Effect of fibre length and fineness on Uster classimat faults and other yarn properties

Transcription

1 IndianJournalof Fibre& TextileResearch Vol.JR, December1993,pp Effect of fibre length and fineness on Uster classimat faults and other yarn properties S M Ishtiaque, H V S Murthy & M M Tadvalkar" Department of Textile Technology, Indian Institute of Technology, New Delhi , India Received 8 October 1992; revised received 28 September 1993; accepted 8 October 1993 The effects of fibre length and fibre fineness on the yam quality, with special reference to the Uster classimatfaults, have been studied usingpolyesterand viscosefibresof differentlengths aj;lddeniers and their blends. It is observed that longer fibres givemore stronger yarn and high strength exploitation but tend to showmore incidenceoffaults in the yarn. On the other hand, coarser fibresresult in spinning oflow strength yarn with less faults. Keywords:Classimat faults, Fibre fineness, Fibre length, Polyester fibre, Viscose fibre, Yarn properties 1 Introduction The consumption of man-made fibres in India is increasing steadily though the rate is sluggish compared to that in the rest of the world. With the growth in the number of mills producing blended yarns, the competition has increased substantially. To counteract the increasing fixed costs and to survive in competition, the mills in India have increased the productivity at the ring frames. To achieve this, many of the mills have started using longer fibres. It has been reported \.2 that the use of longer fibres increases the yarn faults. We have earlier reported3 that the major problem arises due to nep formation and finer fibres. while using longer Considering these points, in the present work the effects of fibre length and fineness on the yarn quality, with special reference to Usterc1assimat been studied. faults, have 2 Materials and Methods Polyester and viscose fibres of different lengths and deniers and their blends (62.5:37.5 and 37.5:62.5) were used. About 4.5 m of 45 Ne yarn was spun for each sample. The characteristics of fibres and yarns are given in Tables 1 and 2 respectively. The yarns were tested on an Uster classimat at a speed of 400 m/min through the yam fault detector (Uster Automatic MK CMTL condenser). The fibre tenacity and elongation at break were tested on lnstron tensile tester and Stclomctcr. "Present address: Victoria Juhilee Tc<:hllicallnstiw\e. Bombay India Malunga. 3 Results and Discussion 3.1 Fibre Tenacity and Elongation at Break The fibre tenacity values (Table 1) obtained from the two instruments show some difference but it is not significant at 5% level of confidence. A comparison of tenacity of polyester and viscose fibres of same length and denier shows that polyester fibre is much stronger than viscose fibre. Also, the polyester fibre has high elongation at break in comparison to viscose fibre. Fibre denier and length have no significant effect on the tenacity of both the fibres. 3.2 Effect of Fibre Denier/Length on Yarn Strength Table 2 shows that single yarn strength and lea strength increase with the increase in fibre length and decrease with the increase in fibre denier for both the fibres. Further, from the yarn strength exploitation values it is observed that the fibres with increasing length (keeping the fibre denier constant) not only tend to give more stronger yarns but also show reasonable rise in yarn strength exploitation, whereas the fibres with increasing denier (keeping the fibre length constant) produce weaker yarns and show considerable decrease in yarn strength exploitation. These observations can be supported by the fact that as these yarns are spun at a constant twist multiplier, fibre length and denier play an important role in judging the surface area of each fibre in the yarn as the surface area is directly proportional to the fibre length and inversely proportional to the fibre fineness. The increase in fibre length increases the fibre-to-fibre fricti OIL which tends to produce more cohesion among the

2 ISHTIAQUE et af.: EFFECT OF FIBRE LENGTH AND FINENESS ON YARN PROPERTIES 171 Fibre Length Fibre Fineness (1/ den , (I Single : cm Tenacity, bundle Table gauge) fibre I-Fibre Elongation gjden characteristics at break, % Single fibre Polyester Viscose den tenacity CV%Ib tiona, J fineness exploitafectionsl m imper Yarn 0/0 at Lea count Fibre 386 strength Corrected Yarn CSP Table 2- Yarn characteristics Elonga U% L Ne I Fibre break strength Yarn Total gld ayam Polyester/viscose strength exploitation = Single yarn strength (g/d cm)/single fibre strength (g/d em) fibres, resulting in high strength values at yarn break. Fibre denier plays a reverse role. Increase in fibre denier decreases the surface area of each fibre in the yarn and hence fibre-to-fibre friction is lowered. Further, increase in fibre denier decreases the number offibres in yarn cross-section. Both these factors work together in lowering down the yarn tenacity and result in lower yarn strength exploitation. As far as elongation at break of yarn is concerned, no trend is observed for variation of fibre length and fibre denier. Blended yarns show intermediate behaviour. 62.5:37.5 P/V yarn shows higher yarn tenacity, lea strength and elongation at break compared to 37.5:62.5 P/V yarn. 3.3 Effect of Fibre Length/Denier on Yam Evenness Table 2 shows some increase in the value of U% with increase in fibre length at constant denier. Similarly, increase in fibre denier at constant fibre length also results in some increase in U% value. As the increase in fibre denier decreases the number of fibres in yarn cross-section, the probability of variation in the mass per unit length of yarn is more while using higher denier, and any small change in the number of fibres in the yarn cross-section due to any reason would affect the yam evenness, to a greater extent, in terms of percentage. Table 2 also shows that the value of U% is lower for all the viscose yarns as compared to the polyester yarns.

3 172 INDIAN 1. FIBRE TEXT. RES., DECEMBER Effect of Fibre Length/Denier on Classimat Faults Table 3 shows the c1assimat faults obtained in different class groups. It is observed that the polyester fibre of any length and denier shows lower incidence of faults in almost all the classes. This can be explained on the basis of the flexural rigidity of polyester and viscose fibres. Polyester possesses more rigidity towards flexures while viscose offers less resistance towards flexures. Hence, the tendency to cause a fault in the viscose yam is more; fibres can easily be bonded or entangled due to any little force in the spinning process. Table 4 shows that for both the fibres the total number of yarn faults increases with the increase in fibre length and decrease in fibre denier. The trend is much prominent in A and B types offault but C and D types of fault do not agree with such trend. This clearly shows that A and B types of fault are mainly raw material dependent whereas C and D types are not. This trend can be explained on the basis of moment offorce which acts on the fibre, during the spinning process, in various directions depending on its position in the whole mass of fibre. The longer fibre tends to bend more easily due to the effect of movement of force acting upon it and hence forms more entangled masses, giving rise to A tind F 'J P'-'O> oftaull. F'Jrther, fibre length is the key factor injudging the degree of opening of the fibre mass. More the fibre length, more is the frictional resistance offered to the opening process, giving rise to the unopened masses of fibre cluster. The decrease in Uster c1assimat faults with increase in fibre denier may be explained by the fact that as the fibre denier increases, the flexural rigidity increases and hence the fibre offers increasing resistance towards bending and due to this fibre cluster formation reduces considerably. Another reason for this is the decrease in the surface contact area of higher denier fibres which makes them to offer low resistance during the spinning process. Hence, the fibre opening process followed by drafting is more smoother and produces less number of faults in the yarn. The length and denier of viscose and polyester fibres do not have any influence on E, F, G, H and I types of fault. The classimat faults of blended yarns (Table 5) show that as the viscose constituent of blend increases the yarn tends to show more occurrence of faults. Figs 1 and 2 show the relationships between different Classes of fault and blend proportion. It is observed that in case of total faults and A type faults, the Polyester ,' 1312 Viscose mrn Table I x Classimat mm mrn den x den faults per 100 km of yarn made from fibres of different lengths and deniers ault class

4 ISHTIAQUE et al: EFFECT' OF FIBRE LENGTH AND FINENESS ON YARN PROPERTIES 173 ter- Unobjec :! , BCD o 'To V denier Fibre "... able Objectiontionable Polyester ratio viscose in the yarns Fibre 51 38A FaultsjlOO. km of Total yam Table 4-C1assimat faults " X ] II : x :62.5 1] I3 ]2 II Polyester/viscose den) BlendViscose Faults/100 Ratio km (38 of mm -'00% I5 o Faults I~Relationship P Blend Ratio 100% Ayarn type faults O'kP V Fig. 2~Relationship between B, C & D types andoffault blend ratio and blend in the C4 yam Polyester/viscose 2400 " faults

5 174 INDIAN 1. FIBRE TEXT. RES., DECEMBER 1993 observed and calculated values are approximately the same, but in case of B, C and D types of fault the observed values are lower than the calculated values. It might be due to the measurement technique constraith because of the different dielectric constants of polyester and viscose fibres. 4 Conclusions 4.1 Polyester fibre yarns show higher tenacity, lea strength and elongation at break compared to viscose fibre yarns. Both the polyester and viscose yarns show increase in strength with the increase in fibre length and decrease in fibre denier. 4.2 The yarn strength exploitation is higher in the yarn spun from longer and finer fibres. 4.3 Yarn unevenness seems to have no real effect of fibre length but it increases with the increase in fibre denier. The value ofu% is lower for viscose yarns as compared to polyester yarns. 4.4 The occurrence of faults in polyester yarns is at much lower level compared to that in viscose yarns. 4.5 Increase in fibre length increases the total faults but increase in fibre denier decreases the total faults. 4.6 Fibre length and denier have significant effect on A and B types of fault. 4.7 Blended yarns show an intermediate behaviour when compared with polyester and viscose yarns. The blends with lower viscose content show less occurrence of the classimat faults. References I Khurana S K, Garde A R & Sood M C, Optimum condition in spinning of man-made fibre and blends. paper presented at the 14th ATIRA textile conference, Ahmedabad, March Grover J M & Garde A R, Spinning of man-madefibre on cotton system-problems and prospects, paper presented at the 42nd all India textile conference, Surat, 1-3 December Ishtiaque S M, Text Asia, 20 (1989) 86.