twin-screw extrusion | Computer modelling
in misinterpretations of torque, melt temperature and other crucial process parameters.
A compounder can, by entering all this data, use the simulation to obtain information that is not usually measured by instruments or other machine-side techniques. For example: where in the screw channel polymer is melting; how much mixing takes place in different barrel sections; and why melt reaches a certain temperature at points of the extruder.
This PolyTech WinTXS analysis shows melt effi ciency based on RPM at various points in the extruder
Simulations run rapidly, and the software’s computa- tional speed lets compounders experiment with a number of different process scenarios and variations. Recent additions to the WinTXS program include a devolatizing module to simulate multi-stage, multi- component operations with volatiles, and availability of a reactive processing module.
There is “not a large learning curve” involved in
using the software “if you understand how a compound- ing machine works,” Dreiblatt says. The process is “very intuitive.”
Meshing hardware and material
The mixing effi ciency of a twin-screw confi guration is simulated at three speeds using PolyTech WinTXS software
compounds, reinforced materials, plastomers and elastomers, blends and colour concentrates. Calibration is an important capability of the WinTXS
software, Dreiblatt says. With calibration, a user can validate the simulated processing of a compound based on the accuracy of the material and machine data entered. Once the model is calibrated, the “results are valid”, he explains. The accuracy of input data is especially critical for
what it allows the software to calculate. Determining exactly where in a barrel melting begins and ends based on material specifi cations and screw design, for example, determines a property such as viscous energy dissipation, which has an effect on the simulation’s ability to adjust the feeding of low-melt-point additives in the compound. In contrast, predicting, rather than identifying, where and when melting occurs can result
38 COMPOUNDING WORLD | February 2015
SCC’s modelling software for optimizing twin-screw extrusion was originally developed by an industrial consortium and uses algorithms and other calculations updated by the French materials research institute CEMEF (Centre de Mise en Forme des Materiaux), Ludovic, the 1-D version for co-rotating twin-screw extrusion, calculates hundreds of process scenarios from input data so that compounders can determine which confi gurations based on screw geometry, material characteristics and process conditions provide the most productive results.
The simulation set-up and analysis steps are straight- forward and based on Ludovic’s so-called “four tabs of technology”. This lets users build the twin-screw system they want and run simulations by selecting engineering and process data from four tabs on a computer screen. The data covers screw geometries and components, barrels, feeding zones and die elements, as well as material specifi cations, some of which can be taken from a Ludovic database, and a defi nition of operating conditions. Once all this information is assembled, the user hits an execution tab to run simulations.
As the simulations run, Chassagnolle says graphics and numerical data are displayed charting parameters such as pressure, shear, viscosity, residence-time distribution curves and energy consumption. A graphic of the screw shows material fl ow and the thermo-me- chanical history of the compound at various points, along with colour-coded temperature data along the screw. The latter allows a compounder to calculate differences in temperature and pressure as material
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