PROCESSING | SIMULATION
Figure 2: Comparison of different temperature profiles of blends under various operating conditions
Image: SC- Consultants
huge benefit,” he says. “We also estimate that shutting down a produc- tion line for just one day of trials in order to perform measurements means a loss of $30- 40,000. Whereas simulations are performed in a few minutes, in a 100% virtual way, and without any monetary loss. Therefore, the use of numerical simulation is necessary from both a financial, but also quality point of view. Indeed, numerical simulation can provide the whole thermo-mechani- cal history of a material, which can highlight areas and parameters to be improved,” he says. SC-Consultants cites two examples where numerical simulation can be of considerable value. Firstly, determining the maximum torque of a twin-screw extruder is important to reach the highest possible level of productivity. Variation of operating conditions allows this to be maximised. Figure 1 shows a comparison of torque values for different sets of operating conditions. The second example is the critical temperature of material, which can often be a limitation in process design. Knowing the temperature profile of the melted material in detail is important and Figure 2 shows a comparison of different temperature profiles of polymer blends under different operating conditions.
Split approaches Process simulation for compounding is currently split between two different approaches, according to SC-Consultants. “There is general purpose software, mostly in one-dimension aimed at provid- ing quick results, and there is Computational Fluids Dynamics (CFD),” says Ratte. “The first approach is dedicated to practitioners skilled in operating twin-screw extruders. The results are immediately accessible and easily interpreted, which facilitate the development of the material and process in a practical way. The second approach is more suitable for numerical analysts – expert users of CFD code.”
42 COMPOUNDING WORLD | March 2021 He says that the current global economic
situation has provided a boost for engineering process simulation and a tool aimed at performing virtual trials is considered to be highly valuable. “All remote or socially distanced tools are currently well appreciated by the market. So, in 2020 we needed to adapt to provide new tools, such as on-line training with recorded video sessions, tutorials on twin-screw simulation tips and webinars for present- ing special features and/or applications,” Ratte says. Like many parts of the plastics industry, new developments in process simulation are highly likely to be driven by the recycling market, accord- ing to Ratte. “Everywhere in the world, national governments are proposing laws for increasing the ratio of recycled material,” he says. “For example, in 2022 Germany will recycle 63% of its plastics packaging compared with 36% now. In France, an ambitious target of 100% by 2025 is envisaged. Recycled plastics will be a fact of life very soon and this will also be the case for compounding. We are looking at new simulation solutions that will anticipate and consider the variable quality and rheology of input material.” According to SC-Consultants, every user of a
twin-screw extruder can potentially benefit from the application of numerical simulation. In particular, the company says it is possible to undertake considerable process re-engineering as compound- ers improve their understanding of their machine capabilities and that this can lead to new develop- ments. It cites addressing of issues with compound- ing of fibres reinforced compounds as an example. To keep pace with new demands and require- ments it is necessary to continually extend the feature set of process simulation software. “Elasto- mers require specific investigations, especially to fit to a viscosity behaviour model,” says Ratte. “As the viscosity evolution continues and will not be reversed, it is now necessary to add new features to
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