Theoretical Study And Experiment Of Strongly Controlled Soft Drafting System Based On The Ring Spinning Frame

Drafting process is the technological core of ring spinning,and research on drafting technology mainly focuses on drafting components,pressurization mechanisms,and process optimization,mainly using a "strong control,heavy pressurization" technical approach aimed at improving the modernization level of the drafting system,improving yarn quality,and increasing product adaptability.Despite significant improvements and innovations in modern ring spinning frames,the double apron drafting system,including drafting technologies such as SKF and HP,is still being used.Breakthrough progress has not been made,and improvements in yarn quality have been relatively slow.Although the elastic clamping of the double apron can reduce the occurrence of uncontrolled and dead control phenomena during drafting,differences in the linear speed between the top and bottom aprons lead to various problems:(1)the speed difference between the aprons may cause rubbing between fiber bundles and top rollers,affecting yarn indicators such as yarn evenness and yarn faults;(2)the speed difference between the aprons could result in unstable frictional forces,affecting yarn stability and increasing spindle-to-spindle variation;(3)the speed difference between the aprons may generate static electricity,causing yarn snarling around components such as rollers,aprons,and guide bars;(4)in severe cases,the aprons may even arch or slip.The research on drafting theory mainly includes three aspects: the position of fiber being accelerated,the thinning curve of sliver,and the unevenness of strip caused by the irregular movement of floating fibers in the drafting zone.These three theories are interrelated and inseparable.Although the motion state of fibers has been quantitatively explored through simulation in drafting research,the study only focuses on the singlespeed change of overall fibers in the sliver,without considering the motion of individual fibers during drafting and the impact of the new fiber distribution formed after fiber speed change on subsequent fiber motion.Therefore,there is still room for improvement in the theory of fiber speed change during drafting.In this context,based on the balance of guiding force and control force that a single fiber is subjected to,this study proposes a theoretical model for calculating the fiber accelerated points using a cyclic iterative method.The model can calculate the theoretical accelerated points of all individual fibers and the distribution of various fibers in the drafting zone,including the thinning curve of the sliver in the drafting zone.Based on this drafting theory model and the drafting systems developed by the textile industry,the characteristics and advantages of the compact spinning system with strong control flexible drafting(referred to as "SDS drafting system" hereafter)are analyzed and compared with those of the double apron drafting system.The impact of process settings on fiber accelerated points is theoretically explored,followed by the selection of key process parameters for single-factor experiments,and subsequent multi-factor optimization experiments are conducted based on the results of the single-factor experiments to regulate yarn properties.The longitudinal correlation between the SDS drafting system and yarn properties is established to achieve the goal of producing the best yarn with optimal spinning performance.Finally,the possibility of replacing combed yarn spun by the double apron system with half-combed yarn spun by the SDS system is discussed.The specific research content and related conclusions of this topic are as follows.(1)A model using iterative cycling was established to simulate the drafting process,which could be applied to both roller drafting and apron drafting.The main parameters affecting the model include fiber length distribution,pressure distribution in the drafting zone,and drafting ratio.Through simulation,the effects of fiber length distribution,drafting ratio,roller center distance,and additional pressure location on fiber acceleration were discussed,and the changes in fiber distribution within the drafting zone were compared.1)Discussion on fiber length: Three types of slivers with skewed distribution,uniform distribution,and equal length distribution were used to explore the influence of fiber length distribution on fiber movement.The results show that a fiber accelerated point is only related to the length of the fiber itself,and not to the number of other length fibers in the sliver;as the length increases,the fiber accelerated point moves forward towards the front roller nip,and the premature acceleration of short fibers is the main reason for the high coefficient of variation in the acceleration distribution.2)Discussion on drafting ratio: As the drafting ratio increases,the fiber accelerated point gradually approaches the nip line of the front rollers;as long as the sliver can be drafted,the effect of drafting ratio on the coefficient of variation of fiber acceleration distribution is not significant.3)Discussion on roller center distance: The longer the roller center distance,the more fibers shorter than the drafting zone,resulting in more premature accelerated fibers and more dispersed fiber acceleration distribution.When fiber lengths are longer than the drafting zone,the fiber accelerated points are more concentrated,and with the increase of roller center distance,accelerated points of long fibers become more concentrated but farther from the nip line of the front rollers.4)Discussion on additional pressure location: Setting a drafting zone without a floating zone,i.e.,the pressure values in the drafting zone are all greater than zero,the results show that a stable and flat pressure distribution in the drafting zone is more favorable for the concentration of fiber accelerated points,but at this time,the accelerated points of fibers are far from the nip line of the front rollers and there is a risk of instability in actual drafting.Secondly,when there is additional pressure in front,not only do the fiber accelerated points move closer to the nip line of the front roller,but the distribution of fiber accelerated points is also more concentrated.Overall,the accelerated point of short fibers moves forward towards the nip line as the additional pressure moves forward.(2)A soft drafting system that uses magnetic pressurization technology to achieve strong control over the drafting channel-SDS drafting system.Compared with the traditional double apron to hold fibers,SDS uses a softer lattice apron and bottom curved plate to hold fibers,which can completely change according to the surface curvature of the bottom curved plate,and maintain a stable and continuous soft grip with the fibers between the bottom curved plate.SDS drafting system can be divided into a soft grip area and a curved draft area.The pressure distribution in the soft grip area is only related to the tension of the lattice apron and the radius of curvature of the bottom curved plate,which can provide a stable friction zone for yarns.The curved drafting area can ensure the drafting efficiency and improve yarn quality under the consideration of yarn structures.The static pressure distribution curves of SDS and double-apron drafting systems were obtained by calculation and experiment respectively.The experimental results show that: the SDS drafting system can provide a longer and stable friction zone,and the length of the floating zone is only 6 mm,which is beneficial to the control of short fibers;SDS drafting system has certain reliability and wide adaptability for improving yarn quality.It can improve yarn evenness and reduce common yarn faults,especially thick places +35% and thick places +50%.(3)To better understand and optimize the SDS drafting system,the project predicts the theoretical accelerated points of fibers using a constructed fiber motion model and explores the impact of various process parameters on the spinning performance of the drafting system through single-factor and multi-factor optimization experiments.The process parameters involved in the single-factor experiment include the front roller pressure,lattice apron tension,block,lattice apron size,and back drafting ratio.Among them,the changes in the distance block and lattice apron size essentially reflect the changes in the lattice apron tension.In addition,since the conclusion in Chapter 2 shows that the variation coefficient of the fiber acceleration distribution is less affected by the drafting ratio,this chapter mainly explores the impact of front roller pressure and lattice apron tension on the theoretical accelerated points of fibers.The simulation results showed that the greater the front roller pressure,the further away from the front roller nip the fiber accelerated point is,but the overall variation coefficient of the fiber accelerated points is smaller,and the accelerated points are more concentrated;the greater the tension of the lattice apron,the closer the fiber accelerated point is to the front roller nip,but the overall variation coefficient of accelerated points is larger.The single-factor experiment results showed that the smaller the block,the better the evenness of the yarn;the front roller pressure shows a decreasing-then-increasing trend in the unevenness index of the yarn,and the overall mass evenness of the yarn is best at 190N;when the lattice apron circumference is 145 mm,the yarn has the highest evenness,and the trends of defects such as thin places,thick places,and cotton knots+140% are similar to the unevenness index of the yarn,the unevenness index,thin places,thick places,and cotton knots+140% of the yarn decrease first and then increase with the increase of the rear drafting ratio,and the evenness of the yarn is highest when the rear drafting ratio is 1.21.The multi-factor optimization experiment results showed that the block,front roller pressure,and back drafting ratio have a significant impact on the evenness of the yarn,but there is no interaction between these parameters.Overall,under normal drafting conditions,changes in process parameters of the SDS drafting system have little significant impact on hairiness and yarn breaking strength.(4)There are two problems in the current SDS drafting system: one is the short life of lattice aprons,which is prone to wear,accumulation and curling;the other is that the yarn faults of thin places have not been significantly improved.Aiming at these two problems,two optimization schemes are proposed.First of all,in view of the problems of flower accumulation and edge curling in the lattice apron,it is proposed to replace the lattice apron with an apron with the same inner diameter and a thickness of 0.65 mm,and an experimental comparison is made.The results show that although the performance of the yarn spun by the apron is not as good as that of the lattice apron,the quality of the yarn is still higher than that of the yarn spun by the double-apron drafting system,which has a certain degree of substitutability.Secondly,in view of the problem that thin places are not significantly improved,it is proposed to reduce the radius of curvature at the rear end of the lower curved plate to increase the pressure in this area and reduce the probability of accidental drafting.The experimental results show that the yarns spun by the SDS with the new curved plate have improved yarn evenness,thin places,thick places and neps,especially the thin places.Both optimization schemes have been proved to be quite feasible through prototype experiments,which provide a basis for the industrial application of SDS drafting system.(5)Based on the properties of the yarns spun by the SDS drafting system far exceeds that of the yarn spun by the double-apron drafting system,explore the possibility of using SDS to spin semi-combed yarn to achieve the quality of the combed yarn of the double-apron drafting system.In the study,the method of mixing carded slivers and combed slivers was used for drawing,and there were four mixing schemes,in which the proportion of combed slivers was 100%,87.5%,72.5% and 62.5%,respectively,and then spinning.The experimental results show that the evenness of the SDS semi-combed yarns of the four schemes is better than that of the double-apron combed cotton yarns,but with the increase of the carded sliver,s the neps in the yarns increase significantly.Therefore,after a comprehensive comparison of various indicators,it is found that when the proportion of combed slivers is 87.5%,the indicators of SDS semi-combed yarns are better than double-apron combed yarns,and can replace double-apron combed yarns.The simulation results also show that the coefficient of variation of the fiber accelerated points in SDS drafting system is smaller than that of the double apron one,and the coefficients of variation of the accelerated points of the four schemes are reduced by 89.1%,90.1%,90.3% and 90.5% respectively.Adding a carded sliver in the first drawing frame,that is,when the proportion of combed sliver is 87.5%,using SDS drafting system to spin semi-combed yarn can reduce the cost of raw materials by 2.375% and the cost of consumption by 7.49%.The preparation of carded slivers does not require pre-drawing and combing,which can improve spinning efficiency,save energy consumption,reduce more electricity costs,and reduce costs for cotton spinning enterprises.