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21.09.2021

Virtual Quality Inspection Optimizes Production of Filter Nonwovens

Nonwoven production received more attention than ever before from the general public in Corona times, because the technical textile is crucial for infection protection. The ultra-fine nonwoven products are manufactured in so-called meltblown processes. A cross-departmental team at the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern is optimizing the entire production chain in the »ProQuIV« project. Simulations help to guarantee the product quality of the filter material despite fluctuations in production.

Nonwoven production received more attention than ever before from the general public in Corona times, because the technical textile is crucial for infection protection. The ultra-fine nonwoven products are manufactured in so-called meltblown processes. A cross-departmental team at the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern is optimizing the entire production chain in the »ProQuIV« project. Simulations help to guarantee the product quality of the filter material despite fluctuations in production.

The abbreviation »ProQuIV« stands for »Production and Quality Optimization of Nonwoven Infection Protection Clothing«. This is because bottlenecks in the production of these materials were particularly evident at the beginning of the Covid 19 crisis. For the meltblown nonwovens, this optimization of the product quality is also particularly difficult because the textiles react very sensitively to fluctuations in the manufacturing processes and material impurities.

Digital Twin Keeps an Eye on the Big Picture
»Meltblown« is the name of the industrial manufacturing process whose ultra-fine fiber nonwovens are responsible for providing the crucial filtering function in face masks. In this process, the molten polymer is forced through nozzles into a forward-flowing, high-speed stream. It is stretched and cooled in a highly turbulent air flow.

»The overall process of filter media production – from the polymer melt to the filter medium – presents a major challenge in simulation,« explains Dr. Konrad Steiner, head of the »Flow and Materials Simulation« department. »In the project, we kept the big picture in mind and developed a completely integrated evaluation chain as a digital twin. In doing so, we take several key components into account at once: We simulate the typical production processes of nonwovens, the formation of the fiber structures and then the material properties – here, in particular, the filter efficiency. This allows us to quantitatively evaluate the influences of the manufacturing process on the product properties.« In each of these individual areas, Fraunhofer ITWM and its experts are among the leading research groups internationally.

Homogeneity of the Material – Fewer Clouds in the Simulation Sky
In the meltblown process, a key factor is the behavior of the filaments in the turbulent, hot and fast air flow. The properties of the filaments are strongly influenced by this air flow. The quality of the filaments – and thus the quality of the nonwovens – is influenced by many factors. Dr. Dietmar Hietel, head of the »Transport Processes« department, knows what this means more precisely in practice. His team has been working at Fraunhofer ITWM for years on the simulation of various processes involving filaments, threads, and fibers. »The focus of the project is the so-called cloudiness, i.e. the non-uniformity of the fiber distributions in the nonwoven,« explains Hietel. »We are investigating the question: How homogeneous is the fabric? Because the quality of the products can be greatly improved if we increase the uniformity. Our simulations help figure out how to do that.«

Objective Evaluation of the Homogeneity of Nonwovens
The researchers also use appropriate image analysis techniques to quantify this cloudiness. The power spectrum plays a special role here. »The cloudiness index (CLI) describes homogeneity complementary to local basis weight and its variance,« describes Dr. Katja Schladitz. She brings her expertise in image processing to the project. »Our CLI ensures a robust assessment of the homogeneity and can thus be used for different material classes and imaging techniques to be used as an objective measure.« The frequencies that go into the CLI calculation can be chosen so that the CLI is meaningful for the particular application area.

Filtration: How Efficient Are the Filters?
For the upscaling to industrial processes such as mask production, the ITWM expertise in filters is also included in the project. The »Filtration and Separation« team led by Dr. Ralf Kirsch has been working for years on the mathematical modeling and simulation of various separation processes.

»What's special about this project is that we calculated the efficiency of the filters for fluctuations of varying degrees in the fiber volume fraction,« emphasizes Kirsch. »This allows us to specify up to what level of cloudiness the required filter efficiency can be achieved at all.« As a current example of this, the figure depicts in the graphic the efficiency of a filter material for N95 masks as a function of the inhomogeneity of the nonwoven.

ITMW Methods Support Across the Entire Process Chain
In »ProQuIV«, digital twins and calculations from Fraunhofer ITWM support a holistic view and better understanding of the processes. The production of technical textiles thus not only becomes more efficient, but the nonwovens can be developed virtually without having to realize this in advance in a test facility. In this way, production capacities can be increased while maintaining or even increase the quality. Together with long-term partners from industry, the research can be put into practice quickly and efficiently.

Simulations save textile companies experiments, allow new insights, enable systematic parameter variations and solve upscaling problems that can otherwise lead to bad investments during the transition from laboratory plant to industrial plant. However, virtual implementation of nonwoven production also opens up new opportunities for optimization at other levels. For example, acoustic insulating nonwovens or even hygiene nonwovens can also be optimized in terms of their product quality precisely with regard to the material properties to be achieved – while taking into account the process fluctuations that occur.

The project is part of the Fraunhofer-Gesellschaft's »Fraunhofer versus Corona« program and was completed in April 2021. The results will flow into several follow-up projects with the nonwovens industry.

Photo: Pixabay
28.04.2020

Meltblown Productive: Fraunhofer ITWM vs. Corona - With Mathematics Against the Crisis

  • Meltblown Productive – ITWM Software Supports Nonwoven Production for Infection Protection

Simulations by the Fraunhofer Institute for Industrial Mathematics ITWM make processes in the manufacturing of nonwovens more efficient. Within the anti-corona program of Fraunhofer the production of infection protection is optimized.
 
Nonwovens production is currently attracting more attention than ever before from the general public, because in times of the corona pandemic, nonwovens are vital for infection protection in the medical sector and also for the protection of the entire population. Disposable bed linen in hospitals, surgical gowns, mouthguards, wound protection pads and compresses are some examples of nonwoven products.

  • Meltblown Productive – ITWM Software Supports Nonwoven Production for Infection Protection

Simulations by the Fraunhofer Institute for Industrial Mathematics ITWM make processes in the manufacturing of nonwovens more efficient. Within the anti-corona program of Fraunhofer the production of infection protection is optimized.
 
Nonwovens production is currently attracting more attention than ever before from the general public, because in times of the corona pandemic, nonwovens are vital for infection protection in the medical sector and also for the protection of the entire population. Disposable bed linen in hospitals, surgical gowns, mouthguards, wound protection pads and compresses are some examples of nonwoven products.

IEspecially in intensive care and geriatric care, disposable products made of nonwovens are used due to the special hygiene requirements. At the moment there are clear bottlenecks in the production of these materials. For the meltblown nonwovens class, however, it is difficult to increase production efficiency because meltblown processes are highly sensitive to process fluctuations and material impurities.
 
Although nonwovens are not all the same, the rough principle of their production is relatively similar to all industrially manufactured nonwovens: molten polymer is pressed through many fine nozzles, stretched and cooled down in an air stream and thus deposited into the typical white webs. "Meltblown" stands for the submicron fiber process whose nonwovens are responsible for the decisive filter function in face masks.
 
With meltblown technology, nonwoven fabrics are produced directly from granules. A special spinning process in combination with high-speed hot air is used to produce fine-fibered nonwovens with different structures. The fibers are highly stretched by the turbulent air flow. During this process they swirl in the air, become entangled and fall more or less randomly onto a conveyor belt where they are further consolidated - a very complex process. Nonwovens manufacturers around the world are striving to massively increase their production capacities.
 
Digital Twin Optimizes Meltblown Process    
This is where the software of the ITWM comes into play. "Our Fiber Dynamics Simulation Tool FIDYST is used to predict the movement of the fibers, their falling and the orientation with which they are laid down on the conveyor belt. Depending on the process settings, turbulence characteristics are generated and thus nonwoven qualities are created that differ in structure, fiber density and strength," explains Dr. Walter Arne from the Fraunhofer ITWM. He has been working at the institute for years on the simulation of various processes involving fibers and filaments.

The methodology is well transferable to meltblown processes. In these processes, one of the specific features is the simulation of filament stretching in a turbulent air flow - how the stretching takes place, the dynamics of the filaments and the diameter distribution. These are all complex aspects that have to be taken into account, but also the flow field or the temperature distribution. The simulations of the scientists at the Fraunhofer ITWM then provide a qualitative and quantitative insight into the fiber formation in such meltblown processes - unique in the world in this form when it comes to simulate a turbulent spinning process (meltblown).

Nonwoven Manufacturers benefit from Simulation
What does this mean for the industry? The production of technical textiles becomes more efficient, but the nonwovens can also be developed without having intensive productions tests in a real facility. This is because the simulations help to forecast and then optimize the processes using a digital twin. In this way, production capacities can be increased while maintaining the same product quality. Simulations save experiments, allow new insights, enable systematic parameter variations and solve up-scaling problems that can lead to misinvestments during the transition from laboratory to industrial plant.

Making a Contribution to Overcome the Crisis With Many Years of Expertise
"We want to demonstrate this in the project using a typical meltblown line as an example - for this we are in contact with partner companies," says Dr. Dietmar Hietel, head of the department "Transport Processes" at the Fraunhofer ITWM. "Within the framework of Fraunhofer's anti-corona program, we want to use our developed expertise and our network to contribute to overcome the crisis", reports Hietel. His department at the Fraunhofer ITWM has been pursuing research in the field of technical textiles for around 20 years. Due to its current relevance, the project not only got off to a quick start, but the implementation and results should now also be implemented quickly: The project is scheduled to run from April 15th 2020 to August 14th 2020. The kick-off meeting took place on April 17th 2020 via video conference.
 
The project "Meltblown productive" and the results are certainly interesting for nonwoven producers. The production of many mass products has often been outsourced to Asia in the past decades; the nonwovens manufacturers remaining in Germany and Europe tend to focus more on high-quality technical textiles. In the medium and longer term, this will also be a scientific preliminary work when production capacities in Germany and Europe are expanded by new plants. One lesson to be learned from the crisis will also be to reduce the dependence on producers in Asia, especially as a precautionary measure for crisis scenarios.

Source:

Fraunhofer Institute for Industrial Mathematics, ITWM