Study On The Drafting Force And Fibers Movement On Drawing Frame

Drafting exists in several processes of the textile processing. The quality of the drafted slivers performance is the primary indicator which is used to evaluate the effects of the drafting. Therefore, the study on drafting is aimed to obtain better yarn qualities. The study on the drafting force is the key issue in the research of drafting theory. The drafting force and its CV not only reflect the process of drafting, but also indirectly indicate the quality of the output slivers. By simulating dynamic drafting through static drafting, drafting force was indirectly studied. Then the draft ratio of the back drafting zone could be predicted when slivers of different raw materials and linear densities were processed, which provided valuable and theoretical references to optimize the assorting of raw materials and processing parameters. There was a close relation between fiber accelerated points and the output slivers unevenness. The changes of fiber accelerated points were mainly reflected by the average position and the CV of the fiber accelerated points. So it was necessary to choose a suitable model for the distribution of fiber accelerated points and the model would conduce to the research of fiber accelerated points distribution. For the qualities of the output slivers, the two key issues of draft, drafting force and fiber accelerated points, have been studied in this thesis.In this thesis, an on-linet system for measuring the drafting force was developed, which can provide a hardware support for the study on the drafting force. By static drafting base on stretch tester, the relationship between the tensile strength and drafting force were studied and the relation-ship model was developed to simulate the dynamic drafting. According to lots of experiment data of fiber accelerated points, the factors affecting fiber accelerated points were analyzed. A model of the distribution of fiber accelerated points was developed by curve fitting.There were five chapters in this thesis. Chapter 1 introduces the background and significance of the study. The existed researches on the drafting force were described. The principles of different drafting force testers were depicted and analyzed. The researches of fiber accelerated points were expatiated and some problems were discussed.In chapter 2, based on the analysis of some representative drafting force testers, a new on-line measurement system of drafting force was developed. When the on-line measurement system was used on the drawing frame, the pressure bar in the front drafting zone was utilized. This also highlights its advantages closed to the actual production. The measuring system mainly includes two weighting sensors, a digital measurement controller, a pressure bar, a computer and software. The structure and principle of the measuring system were described detailedly. The principle of resistance strain type weighing transducer was explained. The disequilibrium problem between two weighting transducers was solved when two weighting transducers were connected in parallel. The signals of drafting force collected by the measuring system were processed by the orthogonal time-frequency wavelet filter. The stress on the on-line measurement system was analyzed. There was a linear relationship between the drafting force and the pressure of the bar acting on weighting sensors, which was proved by experiments.In chapter 3, the factors affecting the drafting force on drawing frame were studied, and the relationship between drafting force, the CV of drafting force and the CV of output slivers were analyzed. Experimed results showed that:the mean drafting force has a good linear relation with the linear density of input slivers. In addition, the drafting force of rayon sliver is higher than that of cotton sliver, because fiber qualities are different. With the increase of draft ratio, the drafting force increased rapidly and then decreases slowly. The trend of drafting force changing with draft ratio is opposite to the trend of the CV of drafting force and the CV of output slivers. As the surface speed of front roller increases, the drafting force increases, and the CV of drafting force and the CV of output slivers both decrease. The unevenness of output sliver usually corresponds to the CV of draft force, while the lower the CV of draft force, the lower the unevenness of output slivers.The static drafting based on stretch tester was also studied in chapter 3. Top clamper and bottom clamper acted as front rollers and back rollers. The affenuation process of the sliver becoming fine is regarded as the process of the sliver drafted under different draft ratio. The model of the relation between tensile elongation and draft ratio was developed, which was verified by experiments. The relationship of tensile strength and the elongation could be converted to the relationship of tensile strength and draft ratio by the model. The curve of tensile-draft ratio and the curve of drafting force-draft ratio could both be fitted using Freundlich equation, the similar trend changing with draft ratio is based on the theory that uses tensile strength to simulate drafting force. In the area of low draft ratio, the corresponding draft ratio is similar, where the maximum tensile strength and drafting force are obtained. The draft ratio, where the maximum tensile strength emerges, is related to the linear density of the input slivers. With the increase of linear density of input sliver, the draft ratio increases. The draft ratio tends to a number and does not keep rise on. In this thesis, this draft ratio is 1.48 when rayon sliver was used. The draft ratio where the maximum tensile strength located is known, and then the draft ratio of back drafting zone can be set when a definite linear density of the material was stretched. The drafting force corresponds to the unevenness of output sliver, while the higher the drafting force, the lower the unevenness of output slivers usually. The method was proved by experiments.In chapter 4, fiber accelerated points were studied on drawing frame. The relationship between fiber accelerated points and the unevenness of output sliver was described and the factors affecting fiber accelerated points were analyzed. The effects of the linear density of input sliver and draft ratio on the average distance and CV of the fiber accelerated points were studied. The research has shown that, when the draft ratio is fixed, with the increase of the linear density of input slivers, the average distance to the front roller grip decreases, the CV of the fiber accelerated points decreases, the unevenness of the output slivers decreases; when the linear density of input slivers is fixed, with the increase of draft ratio, the average distance to the front roller grip decreases, the CV of the fiber accelerated points increases, the unevenness of the output slivers increases. Base on the data about the fiber accelerated points, the Lorentzian distribution was found to be suitable for the distribution of fiber accelerated points by fitting method. After compared with Exp3P2 distribution, Lognormal distribution and Parabola distribution using the different experiment datum of the fiber accelerated points, the Lorentzian distribution was appropriate to the distribution of fiber accelerated points. Chapter 5 summarized this thesis and pointed out some shortcomings. The prospects about this research were also brought forward.An on-line measurement system of drafting force was developed in this thesis and the measuring system was close to the actual process. The on-line measurement system of drafting force was utilized to study the drafting forces of drawing force. On the base of stretch tester, the static draft was performed. The draft ratio corresponding to the maximum stretch strength could be used to fix the draft ratio of the back draft zone. Base on the data about the fiber accelerated points, the Lorentzran distribution was found to be suitable for the distribution of fiber accelerated points by fitting method. The researches in this thesis enrich the draft theories to a certain extent and can provide practical process with reference as well.