1:30 pm – 5:30 pm:
W15-Extrusion: Modeling
(Moderator: Sid Carson)-Room S320F

1:30 pm – 2:00 pm:
Unified Simulation of Extrudate Distortion Due to Non-uniform Exit Velocity and Cooling Shrinkage

Mahesh Gupta, Plastic Flow
Post-die analysis in the polyXtrue software is enhanced to include the effect of cooling shrinkage on extrudate distortion. Extrudate distortion for two different profile dies is predicted. The effect of non-uniform exit velocity as well as that of cooling shrinkage on extrudate distortion is included in the analysis. The extrudate distortion predicted including the shrinkage analysis is compared with the distortion predictions based only upon non-uniform exit velocity. Extrudate distortion due to non-uniform exit velocity is further increased when cooling shrinkage is included in the analysis.

2:00 pm – 2:30 pm:
Modeling of a Simple Numerical Calculation Methodology to Implement Cross Flows in Extrusin Die Design Based on Network Theory

Bianka Jacobkersting, University of Paderborn
Extrusion dies exert influence on later final product quality. Therefore it´ll make a point the dimensional and die design by using programs for calculation and simulation frequently. For the implementation of product design, it is significant to understand the flow conditions and to be able to predict the flow behavior accurately. Special rheological flow phenomena in the plastic melt as cross flows, which flow perpendicular to the main flow, should be taken into account. This phenomenon is caused by pressure gradients transverse to the direction of extrusion and both the flow distribution and the pressure consumption are influenced in the die. Network theory is a simple numerical method for a holistic one-dimensional representation (GEB) in a spreadsheet program (p.e. Excel), which can design an optimal uniform flow rate distribution and low pressure drop. The cross flow behavior can´t be described with this method as yet. Therefor a linear equation system according to the Gauss algorhythm was developed, which can calculate the cross flows in the die with rectangle cross-section. In this network crosslinks are implemented to take into account the cross flows. The equation system is set up from the network, which corresponds to the number of the desired partial volume flows in the number of established equations. Furthermore the technical measurement entry of cross flows was conduced about the evaluation of ellipsoid shape according to the flow direction and the alignment according to the flow direction. Dead-stop experiments were performed by adding a blowing agent to the extrusion process. Negatives of die with gas-filled bubbles were prepared and evaluated with image analysis software across the half width of die. Afterwards the network theory was validated by Computational Fluid Dynamics (CFD).

2:30 pm – 3:00 pm:
Modelling the Contamination Behavior of Polymer Melt Filters and Pressure Loss Simulations of Filtration Media

Volker Schöppner, Paderborn University
In the field of polymer processing, the extrusion is one of the most common processing methods. Not only in the processing of recycled materials, also when using virgin polymers there can be contaminations during the storage or processing of the material. This may adversely affect the melt quality and by this also the quality of the final extrusion product. Examples for possible contaminations are metal particles which are caused by wear and tear of the extruder, or degradation products of the processed material itself. As a result of increasing demands on the quality of extrusion products, especially in the field of fiber and film extrusion, filtration of polymer melts is widely used and state of the art today. To remove unwanted debris out of the melt, different metal filter media is used. Some examples for typical filter media are different kinds of wire mesh, filters out of nonwoven metal fibers or sintered metal powder discs. Using this filter media, it is possible to remove foreign particles like solid particles, as well as soft components, the so called “gels” from the melt. This ensures a high quality extrusion result. In order to compare the filtering effect of different filter media and to assess the contamination and selective filtration it is necessary to develop a possibility for reproducibly rapid contamination of filter materials. In this work this should be elaborated as part of the PET processing. For this, a real filter contamination is analyzed. After this a definition of an adequate substitute dirt is effected. The focus is both on solid particles, as well as on gel contamination. With this it is possible to generate realistic and reproducible filter soiling so that pressure rise curves can be generated in order to compare the behavior of different filter media in the extrusion process.

3:00 pm – 3:30 pm:
Experimental Study on the Melt Encapsulation: An Analysis of Die Pressure and Rearrangement Effects

Christian Hopmann, Institute of Plastics Processing (IKV) in Industry and the Skilled Crafts at RWTH Aachen University
A central challenge in the extrusion process is the interaction of the melt with the metallic die wall. These interactions, such as friction and adhesion, lead to a limitation of mass throughput due to high pressure drop and long material and color changeover times. Since raw material costs are price-determining with a percentage of up to 80 %, it is imperative to reduce these interactions. Extrusion dies in particular offer a very large contact area for these interactions, as the melt is formed out there with usually a large surface area. A possible solution to reduce these interactions is the encapsulation of the melt with a low viscous thermoplastic melt before entering the extrusion die. Hereby, the parabolic flow profile with wall adhesion is converted into a block-like flow profile. The pressure drop and material and color changeover times can be reduced, in this way. In this paper, the influence of the melt encapsulation with two low viscous LDPE resins on the flat film extrusion process with focus on the reduction of pressure drop and rearrangement effects is investigated. Therefor the low viscous encapsulation material, the processing temperature and the layer thickness of the low viscous encapsulation material are varied. For example, the pressure drop of the reference process at 200 °C can be significantly reduced from 47 bar to 12 bar for LDPE65 at a melt pump speed of 0.2 rpm. However, due to rheological effects a rearrangement of the low viscous material appears. This means the low viscous material accumulates in the edge area of the rectangular flow channel. As a result, the usable film width is reduced.

3:30 pm – 4:00 pm:
The Effect of Channel Curvature on the Flow Rate and Viscous Dissipation of Power-law Fluids

Wolfgang Roland, Institut of Polymer Extrusion and Compounding
When modeling the melt-conveying zone of single-screw extruders, generally the flat-plate model is applied. Using a cylindrical reference frame, we investigated the effect of channel curvature on flow rate and viscous dissipation, considering a two-dimensional, fully developed, isothermal flow of a power-law fluid. Re-writing the flow equations and applying the theory of similarity revealed the existence of four independent influencing parameters: Π_(p,z), n, t/D_b , and h/D_b . Based on these, we carried out a comprehensive parametric study investigating flow rate and viscous dissipation. Our results show that the channel-height-to-diameter ratio has a significant influence on both flow rate and viscous dissipation.

4:00 pm – 4:30 pm:
A Heuristic Model for Predicting Three-dimensional Non-newtonian Flows in Metering Channels

Christian Marschik, Institute of Polymer Extrusion and Compounding
Being able to include the shear-thinning behavior of polymer melts in the theoretical analysis of melt-conveying and pressurization generally involves the application of numerical techniques. We have recently proposed a fast and accurate analytical approximation method for predicting the pumping characteristics of power-law fluids in three-dimensional metering channels. Removing the need for time-consuming simulations, this novel theory provides an algebraic throughput-pressure gradient relationship that can be implemented easily in real screw designs. By considering the three-dimensional geometry of the screw channel and the non-Newtonian flow behavior of the polymer melt, our model is a close representation of the actual physical process. Here, we revisit the design of the heuristic model, present further results, and validate the method against additional numerical solutions.

4:30 pm – 5:00 pm:
Modeling the Operating Performance of Melt Filtration in Polymer Recycling

Sophie Pachner, Institute of Polymer Extrusion and Compounding
This paper addresses the generation of a general valid analytic equation for estimating the initial pressure drop of woven screens in terms of polymer recycling. Therefore we performed numerical CFD Simulations as basis for heuristic modeling. Based on evolutionary heuristic algorithms, we applied symbolic regression in order to determine the pecScreen model. We performed experiments at different melt filtration systems for validation of the model using virgin as well as in-house, post-industrial and post-consumer recycling materials. It turned out that the results of the general valid analytic equation are in good agreement with the experimental determined data, yielding a coefficient of determination (R²) of 0.92.

5:00 pm – 5:30 pm:
Optimizing Fluted Mixers

John Perdikoulias, Compuplast International Inc.
The Fluted (aka Maddock) or Spiral Fluted (aka Egan) mixers are commonly used on single screw extruder screws to help disperse particles and homogenize polymer melts. However, these devices are generally added with some “standard” dimensions or designs and are often not optimized for the particular polymer or process conditions being used. A poorly designed mixer can adversely affect the performance of the extruder and create more problems that it is supposed to solve. There are also some design variations that make manufacturing easier but also adversely affect the performance. This presentation will propose some optimization criteria that should be applied to the design of a fluted mixer that can help avoid some problems, which will also be presented.