Study On The Semi-open-end Twisting Model And Pneumatic Condensing Mechanism Of Compact Spinning With Lattice Apron

Compact spinning,a new technology on the basis of traditional ring spinning,is the most rapidly and widely developed spinning technology in the field of spinning in the 21st century.Compact spinning has obvious advantages in the yarn strength,hairiness and other quality indexes compared with the ring spinning,but also encounters some difficulties in the application,such as the prevalence of energy consumption,the lack of rights of independent intellectual property and other issues.Early literature researches are commonly lack of scientific and reasonable explanations on the condensing mechanism and the condensing process analysis.In this paper,the study object is the pneumatic compact spinning system with lattice apron.Combined with the phenomenon of additional twist,and started from the structural analysis of the strand in the compacting zone,asemi-open-end-twisting model is established through reasonable assumptions and kinematics analysis on single fiber.A clearer condensing mechanism is proposed through simulation and experimental verification.The main contents of this paper include five aspects as follows:(1)Study on the layered structure and semi-open-end-twisting model of condensing zoneFirstly,based on the phenomenon of additional twist in the condensing yarn,an idea of the"semi-open-end-twisting" mechanism is proposed.Then the semi-open-end-twisting model is established and the number of open-end fibers is estimated and analyzed.The single fiber is simplified into the model of the bead chain,and the motion equation of the single fiber sphere is deduced.Finally,the experiment is carried out to verify the existence of the layered structure by using the super-depth three-dimensional digital microscope.(2)Establishment and analysis of airflow distribution model in condensing zone.Based on the geometrical model and boundary condition of the condensing zone,the FLUENT software is used to calculate the airflow field of the condensing zone.The airflow characteristics in the condensing zone arethen obtained,which provides the basis for solving the semi-open-end twist model,and an analytical tool for studying the mechanism of airflow in compact spinning.(3)Study on the tension model in condensing zoneThe tension analysis method and the variation rule of the length of the condensing slot are obtained by means of mechanics and kinematics analysis.The effects of the friction coefficient,the radius of curvature of the condensing tube,inclination,negative pressure and the radius of the strand on the tension values are discussed.Then in the same way,the tension of the arc-shaped condensing slot is modeled and analyzed.Finally,the correctness of the tension model is verifiedindirectly by calculating the twist of the compact yarn compared with the experimental values.(4)Solution of semi-open-end-twisting modeland exposition of the condensing mechanismFirstly,the trajectory of the single-fiber ball is solved on the basis of the distribution of the flow field and the tension distribution.Secondly,the effects of the inclination angle,the negative pressure,the fiber strand linear density,the compacting slot width and the compacting groove shape on the trajectory of the fiber are analyzed.And then the correctness of the semi-open-end model is verified by using the super-depth 3D digital microscope to observe the twist of the strand in the condensing zone.Then,the number of open-end fibers in the ring yarns with different linear densities is estimated.Finally,the condensing mechanism is described more clearly,which provides the theoretical basis for the design of energy-saving condensing device.(5)Design and practice of energy saving compact spinning deviceAccording to the above research results,two kinds of airflow guiding devices are designed to separate the adsorption and twisting of the strand in the condensing zone.The yarn quality and the energy saving effect are analyzed by flow field calculation and spinning test.Through the idea,modeling,solution and experimental analysis,the following conclusions can be obtained:(1)Study on the layered structure and semi-open-end twisting model of condensing zoneIn the paper,it is concluded that the strand in the condensing zone is a layered structure,and the open-end fibers at the end of the surface are open,and the inner part is the non-open-endfiberswhich are gripped at both ends.The open-end fibers are twisted around the main fibers under the action of the condensing negative pressure and the slot,that isthe semi-open-end-twisting mechanism.The semi-open-end-twisting model is established by analyzing the mechanical and kinematic analysis of single fiber.The two necessary conditions for solving the model are obtained for the distribution of the flow field and the tension distribution of the strand.The approximate trajectory of the single open-end fiber can be obtained,after the numerical solution of the semi-open end,and the method of estimating the number of open-end fibers in the ring yarn is given.The results of stratified shooting of super-depth 3D digital microscope confirm the existence of stratified yarn layered structure.(2)Establishment and analysis of airflow distribution model in condensing zoneThe simulation results show that the static pressure in the upper part of the condensing slot is close to the atmospheric pressure.The closer to the condensing slot,the lower the static pressure,forminga negative pressure zone in the condensing slot.The static pressureinside the condensing tube is lower than the atmospheric pressure.The outside air from the surrounding flows to the compacting slot.The closer to the condensing slot,the greater the air speed.It is possible for the accelerating airflow flowing from the left and right sides of the slot to the condensing tube to shrink the fiber strand from a flat shape into a circular one.While the accelerating airflow from the upper side of the condensing slot to the condensing tube causes the fiber strand to be adsorbed on the lattice apron.This distribution of airflow in the condensing zone causes the fiber to produce condensing effect.When the inclination angle of the condensing slot changes from 0° to 10°,the distribution rules of the airflow velocity in the x-and z-direction of the condensing zone are similar.With the inclination angle of the condensing slot increasing from 0° to 5°,the airflow velocity increases slightly in the x-direction.When further increasing the inclination angle,the airflow velocity in the x-direction almost remains unchanged.When the width of the condensing slot increases from 1mm to 1.5mm,the airflow velocities in the x-and z-direction in the condensing zone are both increased.When the negative pressure of the condensing tube increases from 2000Pa to 3000Pa,the airflow velocities in x-and the z-direction in the condensing zone are significantly increased,which indicates that a higher negative pressure will increase the condensing effect for the fiber strand.The shape of the condensing slot also has a great influence on the airflow velocity distribution in the condensing zone.The airflow velocities in the x-and z-direction in the condensing zone of the arc-shaped condensing slot are higher than those of the straight condensing slot,indicating that the condensing effect must be better.(3)Study on the tension model of fiber strand in the condensing zoneAnalytical solution of the tension model of fiber strand in condensing zone of the straight slot isThe equations of the tension model of the fiber strand in the condensing zone of the arc-shaped slot are as follows:The results of the simulation show that the inclination angle of the slot ?,the negative pressure p,the radius R of curvature of the condensing tube,the radius r of the strand,the friction coefficient ? of the strand and the latticeapron have different effects on the tension.Finally,the correctness of the tension model is indirectly verified by comparing the calculated value and the experimental value of the additional twist,which provides the necessary conditions for solving the semi-open-end twisting model.(4)Solution of the semi-open-end twisting model and exposition of the compacting mechanismBased on the airflow andthe strand tension distribution in the condensing zone,the approximate trajectory of the single fiber in the condensing zone can be obtained.The effects of the condensing slot inclination angle,the condensing negative pressure and the condensing slot shape on the trajectory are significant.Under the calculated conditions of this test,the inclination angle of the condensing slot is 10°and 5°,and the twist of the strand is increased from 56.5twist/m to 82.6twist/m.Corresponding to the condensing negative pressure of 2000Pa and 3000Pa,the twist are56.5 twist/m and 76.3twistlm.For the arc-shaped and straight condensing slot(inclination angle 5 °),the twist are56.5 twist/m and 76.3twist/m respectively.The twists of the fiber strand of the linear density of 9.7tex and 15.3tex are 61.7twist/m and 56.5twist/m.The condensing slot widthsoflmm and 1.5mm correspond to the twist of 56.5twist/m and 53.2twist/m.Microscopic photo results show that the twist of the 58.3tex strand of in the condensing zone is65.4twist/m,and the calculated value is55.2twist/m.They are agreed well with each other.Although it is estimated that a relatively low percentage of fibers are involved in the open-end twisted,which is about 3 to 8 fibers,the condensing effect of the fibers is very good.Through the analysis,simulation and experiment,the condensing mechanism of negative pressure compact spinning with lattice apron clarifies the two functionsof condensing negative pressure:the adsorption of the strand main body on the lattice apron and the open-end fiber spirally wrapping in the main fibers.The inclination of the condensing slot is good for the airflow distribution,and better condensing effect is achieved by twisting at the semi-open-end.(5)Design and practice of energy saving compact spinning deviceTwo kinds of airflow guiding and energy saving devices are designed.The results show that these two air guiding devices can effectively reduce the negative pressure,the effect of the air guiding device II is more stable.The apparatus is used for spinning at a negative pressure of 1000Pa,compared with a normal compact yarn having a negative pressure of 2000Pa.The yarnsof 15.3tex,20.2tex and 30.6tex almost have no difference in quality,which provides an effective idea and demonstration for reducing the energy consumption of the condensing spinning machine.In this paper,the semi-open-end twisting model and the condensing metchanism of the negative-pressure condensing spinning with lattice apron are studied.The research results not only have a good academic value,but also have practical prospects.At the same time,exploring the energy-saving condensing spinning device can provide reference for the progress and development of the condensing spinning.