Streamlining melt flow in single-screw extruders – a numerical analysis on the role of flight flanks on conveying efficiency and thermal profiles

Abstract Understanding how screw geometry influences melt flow and residence time is critical for optimizing single-screw extrusion, particularly for thermally sensitive polymer melts. While the effects of key geometrical parameters such as screw diameter, screw pitch, and channel depth are well-studied, the specific impact of the flight flanks on conveying efficiency remains poorly quantified. In this study, a numerical parametric study was performed using computational fluid dynamics (CFD) to investigate the conveying behavior of three extruder screws with different flank angles under various rheological and operating conditions, including both isothermal and non-isothermal flows. Key metrics included velocity distributions, the degree of stagnation, throughput, and residence time distributions (RTDs). Non-isothermal simulations additionally captured the influence of flight geometry on axial temperature development. The results demonstrate that increasing the flight flank angle streamlines melt flow, reduces stagnant regions, and slightly decreases throughput due to reduced channel volume. RTDs reveal a significant reduction in long-residence-time trajectories for streamlined screws, particularly at low screw speeds, indicating a lower risk of thermal degradation. Non-isothermal simulations show that streamlined flight geometry slightly increases melt temperature, while thermal effects further contribute to a reduction in degree of stagnation. These findings provide a qualitative and quantitative framework linking screw geometry to local and global melt transport and thermal behavior, offering guidance for the design of single-screw extruders to improve processing efficiency and product quality.