|Title:||Production, properties and structures of short staple low torque singles ring yarn for weaving|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Spun yarns -- Testing.
|Department:||Institute of Textiles and Clothing|
|Pages:||xxiii, 265,  leaves : ill. ; 31 cm.|
|Abstract:||One of the disadvantages related to the conventional ring spinning process is that ring spun yarn possesses high residual torque, which may cause distortion in knitted fabric and woven fabric, bring about difficulties in handling any post-spinning operation, and also produce defects in fabrics. The project is thus conducted with an aim to probe the possibility of producing low torque ring weaving yarns for industrial application by a torque reduction device attached on the conventional ring machine. A preliminary study of the torque reduction device was made. The torque reduction device was composed mainly of a false-twisting system including a pair of spaced rotors, a false-twister in tangential frictional contact with each of rotors and magnetic means. The experimental results show that the resultant yarns had reduced residual torque through modifying yarn structure directly during yarn formation, which eliminates any additional step after the spinning process. In addition, with a false-twister installed between the front roller and the yarn guide, the yarn spinnability is improved. As one of the most important parts for yarn spinning mechanism investigation, a study is conducted on the geometry of ring spinning triangle and its effect on the yarn torque. The observation of spinning triangle indicates that the geometry of spinning triangle in low torque ring yarn exhibits some unique characteristics such as symmetric structure, short height and multi-bundle of fibers. A modified energy approach is presented to study the distribution of fiber tension force in the spinning triangle under the applied of yarn spinning tension. The shape of spinning triangle is represented by a shape parameter newly introduced in the analysis. The effects of shape of spinning triangle on the fiber stress distribution at the spinning triangle are investigated including fiber distributed in the form of multi-bundle and without multi-bundle fibers. The simulated results indicate that the distribution of fiber tension force is influenced obviously by the shape of spinning triangle. A theoretical analysis of the fiber tensile stress distribution within the yarn and its effect on the yarn torque is thus conducted on the basis of the translation of fiber tension at the spinning triangle into the fiber tensile stress within the yarn. A system for investigation of the fiber configuration in staple yarns has been developed in this study. The main feature of the system is that it can capture and store consecutive images of single tracer fiber, thus the image acquisition becomes faster and more accurate. It is also helpful for the analysis and processing of the tracer fiber image information. The investigation of yarn structures demonstrated that low torque ring yarn possesses ring like appearance, compact structure, wrapper fibers in vertical or opposite direction, some parts of fibers arranging in opposite direction to the yarn twist and higher rate of fiber migration, which contributes to the reduction of yarn residual torque and yarn hairiness, as well as to the increase of yarn strength when low twist level was adopted in low torque ring yarns. Statistic models have been developed for the relationship between yarn properties and spinning parameters with the help of Fractional Factorial Methodology and Response Surface Methodology. The model adequacy assessment of Response Surface Methodology demonstrated that the developed model exhibits a good predicating accuracy and this model can reflect the actual relationship between yarn properties and yarn twist and speed ratio. The optimum spinning parameters are found, based on the developed models coupled with the desirability function and overlaid contour plot. The properties of low torque ring yarn and the resultant fabric are comprehensively investigated. The test and analysis exhibit some exciting results of low torque ring yarn with great reduction of yarn snarling and yarn hairiness. Even using low twist level, low torque ring yarn can still maintain its comparable yarn tenacity and evenness to conventional ring yarn with normal twist level. The results also demonstrate that low torque ring yarn fabric exhibits improved denim fabric and twill fabric appearance, a fuller, thicker and more smooth hand. The investigation of the effect of yarn torque on the surface smoothness of denim fabric was conducted theoretically and experimentally. The theoretical analysis results indicate that reducing yarn residual torque, particularly weft yarn residual torque will decrease the difference of the angle of twist between warp yarn sections. As a result, the yarn buckling unevenness may be decreased, which endows denim a more smooth surface and thus decrease the problem of 'small snake' pattern on denim fabric. The experimental study demonstrates that the appearance of the denim fabrics has been greatly improved by using the low torque ring yarns as weft yarns.|
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