Study On Fiber Movement In Drafting Zone

Yarn irregularity is one of the important indexes to measure yarn quality.The causes of yarn irregularity can be divided into theoretical irregularity（also known as limit irregularity）caused by random arrangement of fibers with certain length and fineness distribution in slivers or yarns and additional unevenness caused by spinning processes,among which drafting process is the most significant.Drafting involves many processes in yarn processing.The movement of fibers in drafting zone has been one of the classic topics in textile field.During the drafting process,the hook fibers are further straightened and the slivers are stretch finely.The fibers are rearranged in the drafted sliver.However,due to the variation of the fiber accelerated point in the drafting zone,any two fibers will produce a displacement deviation after acceleration,resulting in additional irregularity,which is the main reason for the deterioration of yarn quality.The distribution of fiber accelerated point in the drafting zone is affected by fiber and yarn properties,processing parameters,drafting form and other factors.Therefore,exploring the movement of fibers in the drafting zone will help to understand the relationship between product quality and the processing parameters more clearly,which has guiding significance for product quality prediction,spinning process optimization and high-quality yarn production.In this study,starting from exploring the fiber movement in the drafting zone,the fiber accelerated point was tested in the simple roller drafting zone of the drawing frame and the double apron drafting area of the spinning frame with full consideration of the raw material properties and drafting process.The effects of raw material properties and drafting process parameters on the distribution of fiber accelerated point were analyzed to provide necessary conditions for accurately predicting the quality of drafted sliver or yarn.Then,considering the dispersion of fiber accelerated point in the drafting zone,the straightening effect of drafting process parameters on different types of hooked fibers was studied by analyzing the relative position relationship between the midpoint of the hook part,the midpoint of the body part,the fiber accelerated point and the front roller nip line.Based on the fiber arrangement in sliver model considering hooked fibers,the drafting process simulation was initially realized.Finally,according to the irregularity of sliver and the sliver variation-length curve,an uneven sliver closer to the actual sliver is established,which provides a basis for intelligent manufacturing.The specific research contents and findings are as follows:（1）Proposing an improved method for determining the fiber accelerated point based on the motion characteristics of fibers in drafting zone and the theory of displacement deviation.By dynamically determining the front roller nip line,the experimental errors caused by marking the front roller nip line due to shut down the machine are reduced,and the feasibility and accuracy of the experiment are improved.Based on this method,the distribution rule of fiber accelerated points in the simple roller drafting zone of the drawing frame is explored with polyester sliver,on the basis of comprehensive consideration of the influence of drafting process parameters and fiber properties.Providing an important reference for simulating the fiber speed change in the spinning process.Simultaneously,the irregularity caused by fiber accelerated point fluctuation was calculated(CV_FAP).It changes the previous understanding that the yarn irregularity after drafting is directly related to the fiber motion stability in the draft zone,and explains the relationship among the yarn irregularity after drafting,the difference of fiber accelerated point and the draft ratio.The relationship between the fitting parameterσof the Gaussian distribution of the CV_FAPis analyzed.The results show that the trend of the two is in consistent,which is also consistent with the empirical spinning experience and theoretical analysis.（2）Based on the test method of fiber accelerated point in the drafting zone introduced in Chapter 2,the fiber accelerated points rule under different drafting forms of spinning frame was tested with polyester sliver.The effects of drafting process parameters,fiber and yarn properties on fiber movement in the double apron drafting zone were quantitatively analyzed.The results show that the distribution of fiber accelerated points in double apron drafting zone can be expressed by Gaussian function,and the distribution of fiber accelerated points is more concentrated and closer to the front roller nip line than that in simple roller drafting.According to the irregularity of the sliver before and after drafting,the irregularity caused by the fiber accelerated point fluctuation(CV_FAP)is calculated.The consistency of CV_FAPand fiber accelerated point fluctuation with parameter variation is consistent with the results obtained from theoretical analysis and practical experience.In addition,by comparing the distribution of fiber accelerated points and the influence of different drafting process parameters on yarn unevenness and strength under the three drafting forms of double apron drafting,single apron drafting and simple roller drafting,the influences of top and bottom apron on fiber movement and yarn quality in the double apron drafting zone are investigated.The results showed that the top apron had little effect on the movement and quality of chemical fibers in the double apron drafting unit,but had a greater effect on cotton fibers.Compared with Chapter 2,this part provides a basis for better understanding of the double apron drafting mechanism,and also provides a basis for further optimization of the drafting process.（3）The influence of the drafting process on the straightening of the hooked fibers were analyzed,which is closer to the actual situation than the previous straightening derivation based on the ideal drafting.By considering the influence of the variation of fiber accelerated point on the different types of hooked fibers movement in the drafting zone,the objective law of the straightening of different types of hooked fibers in the drafting zone was found.The relationship between the output fiber straightness and the position of fiber accelerated point,the fiber length,the draft ratio and the input fiber straightness were established.Based on the arrangement model of hooked fibers in sliver,combined with the straightening analysis of hooked fibers in the drafting zone,the drafting process was simulated on the computer MATLAB software.On the basis of ideal drafting,the simulation results are compared with the previous theoretical studies and the experimental data,which verifies the accuracy of the hooked hook straightening analysis.It can provide a basis for further research on the influence of drafting process on the quality of final product.（4）Based on the model of fiber arrangement in ideal sliver,a sliver fiber arrangement model with uneven structure is established by further considering the total irregularity and the structure unevenness of sliver,which is closer to the reality.The simulated uneven sliver is close to the target sliver not only in terms of sliver irregularity,but also structure unevenness,which shows the rationality of the fiber arrangement model established in the uneven sliver.Compared with the sliver or yarn with even structure,the prediction accuracy of the irregularity of sliver or yarn with uneven structure is significantly improved,and the difference is less than 5%from the measured sliver or yarn irregularity,which indicates the necessity of establishing the model.Compared with the ideal sliver,the prediction accuracy of uneven sliver is significantly improved.Additionally,the uneven sliver after drafting is simulated and compared with the data in the previous literature,which further verifies the reliability of the model.Combining the model of fiber arrangement in uneven sliver with the analysis of fiber movement in drafting zone can provide guidance for yarn quality prediction and drafting process optimization.In conclusion,in this study,the accelerated point distribution of fibers under different process parameters,material properties and drafting forms was measured by the tracer fiber method,which further revealed the quantitative relationship between fiber properties,drafting process and drafted sliver quality.By considering the dispersion of the fiber accelerated point in the drafting zone,the motion of the fiber in the drafting zone is analyzed,and the straightening effect of the drafting process on different types of hooks is explored.By improving the fiber arrangement model in sliver,the prediction accuracy of sliver irregularity is improved,which provides a basis for intelligent drafting processing.