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Spinning-in fibres - A quality factor of rotor yarns
Abstract
The physical-mechanical properties of yarns, similar to those of other solid matters, are a function of their structure. Yarns are composed of fibres of different lengths and shapes, resulting in yarn spirals with varying radii, which can form kinks at intervals, and even project from the yarn surface. Therefore, it is not the overall length of the fibre that contributes to the yarn strength, but only the spun-in part of it. In this work the spinning-in coefficient KF was determined for carded and combed rotor-spun yarns, in accordance with the theory of spun-infibres in yarns. Measurements have shown that the inner structure of cotton rotor-spun yarns, presented by the value of the coefficient varies with the spinning system used The KF values for combed yarns show that most of the fibres were incorporated into the yarn, which gives better physical-mechanical characteristics. In carded yarns, this coefficient is slightly lower, indicating a greater number of looped fibres and fibres incorporated into the yarn with less than half their lengths.
In this paper, a linear dynamic model was established for rotor-spun composite yarn spinning process by force analysis. Numerical approach to the model was calculated. By simulating the trajectories and phase diagrams of convergent points of staple fibers and filaments, the stability of rotor-spun composite yarn spinning process was obtained, which is effective to improve the efficiency of production. The presented study provides a general pathway to understand the motion of convergent point during rotor-spun composite yarn spinning process.
There have been many attempts to pre-determine the yam quality, taking in consideration, besides the fibre type, also the spinning system and machinery working conditions taking part in the process of yam manufacturing. All these attempts can be divided into theoretical ones, when complex mathematical models are obtained, and arithmetically-empirical ones, based on a large number of experimental measurements. One of such attempts is the method by AX Solovjev, which refers to ring spinning. The paper explores the possibility of applying this method for determination the limits of spinnability and tensile properties of OE yams spun from microfibres, which are the basis for the predetermination of the quality of this yarn type.
The standard highest fineness of rotor-spun yarns from 50 to 20 tex can be changed by the use of the combed cotton slivers and the chemical fibre slivers, so-called Ricofil yarn on "Rieter" equipment, or however, by the use of the finer micro fibres in the cotton fibres blend and absolutely. In this paper the mechanical characteristics have been analysed they are: the breaking strength, the relative breaking extension and the work of breaking strength. Besides, the linear irregularity of yarn by thickness has been shown (Uster) with a number of irregular spots (thin spots, thick spots and neps) at 1000 m of yarn as well as their hairiness. According to the analysis of the results, the dependance of some quality parametar from the number of fibres at the cross-cut and the twisting of the rotor-spun yarns is defined and, according to it the relations for projecting the physical-mechanical characteristics of yarns are set.
The free and uncontrolled flight of fibres from one end of the fibre transport channel to the rotor wall is an important factor affecting the quality of rotor spun yarn. It has been reported that reducing this distance will improve the yarn's quality significantly. In this research, the above distance has been reduced further with three designs in comparison to commercial rotor boxes, and yarn properties such as strength, evenness, imperfections, hairiness, and abrasion were measured. The M1 code was given to the standard model, and M2 to M4 were given to the three proposed designs respectively. The test results showed that tenacity, strain and energy at the peak did not vary significantly, but were at a maximum for the M3 model. The hairiness of the yarn was at a maximum of 4.3 for the M4 model, in comparison to a minimum of 1.2 for the M3 model and 1.7 for the M1 model. Although the machine twist for all the models was the same, the twist of the yarn measured by the untwist-twist method was different. It was at a minimum of 369 t.p.m. for the M3 model, and a maximum of 466 t.p.m. for the M4 model, in comparison to 418 t.p.m. for the M1 model. Due to the different levels of yarn twist, the yarn's abrasion resistance may vary. It was at a maximum of 155 for the M3 model, and a minimum of 90 for the M1 model. According to the test results, it was concluded that the M4 model would produce a yarn with a maximum level of twist and hairiness. On the other hand, the M3 model would produce a yarn with a minimum level of twist and hairiness and a maximum abrasion resistance of the yarn, which could be useful for the next processing stages.
A new method of modelling fibre migration in a staple-fibre yarn has been developed. The method uses a Markov process and allows all of the main features of yarn structure, such as irregularities of fibre disposition in a cross-section, unevenness, and hairiness, to be modelled. A novel experimental method is reported which allows the paths of individual fibres in yarn cross-sections to be defined in three-dimensional space. It has been shown that the fibre-migration can be considered as a Poisson's flow of events, and that fibre migration characteristics can be expressed in terms of a transition matrix. The method is able to describe a wide range of different yarn structures. The model would be improved by taking account of the fact that fibre migration between zones is not a memory-less process, but the problems associated with making this improvement have yet to be resolved.