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|Title:||Study of structure, properties and manufacturing conditions of staple yarns in a modified ring spinning system||Authors:||Feng, Jie||Keywords:||Spinning machinery.
Hong Kong Polytechnic University -- Dissertations
|Issue Date:||2013||Publisher:||The Hong Kong Polytechnic University||Abstract:||Ring spinning is the most widely used spinning method because of its high yarn quality and flexibility in processing various fiber materials. Over the past few decades, many spinning methods have been developed in order to develop novel yarn features or improve yarn qualities. In recent years, a novel spinning technique has been developed by incorporating a rotor-pin type false twisting device into the conventional ring frame. This spinning technology has been successfully used for the production of coarser cotton yarns (7-30Ne) with improved yarn and fabric performance. However, due to the low yarn strength of finer cotton yarns and large spinning tensions generated, the current technology has some difficulties in spinning finer cotton yarns with an acceptable spinnability and the same good properties as those achieved for 7-30Ne. In the present study, a newly developed friction-belt type false twisting device was employed for production of finer cotton yarns. A comparative study between the rotor-pin and friction-belt type false twisting devices in the production of coarser modified yarns was carried out in terms of twist level, spinning tension and yarn properties. The measurement results showed that with the similar twist level, the two systems produce comparable yarn properties but a much lower spinning tension force was presented for the friction-belt type false twisting device, indicating an improved spinning stability. It was observed that the direction of yarn spinning tension acting on the spinning triangle in the friction-belt type modified system has an inclined angle relative to the vertical axis of the nip line of front rollers. This is different from the assumption of the vertical spinning tension presented in the earlier studies. Thus an extension of theoretical model was developed with a consideration of the inclined spinning tension force by using the energy method. In this study, the spinning triangle was theoretically analyzed and the effects of inclination angle on yarn properties were investigated. The effects of geometrical shape of spinning triangle on the fiber tension distribution in the spinning triangle were also examined with and without the consideration of fiber buckling. The results were then compared with those obtained by the earlier model. A new theoretical model was originally proposed to quantify yarn twist and tension distributions for two types of friction-belt type false twisting device, namely single belt type (SBT) and double belt type (DBT) false twisting devices. In this study, equations of dynamic equilibrium were established under the steady state and numerical simulations were then carried out for the quantitative predictions of yarn dynamic performance as functions of machine parameters. In order to validate the developed theoretical models, yarn twist and tension on both sides of false twisting device were online measured by using the calibrated high speed camera and tension meter systems. The experimental results indicated that the theoretical models can estimate yarn twist and tension distributions with good accuracy and reliability. The simulated yarn paths generally fit well with the actual yarn paths with higher correlation coefficients. In addition, influences of various system parameters on yarn twist and tension distributions on both false twisting devices were numerically examined. This study provided quantified information about the spinning mechanism of the newly developed modified system.
Experimental investigations on finer cotton yarns (80Ne and 100Ne) were systematically carried out by using combined statistical methods of the fractional factorial methodology and response surface methodology. Analyses on the modified spinning geometry and process were carried out to identify potential influencing spinning parameters on modified yarn properties. Fractional factorial experiments were conducted to study their significances of effects for identifying significant parameters. Then the quantitative relationships between the significant parameters and finer modified yarn properties (80Ne and 100Ne) were examined by using the response surface method and explicitly formulated by the response surface equations with higher fitting coefficients. Verification experiments showed that the response surface equations can be applicable of predicting and explaining the actual relationships between the significant parameters and physical properties of finer modified yarns. The significant parameters were finally optimized by using the desirability function and overlaid contour plot for maximizing yarn strength with lower yarn hairiness. Compared with the finer conventional yarns, the finer modified yarns produced with the optimized parameters show significantly improved yarn tenacity and hairiness with lower yarn snarling. In the present study, the structures of finer conventional and modified yarns (80Ne) were investigated by using the tracer fiber technique, cross-section technique and scanning electron microscope (SEM). The fiber configuration, fiber radial position, fiber orientation angle, fiber packing density and yarn surface appearance were quantitatively evaluated for both types of yarn. Results showed that the modified yarn possessed relatively higher fiber packing densities and a more compact yarn structure with less hairiness on the smooth surface. In addition, the finer modified yarn presented a more irregular and complicated fiber path and fibers in the modified yarn tended to be distributed relatively closer to yarn center and alter their radial positions more frequently with relatively greater migration magnitude. These structural characteristics experimentally explained for the mechanism of the increased yarn strength, abrasion resistance and reduced yarn hairiness. With the optimized spinning parameters, finer modified yarns (80Ne) were produced and their physical properties in the cop and cone forms were examined. Results indicated that the modified yarns have significantly improved tenacity, hairiness and abrasion resistance. With these advantages in yarn properties, woven fabrics were then produced by the modified yarns and their properties were evaluated and compared with the conventional fabrics. Results showed that the modified fabrics possessed great advantages in bursting strength, tearing strength and abrasion resistance.
|Description:||xxv, 283 leaves : ill. (some col.) ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577P ITC 2013 Feng
|URI:||http://hdl.handle.net/10397/6463||Rights:||All rights reserved.|
|Appears in Collections:||Thesis|
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