What is SPIRALCAD? |
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SPIRALCAD is a software package used for flow simulation in spiral mandrel dies. The molten polymer flow is simulated from the die ports as it moves along and leaks from the spiral channels in the gap between the body and the mandrel. It predicts the flow, pressure, and temperature distributions throughout the die and the thickness variation in the final annular extruded film. Regions of heavy or light gage film can easily be identified and design modifications made accordingly.
The control volume method is used. Instead of solving the differential equations, physical principles are used to determine the volumetric flow and pressure relations for a finite number of control volumes. By the judicious choice of control volumes that conform to the port/spiral/mandrel/body geometry, the complex 3-D flow pattern is converted into an equivalent 2-D flow network which can be solved in lay-flat configuration. The periodicity of flow pattern, which is equal to the number of ports, allows for a reduction of the number of simultaneous equations to be solved.
Some small differences were noted between SPIRALCAD predictions and fully 3-D finite element simulations. However, it was not clear whether the 3-D simulations were better than SPIRALCAD. Because of the geometric complexity, a relatively rough 3-D grid had to be used that may have introduced significant errors in the integration process. For the finite element calculations, a powerful supercomputer was used while SPIRALCAD was run on a 486-based PC. Yet the differences were relatively small.
With SPIRALCAD, an engineer may significantly shorten the time required to design a good die. The die geometry can be easily introduced into the program and the role of eventual modifications be determined. For some dies, many different modifications were conducted. However, the program runs quickly (e.g. 1 minute per run on a Pentium III PC). SPIRALCAD takes the guesswork out of spiral mandrel die design. Several hundred successful dies have been designed since the first release of SPIRALCAD, not only for blown film but also for pipe extrusion.
By introducing different parameters in the Power-law, Carreau, Log-polynomial, or Newtonian viscosity models it is easy to evaluate the performance of a given material. Several hundred materials have been used in our simulations including numerous grades of HDPE, LDPE, and LLDPE.
SPIRALCAD 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).
J. Perdikoulias, J. Vlachopoulos and J. Vlcek, "Spiral Die Analysis", To appear in Film Processing, T. Kanai and C.A. Campbell (Eds.), Hanser (1999).