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Conference Proceedings

Heat Transfer Coefficients and Screw Temperature Profiles in Modular Twin Screw Extrusion Machines
Jongmin Keum, James L White, May 2004

For modular co-rotating twin screw extrusion machines, we developed models of the heat transfer coefficients as well as the screw temperature profile in a machine with both starved regions and fully filled regions. The dependence of heat transfer coefficients on screw diameter, screw rotation speed and power law index of polymer melt was investigated. The screw temperatures were calculated along the screw axis and radial directions as well as compared temperature development difference between these two directions. Calculations are made with dimension of commercial machines with varying screw diameter.

Comparison of Residence Time Distributions for Different Materials in the Same Extrusion Operation
Paul Elkouss, David Bigio, Srinivasa Raghavan, Mark Wetzel, May 2004

Kinematic modeling has been shown to be important for the understanding and control of co-rotating twin screw extruders. The residence time distribution (RTD) is often used to characterize an extrusion process. Due to the nature of the polymer flow in the extruder, few have felt that the RTD would be independent of material properties for the same extruder setup. To investigate this question, four different polymers, two polyethylenes and two polypropylenes, were processed on the same 30mm Werner and Pfleiderer co-rotating twin-screw extruder (CoTSE) equipped with reflectance optical probes to compare their RTD's. Additionally, each material was tested to determine its complex viscosity, to better understand the phenomena involved.

Investigation of Melting Mechanism in a Twin Screw Extruder using a Pulse Method and On-Line Measurement
Hongbing Chen, Uttandaraman Sundararaj, Krishnaswamy Nandakumar, Mark D. Wetzel, May 2004

A perturbation method was introduced to investigate the melting phenomena of polystyrene (PS) and polypropylene (PP) blend in a twin-screw extruder. A sliding barrel technique was used to realize the on-line visualization of the processes and to obtain the temperature and pressure profiles along the extrusion region. The melting behavior of PS/PP (80:20) blend was studied under various ratios of the flow rate (Q) over the screw rpm (N). It was found that the melting processes of the PS/PP blend in the TSE can be divided into three sections. Most of the melting occurred in a narrow transition from the partially filled region to the fully filled region. No large deformation of solid polymer pellets was found for all the processes studied here. The relative amount of solid concentration in the flow can be obtained through this perturbation method. It was shown that the solid concentration at the beginning of the fully filled region increased as the ratio of Q/N increased.

Investigation in Power Consumption of Twin Screw Extruders in Respect of Scale-up Theory
H. Potente, T. Preuß, May 2004

In the field of polymer recipe development the homogenization of components is one of the most important points. For reasons of economy on the one side, and to receive a convenient machine configuration on the other, practical investigations are carried out on lab scale extruders. Subsequently the optimized process has to be transferred to an industry scale extruder during a scale-up process.On the basis of temperature and power consumption measurements at a tightly intermeshing, co-rotating twin screw extruder an approach for process transferability is discussed. By keeping the screw diameter constant the influence of throughput on the system energy balance is specified for several polymers. A theoretical approach for partly filled, geometrically similar systems is validated by means of experimental data extracted from a Coperion W&P ZSK-30. The results provide a basis to transfer operating points for co-rotating twin screw extruders.

A Perturbation Method to Characterize Melting during the Extrusion of Polymers and Blends
Mark D. Wetzel, Donald A. Denelsbeck, Susan L. Latimer, Chi-Kai Shih, May 2004

By means of a novel flow perturbation technique, fundamental details during the extrusion of semicrystalline and amorphous polymers, such as Polypropylene (PP), Polystyrene (PS), or PP/PS polymer blends can be analyzed with respect to the kinetics of melting and energy input. The effects of extrusion conditions such as throughput and screw speed were examined. A specialized, high-speed data acquisition system, the “Extrusion Pulse Analysis System” (EPAS) has been employed to enable on-line monitoring and data analysis based on an imposed mass disturbance to provide a real-time diagnosis of extrusion melting processes in laboratory and manufacturing applications.Using the power response profile of the mass perturbation, four key sequential stages of melting have been proposed for twin-screw extrusion of a single component or polymer blends. A “lubricated melting” mechanism is also proposed for the extrusion behaviors of PP/rubber and PS/rubber blends using an Ethylene copolymer and SBS block copolymer as the minor phase ingredient.

In Line Measurement of the Polymer Melting Behavior in Single Screw Extruders
María del Pilar Noriega, Tim A. Osswald, Nicola Ferrier, May 2004

Existing experimental techniques designed to study melting behavior of polymers inside the screw extruder suffer from limited functions or tedious procedures. Their invasive nature affect friction characteristics and heat transfer, significantly influencing the outcome of measured parameters. This paper presents an in-line, non-invasive measuring technique that can accurately capture experimental data and images from inside the extruder through a small quartz window and a rigid boroscope at short response times using a highly instrumented 45 mm single screw extruder with built-in sensors. By sensing the difference in optical properties between the melt and the solid phase, the melting behavior of high density polyethylene was visualized and measured with this non-invasive technique.

Solid Bed Melting in Single Screw Extruders - An Alternative First Order Mechanism
Gregory A. Campbell, Zirong Tang, May 2004

This paper discusses our initial attempt to model the results presented at ANTEC 2003 which demonstrated that for most of the literature data on solid bed melting careful reanalysis indicates that the solid bed consumption is dominated by melting in the thickness not the cross channel direction. A first order model for the melting is presented which focuses on the melting dynamics in the bed thickness direction. A similar analysis would be necessary for the cross channel direction but is beyond the scope of this paper due to space constraints. The model combines the concepts developed by Tadmor in his classical work with the ideas developed in this laboratory focused on the importance of using the velocities based on the screw rotating.

Entropic Mixing Characterization in a Single Screw Extruder
Kirill Alemaskin, Marco Camesasca, Ica Manas-Zloczower, Miron Kaufman, EungKyu Kim, Mark A. Spalding, Walter A. Trumbull, Robert D. Swain, May 2004

The quality of distributive mixing is evaluated via an entropic measure of color homogeneity. We first illustrate this technique in a numerically built rectangular channel representing the unwounded channel of a single screw extruder. We also apply this method for assessing mixing quality of experimentally obtained samples when mixing a color concentrate in ABS resin in a single screw extruder. We discuss application of this technique in numerical simulations of processing equipment.

The Influence of Melt Rheology on the Specific Output Rate of Broad Molecular Weight Distribution Polyethylenes in Single Screw Extrusion
Rajendra K. Krishnaswamy, David C. Rohlfing, Ashish M. Sukhadia, Kevin R. Slusarz, May 2004

The extrusion (single-screw) characteristics of four broad molecular weight distribution (MWD), linear polyethylene resins are discussed with an emphasis on the output rate. Despite the high molecular weights of the subject polyethylenes, their broad MWD (Mw/Mn range: 10 to 60) does not limit the pressure and torque developed during extrusion. However, the specific output of the four polymers was quite varied. The dependence of the specific output on the melt rheology of the polymers is addressed; specifically, the shear-thinning extent of the melt in the metering section was found to influence output rate. The unique and counter-intuitive temperature-dependence of the shear-thinning character of one of the four polymers will also be addressed in relation to its extrusion characteristics. Lastly, a simple and quick method to evaluate the relative solids conveying efficiencies for various polyethylenes will be presented.

Performance Characteristics of Elongational Mixing Screws
Chris Rauwendaal, Giuseppe Ponzielli, May 2004

Elongational mixing (EM) screws have recently become commercially available. Elongational flow allows more efficient mixing, particularly dispersive mixing. Elongational mixing reduces viscous dissipation relative to shear mixing. This results in lower motor load and reduced melt temperatures. This paper will present detailed operational data of a 90-mm mixing screw producing cast film and a 130-mm mixing screw with a special barrier section producing filled polyolefin film. Data produced with the elongational mixing screw is compared to a conventional mixing screw.The data indicates that elongational mixing screws allow increases in output and product quality while at the same time reducing motor load and melt temperature. The ability of elongational mixing screws to disperse gels is a particular advantage in film extrusion.

Melting of Polymer Blends in a Shear Field - Experimental Investigation
D. Chenouf, T. Gabor, M. Moneke, May 2004

The melting of polymers is one of the most difficult problems of the modeling of the process behavior in screw machines. Because it is a complex task to analyze and visualize this phenomenon directly in the extruder, experimental studies are often inadequate. Therefore a model apparatus with parameters close to processing conditions, which can generate a shear flow, was developed. With this apparatus, it is possible to analyze optically the structural modifications during the melting of polymer pellets in a surrounding melt. The melting process can be observed directly with a CCD camera attached to a microscope. In order to quantify the influence of the different parameters, investigations have been performed. For the melting, the most important factors are the material properties of the melt and the granule, the temperature field in the pellet as well as the environment and the flow characteristics.

Real-Time Crystallinity Measurements in a Multilayer Blown Film
G. Giriprasath, S. Cherukupalli, A.A. Ogale, May 2004

Online measurement of crystallinity development in a multilayer blown film using Raman spectroscopy is discussed. The Raman spectrum of a multi-layer film consists of superimposed spectra from the individual layers. For polyethylene (PE) and polypropylene (PP), some peaks are distinctly different but some overlap (1295-1350 cm-1). Offline Raman experiments were used to measure the contribution of polypropylene from the total integral intensity calculated in the range 1295-1350 cm-1, so that crystallinity evolution can be calculated for the two components. Preliminary results suggest that Raman spectroscopy is a useful technique to monitor crystalline growth of PE and PP in multi-layer blown films.

Stability Analysis of the Nonisothermal Film Blowing Process
Joo Sung Lee, Dong Myeong Shin, Hyun Wook Jung, Jae Chun Hyun, May 2004

The stability of film blowing process has been investigated using the governing equations taking care of nonisothermal nature of the process. In this study, on top of the linear stability analysis, employing a newly-devised numerical scheme, the hitherto unavailable transient solutions of film blowing dynamics have been obtained for the first time to produce temporal portrayal of draw resonance instability strikingly close to experimentally observed profiles. Many interesting aspects of the film blowing stability have also been revealed including multiple steady states and their diverse stability characteristics.

Effect of Crystallization Kinetics on the Morphology of Linear Low-Density Polyethylene Blown Films
Srinivas S. Cherukupalli, Amod A. Ogale, May 2004

Previous real time studies during the fabrication of a blown film have reported that the imparted molecular orientation is dependent not only on the stresses acting at the freeze line but also on the crystallization process that takes place along the axial distance. In this study, the relationship between the crystallization kinetics, as estimated using real-time Raman spectroscopy measurements, and the film morphology was investigated for linear low-density polyethylene (LLDPE) blown films. Crystallization half-time (t0.5), defined as the time taken for the polymer to reach 50 % of its equilibrium crystallinity, was proposed as a single parameter to relate the processing conditions with the orientation of the films. The results showed an asymptotically decreasing relationship between crystallization half-time and the a-axis orientation factor for a range of processing conditions.

Rheological Evaluation of the Processability of Polyethylenes for Extrusion Coating
Choon K. CHAI, May 2004

The two key processability characteristics of low-density polyethylenes (LDPE) in extrusion coating applications are principally concerned with the degree of neck-in (NI) and the drawdown ability (DD). Molecular structures like long chain branching (LCB) and molecular weight distribution (MWD) have strong influence on these processability parameters, which, in turn, can be correlated with the melt elasticity of the polymer at processing conditions. These molecular structures effects on melt elasticity can suitably be studied by shear and extensional rheologies. A range of extrusion coating LDPE grades have been rheologically characterised and two models relating their extrusion coating processability parameters (NI and DD) and their melt elastic properties have been established. These new rheological parameters and models enable rapid quality controls and evaluation of potential materials, from catalyst development to products scale-up, for extrusion coating applications, with the desirable processability in terms of NI and DD.

Computational Design of U-Profile Die and Calibrator
Louis G. Reifschneider, Milivoje M. Kostic, Srinivasa Rao Vaddiraju, May 2004

The objectives of this work are three-fold: 1) to validate that an open profile product can be made using simulation alone to design a die (design rules of thumb are not applied), 2) assess the role of the calibrator in shaping the free surface of the extrudate, and 3) quantify the heat transfer in a vacuum calibrator and assess how such data can be used to design calibrators for other products. The scope of this paper includes: 1) three-dimensional flow simulation to design a die to make a U-shaped extrusion, 2) experimental trials to validate the mass flow balance through the die and the cooling performance of the calibrator, and 3) comparison of the heat transfer data obtained during calibration trials to published data for profile calibrators.

Performance of Boron Nitride and its Combinations as Processing Aid in the Extrusion of Ziegler-Natta Polyethylenes
Edward B. Muliawan, Savvas G. Hatzikiriakos, May 2004

The performance of Boron Nitride, and its combinations with fluoropolymer as polymer processing aid in the extrusion of Ziegler-Natta polyethylenes is studied by using a capillary rheometer fitted with capillary and crosshead die. Two different techniques of compounding the polymer with the additives are used. In the first technique, both additives (Boron Nitride and fluoropolymer) are compounded together directly into the polymer. In the second technique, the additives are added separately. Improved performance via the second technique is observed.

Optimizing Purging Time at Product Change in Blown Film Extrusion by Selective Modification of Process Parameters
Carsten Groß, Johannes Wortberg, May 2004

During the product change from colored into colorless especially at blown film extrusion, long purging times arise because of the long continuing colour haze. The purging behavior has been investigated in low density polyethylene (LDPE) films under variation of the process parameters mass flow rate and temperature. Our analysis shows that the improved purge process control and variation of the process parameter modifications during the purging process reduce the purging time and substandard goods compared to the conventional arrangements. Also the study examines the influence of different color pigments into the purging behaviour.

Lip Actuator Performance in Automatic Profile Control Systems for Flat Dies Extrusion
Giuseppe Negri, Peter Cloeren, May 2004

Thermal translators, along with the connected hardware and software controls, represent the core of automatic control of flexible lips in flat die extrusion. The thermo-mechanical efficiency of said translators has a direct impact on the process for ensuring proper gauge uniformity in film extrusion, thus affecting the quality and the economy of the manufacturing process. This paper will investigate the potential advantages and disadvantages related to translators based on different materials of construction and their basic thermal and mechanical performance. The work presented is the result of analytical and FEA computer simulations.

Gentle Compounding of Natural Fiber Filled PVC Composites
Shashank G. Kasliwal, Jerry W. Jones, May 2004

Compounding of thermoplastics with wood flour or natural fibers presents a number of challenges. The temperature and shear sensitivity of the thermoplastic matrix such as PVC, presence of moisture in the cellulosics, and the critical process temperature limitations of the composite are some of them. Lower shear history and melt temperature during primary compounding operations of such composites generally result in better mechanical properties of the finished product. This paper investigates the suitability of CK Continuous Kneader to surmount the imposed process limitations effectively.

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