What is FLATCAD? |
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FLATCAD is a software package used for simulating flat film and sheet dies (coathanger or fishtail). The molten polymer flow is simulated from the feeding tube (lateral flow) and simultaneously downstream through the restrictor gap and relaxation chambers to the die lips. It predicts the volumetric flow rate, pressure, temperature, shear rate, shear stress, and residence time distributions throughout the die and the thickness variation in the final product. Regions of heavy or light gage film or sheet can be easily identified and design modifications made.
The control volume method is used. Instead of solving the differential equations as dx, dy and dz approach zero (finite differences or finite elements), physical principles are used to determine the volumetric flow rate and pressure relations for a finite number of control volumes. By taking advantage of the flat die geometry, the 3-D flow pattern is converted into an equivalent 2-D flow network by allowing flow in the downstream and side directions. The complexity of the problem to be solved is determined by the number of subdivisions across and along the die.
Very small differences were noted when comparing FLATCAD with fully 3-D finite element simulations. The results indicate that a 3-D analysis is not required for flat sheet or film dies. FLATCAD uses the Hele-Shaw flow approximation that works well whenever the die geometry does not have abrupt changes.
With FLATCAD, an engineer may significantly shorten the time required to design a good die. The die geometry can be entered into the program and areas which require modification can be determined. Since the simulation time is short (1 minute per run on a Pentium III PC) many modifications can be made on the computer screen instead of on the shop floor. Several hundred successful dies have been designed since the first version of FLATCAD appeared.
FLATCAD includes four viscosity models (Power-law, Carreau, Log-polynomial, and Newtonian). By introducing different model parameters for different materials it is possible to evaluate the performance of a die for several materials. Several hundred materials have been used in our simulations including HDPE, LDPE, LLDPE, PS, PP, PVC, PET, thermoplastic elastomers, and polymers used in coating applications
FLATCAD 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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J. Vlcek, J. Perdikoulias and J. Vlachopoulos, "Extrusion Die Flow Simulation and Design with FLATCAD, COEXCAD and SPIRALCAD", K.T. O'Brien (Ed.), Computer Modeling for Extrusion and Other Continuous Polymer Processes, 487-504, Carl Hanser Verlag (1992).