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Conference Proceedings

2D Composite Models of Modular Intermeshing Co-Rotating Twin Screw Extruders
Kuen Chang Lin, May 2004

A new 2D composite model with the hybrid FEM/FDM was developed for simulating the fully filled and starved regions with the associated pressure profiles of a modular intermeshing co-rotating twin screw extruder. 1D composite models combine the screw characteristic curve of individual element to analysis flow of an entire modular screw and the flow fields of the whole region are not calculated again. Based on the linear relationship of the drag flow rate and the screw rotating speed under the single screw extrusion theory, the new mesh with artificial screw rotation speed boundary conditions was used to simulate the entire flow analysis for the co-rotating twin screw extrusion process in our 2D composite models.To demonstrate applicability, the results provided by our 2D composite models were found to similar to those of 1D composite models, through Fenner’s single screw example. The pressure and filling factor profiles in a modular TEX44 extruder provided by 2D composite models show good agreements with Fukuoka's calculated results and experiment data.

Study on the Characteristic of Axial Circular Flow Field in Co-Rotating Intermeshing Twin-Screw Extrusion
Xiuqing Ma, Xiaozheng Geng, Linjie Zhu, May 2004

In order to improve the mixing ability and elongate the mean residence time in twin-screw extruders, the axial circular flow was introduced in this study. A non-intermeshing section was set in the co-rotating twin-screw extruder, in which one screw was equipped with reverse conveying elements and the other with forward conveying elements. In the current work, a three-dimensional simulation of the flow in the axial circular flow section was developed by FEM package, ANSYS. Based on the calculated pressure and velocity profile, the pressure-throughput behavior and mixing ability of the axial circular flow section were discussed. Compared with the conventional conveying elements, the circular flow section has reduced ability to conveying but its distributive mixing capability was largely increased. Visualization experiments showed that the simulation results were in good agreement with the experimental outcomes.

3-D Modeling of Polymerization in Conveying Screw Element in Twin-Screw Extruder
Linjie Zhu, K.A. Narh, Kun S. Hyun, May 2004

The polymerization of ?-caprolactone in fully intermeshing conveying screw elements of co-rotating twin screw extruders was simulated with Fluent. The effects of the pitch on the element, temperature, flow rate, and screw rotating speed upon the reaction progression were investigated. It was found that the back-flow in the screw element affects the progress of polymerization. The simulation result from 3-D model differs significantly from 1-D model, especially in relation to slow reactions. This is because reaction is very sensitive to temperature change, and the value of heat transfer coefficient at the barrel and screw surface used in 1-D model may not represent the real conditions in extruders.

Investigation on Extrusion Property of PSE?Polygon Screw Element in Co-Rotating Twin Screw Extruder
Xiuqing Ma, Yanling Yin, Xiaozheng Geng, Linjie Zhu, May 2004

PSE (Polygon Screw Element) is a new screw element, designed to meet the development of co-rotating twin-screw extruders toward high rotating speed and excellent mixing capability. In the present study, a three-dimensional flow field simulation of PSE element was carried out by the ANSYS FEM package. Pressure profile and shear stress profile were obtained. The mixing ability of PSE element was also analyzed. The simulation results of the flow field in PSE element were verified by experiments. It was found that the energy consumed in PSE element is smaller, whereas its mixing ability is better than the kneading block. Furthermore, PSE element is suitable for the fiberglass reinforced processing.

Modeling of Polymer Drop Deformation and Breakup during Melting under Shear Flow Using Volume-Of-Fluid Method
Hongbing Chen, Uttandaraman Sundararaj, Krishnaswamy Nandakumar, May 2004

Polyethylene (PE) or polycarbonate (PC) drop breakup process in PE melt under shear flow was investigated using volume-of-fluid method. Real properties of polymers, and temperature and shear rate dependent viscosity model were incorporated in the modeling. An erosion mechanism was found for both PE and PC drops. Local flow information, such as shear rate, viscosity and shear stress, was obtained from the simulation results. Highest shear stress was observed at the interface, which could explain the erosion breakup mechanism.

A New Machine Conception for the Extrusion of Biodegradable Foams and the Influence of Process Parameters on Product Propert
H. Potente, W. Ernst, May 2004

Foamed products based on renewable raw material have a high application potential e.g. for packaging because of their biodegradeability. This may permit renewable raw materials to substitute polymers like polystyrene in some applications.A common way to process renewable raw material like starch is to produce starch based resins with twin screw extruders. These resins can be used on conventional polymer processing machines, but the step of compounding the starch on twin screw extruders causes costs which make these resins economically unattractive.Due to a new extrusion technology these costs can be reduced by a direct processing of starchy material like maize. A characteristic of this extruder is a very short (2 L/D), conic, multiple flighted screw in a barrel with spiral grooves. The energy for the plasticizing process is yielded just by the transfer of mechanical energy of the rotating screw into friction in a shear gap between screw and barrel.In order to understand the process different geometries of screw and barrel have been used in the experiments, additionally the process parameters have been varied. The results lead to an optimised configuration of the extruder and to a better understanding of the influence of process parameters on the product properties.

Effect of the Full-Slip Condition along Rotors on the Mixing Efficiency of Internal Mixers
B. Alsteens, Th. Avalosse, V. Legat, Th. Marchal, E. Slachmuylders, May 2004

The importance of slip for applications such as extrusion, cable coating, thermoforming, etc. has been widely discussed in the literature. Recent experimental works suggested that slipping along the rotors also impacts the quality of the mixing in batch mixers typically used for Carbon Black dispersion. In batch applications, the slip reduces the mixing efficiency, hence requiring a longer process to get a given mixing quality.Recent developments in CFD allow to include the slip in the numerical models. The advantage of numerical simulation is the ability to turn on or off this phenomenon. Also, the effect of particles behavior along the rotors on both the flow pattern and the mixing efficiency of internal mixer is studied. Two 3D transient simulations are performed with the POLYFLOW package: one simulation assumes sticking boundary conditions along the rotors whereas the other involves a full slip condition.The results obtained in both simulations are compared and validated against experimental results: the slip condition modifies dramatically both the velocity and the shear rate fields. Therefore, the distributive and dispersive mixings generated by the two models are significantly different. Eventually, we observe a better match between numerical and experimental results when the slip condition is taken into account.

Polymer-Clay Nanocomposites: Tailoring Structures with Processing Conditions
C.Y. Lew, W.R. Murphy, G.M. McNally, S. Yanai, K. Abe, May 2004

Nanocomposites based on nylon-12 and synthetic fluoromica were compounded using a single-screw extruder at different combination of shear and residence time and analysed with respect to their morphology, rheological, mechanical, and thermal properties. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) revealed unique structural arrays of the exfoliated layers which were found to be dependent on the extent of shear and residence time during processing. Rheological analysis showed that the melt viscosity of the nanocomposites was considerably lower compared to the unfilled polymer. Furthermore the melt viscosity and properties of each nanocomposite varied depending on orientation of the exfoliated layers. The results show that it may be possible to tailor the structures and properties of the nanocomposites using controlled extrusion conditions.

Extrusion Characteristics of HDPE-Wood Composites
Karen Xiao, Costas Tzoganakis, May 2004

Extrusion characteristics, such as output, pressure profiles and melting profiles, were investigated in a Brampton Engineering single screw extruder with two screw geometries. It was found that for the wood-HDPE1 composite, the channels were not fully filled until the melting process was completed in both screw geometries. The actual experimental results were compared to those simulated using a commercially available software program. It was found that the current extrusion theories do not predict the pressure profiles generated even for the virgin HDPE1 material for one of the screw geometries.

Some New Observations Relative to Melting in Single Screw Extruders
Gregory A. Campbell, Zirong Tang, Chicheng Wang, Matthew Bullwinkel, May 2004

The focus of this investigation was to evaluate literature and run experiments to help understand the mechanism of melting in single screw extruders. Literature data was re-analyzed using video capture and analysis programs to determine the rate of loss of material in the cross channel and solid bed thickness directions. The analysis demonstrates that the polymer solid bed goes to zero dimension in the thickness direction well before the solid bed width is consumed. This observation was confirmed in our laboratory using a specially built glass barrel extruder. These results suggest that the melting in single screw extruders is dominated by the loss of bed thickness and not bed width as predicted by current literature.

The Influence of Morphology on the Failure of Polyethylene Pipes in Hydrostatic Pressure Tests
Rajendra K. Krishnaswamy, Mark J. Lamborn, May 2004

Failure times of plastic and metal pipes subjected to hydrostatic pressure at various levels assist pipe manufacturers to not only design pipes for certain applications, but also to give them an indication of the useful service life-times of these pipes. In order to understand the influence exerted by semicrystalline morphology on the failure of polyethylene pipes under hydrostatic pressure, a medium-density polyethylene resin was converted into various pipes by altering the extrusion processing conditions. These pipes were subsequently subjected to hydrostatic pressure at a constant hoop stress and the failure times were recorded. The failure times were observed to depend strongly on the morphology of the pipes.

Computer Aided Troubleshooting of Extrusion Problems
Chris Rauwendaal, May 2004

When a problem occurs in an extrusion operation it is important to diagnose the problem, determine possible solutions, and implement the best solution in the shortest possible time. In-house personnel are often not well trained in efficient troubleshooting techniques and problem solving. Outside technical assistance may not be immediately available and may not lead to an expedient solution of the problem. As a result, it is important for extrusion companies to have tools available in-house that can help in the troubleshooting and problem solving process.A new tool available to the plastics industry is an expert system that allows computer aided troubleshooting of extrusion problems. This program allows the user to systematically analyze a large number of extrusion problems. In the end the program presents the user with a number of possible solutions to the problem. This paper will describe the capabilities of the program.

Production of Compounds with High Filler or Fiber Loading on Screw Kneaders
Klaus Kapfer, Wolfgang Schneider, May 2004

The production of filled and reinforced compounds has a high economic importance mainly because fillers and reinforcing fibers render the final product to serve very specific applications. In order to understand such operations more the term “highly filled” will be explained and critical aspects analyzed. In essence two different type of compounding machines are utilized for such compounding tasks, the co-rotating twin-screw and the reciprocating single screw (kneader). Fundamental differences of these systems are analyzed and compared. Examples of compounding processes are described.

Study of the Micropelletization Process
Claude Y.F. Xi, Elizabeth Takacs, Mark Tate, Michael R. Thompson, John Vlachopoulos, May 2004

A study has been performed to examine the rheological impact of micropelletization on several polyethylene grades with melt index values between 1-5 g/10 min. The experiments were done on a 50 mm 30:1 L/D extruder with an underwater micropelletizer attached. A 2-D finite element simulation was used to assist in the analysis by comparing the observed results to the predicted shear stresses in the die. The average micropellet size collected was 0.525 mm diameter. Minor sharkskin was observed on the surface of micropellets due to the high stresses experienced in the pelletizer die. However, the rheological properties of the micropellets did not change in comparison to the virgin resins.

Processing Nanocomposites on a Kneader Reciprocating Single Screw Compounding System
Paul G. Andersen, May 2004

Interest in nanocomposites is based on the premise that with a relatively small loading of properly dispersed treated clay, polymers can exhibit substantial improvement in properties. These include thermal properties such as HDT, mechanical properties such as flexural strength and modulus (without significant loss of impact), barrier properties, flame resistance, and abrasion resistance. While the concept behind nanocomposites is sound, implementation has been flawed. Dispersion of 8 micron clay particles into a million or so high aspect ratio platelets is a difficult task. Both chemical modification of the clay for improved compatibility, and development of specific compounding technology have shown promise but not been fully successful. In previous work (1) unit operations that have significant impact on clay dispersion in the co-rotation twin-screw extruder were identified. This presentation will review the design flexibility associated with the reciprocating single screw, or kneader, compounding system and discuss key unit operations necessary to obtain well dispersed clay. It will also compare results from the reciprocating single screw system with those obtained from previous work on a twin-screw extruder.

Wave Interfacial Instabilities at Coextrusion in Flat Dies: Simulation and Experimental Research
M. Zatloukal, M.T. Martyn, P.D. Coates, P. Sáha, May 2004

The work presents both, simulation and experimental findings of the research of two LDPE melts using a flat coextrusion flow visualization cell. The simulation is performed by FEM analysis with full u-v-p-? numerical scheme employing viscoelastic constitutive equations. The predicted stresses, velocities and interface location have been found to be in a good agreement with the measurements. The experimental analysis shows that pronounced wave instabilities are caused by the minor layer break at the merge point of the layers, and extensional viscosity is a driving parameter here. Finally, recently proposed ‘TNSD sign criterion‘ has been successfully tested for the prediction of the onset of wave interfacial instabilities in this type of the die geometry.

Experimental Observations and Analysis of LDPE Melt Flow in Coextrusion Geometries
M.T. Martyn, T. Gough, R. Spares, P.D. Coates, M. Zatloukal, May 2004

The study of two low density polyethylene melt flows in slit coextrusion flow cells with 30° and 90° confluent geometries is presented. The stream flows and polymerpolymer interface in the confluent region and die land are observed through side windows of the cell. Birefringence and image processing techniques are used to quantify stress and velocity fields in the upstream and down stream melt flows. Interfacial instabilities were observed in the LDPE melt flows in both geometries. Instabilities occurred at certain stream mass flow ratios. Digital image processing shows the wave type extrudate instabilities have the same periodicity as perturbation in the flow field in the die land. A recently proposed “TNSD sign criterion” reasonably predicted the onset of the interfacial instabilities in these die geometries.

A Non-Isothermal 3D FEM Study of Spiral Mandrel Dies with Non-Symmetrical Input
Petra Škabrahová, Ji?í Švábík, John Perdikoulias, May 2004

The design of an optimal spiral mandrel die suited to given requirements is quite a complicated task for the die designer. Even for a properly designed spiral section, there is always a question how variations in the flow prior to the spiral channels can influence the melt distribution at the exit of the spiral distribution section. This study uses 3D FEM analysis to investigate an effect of having uneven inputs. Specifically, the influence of uneven mass and temperature input distributions are studied. The influence of the die distributive system is investigated by analyzing the temperature and velocity fields at the exit.

Sensitivity of Flow Distribution and Flow Patterns in Profile Extrusion Dies
J.M. Nóbrega, O.S. Carneiro, P.J. Oliveira, F.T. Pinho, May 2004

Fluctuations of the operating conditions or slight variations of the polymer rheology may occur during longterm productions, affecting the performance of the die in an extent dependent on its flow distribution sensitivity. In this work, four extrusion dies are optimised (balanced) using different design methodologies. These are compared in terms of their performance and stability to some operating conditions and polymer rheological properties. A finite-volume based computational code is used to perform the required simulations of the non-isothermal three-dimensional flows, under conditions defined by a statistical Taguchi technique. Correlation between the flow patterns developed and flow distribution sensitivity is also investigated.

Simulation of Polymeric Flow in a Twin Screw Extruder: An Analysis of Elongational Viscosity Effects
A. Shah, M. Gupta, May 2004

Flow of a polymer in an intermeshing co-rotating twin-screw extruder is simulated. Effect of elongational viscosity on the flow is analyzed using independent power-law models for the shear and elongational viscosities. Axial component of the velocity is found to be maximum in the intermeshing region of the extruder. Axial component of velocity, which determines the throughput of the extruder, decreased as the elongational viscosity of the polymer used for the flow simulation was increased. The pressure in the extruder decreased from a very high positive value on the leading edge to a very large negative value on the trailing edge of the screw. For the same rotational speed the pressure build-up in the twin-screw extruder increased as the elongational viscosity of the polymer was increased.










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