Fraunhofer Institute for Industrial Mathematics ITWMHow must the manufacturing process for a filter nonwoven be modified so that the final product delivers the required filtration performance? We address this challenging question with a holistic modeling approach.
Modellierung Prozessketten für Filtermedien: Die Kombination aus Modellierung und Simulation von Prozess und Produkt hilft dabei die Markteinführungszeit zu verkürzen.
From Process to Product
The combination of process and product modeling and simulation helps to shorten time to market.
© Fraunhofer ITWM / iStockphoto
Model-Based Optimization of Process Chains for Filter Nonwovens
Simulation and Modeling for the Manufacture of Filter Media: From Nonwoven Fabric Production to Optimal Filter Performance
Like virtually all filter materials, nonwovens used for air filtration must meet several requirements simultaneously: They should offer as little air resistance as possible, reliably capture aerosols, and have a long service life. These desirable material properties are closely linked to the parameters of the manufacturing process. However, this relationship is complex and makes it difficult to specifically optimize processes for the production of better products. We therefore combine our expertise in simulating nonwoven fabric processes with our many years of experience in modeling filter properties. This allows us to develop new filter media more efficiently and bring them to market faster.
Simulation of Nonwoven Processes
The starting point of the process chain model is nonwoven production, specifically the fiber formation process. Various production methods, such as meltblowing, electrospinning, spunbond, or airlay processes, can be simulated. To this end, we develop both detailed simulation tools (FIDYST, VISPI) and accelerated simulations based on effective models (SURRO). The models capture the relevant equipment and process parameters and provide information on, among other things, basis weight and fiber diameter distribution. Specific process steps, such as electrostatic charging via hydrocharging, can also be integrated.
Model-Based Prediction of the Properties of Filter Materials
The results of the process simulation serve as input parameters for evaluating flow resistance and fraction separation efficiency. Adapted analytical models are used for this purpose. Compared to 3D simulations on the microscale, these models require virtually no computational effort and yet remain flexible in their application due to their parameterization.
By classifying nonwovens into categories with comparable process conditions, the calibration effort can be significantly reduced. At the same time, the modeling also accounts for material-related changes such as compaction during satin finishing, calendering, or pleating.
Prediction of the fractional efficiency of an electret nonwoven fabric for the calibrated reference material. The circles represent measured values, and the lines represent the efficiencies calculated by the model.
Prediction of the fractional efficiency for a material from the same category. The colors correspond to the media face velocity.
Specific Application Example: Next-Generation FFP Masks
One specific application of the process chain model was the further development of filtering face pieces (FFP2). The goal was to significantly reduce breathing resistance while simultaneously increasing filter performance.
In the project »Sula« (abbreviation for German »Breathe Safer and Easier«), funded by the Federal Ministry for Economic Affairs and Climate Action (German BMWK) and running from 2022 to 2025, we worked closely with the companies Reifenhäuser Reicofil (a manufacturer of nonwoven fabric production lines) and IMSTec GmbH (a developer and manufacturer of technical systems, including those for protective masks). The results show that modeling the process chains can save many hundreds of work hours compared to traditional, experiment-based development.
A Modular Approach With a Wide Range of Applications
The concept of model-based mapping of process chains is not limited to nonwoven fabrics for air filtration. It can also be applied to materials for liquid filtration.
Furthermore, this approach is well-suited for specifically improving the quality of nonwoven fabrics – for example, by ensuring a uniform distribution of the fiber material. This opens up additional opportunities to make manufacturing processes more efficient and to specifically optimize product properties.