Effects of pitched tips of novel kneading disks on melt mixing in twin-screw extrusion

TL;DR

This study investigates how pitched-tip modifications to kneading disks in twin-screw extruders influence melt mixing, showing that backward tips enhance stress and potentially improve dispersive mixing without affecting residence time fluctuations.

Contribution

It introduces the effects of pitched-tip angles on kneading disk performance, providing insights for optimizing mixing device design in polymer and rubber processing.

Findings

Pitched tips increase fluid stress in high-stress regions.

Backward pitched tips raise mean applied stress, improving dispersive mixing.

Residence time fluctuations remain unchanged with pitched tips.

Abstract

In mixing highly viscous materials, like polymers, foods, and rubbers, the geometric structure of the mixing device is a determining factor for the quality of the mixing process. In pitched-tip kneading disks (ptKD), a novel type of mixing element, based on conventional kneading disks (KD), the tip angle is modified to change the channel geometry as well as the drag ability of KD. We discuss the effects of the tip angle in ptKD on mixing characteristics based on numerical simulation of the flow in the melt-mixing zone under different feed rates and a screw rotation speed. It turns out that the passage of fluid through the high-stress regions increases in ptKD compared to conventional KD regardless of the directions and sizes of the tip angle, while the fluctuation in residence time stays at the same level as the conventional KD. Furthermore, pitched tips of backward direction increase the mean applied stress on the fluid elements during its residence in the melt-mixing zone, suggesting the enhancement of dispersive mixing quality in ptKD. These understandings of the role of the tip angle on KD can give a basic guide in selecting and designing suitable angle parameters of ptKD for different mixing purposes.