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 to controls the balance of the pressurization and mixing ability.

Effects of Pitched Tips of Novel Kneading Disks on Melt Mixing in Twin-Screw Extrusion

“…The flow is assumed to be incompressible, and in a pseudo-steady state to screw rotation, as has often been assumed in polymer flow in twin-screw extruders. 11,15,18,20,22,[24][25][26] With these assumptions, the governing equations become…”

“…24) Here we give a summary of the numerical simulation. We focus on the situation where the material fully fills the channel.…”

“…In contrast to this, in pitched-tip KD, the tips of the blocks are twisted to the screw axes. 24) Pitched tips modify the channel geometry of the conventional KD. Furthermore, pitched tips add additional drag ability along with screw rotation to conventional KD.…”

“…The combined choice of the tip angle and the disk-stagger angle can make it possible to control both the distributive and dispersive mixing abilities better than in conventional KD. In the previous study, 24) it has been found that different combinations of tip angle and diskstagger angle actually lead to different mixing characteristics.…”

“…In order to tune the mixing characteristics of conventional KD for application to various purposes, a modified type of KD has been proposed, called "pitched-tip kneading disks" (ptKD). 24) In ptKD, two disk tips are pitched to the screw axes, whereas the tips in the conventional KD are parallel to the screw axes. The combined choice of the tip angle and the disk-stagger angle can make it possible to control both the distributive and dispersive mixing abilities better than in conventional KD.…”