Present challenges in the numerical modeling of polymer-forming processes
ABSTRACT The purpose of the present paper is to present an overview of the main progresses recently made in the numerical modeling of polymer-forming processes and to describe the challenges to overcome in the near future. Examples are presented in different domains, such as die extrusion, injection molding, film processing, reactive extrusion and pipe reinforcement.
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ABSTRACT: A method is described for the minimization of a function of n variables, which depends on the comparison of function values at the ( n + 1) vertices of a general simplex, followed by the replacement of the vertex with the highest value by another point. The simplex adapts itself to the local landscape, and contracts on to the final minimum. The method is shown to be effective and computationally compact. A procedure is given for the estimation of the Hessian matrix in the neighbourhood of the minimum, needed in statistical estimation problems.01/1965;
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ABSTRACT: A basic study of the kinematics, dynamics, and heat transfer occuring during tubular film extrusion of polyethylene is outlined. Three rheologically characterized polyethylenes, a low-density polyethylene (LDPE), a linear-low-density polyethylene (L-LDPE), and a high-density polyethylene (HDPE) were used in this study. The kinematics and stability of the tubular film process were investigated over a wide range of blow-up ratios, drawdown ratios, and frost-line heights. Local deformation rates along the bubble have been determined. Regions of stability and instability are described. Tensions and inflation pressures have been measured and expressed in terms of locol elongational viscosities. Temperature profiles along the bubble were determined and interpreted in terms of local heat transfer coefficients. Positions of crystallization and temperature profiles have been noted and used to estimate rates of crystallization. The characteristics of the LDPE, LLDPE, and HDPE are contrasted.Polymer Engineering and Science 08/2004; 24(15):1185 - 1201. · 1.24 Impact Factor
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ABSTRACT: An experimental study of instabilities in melt spinning, ribbon drawdown and tubular film extrusion of moleculary and rheologically characterized high density (HDPE) low density (LDPE) and linear low density (LLDPE) polyethylenes is presented. The characteristics of the instabilities occuring in these processes are described. The draw resonance instability is found to occur in melt spinning and ribbon drawdown. Special attention is given to tubular film extrusion which has received little treatment in the literature. Three distinctive tubular film instabilities are described. These involve (i) an axisymmetric periodic fluctuation in bubble diameter; (ii) a fluctuation of frostline height and tension; (iii) a helical motion of the bubble. The characteristics and occurrence of these phenomena are discused. In the melt spinning and ribbon drawdown, th LDPE is the most stable and the broad molecular weight distribution HDPEs the most unstable. In tubular film extrusion, the LDPEs are again the most stable but the narrower distribution HDPEs and LLDPEs are much more unstable than the broader distribution HDPE. These results are discussed in terms of convected Maxwell model representations.Journal of Non-Newtonian Fluid Mechanics. 01/1986;