Comparison of fibre reorientation of short-and long-fibre reinforced polypropylene by injection molding with a rotating mold core

Abstract With a rotating mold core during the injection molding of fibre-reinforced plastics, the rotational shear caused by the rotation is superimposed on the injection-induced shear. This allows the fibre orientation in this area to be intentionally manipulated so that, for example, in the case of internal pressure loading, the fibres can be oriented in the tangential main loading direction. This paper deals with the impact of a rotating mold core on the fibre orientation and burst strength of short-and long-fibre-reinforced polypropylene. It is shown that the fibre orientation and strength can be significantly influenced for both short and long fibres, whereby increases in bursting strength of mostly over 80%, in some cases over 200%, could be achieved. The ultimate strength depends, among other things, on the wall thickness used and the fibre content. Major differences between the short-and long-fibre-reinforced polypropylene are less evident in the strength and more in the fibre orientation.