Effect of screw design on fiber breakage and dispersion in injection-molded long glass-fiber-reinforced polypropylene

Fiber breakage occurs during the injection molding of fiber-reinforced thermoplastics, resulting in the deterioration of the mechanical properties of the molded parts. In this paper, we propose an effective screw geometry for improving both fiber dispersion and residual fiber length. The proposition is based on the results of our study in which we evaluated five types of screws by investigating the molded specimens. We found that the screw geometry in the compression zone dominantly affected the residual fiber length, and that the choice of an appropriate geometry for the melting and mixing processes was the most important factor for improving both fiber dispersion and residual fiber length. Our experimental observations were compared with the results of flow analysis and consistency was observed. We also discuss the effects of the screw size on the quality of the molded parts.