Spinning Process Of Hemp/cotton Blended Yarn And Mechanism Study Based On Swirl Nozzle

Hemp fiber is an important textile raw material,however,due to the high fiber rigidity and poor spinnability,its products application have been limited.Swirl nozzle spinning is a new technology to reduce ring spun yarn hairiness,which play its role by high speed rotating airflow.Previous researches on swirl nozzles focused on structural optimization and cotton spinning technology,application of other fibers and the research on the mechanism of airflow on yarn have not been involved.In this paper,the swirl nozzle technology is applied to spin the hemp/cotton blended yarn,and characteristics of airflow distribution in the swirl nozzle and the effect on the yarn/fiber are studied with hydrodynamic software,to improve the quality of the hemp/cotton blended yarn and widen swirl nozzle technology application.Firstly,spinning nozzle spinning technology was used to spin the hemp/cotton blended yarns.Hemp fiber is refined so that it can be blended with the cotton fiber in the cotton spinning equipment.During the test,factors such as the blending ratio,the inlet pressure,the yarn linear density,the yarn twist and direction are explored to investigate their effect on the yarn quality.Experimental results show that when the spindle speed is 9 000 r/min,yarn twist factor is 400 ~ 450,yarn linear density is 20 tex,swirl nozzle can reduce harmful hairiness of different blended ratio yarn significantly,while hemp/cotton 20/80 blended yarn is most significant among them,and the swirl vortex yarn surface smoother,more tightening.Generally,with the increase of the inlet pressure,the reduction effect of the swirl nozzle becomes more and more obvious,but after reaching the optimum pressure value,the number of harmful yarns in the yarn increases.The optimum pressure value of the hemp/cotton 10/90 and hemp/cotton 20/80 blended yarns was 0.2 MPa,and the harmful hairiness reduction rate reached 87.5% and 88.5%,respectively.The optimum pressure value of the hemp/cotton 40/60 blended yarns is 0.15 MPa and the reduction rate is 85%.Swirl nozzle will reduce the number of yarn harmful hairiness as well as slightly increase the number of short hairiness,the increase in hemp/cotton 10/90 yarn is higher than the other two yarns,reaching 8.6%.When the spindle speed is 9 000 r/min,yarn twist factor range is 430 ~ 470,the inlet pressure is 0.2 MPa,Swirl nozzles have different degrees of feather reduction effect on 10,20,30,40 tex hemp/cotton 40/60 yarns,and the best effect on the reduction of 20 tex yarns is 86%,but swirl nozzles slightly deteriorate the breaking strength and evenness of the yarn.When the spindle speed is 9 000 r/min,yarn linear density is 18 tex,inlet pressure is 0.15 MPa,with the increase of yarn twist factor,hemp/cotton 40/60 swirl vortex yarn harmful hairiness index firstly decreased and then increased,hairiness index and evenness is low when twist factor is 400,breaking strength and elongation is best in 450.Swirl nozzles significantly reduced hairiness,slightly reduced breaking strength,and increased unevenness of yarn for both Z and S twisted yarns,The Z-twist yarns exhibited a significant reduction in feathering.Secondly,by means of fluid mechanics numerical simulation method,the flow model of airflow in the nozzle is established to analyze the flow characteristics.The results show that the compressed air is divided into two parts after entering the yarn path from the entrance,the two parts airflow rotate clockwise out of the two outlet ends of the yarn path.At the instant of entering the yarn path,the airflow collides with the wall of the yarn path to generate a shock wave,which increases the pressure of airflow in the area and forms a negative pressure area above the impact area,the airflow speed in this area is large.As the airflow spreads toward the exits on both sides,the pressure and velocity become smaller and smaller.Airflow in yarn channel has obvious eddy current effect,the airflow pressure and velocity in the yarn channel is high near the wall and low near the axis,the more close to the exit the eddy current effect is abate,the pressure and speed difference between the wall and the axis are also smaller.The pressure and velocity distribution on the cross-sections of the yarn path is symmetrical with the air channel as the center.The distribution of airflow pressure and velocity at the exits on both sides is significantly different.This shows that the distribution of airflow is independent of the position of the outlet and is related to the distance from the air inlet.Finally,theoretical analysis and numerical simulation of the yarn/fiber surface force are analyzed.In the theory analysis,the force applied on yarn mainly are pressure of tangential flow,tension from frame,friction force of channel wall,the wall pressure on yarn.The movement of the yarn is not only driven by the rotation of the wire loop,but also by the rotational driving force of the airflow to rotate along the axis of the yarn path.The yarns in the yarn path will undergo successively two regions where the airflow effects are different,this is the opening area and the wrapping area.The Z-twist yarn is wrapped after loosened,this force distribution is more reasonable,and the S-twist yarn opening time is short and the effect is insufficient,so the feather reduction effect is worse than that Z-twist yarn.By calculating the feasibility of airflow wrap yarn hairiness,it can be concluded that the time required for airflow wrapping 10 mm hairiness is less than the time for the yarn to move through the yarn path.Therefore,length design of the yarn path is sufficient for the airflow to reducing feather.Analysis of flow field in yarn-airflow coupling simulation shows that as the air inlet pressure increases,the airflow pressure and the velocity distribution trend and the fluctuation of yarn surface are not significantly different,only the value is different,so reasonable choice of pressure needs to be tested and analyzed for different yarns.For different linear density of yarn,the surface pressure distribution and velocity distribution are different,the differences both in changing trend and fluctuation.Under the conditions of 2 mm diameter of the yarn path and 0.2 MPa inlet pressure,the airflow pressure and velocity of the surface of the 20 tex yarn fluctuate greatly,and the fluctuation frequency is higher,which is favorable for the enveloping effect on the surface hairiness.Analysis of the yarns in the structure field shows that the deformation of the yarn under air flow is the largest at the inlet of air flow,and the deformation near the ends of the yarn path is small,and most of the yarn sections are near the axis of the yarn path.The fiber-airflow coupling simulation results show that the swirling airflow causes clockwise winding deformation of the yarn surface fibers in different positions,in different lengths and in different directions,in which the fiber wrapping effect at the air inlet is poor and the fibers are more shorter the more difficult to be wrapped,the deformation of the fiber ends is greater than the deformation of the proximal yarn body.