Computer modelling | twin-screw extrusion
This year’s model: advances in computer simulation
Modelling and simulation software is an effective, and underused, way of optimizing twin-screw extrusion, reports Pat Toensmeier
Imagine if there was a “silver bullet” that allowed compounders to rapidly tune formulation rheology and machine set-up and thereby achieve cost-effective scale-up to commercial production. Benefi ts could include sizable savings in materials costs, reductions in scrap, faster time to market, more productive use of labour and machine time, and a much-enhanced bottom line. Such a “silver bullet” potentially exists in the form of modelling and simulation software. While this technol- ogy has been available for some years, its use by compounders is not widespread. Mostly it is the largest companies, including resin producers, that take advantage of the capability. This is frustrating to the small number of suppliers
of such software. They all make the point that modelling and simulation software yields signifi cant benefi ts to end-users over conventional development processes. The latter typically involve running a machine and experimenting with settings and formulation tweaks until the right balance of formulation composition and machine set-up emerges. “We have been marketing this software for 15 years but it has limited reach,” says Adam Dreiblatt, director of process technology for Century Extrusion, a global supplier of twin-screw machines and components. The software Century sells is called WinTXS (Twin-Screw Extruder Simulator), a 1-D system that was developed by PolyTech in the US and validated with computational and experimental data by the Polymer Processing Insti- tute of Newark, New Jersey. Modelling software is “not yet widely used in
compounding,” agrees Eric Chassagnolle of Sciences Computers Consultants (SCC), a French company that supplies two programs for twin-screw compounding: Ludovic, a 1-D program for the optimization of screw
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profi les and related hardware, and Ximex 3-D mixing simula- tion software. Other developers include the University of Paderborn in Germany, which is running Sigma, a joint research project focusing on the simulation of co-rotating twin-screw extruders. This involves the university’s KTP plastics technology institute plus a consortium of 11 industrial companies. To maintain a competitive balance, the materials side of the simulation is “intentionally generic,” one source says, so no company gains a competitive advantage over another member by using it. The Polymer Engineering Institute of the University
of Akron in the US released one of the fi rst software modelling programs for compounding 25 years ago. Called Akro-Co-Twin, the product is marketed by Temarex. The latest version is 3A, which features upgraded capabilities including the integrated model- ling of solids conveying, melting and melt fl ow in modular screw confi gurations. In Japan, HASL (Hyper Advanced Simulation
Laboratory) offers a range of fl ow simulation packages for the 3D visualisation of material behaviour in twin-screw extruder. They can map fl ow, pressure, temperature and melt rates along the screws. Ansys offers a very wide range of computer simula- tion packages for a variety of materials, properties and industries. Its Polyfl ow software can be used to model various plastics processes including thermoforming, blow moulding and extrusion. The company says that its mesh superposition technique can be used to take into
February 2015 | COMPOUNDING WORLD 33
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