thesis

Modélisation des éléments de mélange en extrusion par la méthode des éléments frontières

Defense date:

Jan. 1, 2004

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Institution:

Paris, ENMP

Disciplines:

Materials science and engineering

Authors:

Directors:

Abstract EN:

In order to obtain new plastic materials, polymers mixing is a very commonly used process. Polymers processing using single-screw extrusion makes it possible by modifying the screw of extrusion. For this reason, the maddock mixing head is used in ordrer to study its effect on quality of the mixing. In this work, the dispersive mixing is especially studied. The experimental part of this project studies the dispersion of secondary phase in polymer matrix. Beside the experimental study, the numerical methods can be used to provide more detailed information on the mixing flows. In this study the boundary element method (bem) is used. Whereas, the polymer flows exibit non-newtonians behaviors and consequently non-linear constitutive equations, the bem simulations have to take this into account. The classical bem enables to solve this type of problems. Specific techniques have to be developed in order to adapt the bem resolution. For that, the technique of multy domain decomposition together with the dual reciprocity method (drm) has been developed. Software called "poly_bem" has been developed based upon bem. Newtonian and non-newtonian computations have been performed in 3d and 2d respectivly. The dispersion performances of mixing devices are calculated using using the flow number definition. In order to validate these results, preliminary comparaisons have been carried out showing the benefical effect of mixing head. The polimer flow in specific zones of the mixing head (the entry and the exit of the narow gap) exhibits elongational flows improving dispersion more than in other zones.

Abstract FR:

Afin d'obtenir des nouveaux materiaux plastiques, le melange des polymeres est un processus couramment utilise. L'extrusion monovis est un procede de mise en forme des matieres plastiques qui permet d'obtenir un melange efficace en mmodifiant la vis d'extrusion. Pour cela, la tete de melange de type maddock est utilisee, afin d'etudier son effet sur la qualite du melange. Dans cette etude, le melange dispersif est surtout etudie. La partie experimentale de cette these etudie la dispersion de la phase secondaire dans la matrice du polymere (le melange pvc et le melange pp/caco3). Parallelement a cette etude experimentale, un modele numerique a ete develope pour caracteriser le melange des polymeres. Pour cette approche numerique, la methode des elements frontieres (bem) a ete choisie. La methode classique bem ne permet pas de resoudre les problemes d'ecoulements non-newtoniens, ceci nous a amene a utiliser certaines techniques afin d'adapter la resolution par bem. Pour cela la technique de multi domaine combinee avec la methode de la reciprocite duale (drm) est utilisee. Un logiciel "poly_bem" a ete developpe dans le cadre de cette these. Des simulations numeriques en comportement newtonien et non-newtonien respectivement en 3d et en 2d ont permis de calculer la dispersion a l'aide de l'indice d'ecoulement (flow number). Afin de valider ces resultats, une confrontation qualitative a ete realisee montrant notamment l'effet benefique de la tete de melange. L'ecoulement dans certaines zones de la tete de melange (l'entree et la sortie du passage entre canaux) exerce un type d'ecoulemement elongationel favorisant la dispersion plus que dans d'autres zones.