Visualization analysis of reciprocating‐screw plastication process of glass fiber‐reinforced resins in a glass‐inserted heating cylinder

Abstract

One challenge in injection molding of long fiber‐reinforced resins is minimizing the fiber breakage during resin plastication and resin flow into a mold. Such fiber breakage reduces the strength of the molded product. Reciprocating plastication is subjected to periodic positional fluctuations of the screw and cylinder in the molding cycle. In this study, visualization experiments were conducted on the reciprocating plastication of long glass fiber (GF)‐reinforced polypropylene with 50 wt% GF. It was found that: (1) temporary voids form in the resin during the metering process, and the pellets rotate from an orthogonal to parallel orientation in the flight direction; (2) length of the weight‐averaged fiber temporarily decreased in the middle stage of the injection process; (3) length of the weight‐averaged fiber was most strongly influenced by the waiting time; and (4) for constant waiting time, the fiber breakage could be minimized by lowering the rotation speed, lowering the back pressure, and shortening the charge stroke. POLYM. ENG. SCI., 59:846–853, 2019. © 2018 Society of Plastics Engineers

Visualization Analysis of Defibration and Distributive Uniformity of Fibers in Long-fiber-reinforced, Injection-Molded Resins

“…In addition, the brightness gradually decreased from the start of injection and then increased again at the end of injection. As stated in Section 3.1.2, this phenomenon corresponds to the phenomenon [19] in which the fiber length distribution of long-glass-fiber resin decreases temporarily in the middle of the plastication process' metering. These results confirm that high BP promoted distributive uniformity while reducing average brightness.…”

“…At a BP of 4 MPa, P showed substantial variation across points during injection, but at BPs of 8 MPa and 12 MPa, P was elevated only at the injection sequence's beginning and end. This behavior is interpreted as promotion of defibration and distributive uniformity in the middle of the plastication process, preceded and followed by a temporarily lower fiber length distributive uniformity during the long-fiber-reinforced resin's reciprocating-screw plastication process [19]. Figure 7 shows an example of the evaluation image, (a) showing the original image and (b) showing the extracted dark area.…”