Optimizing Production Processes of Nonwovens with FIDYST
Spunbond, meltblown, and airlay processes can be optimized by using FIDYST, the Fiber Dynamics Simulation Tool developed by the Department Transport Processes (TV) of the Fraunhofer ITWM in Kaiserslautern – a software that simulates fibers driven by air and their contacts with machinery parts of the plant. By evaluating the CV values of the mass regularity the quality of the nonwoven is automatically judged. Its purpose is the simulation of the fiber dynamics in turbulent air flows in a very general way. Hence, there is a broad spectrum of different applications for it, but FIDYST has become most important for production processes of technical textiles.
The optimization of nonwoven production processes using FIDYST follows the procedure simulation, validation, and optimization. First, a reference scenario of the production process is simulated with FIDYST. Second, the simulation results are validated by comparing them with measurements. Then the influencing variables on the process are identified. In particular, the effect of all determining factors on the process is quantifiable. This process analysis can be used for an innovative redesign of the plant or an optimization of the operating conditions, respectively. In practice, the optimization goals are often conflicting. On the one hand, manufacturer wish to run the production processes with maximal speed and high quality of the end products. On the other hand, they aim at low energy and low raw material consumption. Using simulations the nonwoven production processes can successfully be designed for optimal operating conditions.
In the beginning of the simulation chain the computer-aided design (CAD) model of the plant is constructed. Based on the process parameters of a reference scenario a computational fluid dynamics (CFD) simulation of the air flow is performed. Since FIDYST runs with an open documented data format called EnSight Gold Case Format, any flow solver can be used for the CFD simulations. In particular, the commercial simulation tools of the company ANSYS (Fluent, CFX) support this data format. FIDYST imports the results of the CFD calculation and displays them in a preview window. In the background the imported geometry of the machinery is automatically pre-processed for the fiber dynamics simulation.
In the next step the development engineer specifies the material parameters of the fibers. At least titer, density of the fiber material, and elasticity modulus must be entered by the engineer. For simulation experts FIDYST offers the possibility to define advanced settings, e.g., time-varying material parameters (mean velocity of the fibers at the inlet or even the inlet positions, etc.) can be specified.
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