Characterization Of Fiber Geometrical Characteristics And Its Application To Yarn Unevenness

Study on fiber properties and its impact on the spinning process and yarn performance has been the most basic research topic in the field of spinning.The selection of fiber raw materials,fiber properties characterization and evaluation,and the spinning process parameters configuration and optimization,to the yarn performance analysis and prediction,have always been widespread concern.In this study,the geometrical properties(length and fineness)of the fibers forming the yarn were studied.By means of the yarn unevenness,which was dominant in the evaluation index of yarn formation,the formula of the theoretical yarn unevenness was formed by the fiber geometrical characteristics' distribution.The effect of fiber geometric characteristics on yarn unevenness was revealed.It provides a solid theoretical fundation for the raw materials allocation optimization,reasonable development of spinning process and successful prediction of yarn performance.Starting with the characterization of fiber geometrical characteristics(length and fineness)expressed by the probability density functions,this study completed the comprehensive characterization of fiber performance distribution and enabled it accurate calculation.When analyzing the application of fiber geometric characteristics,the influence of different fiber geometrical characteristics on the unevenness of the yarn was studied.The work of this study corresponds to Chapters Two to Five in this dissertation.In Chapter Two,based on the histogram data of cotton fiber length and ramie fiber length in different spinning process,the fiber length distribution was fitted with the curves of density function from different mixed distributions.The fitting results showed that the fitting curves of the mixed Weibull distribution were continuous and smooth.While,the fitting of the mixed Weibull distribution were closer to the measured value and has a good fitting effect.In view of the difference between the histograms by number and by weight measured by the USTER AFIS single fiber tester,the relationship between fiber length distributions by number and by weigtht was analyzed.It is found that when the fibers satisfied the uniformity assumption of the same thickness and the same shape,that is,without considering the difference in linear density between the fibers and the difference in the lengthwise direction of the cross-sectional area of a single fiber,there is a linear relationship between the density function of length distributions by number and by weight.In the case where only the histogram by number of cotton fiber length distribution was known,not only the density function of the length distribution by number but also the length distribution by weight can be obtained.Considering the discrete fiber length parameters used in the production practice,based on the mixed Weibull distribution model in Chapter Two,Chapter Three obtained the relationship between fiber length parameters and the parameters of the density function of fiber length distribution with the mathematical derivation method.Then,according to the given fiber length parameters,the general global solution method was used to obtain the optimal mixed distribution parameters.In addition to fiber length,fiber fineness is also an important factor affecting the spinning process and yarn quality.In Chapter Four,cotton fiber fineness was studied.The research includes the comparison of different fineness measurement methods,the characterization of fineness distribution and the relationship between fiber fineness and length.Firstly,in the study of different measurement methods of cotton fiber fineness,we mainly compare the results(average fineness and fineness unevenness)of middle part cut and weight method with AFIS,HVI,FAVIMAT,the results showed that AFIS was the best way for fiber fineness test,not only the accuracy of fiber fineness but also the convenience of operation.Secondly,the histogram data of the fiber fineness distribution obtained by AFIS were fitted,both the density function of normal distribution and Weibull distribution can be used to characterize the fiber fineness distribution.In comparison,the goodness of fit of the normal distribution was better.Thirdly,for the correlation of fiber fineness and length,the independence of the fineness and length of the cotton fibers was further confirmed by solving the correlation coefficient.Since length and fineness are two main properties of the fibers in the yarn,there is no doubt that they have important influence on the yarn unevenness.Because the additional unevenness is difficult to describe quantitatively,the key point of yarn unevenness research is on the theoretical yarn unevenness.In this paper,the influence of the geometric fiber characteristics on the theoretical yarn unevenness was studied.In Chapter Five,the application of fiber geometric characteristics(length and fineness)on yarn unevenness was studied in two aspects:(1)Based on Martindale's basic hypothesis about ideal yarn,fiber fineness was added to the theoretical model of Suh,new formula of the theoretical yarn unevenness was obtained.This formula took full consideration of the effects of fiber length and fiber fineness and made up the deficiency of Martindale's and Suh's theory.The rationality of this new formula was verified by the comparison of calculated values of yarn unevenness from new formula with the calculated ones from Martindale's,Suh's formula.(2)Based on the new theoretical formula of yarn unevenness and the density function of fiber geometric characteristics distribution,the influence of geometrical parameters(ML?LCV?Tf?CV(T))on the theoretical yarn unevenness was analyzed quantitatively.The order of influence of fiber parameters on the theoretical yarn unevenness was shown below: Martindale model,Tf > CV(T),Suh model,Tf > ML > LCV;improved model(new formula),Tf > CV(T)> ML > LCV.In summary,based on the mixed Weibull distribution model,in this study,the probability density function fully characterizing the fiber length and fineness distribution was constructed.The application of fiber geometric characteristics to yarn unevenness was studied.It was revealed the mechanism of the effect of fiber geometric characteristics on yarn unevenness,which provided a plausible way in spinning control and predicting the yarn properties.