Simulation extruder

The following steps are concerned with the design of the compounding step. They are supported by the flow diagram editor and the simulation tool MOREX. The extruder simulation expert models the compounding process as a part of the overall chemical process with the help of the flow diagram editor. The respective part of the flow diagram is used to derive a model for ID simulation in MOREX. 

The tertiary goals of extruder simulation as introduced in Subsect. 4.1.4, and some other categorizations, are modeled as categorization schemes in the descriptive area. Each of the schemes is composed of a set of categories (which are not shown in Fig. 4.7). This allows to integrate the TRAMP functionality of annotating weakly structured (multimedia) documents. 

The groundwork for all this was laid by F. Laenger at HANDLE GmbH and made public in a number of articles dealing with an extruder-simulation model [17]. 

In principle there are two possibilities to get the informations over the material parameters. First we have a theoretic model modified from the model over high filled polymere melts. This model allows to meassure and evaluate the rheological parameters. On the other hand we have a rheological computer model called ESM (extruder simulation model), developed by the author, which brings us in the position to simulate the material parameters. 

The extruder simulation model (ESM) was developed by Handle GmbH. The theoretical fundamental principles and examples for application of the ESM are described in detail in various articles published by Laenger [17]. This model is based on measurements obtained from a special laboratory version measuring extruder of 80 mm barrel diameter. 

Table 2 Variables and target values of the Extruder-Simulation-model [17 part 4a]...

In this chapter an important recommendation will be noted From the aforementioned steps, indispensable for a FEM-extruder-simulation, the correct initiation of material parameters is required. Inaccurateness of measurement of the material parameters jUo, Tf, Ts and k together with impreciseness of the numerical solution is the major element of uncertainty of such extruder simulations. 

When using commercial simulation packages it is important that the theory behind it is clearly described with assumptions and simplifications. If this is not the case and the user does not really know what type of analysis they are actually using, the value of the results will be questionable. Early extruder simulation packages had... 

Figure 4.7 Typical results from a commercial software (EXTRUCAD) for extruder simulation showing the development of solids bed, pressure, and temperature as a function ofthe number of turns of the screw [17].

Extruder, simulation, solids conveying, distinct element method... 

Computer-aided flow-simulation programs are also available for dies. All the programs can successfully predict a certain amount of shrinkage under specific conditions that can be applied to experience. The actual shrinkage is finally determined after molding or extruding the products. When not in spec process control changes can meet the requirements unless some drastic error had been included in the analysis. 

Topaz was used to calculate the time response of the model to step changes in the heater output values. One of the advantages of mathematical simulation over experimentation is the ease of starting the experiment from an initial steady state. The parameter estimation routines to follow require a value for the initial state of the system, and it is often difficult to hold the extruder conditions constant long enough to approach steady state and be assured that the temperature gradients within the barrel are known. The values from the Topaz simulation, were used as data for fitting a reduced order model of the dynamic system. 

In an extension of this work, pellets of a blend of PCL and hy-droxypropylcellulose containing fluridone were prepared by grinding, blending, and then melt-spinning the mixture with a Berstorff twin screw extruder (78). The extruded rod was subsequently water-quenched and pelletized. Pellets were also prepared by coating bundles of extruded rods with the water-soluble excipients PEG 3350 and PEG 600 (95 5). In vitro release rate measurements were conducted in the simulant medium of 50% aqueous ethanol or hardened water. 

Fairbanks has also studied the effect of ultrasonic energy on the flow characteristics of a poly(methyl methacrylate) melt in a simulated injection moulder. Initially the ultrasound (20 kHz, 0-105 W) was applied either simultaneously or independently to both the extruder tube and the cylinder of the moulder. However, since no discernible effect was observed when ultrasound was applied at the extruder tube, further work with the horn in this position was discontinued. 

A number of issues relative to the prediction of solids conveying in smooth bore single-screw extruders are exposed from the theoretical fits to the data in Fig. 5.32. First, the data needed to carry out an effective simulation is difficult to take and is very time consuming, and only a few labs have the proper equipment that is, bulk density measurement, dynamic friction data, lateral stress, and solids conveying data. Moreover, care must be taken to develop an accurate representation of the surface temperature for the barrel and screw as a function of the axial position. This would be quite difficult in a traditional extruder with only a control thermocouple to measure the temperature at the midpoint of the barrel thickness. Second... 

Moysey, P. A. and Thompson, M. R., Plastic Contact Mechanics and Its Impact on DEM Simulations of Solids Transport in Extruders, SPE ANTEC Tech. Papers, 52, 882 (2006)... 

Moysey, P.A. and Thompson, M.R., Investigation of Solids Transport in a Single-Screw Extruder Using a 3-D Discrete Particle Simulation, Polym. Eng. ScL, 44, 2203 (2004)... 

Klein, 1., The Melting Factor in Extruder Performance, SPEL, 28, 47 (1972) Altinkaynak, A., Three-Dimensional Finite Element Simulation of Polymer Melting and Flow in a Single-Screw Extruder Optimization of Screw Channel Geometry, Ph. D. Thesis, Michigan Technological University, Houghton, MI (2010)... 

Altinkaynak, A., Gupta, M., Spalding, M. A., and Crabtree, S. L., Melting in a Single-Screw Extruder Experiments and 3D Einite Element Simulations, Int. Polym. Process., 26, 182 (2011)... 

With the development of modern computation techniques, more and more numerical simulations occur in the literature to predict the velocity profiles, pressure distribution, and the temperature distribution inside the extruder. Rotem and Shinnar [31] obtained numerical solutions for one-dimensional isothermal power law fluid flows. Griffith [25], Zamodits and Pearson [32], and Fenner [26] derived numerical solutions for two-dimensional fully developed, nonisothermal, and non-Newtonian flow in an infinitely wide rectangular screw channel. Karwe and Jaluria [33] completed a numerical solution for non-Newtonian fluids in a curved channel. The characteristic curves of the screw and residence time distributions were obtained. 

Large diameter, melt-fed extruders are commonly used for the final devolatilization and pelletization of LDPE and PE copolymers in resin manufacturing plants. A full description of this type of extruder and process is provided in Section 15.3. Simulation of these processes is complicated by the multiple flights used in the design and the high H/W aspect ratios of the channels. The processes can be simulated from the feed hopper to discharge, however, since they are not required to convey solids and melt resin. This section will show the requirements and difficulties for simulating these processes. 

A three-dimensional simulation method was used to simulate this extrusion process and others presented in this book. For this method, an FDM technique was used to solve the momentum equations Eqs. 7.43 to 7.45. The channel geometry used for this method was essentially identical to that of the unwound channel. That is, the width of the channel at the screw root was smaller than that at the barrel wall as forced by geometric constraints provided by Fig. 7.1. The Lagrangian reference frame transformation was used for all calculations, and thermal effects were included. The thermal effects were based on screw rotation. This three-dimensional simulation method was previously proven to predict accurately the simulation of pressures, temperatures, and rates for extruders of different diameters, screw designs, and resin types. 

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