Abstract
In the polymer sheet processing industry, the primary objective when designing a coat-hanger die is to achieve a uniform velocity distribution at the exit of the extrusion die outlet. This velocity distribution depends on the internal flow channels of the die, rheological parameters and extrusion process conditions. As a result, coat-hanger dies are often designed for each polymer based on its individual rheological data and other conditions. A multi-rheology method based on a flow network model and the Winter–Fritz equation is proposed and implemented for the calculation, design and optimization of flat sheeting polymer extrusion dies. This method provides a fast and accurate algorithm to obtain die design geometries with constant wall-shear rates and optimal outlet velocity distributions. The geometric design when complemented and validated with fluid flow simulations could be applied for multi-rheological fluid models such as the power-law, Carreau–Yasuda and Cross. This method is applied to sheet dies with both circular- and rectangular-shaped manifolds for several rheological fluids. The designed geometrical parameters are obtained, and the associated fluid simulations are performed to demonstrate its favorable applicability without being limited to only the power-law rheology. The two such designed dies exhibit 32.9 and 21.5 percent improvement in flow uniformity compared to the previous methods for dies with circular and rectangular manifolds, respectively.
Highlights
One of the most important processes in the polymer processing industry is the extrusion of sheets
As it can be seen, our method shows good agreement with the experimental data and the computational fluid dynamics (CFD) simulation results
A general rheology network method for the design of sheeting extrusion dies in the polymer processing industry is proposed based on the Winter–Fritz constant wall shear-rate conditions and conservation laws of fluid flows in the network
Summary
One of the most important processes in the polymer processing industry is the extrusion of sheets. The majority of previous studies have been focused on power-law fluids Another possible approach is devising a semi-analytical method, such as the flow network method, for the fast and accurate design of an extrusion die. Michaeli et al [16] combined the finite element method with the network theory to find the optimum velocity distribution They demonstrated this network as being optimal for the design of rectangular- and circular-shaped manifold extrusion dies for Carreau–Yasuda and power-law fluids. The method utilizes a modified discretized form of the Winter–Fritz equation on a flow network, which is considered a novel extension and contribution to the circuit network method for die design This method enforces additional uniform velocity distribution constraints, resulting in a significant improvement in the velocity distribution without conducting full-fledged CFD analyses on the manifold
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