Application of Network Analysis to Flow Systems with Alternating Wave Channels: Part A (Pressure Flows)

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.

Application of Network Analysis to Flow Systems with Alternating Wave Channels: Part B. (Superimposed Drag-Pressure Flows in Extrusion)

“…Table 1 lists the Carreau-Yasuda parameters and the melt densities of the materials. For detailed information on data measurement, the reader is referred to Part A [ 34 ].…”

“…In Part A [ 34 ], we developed a calculation routine based on network theory to analyze pressure-driven flows in double-wave zones. Omitting the influence of the drag flow, the theory predicts the pressure distribution, the local down- and cross-channel flows, and the transverse mixing capability.…”

“…In Part A [ 34 ], we linearized a nonlinear die-flow equation for power-law fluids to determine the properties (theoretical drag flow and conductance) of each network element. The modeling approach presented here considers the nonlinear conveying behavior of the wave channel by linearizing our melt-conveying models and with respect to the current operating point.…”

“…As in the previous part [ 34 ], the cross-channel network elements were initialized with three elements connected in series: (i) one element from the channel center to the pushing flight, (ii) one element over the flight, and (iii) one element from the trailing flight to the center of the channel one turn behind. This procedure allowed us to accurately model the stepwise changes in channel height between the subchannels.…”

“…Our semi-numerical simulation routine is based on the procedure shown in Figure 11 . A detailed discussion was given in Part A [ 34 ].…”