Analyses On The Internal Structures And Properties Of Low Torque Singles Ring Yarn

Low torque spinning technology, developed in Hong Kong Polytechnic University, is a novel spinning technology which is achieved by installing a modification unit, namely a false twisting device, between the front rollers and the yarn guide on the conventional ring frame. The resultant yarn has low residual torque, lower twist level, high yarn strength and low hairiness. The structure of yarns plays a rather important role in the properties of yarns and the finial garments, thus it is essential to give a deep analyses on the structure of the novel yarns. This study aims to the further investigation on the structural characteristics of low torque singles ring yarn as well as the effects of two major spinning parameters on the properties of low torque singles yarns.A continuous and universal system to acquire spatial distributions of multiple yarn structural parameters and a three dimensional (3D) configuration of tracer fibers in the yarn simultaneously was developed in order to make a deep analysis on the structure of the novel yarns. Besides the measurement of the yarn profile and diameters on two perpendicular planes, twist distributions of the yarn in short segments, fiber spatial orientation angle, radial position,3D configuration and other migration characteristics can be all measured in a simultaneous fashion. The present multifunctional system has been verified through series of experiments on various types of yarn and comparative study on structural analysis of low torque singles ring yarn and conventional yarn.The direction of fiber orientation angle was proposed as it is very important for the unique structural features like low torque yarns with local reversion in fiber segment. A method to evaluate fiber radial position was also suggested by assuming the yarn cross section as an ellipse approximately. From the analyses on the structural characteristic parameters of ring spun and low torque yarns with identical counts and twists, the majority of fibers in the low torque yarns follow a configuration of deformed non-concentric helixes with the axis of helix varying significantly in space. In contrast, most fibers in ring spun yarns have two helix forms, that is, concentric cylindrical helix and concentric conical helix where the helical axis coincides with the yarn axis. Furthermore, many segments of fiber in the low torque yarns exhibit local reversion of helix direction in a random fashion, that is, there are significant fiber segments with negative fiber orientation angles, thus the mean orientation angle of individual fibers in the low torque yarn is often smaller than that of the ring spun yarns at the same radial position. Most fibers in the low torque yarn tend to be distributed close to the yarn center, and alter their radial positions frequently with relatively greater migration amplitude.An apparatus for preparation of yarn samples under different axial tensions for fiber packing density measurement by microscope was developed in this study to analyze the fibers distribution in yarn cross section. It can be used to prepare various samples under various axial tension, thus the stability of the experiment can be improved. The practicability of the device was verified by series analyses on the fiber packing density on cross section of Tencel yarns as well as wool yarns. The comparative studies between low torque singles yarn and normal ring yarns show that the fiber packing density in ring yarn cross section is much more sensitive to the external tension, especially the ring wool yarn. Under the same condition, the packing density of fiber in the low torque yarn is much bigger than that of the ring yarn. Fibers in the cross sections of low torque yarn distribute more concentrated, which is consistent with the analyses on the 3D fiber configurations. Meanwhile, the relationship between the fiber packing density and the yarn radial position can be plotted.As the cross section of fibers varies with the change of helical angles which were influenced by the yarn twist significantly, a modified method to evaluate the fiber packing friction on yarn cross section was proposed by taking the elliptical cross sections of fibers at different yarn radial positions into account. Result shows that there is no significant difference comparing with the traditional method in which perfect circular cross sections of fibers were used. Meanwhile, helical angle increases with the increase of yarn twist, then the fibers contained in each fibrous layer decreases according to the present theory, and the area of those fibers will increase, thus there is no obvious changes on the packing friction of each fibrous layer. In addition, based on the energy method, discrete-fiber-modeling and short-path hypothesis, the packing density of fibers as the function of radial position was introduced in a model to evaluate the tensile properties of low torque yarns. Modulus of strain-stress curve of ring yarn is much lower than that of the fiber materials while the strain-stress curve of low torque yarn and the fibers are almost identical. It shows that a significant portion of fibers in ring yarns didn't contribute to the yarn strength during the yarn rapture process while most of fibers in low torque yarns were stretched simultaneously, thus the strength efficiency of the fiber was improved greatly. Although there is still distance between the predicted results and the real data, yarn tensile properties can be explained qualitatively by combining with the analyses on internal structures of yarns.As another important part, the effects of two important parameters in low torque yarn spinning, D/Y ratio and twist, on the yarn properties were analyzed by using Response Surface Methodology. Based the results, two groups of low torque singles yarns were produced and compare the properties with normal ring yarns in terms of cops and cones made under same conditions. At the same time, properties of knitted fabrics made by low torque yarns and ring yarns were evaluated, such as spirality, bursting strength, air permeability, and so on. Results show that both the tenacity and wet snarlings of low torque yarns increase with the increase of twist level in the given range while the yarn hairiness decreases. With the increase of the D/Y ratio, the tenacity of low torque yarns trends to be decreased, particularly on higher twist range. And the number of wet snarlings and hairiness S3 decreases with the increase of D/Y ratio to some extent. Comparative study on the yarn properties between the low torque yarn and normal ring yarn shows that the exciting spinning ability and physical properties of low torque yarn on reduced yarn residual torque and hairiness and improving yarn strength under low twist level. Spirality after repeated washing cycles was significant improved for the low torque knitted fabrics. Furthermore, the bursting strength of low torque knitted fabric is much greater than that of the ring knitted fabric with same twist level, and close to that of the ring fabrics with normal twist. The air permeability and anti-pilling property of low torque fabrics is also better than the normal ring fabrics. Those properties can be explained by the unique structural features of low torque singles yarns. Local reversion phenomenon in the fiber segments contributes to the decrease of yarn residual torque. The existence of the deformed non-concentric helices with varied helix radius facilitates the enhancement of frictional force between fibers arising from the increment of lateral pressure, and then significantly improves the cohesion between fibers, thus minimizing the chance of fiber slippage during the yarn rupture process.