A Numerical and Experimental Study on a Pre-Twisted Ring Spinning System

polymers

Article A Numerical and Experimental Study on a Pre-Twisted Ring Spinning System

Keyi Wang 1,2, Wenliang Xue 1,2 and Longdi Cheng 1,2,*

1 Key Laboratory of Textile Science & Technology, Ministry of Education, Donghua University, Shanghai 201620, China; [email protected] (K.W.); [email protected] (W.X.) 2 College of Textiles, Donghua University, Shanghai 201620, China * Correspondence: [email protected]; Tel.: +86-21-6779-2689

Received: 26 April 2018; Accepted: 14 June 2018; Published: 16 June 2018

Abstract: The ring spinning process is the most widely used method in the spinning industry. Nowadays, the labor cost become more and more expensive, and it is essential to improve productivity. For increasing the productivity, a modification of adding a pre-twister and holding roller on the traditional ring spinning system have been discussed in this paper. The computational fluid dynamics (CFD) are introduced to study the effects of pre-twister and spinning tests are implemented for verification. The numerical simulations show that the cavity conical degree and nozzle numbers of the pre-twister are the key parameters which affect the airflow fluctuation in the cavity, and have obvious effects on the resultant yarn twist. By contrast, the axial angle and tangential angle of the nozzle have less effect on the resultant yarn twist. When the fiber bundles pass by the front nip, they are affected by the vortex and result in a partially strengthened and wrapped structure which could be subsequently twisted less by the traveler and ring, so the productivity could be potentially increased. According to the spinning tests, an evident productivity increase by nearly 30% for medium cotton yarns can be achieved, and the yarns have an acceptable reduction in nearly all properties.

Keywords: ring spinning; pre-twister; CFD; nozzle; productivity; yarn properties

1. Introduction Staple fiber spinning has a long history of more than 20,000 years [1]. Keeping in pace with scientific technologies, many new open-end and non-open-end spinning systems such as rotor spinning, air-jet spinning, vortex spinning, and self-twist spinning have appeared in succession. These new technologies have led to increases in spinning speed and, subsequently, production [2]. However, the ring spinning method is still the most widely used in today’s textiles mills due to the high quality of the yarn, being both finer and stronger than the yarn produced by open-end and non-open-end spinning systems [3]. With the increasing cost of labor in recent years, the importance of increasing spinning productivity through technological improvements is evident. In order to achieve higher productivity, many developments have occurred that are intended to increase the spindle speed, or to reduce or eliminate the friction between ring and traveler [4–11]. However, these developments have improved the ring spinning productivity in a very limited range or have not yet been implemented in industry due to their complexity. For the purpose of improving ring spinning productivity, Sawhney and Kimmel [12] worked on a “air-plus-ring” tandem spinning system, which could produce a low-twist, novel ring yarn at a relatively high speed. Their preliminary investigations showed that the yarn was weaker than a comparable ring-spun yarn although spinning speeds for certain yarns may be up to 50% higher than those prevalent in conventional ring spinning. No further research has been reported since then.

Polymers 2018, 10, 671; doi:10.3390/polym10060671 www.mdpi.com/journal/polymers Polymers 2018, 10, 671 2 of 11 Polymers 2018, 10, x FOR PEER REVIEW 2 of 10

ManyMany researchers havehave worked on yarn formation theory focusing on the airflow airflow characteristics. characteristics. InIn the earlier reports, reports, Kong Kong and and Platfoot Platfoot [13 [13] ]studied studied the the two two-dimensional-dimensional simulation simulation of ofairflow airflow in inthe the transfer transfer channel channel of rotor of rotor spinning. spinning. Zeng Zeng and Yu and [14,15 Yu []14 studied,15] studied the airflow the airflow in the first in the and first second and secondnozzle nozzle of air- ofjet air-jet spinning spinning from from two two-dimensional-dimensional to tothree three-dimensional-dimensional simulation. simulation. Some Some of of the the researchersresearchers [[1616––1818]] studiedstudied thethe principleprinciple ofof yarnyarn formation ofof Murata vortex spinning,spinning, alsoalso by airflowairflow simulation.simulation. Bergada et al. [[19]] studiedstudied thethe flowflow characterizationcharacterization inin cylinderscylinders forfor pneumaticpneumatic spinningspinning andand got got a a clear clear understanding understanding ofof thethe vortexvortex with with extensive extensive CFD CFD (computational(computational fluidfluid dynamics) dynamics) simulationsimulation ofof thethe airflow.airflow. ZouZou etet al.al. [[2020]] studiedstudied thethe twistedtwisted strengthstrength ofof thethe whirledwhirled airflowairflow inin MurataMurata vortexvortex spinningspinning by an analytical model based on simulating the flow flow field field inside the nozzle block. RengasamyRengasamy etet al.al.[ [21,2221,22]] studied studied the the airflow airflow in in nozzle-ring nozzle-ring spinning spinning by by CFD CFD to to explain explain the the principle principle of reductionof reduction in yarnin yarn hairiness. hairiness. InIn thisthis paper,paper, wewe introduceintroduce thethe modelmodel ofof aa pre-twisterpre-twister spinningspinning system,system, whichwhich couldcould produceproduce pneumaticallypneumatically entangled entangled real-twistsreal-twists onon the the fine fine strand strand priorprior to to the the twistingtwisting by by thethe ring/travelerring/traveler system.system. Less twist will be added to the yarnyarn in thethe subsequentsubsequent process, and the productivityproductivity can be increased.increased. The design of the pre-twisterpre-twister is investigated through the airflow airflow characteristics with CFD. TheThe spinningspinning teststests areare carriedcarried outout forfor verificationverification andand the yarn properties are compared withwith thosethose ofof classicclassic ring-spunring-spun yarn.yarn.

2.2. ModelModel of the Spinning System andand thethe Pre-TwisterPre-Twister TheThe model model of of thethe modiﬁedmodified ring ring spinning spinning system system is is shown shown in in Figure Figure1 . 1. Compared Compared with with thethe conventionalconventional ring ring spinning spinning system, system, a pre-twister a pre-twister and and a holding a holding roller roller were were added added to the tosystem, the system, which iswhich also differentis also different from the from former the researchers former researchers [21–25] whose [21–25 purposes] whose purpose were reducings were yarnreducing hairiness yarn withhairiness an air-jet with andan air without-jet and a without holding a roller. holding roller.

Figure 1.1. Schematic diagram ofof the spinningspinning system.system.

InIn thisthis model, the pre-twisterpre-twister isis locatedlocated veryvery closeclose toto the front roller nip.nip. After draft of the roving, thethe strand strand of of ﬁbers fibers from from the thenip of nip the of front the rollerfront is roller fed into is fed the pre-twister into the pre where-twister the air where is compressed the air is fromcompress the 4ed nozzles, from the as 4 shown nozzles, in Figureas shown2. in Figure 2.

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FigureFigure 2. 2. CrossCross-sectional-sectional view view of of the the pre pre-twister.-twister.

3. Numerical Simulation of Pre-Twister 3. Numerical Simulation of Pre-Twister The key to this supposed spinning system is the design of the pre-twister. The airflow pattern The key to this supposed spinning system is the design of the pre-twister. The airflow pattern inside the pre-twister was analyzed and simulated using a fluid flow analysis package, ANSYS inside the pre-twister was analyzed and simulated using a fluid flow analysis package, ANSYS Fluent14.0.0 (ANSYS, Canonsburg, USA), so as to optimize the design of the pre-twister. Fluent14.0.0 (ANSYS, Canonsburg, USA), so as to optimize the design of the pre-twister. According to the calculation of fluid mechanics in the Reynolds number, According to the calculation of fluid mechanics in the Reynolds number,

Re =  uD / (1) Re = ρµD/µ (1) where ρ is the air density (kg/m3), u is the air velocity (m/s), D is the inner diameter of the pre-twister, 3 andwhere μ isρ theis the viscosity air density of air (kg/m (N·s/m),2).u isThe the Reynolds air velocity number (m/s), ofD theis the airflow inner in diameter the pre- oftwister the pre-twister, is in the µ · 2 orderand ofis 10 the5, and viscosity the airflow of air (Nis classifieds/m ). The into Reynolds turbulence. number In order of the to airflow simplify in the the calculation, pre-twister iswe in 5 consideredthe order ofthat 10 the, and airflow the airflow was not is affected classified by intothe fiber turbulence. and the Inair order was considered to simplify as the viscous calculation, and compressible.we considered Regardless that the airflow of heat wasexchange, not affected the Realizable by the fiber k–ε Model and the was air used was for considered constant asenthalpy viscous ε flow.and compressible. Regardless of heat exchange, the Realizable k– Model was used for constant enthalpyThe basic flow. geometry of the pre-twister is a cavity with 4 nozzles as shown in Figure 2. The cavity shapeThe is conical basic geometrywith 6 mm of length. the pre-twister The nozzles is a cavityare conical with in 4 nozzles shape with as shown 0.8 mm in Figure× 0.6 mm2. The diameter cavity andshape 2 mm is conical length withconnected 6 mm to length. the cavity The nozzleswall. The are axial conical angle in shapeα is the with angle 0.8 between mm × 0.6 the mm nozzle diameter axis andand the 2 mm cavity length axis connectedand the tangential to the cavity angle wall. β is the The angle axial between angle α isthe the nozzle angle axis between and the the cavity nozzle wall. axis β Theand conical the cavity degree axis of and the the cavity tangential and the angle axial isangle, the angle tangential between angle, the nozzleand number axis and of thenozzle cavitys were wall. selectedThe conical as geometry degree of design the cavity parameters and the for axial computation. angle, tangential Nine geometries angle, and of number the pre of-twisters nozzles were were chosen,selected as as given geometry in Table design 1. parameters for computation. Nine geometries of the pre-twisters were chosen, as given in Table1. Table 1. Characteristics of the investigated geometries. Table 1. Characteristics of the investigated geometries. Case1 Case2 Case3 Case4 Case5 Case6 Case7 Case8 Case9 Cavity Conical Degree (°) 29.1 Case143.6 Case214.5 Case329.1 Case429.1 Case529.1 Case6 29.1 Case7 29.1 Case8 29.1 Case9 CavityAxial Conical Angle Degree α (°) (◦)10 29.110 43.610 14.530 29.150 29.110 29.110 29.1 10 29.1 29.110 Tangential Angle β Nozzle Axial Angle α (◦)0 100 100 100 300 5020 1040 100 100 10 (°) Nozzle β ◦ NumbersTangential Angle (4 ) 04 04 04 04 04 204 403 06 0 Numbers 4 4 4 4 4 4 4 3 6 For each case, the boundary conditions are set as follows: the inlet air pressure is 0.2 MPa (absolute) and the outlet air pressure equal to the external atmospheric pressure, the face space is 0.2 mm, and the wall is stationary. The computational grid is generated by a patch-independent tetrahedral grid and the computational domain contains about 200,000 cells for each case.

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For each case, the boundary conditions are set as follows: the inlet air pressure is 0.2 MPa (absolute) and the outlet air pressure equal to the external atmospheric pressure, the face space is 0.2 mm, and the wall is stationary. The computational grid is generated by a patch-independent

Polymerstetrahedral 2018, grid10, x FOR and PEER the computationalREVIEW domain contains about 200,000 cells for each case. 4 of 10

4. Spinning Spinning Experiment Experiment In order to verify the model, we used a six six-spindle-spindle la labb Spintester operating in a standard textile lab to produce 15. 15.33 tex spun yarns, employing (a) 370 tex carded cotton rovings, (b) the traditional traveler and and optimum optimum spindle spindle speed speed of of 10 10,000,000 rpm for the given 4.2 cm diameter ring ring,, and (c) the standard yarn twist level (800 tpm). We We then modified modiﬁed the Spintester by installing the pre pre-twister-twister (Case1) located in in the the yarn yarn path path close close to to the the front front roller roller nip nip ( (FigureFigure 33).). WeWe foundfound thatthat thethe nozzlenozzle airair pressure from 0.2 to 0.3 MPa (absolute) was optimum forfor satisfactorysatisfactory spinningspinning afterafter multitests.multitests.

Figure 3. Modified Spintester. Figure 3. Modified Spintester. Except for a lower twist level (650 tpm), we employed the same rovings and other spinning conditionsExcept to for produce a lower 15.3 twist tex levelyarns(650 on the tpm), modified we employed Spintester the under same a rovingsreasonably and acceptable other spinning level (lessconditions 40 ends to down/1000 produce 15.3 spindle tex yarns hours). on the modified Spintester under a reasonably acceptable level (lessThe 40 ends tensile down/1000 properties spindle of the hours).yarns were measured on an USTER TENSORAPID (Uster, Uster, SwitzerlandThe tensile) under properties a gauge of length the yarns of 500 were mm measured and a crosshead on an USTER speed TENSORAPID of 200 mm/min. (Uster, The Uster, yarn evennessSwitzerland) characteristics under a gauge were lengthtested o ofn 500an USTER mm and ME100 a crosshead (Uster, Uster speed, Switzerland of 200 mm/min.) with Thea 1000 yarn m lengthevenness of yarn characteristics and everywere test was tested performed on an USTER at a speed ME100 of (Uster,200 m/min. Uster, The Switzerland) sensitivity withsettings a 1000 used m forlength counting of yarn thick, and everythin, and test neps was performedwere +50%, at − a50%, speed and of +200% 200 m/min., respectively The sensitivity. settings used for countingYarn thick,samples thin, were and kep nepst in were the standard +50%, −50%, test environment and +200%, respectively. (temperature: 20 ± 2 °C, humidity: 65 ◦ ± 4%)Yarn for 24 samples h prior wereto testing. kept inThirty the standardreadings were test environment taken for each (temperature: sample. 20 ± 2 C, humidity: 65 ± 4%) for 24 h prior to testing. Thirty readings were taken for each sample. 5. Results and Discussion 5. Results and Discussion 5.1. The Airflow Trace in the Pre-Twister 5.1. The Airflow Trace in the Pre-Twister The airflow in the pre-twister is mainly formed by two parts. The simulation of airflow trace is The airflow in the pre-twister is mainly formed by two parts. The simulation of airflow trace is shown in Figure 4. One is the airflow compressed from the nozzles which moves forward spirally shown in Figure4. One is the airflow compressed from the nozzles which moves forward spirally (main-stream). Another is the airflow that is sucked into the pre-twister from the fiber inlet (sub- (main-stream). Another is the airflow that is sucked into the pre-twister from the fiber inlet (sub-stream), stream), which moves downward axially. which moves downward axially.

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Figure 4. Airﬂow trace in the pre-twister. FigureFigure 4. Airflow 4. Airflow trace in inthe the pre- twisterpre-twister. .

AsAs the the drafted drafted fibers fibers emerge emerge from from the the front front roller roller nip nip and and are are fed fed into into the the pre pre-twister,-twister, the the leading leading As the draftedendsends of of somefibers some marginal marginal emerge fibers fibers from are are sucked sucked the front into into the the roller pre pre-twister-twister nip byand by the aresub sub-stream- streamfed into while the the pre other -twister, ends the leading ends of some aremarginalare held held by by the the fibers front front nip nip;are; we sucked call those into leading the ends ends pre the the-twister “ “freefree leading by theends ends”. ”sub. As As -shown shownstream in in Figure Figurewhile 5, the other ends are held by thebecausebecause front the the nip respective respective; we call ends ends thoseof of the the core coreleading fibers fibers are areends firmly firmly the held held “ byfree by the the leading front front roller roller ends and and holding holding”. As roller,shown roller, in Figure 5, thethe free free leading leading ends ends would would be be wrapped wrapped on on core core fibers fibers with the help of the main main-stream.-stream. With With the the because the respectiveentanglementsentanglements ends by the of freefree the leadingleading core endsends fibers which which are are continuously continuouslyfirmly held controlled controlled by the by by the frontthe holding holding roller roller, roller, theand the air holding roller, the free leadingairvortex vortexends converts convertwould thes draftedthe be drafted wrapped fibers fibers into a intoon partially core a partially strengthened fibers strengthened with and wrappedthe and help wr structure.apped of the structure. This main partially This-stream. With the partiallyfabricated fabricated and strengthened and strengthened yarn structure yarn continues structure its uninterrupted continues its journey uninterrupted to a conventional journey to ring a entanglementsconventionalspinning by the zone, free ring where leadingspinning it is finallyzone, ends where and which positively it is finallyare twisted continuously and positively (unidirectionally twisted controlled by(unidirectionally the ring by and the traveler by holding the roller, the air vortex convertringcombination) ands travelerthe into drafted combination) a novel yarn. fibers Thisinto intoisa anovel continuous a yarn. partially This process. is a strengthenedcontinuous Due to this reason,process. twists and Due byto wr thethisapped travelers reason, structure. This partially fabricatedtwistwoulds by be the decreasedand travelers strengthened and would productivity be decreased yarn could and potentially structure productivity be increased. continuescould potentially its be uninterruptedincreased. journey to a conventional ring spinning zone, where it is finally and positively twisted (unidirectionally by the ring and traveler combination) into a novel yarn. This is a continuous process. Due to this reason, twists by the travelers would be decreased and productivity could potentially be increased.

Figure 5. The pre-twisting process. Figure 5. The pre-twisting process.

The characteristics of the airflow in the pre-twister for each case in Table 1 were simulated, and are shown in Figures 7–10. The air field can be described with the airflow trace and its velocity which will directly influence the wrapping effect of the pre-twister. The air velocity is resolved into three components, viz., tangential velocity (Vx), radial velocity (Vy), and axial velocity (Vz), as shown in Figure 6. Wrapping action is created by the tangential and axial velocity components of the air velocity. The total width of the drafted fibers emerging from the front roller nip is 2~4 mm (varied by the roving count), so the distance from core to marginal fiber is 1~2 mm. Thus, on the radial direction along the axis 1 and 2 mm away from it, the tangential and axial velocities from inlet to outlet are discussed. Figure 5. The pre-twisting process.

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The characteristics of the airflow in the pre-twister for each case in Table1 were simulated, and are shown in Figures 7–10. The air field can be described with the airflow trace and its velocity which will directly influence the wrapping effect of the pre-twister. The air velocity is resolved into three components, viz., tangential velocity (Vx), radial velocity (Vy), and axial velocity (Vz), as shown in Figure6. Wrapping action is created by the tangential and axial velocity components of the air velocity. The total width of the drafted fibers emerging from the front roller nip is 2~4 mm (varied by the roving count), so the distance from core to marginal fiber is 1~2 mm. Thus, on the radial direction along the axis 1 and 2 mm away from it, the tangential and axial velocities from inlet to outlet are discussed. Polymers 2018, 10, x FOR PEER REVIEW 6 of 10 Polymers 2018, 10, x FOR PEER REVIEW 6 of 10

Figure 6. The definition of velocity in the pre-twister . Figure 6. The definition of velocity in the pre-twister. Figure 6. The definition of velocity in the pre-twister. 5.1.1. Effects of Conical Degree 5.1.1. Effects of Conical Degree 5.1.1. Effects of Conical Degree Figure 7 shows that the tangential velocities in the axis along fiber inlet to outlet are not Figure7 shows that the tangential velocities in the axis along fiber inlet to outlet are not obviously obviouslyFigure affected 7 shows by that conical the degree,tangential but the velocities tangential in thevelocities axis along in the fiberpositions inlet of to 1 and outlet 2 mm are away not affected by conical degree, but the tangential velocities in the positions of 1 and 2 mm away from obviouslyfrom the axisaffected in Case2 by conical are higher degree, than but those the tangentialin Case1 and velocities Case3. inWhen the positionsthe conical of degree1 and 2 gets mm bigger, away the axis in Case2 are higher than those in Case1 and Case3. When the conical degree gets bigger, the fromthe tang the axisential in velocitiesCase2 are inhigher the positions than those away in Case1 from and the Case3.axis will When be built the conical up, which degree, in getsturn, bigger, allow s tangential velocities in the positions away from the axis will be built up, which, in turn, allows the free thethe tang freeential leading velocities ends to inwrap the onpositions core fibers away strongly. from the axis will be built up, which, in turn, allows leading ends to wrap on core fibers strongly. the free leading ends to wrap on core fibers strongly.

(a) Axial velocity (b) Tangential velocity (a) Axial velocity (b) Tangential velocity Figure 7. Velocity comparisons among Case1, Case2, and Case3. Figure 7. Velocity comparisons among Case1, Case2, and Case3. Figure 7. Velocity comparisons among Case1, Case2, and Case3. For axial velocities in the positions 1 and 2 mm away from the axis along fiber inlet to outlet, the variationsFor axial caused velocities by conical in the degreepositions are 1 not and significant. 2 mm away When from the the conical axis along degree fiber gets inlet bigger, to outlet, the axial the variationsvelocities causedin the axis by conical will be degree smaller. are The not variations significant. of When axial velocitiesthe conical caused degree by gets conical bigger, degree the axial have velocitiesa slight effect in the on axis the will entanglement be smaller. of The free variations leading ends of axial. velocities caused by conical degree have a slight effect on the entanglement of free leading ends. 5.1.2. Effects of Nozzle Axial Angle α 5.1.2. Effects of Nozzle Axial Angle α As shown in Figure 8, the axial velocities and tangential velocities among Case1, Case4, and Case5As areshown nearly in theFigure same. 8, Alongthe axial the velocities axis, the axialand tangentialvelocities closevelocities to the among fiber inlet Case1, are Callase4 about, and 90 Cm/s.ase5 Inare the nearly positions the same. 1 and Along 2 mm theaway axis from, the theaxial axis, velocities tangential close velocities to the fiber along inlet fiber are inlet all about to outlet 90 m/s.are Inalso the kept positions at the 1same and level.2 mm Itaway is noted from th theat axis,the nozzle tangential axial velocities angle α hasalong a slightfiber inletimpact to outleton the arewrapping also kept effect at the on samethe free level. leading It is endsnoted. that the nozzle axial angle α has a slight impact on the wrapping effect on the free leading ends.

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For axial velocities in the positions 1 and 2 mm away from the axis along ﬁber inlet to outlet, the variations caused by conical degree are not signiﬁcant. When the conical degree gets bigger, the axial velocities in the axis will be smaller. The variations of axial velocities caused by conical degree have a slight effect on the entanglement of free leading ends.

5.1.2. Effects of Nozzle Axial Angle α As shown in Figure8, the axial velocities and tangential velocities among Case1, Case4, and Case5 are nearly the same. Along the axis, the axial velocities close to the ﬁber inlet are all about 90 m/s. In the positions 1 and 2 mm away from the axis, tangential velocities along ﬁber inlet to outlet are also kept at the same level. It is noted that the nozzle axial angle α has a slight impact on the wrapping effect on the free leading ends. Polymers 2018, 10, x FOR PEER REVIEW 7 of 10

(a) Axial velocity (b) Tangential velocity

Figure 8. Velocity comparisons among Case1, Case4, and Case5. Figure 8. Velocity comparisons among Case1, Case4, and Case5. 5.1.3. Effects of Nozzle Tangential Angle β 5.1.3. Effects of Nozzle Tangential Angle β Figure 9 shows that among different cases, the variations in axial and tangential velocities in the Figure9 shows that among different cases, the variations in axial and tangential velocities in the cavity caused by the nozzle tangential angle β are similar to the conditions of the nozzle axial angle. cavity caused by the nozzle tangential angle β are similar to the conditions of the nozzle axial angle. When close to the fiber inlet, the axial velocities are all about 85 m/s. When close to the ﬁber inlet, the axial velocities are all about 85 m/s. The tangential velocities in the positions 1 and 2 mm away from the axis along ﬁber inlet to outlet of Case7 are smaller than those of Case1 and Case6. In Case7, nozzle tangential angle β is set to 40◦. Compared with β variation, the velocity’s variation is relatively small. The nozzle tangential angle also can be considered as a parameter which has a slight impact on the wrapping effect on the free leading ends.

(a) (b)

Figure 9. Velocity comparisons among Case1, Case 6, and Case 7. (a) Axial velocity; (b) tangential velocity.

The tangential velocities in the positions 1 and 2 mm away from the axis along fiber inlet to outlet of Case7 are smaller than those of Case1 and Case6. In Case7, nozzle tangential angle β is set to 40°. Compared with β variation, the velocity’s variation is relatively small. The nozzle tangential angle also can be considered as a parameter which has a slight impact on the wrapping effect on the free leading ends.

5.1.4. Effects of Nozzle Number

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(a) Axial velocity (b) Tangential velocity

Figure 8. Velocity comparisons among Case1, Case4, and Case5.

5.1.3. Effects of Nozzle Tangential Angle β

PolymersFigure2018 9, 10 shows, 671 that among different cases, the variations in axial and tangential velocities in8 the of 11 cavity caused by the nozzle tangential angle β are similar to the conditions of the nozzle axial angle. When close to the fiber inlet, the axial velocities are all about 85 m/s.

(a) (b)

FigureFigure 9 9.. VVelocityelocity comparisonscomparisons among among Case1, Case1, Case Case 6, and6, and Case Case 7. (a )7 Axial. (a) Axial velocity; velocity (b) tangential; (b) tangentialvelocity. velocity. Polymers5.1.4. 2018 Effects, 10, x FOR of Nozzle PEER REVIEW Number 8 of 10 The tangential velocities in the positions 1 and 2 mm away from the axis along fiber inlet to outletFigure Figureof Case7 10 10 shows showsare smaller that that the thethan influence influence those of on Case1on airflow airflow and caused Case6. caused by In number byCase7, number nozzle of nozzles of tangential nozzle is obvious.s isangle obvious. Tangential β is set Tangentialtovelocities 40°. Compared velocities in the positionswith in the β positionsvariation, 1 and 2 1 mmthe and velocity’s away 2 mm from away variation the from axis the is along relatively axis fiberalong inletsmall. fiber to inletThe outlet nozzleto outlet in the tangential i cavityn the of cavityangleCase9 of also Case9 are can much are be much higherconsidered higher than as those than a parameter ofthose Case1, of Case1which and tangential, hasand a tangential slight velocities impact velocities inon the the cavityin wrapping the cavity of Case1 effect of areCase1 on much the arefree highermuch leading higher than ends those than. th ofose Case8. of Case8. The tangentialThe tangential velocities velocities in the in fiberthe fiber inlet inlet area area are are stronger stronger with with more morenozzles. nozzles. When When close close to to the the fiber fiber inlet, inlet, tangential tangential velocities velocities and and axial axial velocities velocities are are kept kept at theat the same same5level.1. 4level. E inffects in all all cases. of cases. Nozzle When When Number the the nozzle nozzle number number is increased, is increased, the the wrapping wrapping effect effect on theon freethe free leading leading ends is endsstronger is stronger but maybut may bring bring slight slight destruction destruction to the to parallel the parallel structure structure of core of fibers. core fibers. When When energy energy saving is savingtaken is taken into consideration, into consideration, the number the number of the of nozzles the nozzles must bemust controlled be controlled under under 6 [26– 286 ].[26–28].

Figure 10. Velocity comparisons among Case1, Case8, and Case9. Figure 10. Velocity comparisons among Case1, Case8, and Case9. 5.2. Yarn Testing Results The yarn properties measured in terms of evenness, imperfections, and tensile properties are shown in Table 2. All properties of yarns produced on the modified Spintester are slightly worse than those of the classic ring-spun yarns. However, all typical properties of the modified spun yarn are generally satisfactory. Compared to the throughput spinning speeds of classic ring-spun yarns, the yarn productivity increase for the modified Spintester is 27.13%. Obviously, for the modified Spintester, the ability to produce a novel yarn with relatively low twist, which the traveler does, is the key to relatively higher yarn productivity. In this paper, we just conduct a preliminary investigation and this assumption may be a chance to improve the productivity of ring spinning.

Table 2. Parameters and properties of yarns produced on the pure ring and modified Spintester.

Spinning Method Ring Spun Modified Yarn size (tex) 15.3 15.3 Max yarn production rate Attained (m/min) 12.68 16.12 Increase in productivity over pure ring spinning (%) N/A 27.13 Yarn twist level (tpm) 800 650 Tenacity (cN/tex) 20.66 18.02 C.V. of bkg. St. 9.6 10.5 Single-strand bkg. Elongation (%) 5.79 5.37 Unevenness, C.V. (%) 17.28 18.64 Thin places (−50%) 42.5 90 Thick places (+50%) 417.5 522.5 Neps (+200%) 565 655

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5.2. Yarn Testing Results The yarn properties measured in terms of evenness, imperfections, and tensile properties are shown in Table2. All properties of yarns produced on the modified Spintester are slightly worse than those of the classic ring-spun yarns. However, all typical properties of the modified spun yarn are generally satisfactory. Compared to the throughput spinning speeds of classic ring-spun yarns, the yarn productivity increase for the modified Spintester is 27.13%. Obviously, for the modified Spintester, the ability to produce a novel yarn with relatively low twist, which the traveler does, is the key to relatively higher yarn productivity. In this paper, we just conduct a preliminary investigation and this assumption may be a chance to improve the productivity of ring spinning.

Table 2. Parameters and properties of yarns produced on the pure ring and modiﬁed Spintester.

Spinning Method Ring Spun Modiﬁed Yarn size (tex) 15.3 15.3 Max yarn production rate Attained (m/min) 12.68 16.12 Increase in productivity over pure ring spinning (%) N/A 27.13 Yarn twist level (tpm) 800 650 Tenacity (cN/tex) 20.66 18.02 C.V. of bkg. St. 9.6 10.5 Single-strand bkg. Elongation (%) 5.79 5.37 Unevenness, C.V. (%) 17.28 18.64 Thin places (−50%) 42.5 90 Thick places (+50%) 417.5 522.5 Neps (+200%) 565 655

6. Conclusions According to the simulation and spinning tests mentioned above, a modified ring spinning system is introduced. For producing a low-twist and novel ring yarn at a relatively high speed, the drafted fibers from the front roller nip need to be wrapped and well controlled during pre-twisting. The wrapping degree of the free leading ends of fibers onto the core fibers will determine the result of the pre-twisting. Therefore, the airflow in the pre-twister is important. By numerical simulation, some parameters that are important to the airflow in the pre-twister are noted, such as the cavity conical degree and the nozzle number. When these parameters are changed, the airflow will be changed obviously. A stronger vortex can be reached with bigger conical degree, but the parallel structure of the core fibers will be destroyed if the conical degree is too big. A stronger vortex can also be reached with a higher number of nozzles. Increasing the number of nozzles also increases the consumption of energy. We suggest 4 to 6 nozzles on a pre-twister. Nine different cases of the pre-twister were investigated by computation, and Case1 was the optimized one. The spinning tests show that even though the yarn is weaker than classic ring-spun yarn, potentially higher yarn productivity is reached. This is expected to generate some commercial interest. Another advantage of this new spinning system is that it can be easily installed on existing ring spinning frames to maximize yarn productivity. When an optimized pre-twister is available, it will be a revolution in the spinning industry.

Author Contributions: Conceptualization, L.C.; Data curation, K.W.; Formal analysis, K.W., W.X. and L.C.; Methodology, K.W.; Project administration, L.C.; Validation, K.W. and W.X.; Writing-original draft, K.W.; Writing-review & editing, L.C. Funding: This research was funded by [the National Key R&D Program of China] grant number [2017YFB0309100] Conﬂicts of Interest: The authors declare no conﬂict of interest. Polymers 2018, 10, 671 10 of 11

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