NUMERICAL DIMENSIONING MODEL FOR INJECTION HEADS AND TOOLS USED FOR RUBBER EXTRUSION Herbert W. M¨ullner*, Andr´e Wieczorek**, Wolfgang Fidi**, Josef Eberhardsteiner* *) Institute for Mechanics of Materials and Structures Vienna University of Technology (TU Wien), Austria E-mail: [email protected] **) Semperit Technische Produkte Ges.m.b.H. Wimpassing im Schwarzatale, Austria

KEYWORDS: viscoelasticity, die swell, rubber blends, numerical prediction The dimensioning of injection heads for the extrusion of rubber profiles is exclusively based on empiric knowledge of the non-linear viscoelastic flow behavior of elastomers especially of the so-called die swell. Thus, the design of injection heads is carried out with subject to the used rubber blend, whereas the geometry of the appropriate profile is achieved by empiric adaptation of the extrusion die. This adaptation process is mainly influenced by the swelling after the extrusion of rubber and is carried out in up to three steps. The disadvantages of the current production process are the process technology which is non-reproducible over a long time frame and the design of dies which is connected with long development time. This affects the capacity of the running production relevantly. This fact was one of the motivations for a research project concerning the characterization of the die swell properties of rubber blends. The research work is performed in cooperation with Semperit Technische Produkte Ges.m.b.H. Based on an experimental investigation of different rubber blends by means of a capillary-viscometer, the extrusion pressure and the die swell of the blends was determined for all considered tests. For the description of the shear rate dependent viscosity the power law [1] is used. For the characterization of rheological properties a genetic algorithm also described in [1] can be used alternatively. It is well-known that the respective parameters depend on the geometry of the used capillary. Thus, the parameters change after the exit of the capillary, too. By adaptation the fitness equation of the used genetic algorithm it is possible to study the influence of the die swell on the viscous properties. With this knowledge a more realistic simulation of the die swell phenomenon and its influence on the resulting profile geometry is possible [2]. This strategy was validated by means of numerical simulations of the capillary-viscometer [4]. In this contribution numerical simulations of realistic extrusion tools will be presented. Generally, the geometry of the desired rubber profile cannot be used for the dimensioning of the tool. Thus, the shape of the corresponding tool under consideration of the material behavior needs to be predicted. Therefore, simulations were performed with the finite element based CFD (computational fluid dynamics) program POLYFLOW Version 3.92 under usage of the inverse extrusion option and the material model proposed in [2]. These simulations will be validated by means of experiments with existing tools, which were already manufactured empirically [3].

REFERENCES [1] H.W. M¨ullner, J. Eberhardsteiner, A. Wieczorek. Constitutive Characterisation of Rubber Blends by means of Genetic Algorithms. Constitutive Models for Rubber IV, 361-368, 2005. [2] H.W. M¨ullner, J. Eberhardsteiner, K. Hofstetter. Viscosity Characterisation for Rubber Blends from Die Swell Data by Means of a Genetic Algorithm, PAMM – Proceedings in Applied Mathematics and Mechanics, 6:575-576, 2006. [3] H.W. M¨ullner, A. Wieczorek, J. Eberhardsteiner. Numerical Prediction of the Dimensioning of Tools for the Extrusion Process of Rubber Profiles, Proceedings of the 10th ESAFORM Conference on Material Forming, 2007, accepted. [4] P.I. Petracek. Experimentelle Validierung eines viskoelastischen Materialmodells f u¨ r die numerische Simulation der Extrusion von Kautschukmischungen, Master’s Thesis, Institute for Mechanics of Materials and Structures, Vienna University of Technology, 2007.