Printed with customer permission

The plastics industry uses spiral dies for tubular multi-layer extrusions of films and pipes. This construction is designed to ensure equal flow path resistance and even flow distribution, which are critical to high quality (e.g., uniform film thickness) in the products. However, residence time and the surface area for heat transfer differ significantly, creating the potential for flow non-uniformity due to differences in temperature and viscosity.

The sophisticated template was possible due to the FIDAP macro capability.

Fluent's consulting staff used FIDAP to model the spiral mandrel die shown here and to examine the flow-related causes of product non-uniformity. The FIDAP models predicted residence time and shear heating variations in the configuration that corresponded to the product non-uniformities observed on the process line.

Figure 1. Template-based meshing allowed alternate die geometries to be considered.

After establishing the required modeling procedures for the baseline die configuration, a parameterized template was developed that allowed our customer to do further design optimization. The parameterized model allows the user to easily change the diameters and distances within the die, as well as more complex design features like the number of spirals and the type of cross section.

The sophisticated template was possible due to the FIDAP macro capability, with similar parts of the model built by executing a macro script. When the macro is executed, independent pieces of geometry and mesh are created. Modifications to one piece of the script will automatically produce multiple modifications in the model.

Macros are created by modifying standard FIDAP journal files. Fluent provides information, examples, scripts, and templates through ftp, and classes in the macro method are available.

Figure 2. Temperature distribution in the spiral extrusion die revealed how shear heating could lead to product non-uniformity.

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