What is LAYERCAD?

LAYERCAD is a software package used for simulation of multimanifold coextrusion. When molten polymer flows are combined to form several layers of blown film, flat film, or sheet, LAYERCAD can be used to predict the thickness of each layer, the velocity, shear rate, shear stress, and viscosity profiles, and the pressure drop. The onset of interfacial instability can be inferred from interfacial values of stress. While SPIRALCAD or FLATCAD may be used to design the individual dies (manifolds), LAYERCAD is used for the combination of the different layers (up to 20 with the current version).

Could such a problem be solved with POLYCAD 2-D or a 3-D package?

Yes, provided that the layers are limited to two or three. For more layers any fully 3-D, or even 2-D, solution would be uneconomical, if not impossible. The number of elements required for each layer to give an accurate solution renders 2-D or 3-D finite element formulations very time-consuming and clumsy for practical design problems. A 2-D or 3-D finite element method is not really suited for coextrusion of many layers.

What is the numerical method used?

1-D finite elements are used to solve the appropriate flow equations. The assumption is made that the multimanifold flow channel consists of several nearly parallel flat plates. This approximation is accurate for most practical problems involving several layers. For more accurate determination of the exact flow pattern at the combining point or other critical regions, POLYCAD 2-D can be used. However, the application of a 2-D finite element analysis is easier when the interface locations have been predetermined with LAYERCAD.

How difficult is it to design a die / manifold system?

While FLATCAD and SPIRALCAD are used for die design, LAYERCAD is used when the individual layers are combined (up to 20 layers). With LAYERCAD an engineer may significantly shorten the time required to design a good die/manifold system. The geometry of the system can be entered into the program and the areas where modifications are required can be determined. Since the simulation times are short (1 minute per run on a Pentium III PC) the effect of several modifications can be explored on the computer screen instead of on the shop floor. LAYERCAD is an excellent tool for the determination of conditions for the onset of interfacial instabilities.

How can we determine the performance of different polymer grades?

LAYERCAD includes four viscosity models (Power-law, Carreau, Log-polynomial, and Newtonian). By using different model parameters for different materials it is possible to evaluate the performance of a die/manifold system for up to 20 coextruded polymers. Several hundred material combinations have been used in our simulations since the first release of LAYERCAD.

How do the predictions compare to experimental data and real-life situations?

From comparisons with experimental data available from the industrial users of LAYERCAD, we have sufficient evidence to support the validity of LAYERCAD predictions. Of course, there are several unanswered questions in coextrusion regarding the causes of interfacial instability and the role of viscosity differences and polymer elasticity. We have a very active research program in this area.

LAYERCAD 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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