Abstract:

Objective The uniformity of airflow inside the air duct of the airflow web forming machine affects the trajectory of fiber movement, thereby affecting the uniformity of fiber web laying. The study aims to investigate the influence of the air duct structure of the airflow web forming machine on the uniformity of air flow, improve the structure of the air duct of the airflow web forming machine, and at the same time, based on determining the optimal air duct model, study the motion of fiber length under the conditions of the optimal model, providing reference for the design and production of the air flow forming machine.

Method Finite element analysis was adupted to simulate the air duct of the airflow web forming machine. Using SolidWorks software to establish a model of the airflow web forming machine's air duct, the model was imported into the commercial software Cradle CFD for simulation calculation. Boundary conditions were set according to actual working conditions, and simulations were conducted to draw velocity and pressure cloud maps for different situations. The Choi model was adopted to describe the bending motion of fibers, and the motion trajectory cloud map of fibers was drawn. The changes in the motion trajectory of fibers with two different lengths in the flow field were compared.

Results The analysis results indicate that the maximum velocity of the three types of air duct tail opening structures is generated at the same position, but there is a significant difference in their velocity distribution. The airflow distribution of the air duct structure with a tail opening of 10° is more uniform compared to the air duct structures with openings of 20° and 30°, and its average wind speed of 21.8 m/s occupies more than half of the duct. Meanwhile, in the comparison of the airflow velocity cloud maps at the outlet, the average velocity of the air duct model with an opening of 10° can fully cover the width direction of the air duct outlet and occupy more than two-thirds of the area. The air duct model structure with an opening of 20° does not fully occupy the width direction, while the air duct model structure with an opening of 30° has an average velocity that is also fully covered in the width direction, but occupies a smaller area. Therefore, from the above comparison, it can be concluded that the airflow situation in the air duct with an opening of 10° is better than the other two. The coupling calculation of the airflow field model with an opening degree of 10° and the fiber model of the airflow web forming machine shows that the fibers with a length of 15 mm can be uniformly dispersed without entanglement or accumulation, and remain dispersed at the outlet. Fibers with a length of 30 mm will tangle and accumulate after moving in the airflow for a period of time. This entanglement and accumulation will continue all the way to the outlet of the air duct and be blown out of the air duct in the form of entanglement and accumulation. Fibers with lengths of 45, 60 and 75 mm will also show tangling at the outlet position, and the tangling of 75 mm fibers at the outlet position is more severe.

Conclusion The distribution structure of the airflow web forming machine has a significant influence on the airflow field. Adopting an appropriate air duct structure can make the airflow field more uniform. When the opening degree of the air duct of the air flow forming machine is 10°, the airflow field is the most uniform and the outlet velocity is also more appropriate. Fibers with a length of 15 mm can be blown out more evenly from the air duct outlet compared to fibers of other lengths.

Key words: airflow web forming machine, air duct, flow field, structure model, fiber movement morphology