Hideki Tomiyama

Melt-mixing by novel pitched-tip kneading disks in a co-rotating twin-screw extruder

Abstract Melt-mixing in twin-screw extruders is a key process in the development of polymer composites. Quantifying the mixing performance of kneading elements based on their internal physical processes is a challenging problem. We discuss melt-mixing by novel kneading elements called “pitched-tip kneading disk (ptKD)”. The disk-stagger angle and tip angle are the main geometric parameters of the ptKDs. We investigated four typical arrangements of the ptKDs, which are forward and backward disk-staggers combined with forward and backward tips. Numerical simulations under a certain feed rate and screw revolution speed were performed, and the mixing process was investigated using Lagrangian statistics. It was found that the four types had different mixing characteristics, and their mixing processes were explained by the coupling effect of drag flow with the disk staggering and pitched-tip and pressure flows, which are controlled by operational conditions. The use of a pitched-tip effectively controls the balance of the pressurization and mixing ability.

The Sequential Analysis of Film Deformation Behavior during Successive Biaxial Stretching Process

The deformation behavior of Polypropylene (PP) film during successive biaxial stretching process which consists of machine direction (MD) stretching process with a roll drawing and transverse direction (TD) stretching with a tentering was analyzed sequentially by using a finite element method (FEM). In order to analyze it, stress-strain curves of casted PP film and uni-axially oriented PP film in MD were measured and fitted into the constitutive equation that the authors developed previously, respectively, and then, material constants for both films were obtained. Deformation behavior during successive biaxial stretching were calculated by applying the constitutive equation with the material constants of casted PP film for MD stretching and uni-axially oriented PP film in MD for TD stretching, respectively. Analytical conditions were the draw ratio of 5 for MD analysis and the stretching ratio of 9.5 for TD analysis. The authors also experimentally measured the thickness of film during and after MD and TD stretching using a pilot plant under the same conditions as analytical condition. Calculated results were able to express qualitatively the experimental deformation behavior of PP film such as the neck-in phenomena during MD stretching and the change of film thickness during MD and TD stretching.

Improving mixing characteristics with a pitched tip in kneading elements in twin-screw extrusion

In twin-screw extrusion, the geometry of a mixing element mainly determines the basic flow pattern, which eventually affects the mixing ability as well as the dispersive ability of the mixing element. The effects of geometrical modification, with both forward and backward pitched tips, of a conventional forward kneading disks element (FKD) in the pitched-tip kneading disks element on the flow pattern and mixing characteristics are discussed. Numerical simulations of fully filled, nonisothermal polymer melt flow in the melt-mixing zone were performed, and the flow pattern structure and the tracer trajectories were investigated. The pitched tips largely affect the inter-disk fluid transport, which is mainly responsible for mixing. These changes in the local flow pattern are analyzed by the distribution of the strain-rate state. The distribution of the finite-time Lyapunov exponent reveals a large inhomogeneity of the mixing in FKD is suppressed both by the forward and backward tips. By the forward tips on FKD, the mixing ability is relatively suppressed compared to FKD, whereas for the backward tips on FKD, the mixing ability is enhanced while maintaining the same level of dispersion efficiency as FKD. From these results, the pitched tips on the conventional KD turn out to be effective at reducing the inhomogeneity of the mixing and tuning the overall mixing performance.

The Evaluation of Mixing Characteristics of Dulmage Screw

The mixing performance of Dulmage screw was studied experimentally and numerically. In the experiment, Low density polyethylene and red colored mastebatch were mixed and extruded by using Dulmage screw or Full Flight screw. And then, the degree of color uniformity was measured on the cross-section of the extrudate. The masterbatch was distributed more uniformly on the cross-section of Dulmage screw than that of Full Flight screw. The degree of color uniformity for Dulmage screw was about two times higher than that for Full Flight screw. In the numerical analysis, the flow pattern of the masterbatch in the screw channel of Dulmage screw was visualized by means of particle tracking technique. The degree of the distribution of the masterbatch was quantified as the information entropy. The information entropy at the outlet of the screw changed periodically with the screw rotation speed. Furthermore, the masterbatch circulated between the screw surface and the barrel surface in the fin section, consequently the degree of the distribution of the masterbatch changed periodically. In case the masterbatch was distributed uniformly along the channel depth at the outlet of the fin section, the information entropy at the outlet of the screw became high. The result shows the mixing performance of Dulmage screw strongly related to the degree of the distribution of the masterbatch at the outlet of the fin section.