Abstract
Wave-dispersion screws have been used industrially in many types of extrusion processes, injection molding, and blow molding. These high-performance screws are constructed by replacing the metering section of a conventional screw with a melt-conveying zone consisting of two or more parallel flow channels that oscillate periodically in-depth over multiple cycles. With the barrier flight between the screw channels being selectively undercut, the molten resin is strategically forced to flow across the secondary flight, assuring repeated cross-channel mixing of the polymer melt. Despite the industrial relevance, very few scientific studies have investigated the flow in wave-dispersion sections in detail. As a result, current screw designs are often based on traditional trial-and-error procedures rather than on the principles of extrusion theory. This study, which was split into two parts, was carried out to systematically address this issue. The research reported here (Part A) was designed to reduce the complexity of the problem, exclusively analyzing the pressure-induced flows of polymer melts in wave sections. Ignoring the influence of the screw rotation on the conveying characteristics of the wave section, the results could be clearly assigned to the governing type of flow mechanism, thereby providing a better understanding of the underlying physics. Experimental studies were performed on a novel extrusion die equipped with a dual wave-channel system with alternating channel depth profiles. A seminumerical modeling approach based on network theory is proposed that locally describes the downchannel and cross-channel flows along the wave channels and accurately predicts the pressure distributions in the flow domain. The solutions of our seminumerical approach were, moreover, compared to the results of three-dimensional non-Newtonian CFD simulations. The results of this study will be extended to real screw designs in Part B, which will include the influence of the screw rotation in the flow analysis.
Highlights
Single-screw extruders are the processing machines of choice for shaping polymers
We describe the shear-thinning flow behavior of the polymer melt by an Ostwald–deWaele power law model [31]:
After entering the dual wave section, white material flowed across the barrier flight from channel 1 into channel 2
Summary
Single-screw extruders are the processing machines of choice for shaping polymers. They are used in various continuous manufacturing processes to produce finished or semifinished products such as films, pipes, profiles, and sheets. The most important machine components of single-screw extruders are a feeding system, a drive unit, a barrel, a temperature control system, and a screw. The latter is the most important element of the processing machine. Many single-screw extruders operate significantly below the maximum possible performance because of improper screw design.
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