Effects Of Airflow And Fiber Motion On The Yarn Tenacity In Air-jet Vortex Spinning

The vortex spinning technology has the advantage of shorter spinning process,fewer manpower requirement,lower electric power expenditure and higher spinning speed.In terms of industrial structure,due to the need of adjustment of industrial structure in China's textile industry,the MVS spinning technology is an important part of the textile technology development Plan(2016-2020),which accelerated the promotion and technical advance of textile industrial structure.Therefore,it has the very profound meaning to tap and manufacture this kind of high automation vortex spinning equipment with the intelligent property right.On the other hand,it is necessary to change the present situation of viscose fiber as the main raw material in this field.In this paper,the twisting mechanism and the twisting efficiency of the tube twister in electrostatic spinning have been analyzed.And then through the analysis of the simulation and experimental results,the effect and influence of structural parameters of nozzle and the fiber performance on yarn strength were presented.Hence,this article attempts to carry out some exploration on high tenacity Vortex yarn from three aspects: optimize the structure of nozzle,fibers blend,changes cross section of fiber.Air-jet vortex spinning is a new technology for spinning yarn by using high-speed airflows and the coordinated action of various components inside the jet nozzle,so the structure parameters of nozzle play an important role in improving the yarn quality substantially.The theoretical calculation formula for air-jet vortex yarn strength could be applied to different type nozzles,giving a reliable theoretical basis for designing appropriate related parameters.On the other hand,the status of airflow field can be as an auxiliary reference.Using the method of Computational Fluid Dynamics(CFD),the distributions of pressure and velocity in the nozzle with displacement ventilation system with many heat sources have been simulated.From the theoretical analysis,and then through data simulation and spinning experiment,this paper eventually established a more scientific system for Air-jet vortex spinning technology.The main contents and results of this paper were as follows:1.Research on the theoretical formula of yarn breaking strength in the air-jet vortex spinning.Established airflow state formula of the nozzle according to the mechanics' theory(aerodynamics,jet mechanics,and Newtonian mechanics,etc.),and made some theoretical analysis on the force and movement of the fiber in the nozzle;Established twist model of air jet vortex spinning,and through this the calculation formula of jet vortex spinning single yarn breaking strength ?y was deduced.According to this formula,single yarn breaking strength is related to five aspects: 1.Air flow state(Ca,?a,va,var),2.Fiber properties(L,Fb,?f,rf,?f,?f),3.Single yarn properties(n,?y),4.Nozzle structure(????r0),5.Spinning speed.At the same time,the nozzle structure and assembly will also affect the air flow in the nozzle to a certain extent,such as the cone assembly position will affect the position of negative pressure in the air vortex and the collision problem in on the outer wall of the cone body,these all have an effect on the quality of yarn.In the case of single yarn attribute(textile machinery nozzle entrance pressure,nozzle position and spinning speed etc.)determined,the single yarn breaking strength will be directly affected by the nozzle structure and fiber properties.When the spinning material and the process parameters are determined,the single yarn breaking strength will only related to the air velocity and nozzle structure(????r0).2.Research on the length of fiber slippage and wrapped in the air-jet vortex yarn.The u-value in the slip length formula is the average radial position of the wrapped fiber in the single yarn,the smaller the u-value,the smaller the slip length.? is the tilt angle of fiber,namely the wrap angle,and when ? is 45°while the fiber is in the vortex chamber the slippage length get the minimum value.In addition,the thinner the fiber,the smaller the modulus,the greater the friction coefficient,the greater the modulus,the smaller the slip length.According to ignoring the transfer twisted length or not,two situations were discussed When defining the twisted length: one is the regular twisting length,the other is the total length of fiber twisting length.Overall,the airflow velocity increasing,the outer wall of the cone angle is small,fiber inclination angle is bigger,the greater the length of wrapping.In addition,the fiber twisted length is longer with the bigger friction coefficient,the smaller fiber density,and the smaller fiber fineness.3.Research on the influence of some related parameters of nozzle structure on the air flow in nozzle and the yam breaking strength in the air-jet vortex spinning.The structural parameters of the nozzle in air jet vortex spinning have important influence on the yam breaking strength.This paper analyzed the influence on the single yarn breaking strength of the air jet vortex spinning with the selected six parameters of nozzle spray hole angle ?,cone angle ? of cone outer wall,cone body position(the distance Lc from the body to the conical guide),distance d1 from the spray holes to the center shaft,cavity structure of the vortex tube and cone entrance configuration through theoretical derivation,numerical simulation of air flow field and spinning experiments.In a certain range,single yarn breaking strength is in line with the trend of sine function with spray angle;and has a negative linear relationship with the cone angle of tan(?)value;and has a liner relationship both Lc-value and d1-value.The spray angle of air jet vortex spinning vortex tube,should be about 50°.The cone angle of outer wall is smaller,the single yarn strength will be greater.Lc-value between the cone body and the guide distance is appropriate at 2~3mm.The selection of distance should avoid the air flowing around the wall,and make the air flow diffuse freely in the vortex chamber as far as possible.In this situation,the d1-value greater the better.Adding a transition cavity between the middle column cavity and the cavity expanding area in the vortex tube,will make the distance from the head of fiber position out of nozzle to the negative pressure position in vortex cavity closer.Then it will generate a greater negative pressure,greater tangential velocity,and the fiber will be more easily inhaled and separated.At last this makes more fiber free end,longer fiber twisting section,and higher yarn strength.4.Research on the effect of the fiber flexural rigidity and torsional rigidity on the wrapped angle and the yarn breaking strength in the air-jet vortex spinning.The motion of the fiber in the vortex chamber is less affected by the torsional stiffness of the fiber,while greater affected by the bending stiffness and the dynamic friction coefficient of the fiber.Under the same force conditions,the fiber bending stiffness smaller,the wrap angle greater.When the fiber twisted greatly during twisting,the influence of fiber torsional rigidity should also be considered.The greater the bending stiffness and the friction coefficient of the fiber,the greater the impact on the surrounding fibers,so the wrap angles of five materials in this paper get sorted by size: acrylic staple fiber > combed cotton fiber > long acrylic fiber > viscose staple fiber > polyester staple fiber.On the other hand,the smaller the bending stiffness,the greater the friction coefficient,the better spinnability,thus the ordering of three kinds of chemical fiber in the paper in the spinnability is: viscose fiber > acrylic fiber > polyester fiber.5.Research on the impacts of fiber cross section on the yarn breaking strength.Under the same fiber fineness,the diameter with triangle feature is the biggest.And the bending stiffness and torsional stiffness decrease significantly,the flow area is relative large,so the triangle fiber will be greater forced in the nozzle and the yarn formed by triangle fiber will have strong strength.The next is cruciform fiber.That's also the reason why the triangle and the cruciform fiber have a better spinning property than ordinary circular polyester.Hollow fiber bending stiffness is larger than ordinary fiber,but in the air flow field is larger forced than the circle,from the perspective of the spinning results,the single yarn breaking strength of hollow yarn is also improved.The bending stiffness and torsional stiffness of square cross section fibers are larger than other fibers,coupled with their stress in the air flow field is smaller than ordinary polyester fiber,so it's spinning property is not as good as ordinary polyester fiber.6.Exploration of developing terminal products of air jet vortex spinning through analyzing the blending and changing the shape of fiber cross section.Jet vortex spinning is better for flexible fiber,but is not suitable for the fiber with large rigidity,and is difficult for production.In order to improve the spinnability,two aspects are considered: one is to blend with flexible fiber.Determine the reasonable blending ratio,keep the fiber with large rigidity in a certain proportion,and optimize the spinning process,then the spinnability can be improved significantly.This will have a positive significance to expand the range of raw materials and product usage of air jet vortex spinning;The other is to improve the fiber cross-sectional configuration.Increase grooves or hollow to reduce the bending stiffness and increase the flow area.In addition,other properties of the fiber are also considered except for the spinnablility properties.Such as the triangle fiber which besides the high strength,due to the silk gloss appearance,spinning single yarn is of high brightness;Cruciform fiber has groove structure on the surface,which cause the capillary phenomenon,and due to the less contact point with skin,so as to achieve the purpose of quick drying moisture;hollow fiber has the characteristics of light and warm.So the spinnability can be changed and the functionality can be extended by changing the shape of the fiber cross section.And then the added value of the air jet vortex spinning products can be greatly improved.