Effect of backsuction on the twist-tensile strength characteristics of polyester open-end friction-spun yarns

Transcription

1 Indian Journal of Fibre & Textile Research Vol. 17, June 1992,pp Effect of backsuction on the twist-tensile strength characteristics of polyester open-end friction-spun yarns ARB Ibrahim Department of Textile Science and Technology, Ahmadu Bello University, Zaria, Nigeria Received 25 February 1991; revised received 4 February 1992; accepted 28 February 1992 Six yarn packages were spun under different spinning conditions using a laboratory open-end friction-spinner to observe the effect of back suction on the twist-tensile strength characteristics of polyester open-end friction-spun yarns. An optical method based on tracer fibre technique was used to investigate the distribution oftwists in the yarn structure and a Textechno Statimat M Test Machine (a computerised tensile strength tester) was used to determine the tensile-strength characteristics. It is observed that backsuction increases the amount of twists along the length of yarns while the magnitude of pressure used in spinning influences this effect. The yarns spun with backsuction show higher tenacity, breaking elongation, initial modulus and work to rupture than the yarns spun without backsuction. Backsuction reduces the yarn diameter, makes the yarn finer and so should be employed for better mechanical properties of the yarns. Twist distribution in open-end friction-spun yarns varies much, probably due to the complexity of the mechanics of twist insertion. The highest tenacity (14.85 cn/tex) shown by the package backsuctioned at mm pressure is still low for commercial utilization of the yarns. Keywords: Backsuction, Friction-spun yarn, Open-end friction spinning, Polyester yarn, Twist-tensile strength characteristics 1 Introduction The need to have increased production in yarn spinning for the money invested has led to the introduction of new yam production systems. In both ring- and rotor-spinning systems, the spinning speed is strictly dependent on the count and twist, about 20 m/min for ring and 150 m/min for rotor spinning, whereas in OE friction spinning, speed does not depend on count and twist and is above 200 m/rnin I. But, the spinning speeds in ring- and rotor-spinning can be increased up to 30 m/min and 200 m/min respectively, while the speed in OE friction-spinning system can be increased up to 450 m/rnin. Open-end friction-spinning system gives extremely high machine productivity, higher than all other commercial systems. But the product from this new spinning system still suffers from low tensile strength due to lack of proper fibre orientation in the structure of the yarns. Lord et al? reported that open-end friction-spun yams have about 60% of the tenacity of ring-spun yarns or about 90% of that of rotor-spun yams. In this spinning system, yams are consolidated by supplying separated fibres to a torque zone within a shear field followed by removal of yarn being formed. The shear field is created by one or more solids rotating in the same direction, e.g. cylinders. Open-end friction-spun yarns can also be produced by introducing fibres to the appropriate zones", and a popular solution is to make at least one of the moving surfaces a non-flat revolving solid. This permits a fibre supply channel to be brought close to the torque zone, which helps control the fibre-assembly process. In this case, the torque is generated by the oppositely moving surfaces, and the arriving fibre is carried into mesh with the yarn by one of those surfaces or by the yarn itself. However, the emerging yarn does not rotate, and only a rotating envelope of fibres at open-end is capable of twisting in the arriving fibres. The direction of arrival of the fibres is said to be more or less opposite to the direction of departure of the yarn. This is called backward spinning. Though, it is possible for the fibres to approach at other angles with respect to the yam, the best arrangement is not known yet. The concept of enclosing the yarn between two frictional surfaces is found in all OE friction-spinning methods published in the patent literature. Twist can be imparted by friction using two

2 IBRAHIM: EFFECT OF BACKSUCTION ON CHARACTERISTICS OF FRICTION-SPUN YARNS 73 rotating symmetrical bodies. Either outside or inside friction may be used". OE friction-spun yarns have no systematically formed wrapped fibres', with lower fibre straightened.and orientation compared to the ring and rotor yarns. It remains to be seen whether the advantages of the yarn structure, considering the restricted application field due to lower strength, offer so many economic advantages that a market introduction of OE friction-spinning technology is justified". Brockmanns and Lunenschloss' reported that both the tenacity and elongation of OE friction-spun yarns depend, to different degrees, on the final yarn count and spinning speed. Due to the tensional torsion insertion during open-end friction-spinning the mass variation in the fibre feeding stream leads to changes in the friction conditions and also to stronger twist variations" in the yarn. A large number of fibres in the rotor yarns are loosely wrapped around the yarn, with some forming rings or wrappers around the yarn giving a bulk appearance". This is also found in open-end friction-spun yarns and is a contributing factor to yarn imperfection. As with all spinning systems, the mass irregularity of open-end friction-spun yarns depends on the count" with optimum passage of drafting. The quality and structure of open-end friction-spun yarns depend essentially on the arrangements for fibre opening and fibre feeding". The regularity of the fibre flow and the degree offibre stretching and orientation during the attachment of the fibre to the rotating yarn end are, in particular, of major importance 1o. Due to the mechanics of yam formation' ~the yam is weak.the present study was aimed at seeing the effect of backsuction on the structure and twist-tensile strength characteristics of polyester open-end friction-spun yarns for full commercial utilization. 2 Materials and Methods For spinning, 100% polyester fibres were used and six different yarn packages were spun in the count range of tex. These fine counts were chosen to forecast the limitations of OE friction-spinning system using single sliver feed method which has not been employed commercially because of the low strength of yams obtained from this method. The OE friction-spinning machine using single sliver feed method, installed in the spinning laboratory of the Department of Textile Industries, University of Leeds, UK was used for spinning the yarn packages. The packages were spun under different spinning conditions. The count of the polyester fibre used was 1.3 dtex while that of the sliver 2.8 g/m with four drawing passages and a draft of 140. The fibres were in the staple form with a staple length of 32 mm. The tracer fibre used for twist investigation was obtained from France. It was made from viscose rayon fibre and dyed black and had a count of 1.5 den with a staple length of 32 mm. The amount of tracer fibre used in the bulk materials was of the order of I%. This amount was adequate for twist investigation to be carried out properly. Methylsalicylate solvent was used to isolate the polyester fibres for twist investigation. The remaining materials include microscope, camera, video and television. 2.1 Preparation of Yarn Samples All the yarn packages were spun with I % tracer fibres at a speed of 160 m/min using OE friction-spinning machine based on single sliver feed method (Platt Saco Lowell). Single sliver was supplied to the torque zone, which after its opening into single fibres was fed perpendicularly to the yarn take off direction. The operations involved in the OE friction-spinning method used can be shown in a simplified form as given below: Single Separation Collection of Twist sliver ~of sliver -+ fibres in the ~ insertion into feed into torque zone the collection of individual created by fibres by friction fibres frictional to produce a elements yarn t Winding yarn onto package The fibre opening device plays an important role here in determining the yarn characteristics since all the fibres have to be oriented, straightened and parallel for better yarn properties. The best opening device position to the spinning zone and the types of opening and feeding devices to obtain the best results are not known yet, and hence the poor performance of the yams from the system. In this study, the feeding of the sliver was kept perpendicular to the spinning zone. Of the six packages, three were spun with backsuction and the remaining three without backsuction under three different spinning pressures of , and mm water gauge to observe the effects of suction and pressure on the spinning system. Packages I and 2 were spun under a pressure of mm water gauge while the packages 3 and 4 were spun under mm water gauge and the packages 5 and 6 were spun under mm water gauge.

3 74 INDIAN J. FIBRE TEXT. RES., JUNE Optical Method of Twist Investigation The presence of wrapper fibres on the surface of open-end friction-spun yarns and the complexity of the yarn structure make the methods used for investigating twist characteristics in conventional yarns unacceptable for this type of yarn structure'? -15. Hence, the optical method was used for this study. The twist t in a yam can be expressed in terms of the twist angle 9 as: tan (J (=-- nd where D is the yarn diameter. If the twist angle is measured along with the corresponding diameter of the yarn with the help of an optical microscope, the absolute yarn twist may easily be calculated without actually untwisting the yarn. Thus, the principle is to measure the absolute twist in the core of open-end friction-spun yarns. A long-stem camera was set over an ordinary microscope and the camera was connected to a television through a video. Each yarn sample was suitably mounted on a glass microslide by wrapping at parallel and lengthwise. The yarn ends were fixed at the slide ends with the help of a quick drying adhesive. The yarn wraps from one side of the slide were removed with the help of a razor blade. For the optical isolation of tracer fibres in the polyester yarns, a few drops ofmethylsalicylate solvent were spread evenly on these yarns with the help of a slide cover. These slides were then mounted on an optical microscope having a micrometer scale in the eye-piece for measuring the yarn diameter after the structure has been fully focussed on the television screen. A protractor, graduated in degrees, was used to measure the angle of twist of the focussed tracer fibres on the television screen. The magnifications used for optical camera and microscope were x IS and x 10 respectively, making the total magnification x 150. Since it was the angle of twist (9) of the tracer fibres in the core of the yarns that was measured with respect to the yarn axis, the diameter corresponding to inflexions of the tracer fibre on the surface of the core in each case was observed on the microscale and was corrected for magnification to provide the values in meter. On an average, seven slides with 8-10 yarns on each were prepared for each of the yam packages to measure the twist by the optical method using Eq. (l). One hundred results were obtained from each of the six packages spun. 2.3 Determination of Tensile Strength The strength characteristics of the yarn packages were determined using Textechno Statimat M Test Machine, a computerized tensile strength tester. Twenty tests were carried out for each of the six packages and the mean values noted. 3 Results and Discussion The average mean and the coefficient of variation (CV%) of twist characteristics are given in Tables 1 and 2 and the tensile strength characteristics are given in Table 3. The results show that the effect of backsuction on twist characteristics of polyester open-end friction-spun yarn is significant. The yarn packages spun with backsuction have much higher tpm than those spun without backsuction at all the pressure levels (Table 1). However, the difference is more for packages spun under mm water pressure. This suggests that the spinning pressure (water gauge) alscaflects the twist distribution in open-end friction-spinning system. The present study has shown that the higher the tpm, the higher the strength. The yarn package 3 (backsuctioned) with the highest tpm (982.2) has the highest tenacity (14.85 cn/tex). But, this tenacity is still low for commercial utilization and is about 60% of that of ring-spun yarns or about 90% of that of rotor-spun yarns". If the individual values of twist angle and yarn Property Overall mean twist angle, tans Overall mean numerical value of tans Overall mean diameter, mm Overall mean turns/mm Table I-Yam twist characteristics (mean values) la (1219.2)b Package 3" (I 320.8)b No sa (1422.4)b (1422.4)b "Backsuctioned packages; "Spinning pressure, mm

4 IBRAHIM: EFFECT' OF BACKSUCTION ON CHARACTERISTICS OF FRIcnON-SPUN YARNS 75 diameter of these yarns are considered even on the same package, it is observed that the yarns vary much along their structures. This is in agreement with the findings of Lunenschloss and Brockmanns I. This study has shown that in open-end friction-spinning system, there is probably a maximum spinning pressure under which the yarns are hard twisted and above this pressure the tpm would reduce and hence the changes in the structure and properties of the yarns (Table l). All the yarn packages spun with backsuction have lower diameter than those spun without backsuction. Fig. 1 shows the average force-elongation curves for the open-end friction-spun yarns. It could be seen from the curves that all the backsuctioned packages have higher initial modulus and elongation than those spun without backsuction and hence the higher work to rupture (Table 3). Table 2 shows the coefficient of variation (CV%) of the yarn twist characteristics. It is observed that CV% values of twist angle (tan 0) for all the yarns spun with backsuction are lower than those for the yarns spun without backsuction. Similarly, the CV% values of tpm for backsuctioned packages are lower than those Table 3- Tensile strength characteristics Yarn Mean Mean Mean work Count package tenacity elongation to rupture tex cn/tex % N cm la a " "Backsuctioned Property Table 2-Yam twist characteristics (CV% values) Package No. Overall CV% of twist angle tane Overall CV% of numerical value of tanf) Overall CV% of diameter Overall CV% of turns/mm I" " " (I 422.4)b (I 422.4)b "Backsuctioned packages; bspinning pressure, mm 15 Packag~ 1 ( Backsuction~d ) Packag~ 2 Packag~ 3 (Backsuction~ ) 10 ~ 15, , Package 4 v ~ 10 Packag~ 5 (Backsuctio~ ) Packag~ 6 5 o Elongation,.,. Fig. I-Average force-elongation curves of the yarns as given by Textechno Statimat M test machine 12

5 76 INDIAN J. FmRE lext. RES., JUNE 1992 for packages spun without backsuction except for package 1. But the CV% values of yarn diameter follow a different trend with some backsuctioned packages having higher values than their counterparts spun without back suction (Table 2). The shapes of the average force-elongation curves also show the effect of backsuction in open-end friction-spinning. All the yarns spun with backsuction have their curves moved more to the average force axis than the yarns spun without backsuction. Acknowledgement This research work was-performed by the author at the Department of Textile Industries, University of Leeds, Leeds, UK. The author gratefully acknowledges the help and encouragement given by the members of the staff of the University of Leeds. References I LunenschlossJ & Brockmanns KJ, Int Text Bull, Spinning, (3) (1985) Lord P R, 100 C W & Ashizaki T, J Text Inst, 78 (4) (1987) Lunenschloss 1& Brockmanns K J, Melliand Textilber (Eng. Ed), 63 (3) (1982) Lunenschloss J & Brockmanns K J, Int Text Bull, Spinning, (2) (1986) 7. 5 Brockmanns K 1 & Lunenschloss 1, Int Text Bull, Spinning, (3) (1984) Lunenschloss J, Brockmanns K J & Phoa T K, Int Text Bull, Spinning, (2) (1986) 7. 7 Louis G L, Salaun H L & Kimmel L B, Text Res J, 55 (6) (1985) Gilhaus K F, Ernst H & Wulfhorst B, Chemiefasernl Text-Ind, 34/86 (1984) 629, E84. 9 Brockmanns K 1 & Johnson N, Int Text Bull, Spinning, (3) (1986) Lunenschloss 1 & Brockmanns K 1, Betrachtugen Zum DE Friktions Spinnen, MTB. 63 (1982) II Lunenschloss 1& Brockmanns K 1,1111 Text Bull. Spinning, (3) (1984) Lunenschloss 1 & Brockmanns K J, Melliand Textilber, 63 (1982) Stalder H, Chemiefasern Text-Ind, (1980) Lunenschloss 1 & Brockmanns K J, Melliand Textilber, 63 (1982) Schlafhorst Information, 8 (1983) 8.