Airflow simulation in nozzle for hairiness reduction of ring spun yarns. Part Ⅰ: Influence of airflow direction, nozzle distance, and air pressure

摘要

An air nozzle having a axial angle of 50° and inner diameter of 2.2 mm was placed below the front roller nip in a ring frame, at various distances. Simulation of the airflow pattern inside the nozzle provides some useful insight into the actual mechanism of hairiness reduction. A CFD (computational fluid dynamics) model has been developed to simulate the airflow pattern inside the nozzle using Fluent 6.1 software, to solve the three-dimensional flow field. To create a swirling effect, four air holes of 0.4 mm diameter are made tangential to the inner walls of the nozzle. Airflow directions viz., against and along the direction of yarn movement are studied by changing the nozzle position, and the best results are obtained for the former case. Thirty tex Z-twisted ring spun yarns were produced with and without nozzle and tested for hairiness, tensile, and evenness properties. The total number of hairs equal to or exceeding 3 mm (i.e., the S3 values) for yarn spun with nozzle (NozzleRing yarn) is nearly 36—58% less than that of ring spun yarns (without placing nozzle), while both the yarn types show little difference in evenness and tensile properties. Hairs are wrapped along the direction of twist in the NozzleRing yarns. It is observed that air pressure, distance of the nozzle from the nip of the front roller, and direction of airflow affects the hairiness. An air pressure of 0.5 kgf/cm~2 (gauge) is found sufficient to reduce S3 values. Finally, based on the airflow simulation inside the nozzle, a mechanism of hairiness reduction has been proposed.