Interdependence of fibre type and the design of the nozzle of air-jet spinning machine

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1 Indian Journal of Fibre & Textile Research Vol. 24, March 1999, pp Interdependence of fibre type and the design of the nozzle of air-jet spinning machine A Basu & W Oxenham b Department of Textile Industries, University of Leeds, Leeds LS2 9JT, U.K. Received 25 December 1997; revised received and accepted 19 March 1998 The effect of second nozzle design on the properties of yams made of cotton, polyester and regenerated cellulosic fibres has been studied. The axial orifice angle of the second nozzle has been varied and its influence on the yam properties studied. The optimum axial orifice angle is found to be different for different fibres. Keywords: Air-jet spinning, Air-jet ilozzle, Axial orifice angle, Tenacity, Unevenness, Work of rupture, Wrapper 1 Introduction Air-jet spinning offers advantages in respect of processing speed and cost. The heart of this spinning technology is the air-jet nozzle which converts the fibre strand into yam. Several researchers have reported tht: influence of various process parameters on the structure and properties of air-jet spun yams l.? But very few publications have appeared regarding the influence of the design parameters of the nozzles on the structure and properties of the air-jet spun yams. We have reported earlier 8 that the various design parameters of second nozzle such as axial orifice angle, diameter of twisting chamber and the diameter of air nozzle throlugh which the air passes to the twisting chamber CM influence the structure and properties of yams. The single design parameter which has the maximum influence on yam properties is the axial orifice angle of the nozzle. The present work aims at finding out the optimum axial orifice angle of the second nozzle while processing different fibres. 2 Materials and Methods 2.1 Materials Three varieties of cottons marked as Cotton 2, Cotton 3 and Cotton 4, one polyester, one polyester/ cotton blend and one regenerated cellulosic fibre were used in the trials. The physical properties of these fibres are shown in Table I. 'Present address: The South India Textile Research Association, P.B. No. 325, Coimbatore India bpresent address: Department of Textile and Apparel Management, College of Textiles. North Carolina State Uni versity, Raleigh, USA 2.2 Methods Preparation of Yarn Samples For producing the yams, an experimental ng described elsewhere 8 was used. The process parameters and the design parameters can be easily modified in this rig. The spinning principle used is MJS twin jet principle where the air is forced througlh two nozzles in such a way that the rotation of the fibre assembly takes place in the opposite directions. BotJh first and second nozzles are made of brass. The specifications of the nozzles are as follows: First Nozzle Diameter of twisting chamber Diameter of jet orifice Jet axial orifice angle Second Nozzle 2. mm. 5 mm 45 Diameter of twisting chamber 1.6 mm Diameter of jet orifice.5 mm Outlet divergence angle 4 Jet axial orifice angle 4, 45 and 5 (Nozzles B, C and D ) A schematic diagram of the second nozzle is showlll in Fig.l. Throughout the experiments, the take-u JP ratio was maintained at 95%, the air supplied to the first nozzle at a pressure of 2.5 kg/cm2 and the delivery speed was maintained at 65 m/min Tests The fibre properties were assessed by IIC-Shirley fineness maturity tester and Instron tensi le tester. The tensile properties of the yarns were assessed by Textechno statimat instrument. Gauge length was 5 cm

2 BASU & OXENHAM: INTERDEPENDENCE OF FIBRE TYPE & DESIGN OF NOZZLE 11 Table I - Fibre properties Property Cotton 2 Cotton 3 Cotton 4 Polyester Tencel Staple length, mm Micronaire Maturity ratio ~) Fineness,dtex \ \.25 \.6 \.7 Tenacity, g/dtex Elongation at break, % Table 2-2nd nozzle 1st nozzle Actual ori fice pressure count angle, deg kg/cm 2 tex Effect of second nozzle orifice angle on yam properties Tenacity Elongation Irregularity Thin Thick Neps cn/tex at break CV % places places (+2%) % (-5%) (+5%) COTTON 2 COTTON 3 COTTON <)() loo \(,() IXO I O() XO and the traverse speed of the jaw was adjusted to maintain the yarn breaking ti me at 2 ±2 s. The yarn unevenness and imperfections were measured by Zell weger Uster Tester 3 at a testing speed of 4 m/min. Fig. I - Basic design of second nozzle 3 Results 3.1 Cotton Yarns The propert ies of yarns spun us ing Cottons 2, 3 and 4 are given in Table 2. The resul ts show a similar trend fo r all the three cottons. The yarns which were spun using nozzle (axia l ori fice angle, 5 ) as second nozzle show the hi ghest tenacity va lues as compared to the other yarns (Fig.2). The irregu larity values expressed by CY % show the m inimum va lue when nozzle is used fo r spinn ing the yarn s.

3 12 INDIAN 1. FIBRE TEXT. RES., MARCH ' k 8 5 II... z.... ~ 1 5 'u C II t (Cotton 2) t (Cotton 2) t (Cotlon 3) 11-2t (cotton 3) -*- 9t.. (Cotton4) -.- 1St (Cotton 4) 3.2 Polyester Yarns The yams were spun at varying first nozzle pressure (1-4 kg/cm 2 ). Table 3 shows that th(~ strongest yarns are produced when the first nozzl(~ pressure is 3.5 kg/cm 2 The yams spun by using nozzle and nozzle C (axial orifice angle, 45 ) are stronger (Fig.3), but the yams produced by using nozzle C have better elongation at break as well as work of rupture. It is expected that the yam with higher work of rupture perfonns better in further processes such as warping, weaving, etc. In all, the nozzle B (axial orifice angle, 4 ) produced better yarns as compared to nozzle C (Table 3). In general, the CY % of yarn is lower when nozzle B is used ~...-:::;:;.,...::::::: =-.,... ~ nd Nont. Orific. Angt.,d.g Fig. 2 -Influence of second nozzle orifice angle on tenacity of colton yams 3.3 Polyester/Cutton Blended Yarns 5/5 polyester/cotton yarns were spun using nozzles B, C and D. The first nozzle pressure was varied from I kg/cm 2 to 4 kg/cm 2 (Table 3). Fig. 4 shows the change in tenacity values. It is seen that the best yams (as per strength is concerned) are produced when nozzle C IS used as second nozzle. 3.4 Tencel Yarns Yarns of fineness 15 tex were spun from Tencel, a regenerated cellulasic fibre, at varying first nozzle pressure ( kglcm\ Fig.5 shows that the strongest yarns are produced when nozzle B is used as Table 3 - Effect of second nozzle ori fice angle on yam properties 2nd nozzle 1st nozzle Tenacity Elongation Work of Irregul arity Thin Thick Neps orifice pressure cn/tex at break rupture CV % places places (+2%) angle, deg kg/em) % g en (- 5%) (+5%) 1% Polyester (Count, 18.5 tex) /5 Polyester/Cotton (Count, 2 tex) Contd

4 BASU & OXENHAM: INTERDEPENDENCE OF FIBRE lype & DESIGN OF NOZZLE 13 Table 3 - Effect of second nozzle orifice.angle on yam properties--contd 2nd nozzle 1st nozzle Tenacity Elongation Work of Irregularity Thin Thick Neps orifice pressure cn/tex at break rupture CV % places places (+2%) angle, deg kglcm 1 % gcn (-5%) (+5%) 'tO Tencel (Count, 15 lex) Nozzle C Nozzle 17 Nozzle 5 5 )( )( 4!! 15 ::: -z z u u Nozzle B?: 4 5 Nozzle C?:- v u c 13 t ~ Nozzle B ) 9 L-----'---_L-- L-_---J 1----' st Nozzle Pressure. kg/em 2 Fig. 3 -Influence of second nozzle orifice angle and fjrst n7.zle pressure on tenacity of 1 % polyester yarn second nozzle from front roller. There is not much difference in CY % of the yarn tenacity when nozzle B and nozzle C are used as second nozzles (Table 3). 4 Discussion From the above results it IS observed that the 25 L--.-..l.! L-_ , 1 I st Nozz le Pressure, k g/c m 2 Fig. 4 -Influence of second nozzle orifice angle and firsl nozzle pressure on tenacity of 5/5 polyester/cotton yarn nozzle design optimum for cotton fibres is not optimum for other fibres. The possible explanations are as follows: When the compressed air is forced through a nozzle at high pressure, the force dissolves into two

5 14 INDIAN J. FIBRE TEXT. RES. MARCH r , Horizontal Component O-;sting Force) ~ ~~.. " z u~?: v co Vertical Component (pulltng Force) Compressed Air through ~ Nozzle Fig. 6-Components of force t5~j5r j Nozzle- B st Nozzle- Pre-ssure-, kg/cm 2 ~ '" o ~ D Fig. 5 - Influence of second nozzle orifice angle and first nozzle pressure on tenacity of Tencel yarn components. The part, vertical to the axis of the nozzle, helps in false twisting of the fibres and the horizontal part helps in pulling the fibres towards the delivery side (Fig.6). The cotton fibres generally contain a considerable amount of short fibres and when the strands of cotton fibres face the high twisting force generated by air turbulence inside the twisting nozzle, the short fibres get disturbed and as these move out from the axis they cannot take part in sharing the load under strain. With wider axial orifice angle, the drag or pull on the fibre strand towards delivery side increases which helps the fibres to consolidate with the core fibres and, in tum, improves the yam tenacity. This phenomenon holds good for polyester/cotton blended yarns al so. Moreover, Grossberg et at.7 observed that the generation of the wrapping fibres depends on the production of free and edge fibres and the creati on of sufficient di stance fro m the fro nt ro ller nip to where the fibres end converge w ith the tw isting strand. According to them, the pressure in the second jet, i.e. the twist level, Fig. 7 - Ai r Pressure, kg /cm 2 Influence of air pressure on drag force (second nozzle) determines the number of edge fibres being escaped from twisting-in by the strand. When nozzle D is used for cottons, the twisting fo rce becomes lower which helps in creating more wrapper fibres in addition to the bett er consolidati on of core fibres. When the po l ye ~ te r fibre strand is processed. the above factors do not affect much due to the abscnce of large number of short fi bres. In these ca ses. nozzl e C, which has th e optimulll t\vistin g force and pu ll. IS found optimulll.

6 BASU & OXENHAM INTERDEPENDENCE OF FIBRE TYPE & DESIGN OF NOZZLE 15 To simulate the actual spinning condition the same second nozzles used in the experimental frame were fixed below the upper jaw of a Instron tensile strength tester. A cotton yam was passed through the nozzle as on the spinning frame and one end was fixed with the upper jaw of the Instron tester. The compressed air was passed through the nozzles at the levels which were used during the production of yams. The drag or pull felt by the load cell of the (nstron tester was recorded in the charts. The forces at different levels of air pressure are shown in Fig. 7. It is seen from the results that the maximum force is recorded when nozzle D (axial orifice angle,5) is used as at the same input pressure of air. This result corroborates the earlier explanation. 5 Conclusions The design of the nozzle plays an important role in determining the quality of air-jet spun yarns. For cotton or blend fibres, the second nozzle with axial orifice angle of 5 is the optimum. For man-made fibres where the fibre length variation is low, the nozzle with axial orifice angle of 45" is optimum. Whilst jet spinning may produce acceptable ya rns from polyester rich blends, it is apparent that jet-spun ya rns produced from cotton possess very low tenaci ty. Some modifications in the design of certain critical components can afford improvements in the tenacity of cotton yarns, but the benefits are evident for fine counts (about 1 tex) only. Other design parameters of nozzles may affect the properties of yarns in different way depending on the fibre properties. Acknowledgement One of the authors (A.B.) is grateful to the Mini stry of Human Resources Development, Government of India, for providing financial assistance for this project. References Chasm,l\I ala R J. Ilansen S M & Jayaraman S. Text Res.J. 6 ( 19<)() ) 61 2 I\rlLt 1'. Dallman II & Ziegler K. Chel1lie/asern {ext-ind. 35 (1 9 85) 876..\ Wang K Y & Jar-dan G. II /cl/iwul Textilber, 65 (1984) Punj S K. Ish'tiaque S M &Dhingra L K. Indian.J Fibre Texl Res. 22 (1997) Rajamanickam R. Hansen S M & Jayaraman S. Text Res (I <)97) La\\n:nce C 1\ & Baqui M A. Text Res.l. 6 1 ( 19<) I) Grossberg P. Oxenhalll W & Miao M..J Text Illst. 78 ( 1 ()X7) 189. X Oxcnham W & Basu 1\. Text Res.l. 63 ( 19<)3) 674.