What is POLYCAD 2-D? |
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POLYCAD 2-D is a software package that solves the equations of conservation of mass, momentum, and energy for molten polymer flow through process equipment for planar 2-D or axisymmetric geometries. While most of the applications are in polymer extrusion, the package is also useful in injection molding, blow molding, calendering, wire coating, cable jacketing, fiber spinning, mixing, and other processes. It is an accurate equation solver and, as such, it is left up to the experience and imagination of the user to identify and apply the solution to real-life problems.
The finite element method is used. This is a rigorous solution of the differential equations. The Galerkin formulation is used to obtain solutions expressed as polynomials within small triangular elements and finally the individual solutions are assembled together to provide the velocity, pressure, and temperature throughout the whole flow field. From the velocity field, the streamlines, local shear and stretch rates, stresses, and particle residence times are calculated and plotted. POLYCAD 2-D is also capable of determining the location and shape of free surfaces (e.g. for extrudate swell) or interfaces (e.g. for coextrusion).
Absolutely none! The program is menu-driven and very user-friendly. The engineer must understand the problem well and identify the appropriate boundary conditions and material parameters. The triangular finite element grid is generated automatically through the user interface.
Four viscosity models are available within POLYCAD 2-D (Power-law, Carreau, Log-polynomial, and Newtonian). Once a viscosity curve is fitted (using VISCOFIT for example), it is extremely easy to introduce the model constants into POLYCAD 2-D through POLYBANK, the material data bank program. Viscoelasticity is a very controversial subject. The available "named" constitutive equations give poor predictions for most problems. In the research and development work carried out during the creation of POLYCAD 2-D, the Second Order, CEF, Maxwell, and Phan Tien-Tanner constitutive equations were used. In the commercially available version of POLYCAD 2-D we have introduced correlations for the first normal stress difference and elongational stress and have had success in predicting entry pressure losses, recirculation flows, and extrudate swell. Needless to say, without good material property data, practical problems in polymer processing cannot be solved.
A user was able to identify that polymer degradation in an extrusion die was caused by hot spots due to viscous dissipation. A virtually stagnant flow region was discovered in an extrusion die by another user. Errors in capillary viscometry were eliminated by yet another user. The flow configuration in the calender gap of a twin screw extruder was studied in detail. Determination of local shear stress led to an explanation of why sharkskin appeared on only one side of an extruded pipe. Understanding of local flow structure led to a modification of die lip geometry to reduce die-lip buildup. Accurate pressure drop calculations led to an improved design of a die for extrusion blow molding. Detailed studies of a hot runner system and cavity gate led to better mold design. Another user carried out corrections of elongational viscosity measurement using POLYCAD 2-D and Cogswell's entrance pressure method. The differences in processing various grades of LDPE, LLDPE, and HDPE through flat dies were determined. It is the detailed knowledge of local velocity, pressure, temperature, shear rates, and stresses that leads to solution of problems. It is like visualizing the flow and carrying out accurate "measurements" on the computer screen.
POLYCAD 2-D 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. Vlachopoulos, N. Silvi and J. Vlcek, "POLYCAD®: A Finite Element Package for Molten Polymer Flow", 85-102, K.T. O'Brien (Ed.), Computer Modeling for Extrusion and Other Continuous Polymer Processes, Carl Hanser Verlag (1992).