What is PROFILECAD?

PROFILECAD is a rigorous finite element method program that solves the conservation of mass and momentum equations for unidirectional polymer melt flow through channels of arbitrary cross-section. Unidirectional flow means that the downstream velocity (in the z-direction) is allowed to vary in the crosschannel (x and y) directions. Output includes local velocities, flow rates, shear stresses, shear rates, and pressure drop. PROFILECAD allows the user to balance the flow rate through varying channel widths.

What is the design philosophy?

The profile die designer faces the daunting task of converting a melt stream from the end of the extruder into the final profile shape of arbitrary cross section. To achieve this, narrow and wide sections are necessary to distribute the melt from the extruder end to the die lips. It is tempting to try to use a fully 3-D finite element solver to simulate the flow. Such solvers can indeed simulate the complex flow field, but do not provide much guidance on how to correct the channel gaps to achieve the uniform flow required at the lip exit. However, it is known from practice, and as design consultant S. Levy puts it in a description of profile tooling technology: "The cases where the die orifice geometry can permit flows across the machine direction make die design difficult." PROFILECAD was created with the assumption that there is no cross-flow at all. The program simply simulates the flow through an arbitrary cross-section with the assumption that the material flow is perpendicular to the flow area.

PROFILECAD facilitates the balancing of pressure drops and flow rates for each die section so that the desired amount of melt is delivered to the die lips for a final product having the required wall thicknesses.

With PROFILECAD we will not be in futile pursuit of all possible designs but we are searching for the designs that provide a uniform linear speed for each part of the die. Of course, there will be sections of the die where the flow is complicated causing a flow distortion. This happens at intersections of thin and thick regions. With PROFILECAD it is possible to provide the correct amount of flow in each die section and to minimize or control the amount of cross-flow.

How difficult is it to design a good die?

With PROFILECAD it is possible to do trial-and-error on the computer screen rather than on the shop floor. The time required for design can be significantly shortened. We received reports from licensees of PROFILECAD of total time savings of more than 60%, and floor shop trial reductions of 80%. Some designs went into production without any corrections whatsoever. Yes, it is possible to reasonably predict the performance of a die and to make the necessary corrections required to produce the desired shape on the computer screen with PROFILECAD.

What about the differences in design of profile dies for PVC and other materials?

PROFILECAD includes four viscosity models: Power-law, Carreau, Log-polynomial, and Newtonian. The differences of materials is reflected to a large extent in their viscosity behavior which can be adequately described by the above viscosity models. Swelling at the exit, which is due to viscoelasticity (small for PVC, larger for polyolefins) is not included in the present version of PROFILECAD. However, regions of potential problems relating to swelling may be assessed from the local shear stresses. Also, the maximum throughput for profile extrusion may be determined by calculating the shear stress for the onset of sharkskin / melt fracture.

PROFILECAD is a DOS-based software package. It can be run directly on PCs with Windows 95/98.
For PCs with Windows NT/ME/2000/XP, Polydynamics will provide a custom bootable floppy diskette or bootable CD-ROM for running the program.

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References

W. Michaeli, Extrusion Dies for Plastics and Rubber, Carl Hanser Verlag, Munich (1984).

B.L. Koziey, J. Vlachopoulos, J. Vlcek and J. Svabik, "Profile Die Design by Pressure Balancing and Cross-Flow Minimization", ANTEC Proceedings, SPE, Indianapolis, 247-252 (1996).

S. Levy, "The Technology of Plastics Profile Tooling", Adv. Plas. Tech., 8-53 (Jan. 1981).

S. Levy, "Extrusion Die Design for Thermoplastic Materials: Comparison of Extrusion Ease With PVC Materials", Adv. Plas. Tech., 24-31 (Oct. 1981).