according to which the segregation of particles at the cavity mid-plane and their accumulation towards the free surface is the result of the combined action of convection, fountain flow and lateral particle migration. The configuration of the gate is shown to have a marked effect on the observed microstructures in edge-gated mouldings, depending on the ratio of the gate size over the particle size, as is clearly illustrated through X-ray radiography in polydisperse systems. As a result of particle accumulation at the free surface, the formation of particle-rich weld lines in mouldings with inserts is also observed through X-ray radiography. The observed microstructures are shown to be strongly influenced by the size of the particles.