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

摘要

In mixing highly viscous materials, like polymers, foods, and rubbers, thegeometric structure of the mixing device is a determining factor for thequality of the mixing process. In pitched-tip kneading disks (ptKD), a noveltype of mixing element, based on conventional kneading disks (KD), the tipangle is modified to change the channel geometry as well as the drag ability ofKD. We discuss the effects of the tip angle in ptKD on mixing characteristicsbased on numerical simulation of the flow in the melt-mixing zone underdifferent feed rates and a screw rotation speed. It turns out that the passageof fluid through the high-stress regions increases in ptKD compared toconventional KD regardless of the directions and sizes of the tip angle, whilethe fluctuation in residence time stays at the same level as the conventionalKD. Furthermore, pitched tips of backward direction increase the mean appliedstress on the fluid elements during its residence in the melt-mixing zone,suggesting the enhancement of dispersive mixing quality in ptKD. Theseunderstandings of the role of the tip angle on KD can give a basic guide inselecting and designing suitable angle parameters of ptKD for different mixingpurposes.