Analysis of Fiber Orientation and Velocity Distribution in Flow of Short Fiber-Polymer Melt Mixture through Cooled-Mold Slit Channel in Consideration with Fiber-Mold Wall Interaction.

Abstract

In injection molding of short fiber-polymer melt mixture, influence of the interaction between a fiber and a mold wall on fiber distribution and flow property cannot be neglected, when fiber length is not very short comparatively to the thickness of a mold cavity. In the flow through a cooled mold cavity, solidifying layer grows and it affects that relation further. In this paper, effiects of these causes on fiber orientation and velocity distribution have been made clear by using numerical analysis, in which each fiber motion is analyzed from equilibrium conditions and fiber orientation distribution is obtained by integrating frequency of orientation angles of each fiber over the whole angles, and the following results have been obtained. (i) Near a mold wall, mixture is cooled and no flow layer is generated. On the other hand, apparent viscosity increases in the region, apart from a mold wall by more than half of fiber length, because of high fiber concentration, and plug flow-like velocity distribution is generated. (ii) Pressure gradient increases toward downstream in low injection rate, because of cooling of mixture, whereas it decreases in high injection rate, because of viscosity decrease due to shear heating. (iii) As fiber length decreases, pressure gradient decreases. (iv) Fiber orientation distribution changes considerably with injection rate change.