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An octa-screw extruder (OSE) is equipment for pelletizing, blending, and mixing polymers and composites. In this study, the degree of resin filling, residence time distribution (RTD) of molten resin, and temperature profile in the octa-screw extruder were evaluated both experimentally and numerically. An intermeshing corotating parallel octa-screw kneading extruder was used for the experiments. For the comparison study, the results obtained from this extruder were compared with the twin-screw extruder. High-density polyethylene was selected as the material for extrusion. Meanwhile, a numerical code, based on a 2.5 D finite element method derived from the Hele–Shaw flow model, was developed to simulate the octa-screw extrusion process. The empirical outcomes suggest that octa-screw extrusion exhibited a narrower RTD of the molten resin compared with the twin-screw extrusion, suggesting better extrudate quality. The octa-screw extrusion also showed a lower temperature profile than twin-screw extrusion. The results of the simulation were also found to be in good agreement with experimental measurements. Experimental and numerical investigations of an OSE enable detailed comprehension and visualization of resin distribution in the entire length of the OSE, thus providing advantages in terms of process optimization.

Devolatilization is an important process for separating and removing unnecessary residual volatile substances or solvents during the production of polymers using twin-screw extruders. Latinen proposed a surface renewal model to determine the concentration of volatile components in the extrudate of a single-screw extruder. When a twin-screw extruder is used to calculate the concentration, it is necessary to use the exposed surface area of the resin in the starved region of Latinen&rsquo, s model, which, however, is difficult to estimate. In our previous work, we numerically determined resin profiles of the screws using the 2.5D Hele&ndash, Shaw flow model and the finite element method, which helps in estimating the surface area of devolatilization. In this study, we numerically analyzed the volatile concentration of the extrudate in a self-wiping corotating twin-screw extruder using Latinen&rsquo, s surface renewal model along with our resin profile calculation method. The experimental results of the concentrations of the volatile component (toluene) in the extrudate of polypropylene agreed well with its numerical calculation with a relative error of 6.5% (except for the data of the lowest rotational speed). Our results also showed that decreasing the flow rate and increasing the pump capacity were effective for removing the volatile component. The screw pitch of a full-flight screw was not affected by the devolatilization efficiency with a fixed flow rate and screw speed.

A straight vacuum-forming process is simulated by use of the commercial blow molding CAE system “SIMBLOW”. The accuracy of numerically predicted values of thickness distributions are compared with experimental ones. Rheological properties of a lightly cross-linked poly (methyl methacrylate) (PMMA) are expressed using the Kaye-Bernstein-Kearsley-Zapas (K-BKZ) constitutive equation with the damping function of the Papanastasiou-Scriven-Macosko (PSM) model. The simulation conditions are based on an analysis of actual vacuum-forming behavior. The relaxation spectrum is obtained from dynamic moduli data, and the PSM model parameters are determined from experimental data of uniaxial extension by trial and error. The predicted thickness distributions along the center and corners of the mold agree very well with the experimental results. On the other hand, the accuracy of prediction decreases in the vicinity of large bending deformation, where deviation from the biaxial extension is expected.

Non-Newtonian, non-isothermal, 3D finite-element simulation of mixing performance in a pin mixing section with different axial gaps in the pins has been carried out according to their realistic configurations. The quantitative evaluation of mixing ability was based on the theory of kinematics of fluid mixing. To learn and to compare the local mixing performance in a standard screw and a pin mixing section, the local mixing efficiency distribution proposed by Ottino was calculated. Also, the RTDs of these mixers were calculated in an attemt to measure mixing. The integration of the two, namely, the integrating local mixing efficiency along a number of particle pathlines from entrance to exit, together with statistical treatment, which was referred as integral mixing efficiency, then gives a quantitative judgment of the total mixing ability of a continuous mixer. The calculated results showed a nonlinear dependence of the mixing ability of a pin mixing section on the axial gap of the pins. Finally, the calculation results were compared with the experimental ones obtained in our previous study.

This paper focuses on the overall numerical simulation of the parison formation and inflation process of extrusion blow molding. The competing effects due to swell and drawdown in the parison formation process were analyzed by a Lagrangian Eulerian (LE) finite element method (FEM) using an automatic remeshing technique. The parison extruded through an annular die was modeled as an axisymmetric unsteady nonisothermal flow with free surfaces and its viscoelastic properties were described by a K-BKZ integral constitutive equation. An unsteady die-swell simulation was performed to predict the time course of the extrudate parison shape under the influence of gravity and the parison controller. In addition, an unsteady large deformation analysis of the parison inflation process was also carried out using a three-dimensional membrane FEM for viscoelastic material. The inflation sequence for the parison molded into a complex-shaped mold cavity was analyzed. The numerical results were verified using experimental data from each of the sub-processes. The greatest advantage of the overall simulation is that the variation in the parison dimension caused by the swell and drawdown effect can be incorporated into the inflation analysis, and consequently, the accuracy of the numerical prediction can be enhanced. The overall simulation technique provides a rational means to assist the mold design and the determination of the optimal process conditions.

In the present study, a mathematical model employing the K-BKZ integral type viscoelastic constitutive equation was developed for a numerical analysis of the parison formation process in extrusion blow molding. The parison shape is controlled by the two competing influences of swell and draw-down. This mathematical model was made on the assumptions that swell and draw-down contributions could be separately considered and simply added in order to avoid elaborate computations. The swell phenomena was estimated by a steady state viscoelastic flow analysis using a streamline finite element method. On the other hand, the draw-down was modeled in terms of the uniaxial extension that could be analyzed by an unsteady numerical technique. To evaluate the capability of the present model, firstly, steady sate annular die swell simulations were carried out using the flow characteristics of high density polyethylene (HDPE) resin. By a modification of the model prediction for the elongational viscosity at high stretching rates beyond the experimental range, the calculated swell ratio was in reasonable agreement with the experimental data. Secondly, unsteady numerical simulations were performed for the extrusion experiment with HDPE and polycarbonate (PC) under conditions of severe draw-down. In the HDPE extrusion simulation, there was good qualitative agreement between numerical results and the experimental data for time-dependent effects on the parison shape. The good model fitting of the elongational viscosity for the PC extrusion simulation yielded a good prediction of the parison length as a function of the extrusion time.