  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.
