Research on the mechanism of the modified ring-spinning system using a dynamic twist-resistant device and its yarn quality

Abstract

The spinning triangle is a critical area in the ring-spinning process; the geometry of the spinning triangle influences the distribution of the fiber tension, and affects the qualities of the spun yarn. In this paper, a kind of dynamic twist-resistant device that can affect the geometry of the spinning triangle is employed for improving the conventional ring-spinning system.

The yarn twists between the front roller nip and dynamic twist-resistant device were captured in the spinning process using a high-speed camera. Comparing yarn twists of the two types of yarn, the modified yarns have a lower twist angle, indicating that the device can produce resistant torque. Particle Flow Code software was used to simulate the acts of the device on the yarn, and the results verified the existence of resistant torque. The resistant torque on the yarn affects the geometry of the spinning triangle and the distribution of fiber tension. In addition, 19.4 and 14.5 tex cotton yarns with three different twists, 700, 800 and 900 tpm, were produced by the modified and conventional ring spinning. The comparative study revealed that the modified yarns have a better performance in terms of yarn strength and hairiness, and show no significant difference in terms of the yarn evenness when compared with the conventional yarns at the same twist level. The mechanism of the effect of the dynamic twist-resistant device on yarn qualities is discussed by analyzing the distribution of fiber tension.

Keywords

dynamic twist-resistant device twist propagation spinning triangle fiber tension distribution

In the ring-spinning process, the drafted roving leaves the front roller nip with a width and all the fibers are almost parallel to the strand axis. Then, because of the twisting effects, the width of the fiber strand starts to decrease and the fiber strand is tied into a yarn at the twist point. The twisting area between the front roller nip and the yarn twist point is recognized as the spinning triangle or twisting triangle.¹ The geometry of the spinning triangle influences the distribution of fiber tension in the spinning triangle and the fiber tensile stress within the yarn, and thus affects the qualities of spun yarn.^2,3 Therefore, the spinning triangle is the most important part in the ring-spinning process. Researches on improving yarn qualities by changing the spinning triangle have been attracting more and more attention.⁴

In the past decades, many theoretic results have been given about the mechanical characteristics of the ring-spinning triangle. Fujino et al.⁵ found that the height of the spinning triangle is influenced by many factors, such as the twisting torque and spinning tension, the number of fibers in the spinning triangle, the fiber distribution at the roller nip, the fiber orientation and the elastic modulus of the fibers. Klein⁶ pointed out that the geometry of the spinning triangle influences the end breakages and yarn structure, especially a long spinning triangle, which shows a much more uniform distribution of force. To reduce yarn hairiness, Wang and Chang⁷ changed the yarn path and the geometry of the spinning triangle in worsted ring spinning. In the study of theoretical models, Hua et al.¹ adopted a modified energy approach to predict the distribution of fiber tension in the spinning triangle.

Inspired by the research works above, some new ring-spinning methods have been devised by changing the spinning triangle, such as the sirospun,⁸ solospun,⁹ Nu-Torque spinning¹⁰ and compact spinning.¹¹ All of these spinning technologies are achieved by changing the ring-spinning triangle.¹² From the research above, we know that a longer spinning triangle shows a much more uniform distribution of fiber tension. In this paper, a type of dynamic twist-resistant device was employed to impede the twist propagation process of the ring-spinning system, and the geometry of the spinning triangle was changed correspondingly. Also, the friction between the device and the yarn balanced part of the spinning tension; thus, the spinning tension in the spinning triangle was reduced, which protected the spinning triangle from breaking. Thus, this paper aims to investigate the mechanism of the effects of the dynamic twist-resistant device and the qualities of the modified yarns. Two different kinds of yarns, 14.5 and 19.4 tex, were spun in the modified and conventional ring-spinning system with three different twists, namely 700, 800 and 900 tpm. The effects of the dynamic twist-resistant device on the yarn were investigated by PFC (Particle Flow Device) software, where the image of yarn twists between the front roller and the twist-resistant device were captured to verify the twist resistance. Then, the influences on yarn qualities were discussed by comparing the yarns spun by conventional and modified ring spinning and analyzing the fiber tension distribution in the spinning triangle.

Modified ring-spinning system

The dynamic twist-resistant device used in this paper was equipped in the conventional ring-spinning system, as shown in Figure 1. The dynamic twist-resistant device was installed between the front roller and the pigtail guide, and it was closer to the front roller. The dynamic twist-resistant device is shown in Figure 2. It is a cuboid container containing circle cylinders that are parallel to each other in two columns. The diameter of the cylinder is 5 mm and the height is 10 mm. The fiber strand formed a certain yarn structure in the spinning triangle, then passed through the device, perpendicular to the cylinders. In this modified ring-spinning system, the cuboid container oscillated with a frequency of 50 Hz, which drove the cylinders to act on the yarn body. Thus, the twist resistance is produced by the applied dynamic normal force on the yarn body. In addition, the friction between the yarn body and the cylinders would also produce twist resistance. The continuous twist resistance impedes the twisting propagation process, which reduces the twisting torque at the twist point. Low twisting torque make the geometry of the spinning triangle become longer compared with conventional ring spinning, and the fiber tension distribution in the longer spinning triangle becomes more uniform.⁶ The spinning region between the front roller nip and the yarn guide is divided into three parts by the device, as shown in Figure 1: the first part is from the front roller nip to the top of the dynamic twist-resistant device, the second part is the area in the dynamic twist-resistant device and the third part is from the bottom of the dynamic twist-resistant device to the yarn guide.

Figure 1.

The modified ring-spinning system with the dynamic twist-resistant device: (1) front roller; (2) the dynamic twist-resistant device; (3) yarn; (4) guiding plate; (5) pigtail guide; (6) bobbin; (7) ring; (8) traveler.

Figure 2.

The dynamic twist-resistant device: (1) cylinder; (2) container; (3) yarn.

In the first part, the drafted fiber strand passes through the front roller nip and enters the spinning triangle, which was changed by the modified system. Therefore, the height of the spinning triangle became longer than in conventional ring spinning.⁵ The image of the spinning triangle in the conventional and modified ring spinning is given in Figure 3. In the spinning triangle, fibers had different tension due to the different path lengths, and the difference of fiber tension affected the qualities of yarn. The longer spinning triangle reduces the path difference of those fibers geometrically.

Figure 3.

(a) the spinning triangle of conventional ring spinning and; (b) the spinning triangle of modified ring spinning.

In the second part, the modified device blocks the propagation of twists. Thus, fewer twists are delivered upward compared with the conventional ring spinning. Meanwhile, the friction between the cylinders and the yarn body balances part of the spinning tension, thus reducing the fiber tension in the spinning triangle. The fiber tension is the most significant factor contributing to yarn torque,^13,14 and smaller magnitudes of fiber tension in the spinning triangle will produce lower yarn torque.³

In the third part, there are more twists compared with the conventional spinning method, because the twist resistance produced by the modified device prevented the twists from propagating. So, a highly twisted zone is formed. In addition, the device is used simply to block the twist delivering upward, not to increase or decrease the twist.

To investigate the force acting on the yarn body, PFC (Particle Flow Code) was utilized to simulate the mechanical behavior of the cylinders and its effects on the yarn body. The PFC software allows the discrete elements to have finite displacement and rotation, including complete separation. In addition, the discrete elements can form new contacts in the calculation process. The contact force and displacement of discrete elements are calculated by tracking the movement of elements. The density of the cylinder is 6000 kg/m³ and the rigidity is 1 × 10⁸ N/m. The rigidity of the yarn is 1 × 10² N/m. In the simulation process using PFC, it is assumed that the yarn will not make a large bending deformation and it will move with the oscillation of the device. The normal force on the yarn is shown in Figure 4. Figure 4 shows the change of normal force within 0.5 s. From Figure 4, it can be seen that the yarn in the modified device is subjected to positive and negative normal force. The normal force changes with a high frequency throughout the entire signal, and the high frequency is continuous and uniform. The maximum normal force is 10.9 cN.

Figure 4.

The force applied by the cylinders on the yarn.

Based on the above discussion, it can be found that the dynamic twist-resistant device can be regarded as a working unit. The main function of the dynamic-resistant device is to improve the fiber tension distribution at the spinning triangle by reducing twist torque between the spinning triangle and the modified device. However, in the Nu-Torque¹⁰ spinning technology, a false twist device is installed between the front roller and the pigtail guide, and the insertion of false twists increases the twists between the spinning triangle and the false twist device. Therefore, the working principle of the modified ring-spinning system in this paper is different from that of the Nu-Torque spinning.

Experimental details

Carded cotton roving of 5 g/10 m was used as the raw material. The fibers have a linear density of 2.1 dtex with a length of 28 mm, and the micronnaire value of 4.8. In the experiments, two types of yarn, 19.4 and 14.5 tex, with three twists, 700, 800 and 900 tpm, were spun by the conventional and modified ring-spinning systems on a DHU X-1 frame at the same spindle speed of 15,000 rpm. The high-speed camera i-speed was used to capture the yarn twist between the front roller nip and the dynamic twist-resistant device. The yarn in the same area spun by the conventional ring spinning was captured too. By comparing the twist angle of the two types of yarn in this spinning section, the resistance in the modified spinning system was verified. In order to make a clearer observation of the twist, it was necessary to dye some fibers in the roving. In addition, for the modified spinning method, to enhance the effects of the modified device on the spinning process, the distance between the front roller nip and the dynamic twist-resistant device was 30 mm; if the distance exceeded the fiber length too much it would weaken the effect of the modified device on the spinning triangle.

Before testing yarns, all samples were conditioned under the standard condition at 20 ± 2℃ and 65 ± 2% relative humidity (RH) for at least 24 h. Then, the yarn strength, hairiness and evenness were tested. The test instruments are as follows: single yarn tester YG061; hairiness tester YG172A; evenness tester CT3000. For each type of yarn, the strength of the yarn was tested 10 times at a speed of 500 mm/min with pretension of 1.8 cN/tex, and the average value of the 10 tested results was taken as the strength of the yarn; the hairiness was tested 10 times with the fragment length of 10 m and the average value of the result was taken as the hairiness of the yarn; the evenness was done 10 times at the speed of 100 m/min with the fragment length of 100 m, and the average value was taken as the evenness of the yarn.

Results and discussion

Comparison of yarn properties

In this section, 19.4 and 14.5 tex yarn with twists of 700, 800 and 900 tpm were spun by conventional ring spinning and modified ring spinning. Pictures of the yarn twist between the front roller nip and the dynamic twist-resistant device and the yarn twist spun by conventional ring spinning in the same area are presented in Figure 5. From Figure 5, it is easy to see that the twist angle of the modified yarn is lower than that of the conventional yarn. The twist angle of the modified spinning method is 16° and for conventional ring-spinning yarn is 34°. The lower twist angle results from the twist resistance of the device. In addition, the device is to affect the distribution of the twist in the spinning process, not to increase or decrease the twist of the final products.

Figure 5.

(a) the twist angle of conventional ring spinning and; (b) modified ring spinning.

Twists of 700, 800 and 900 tpm were adopted for 19.4 and 14.5 tex, respectively, in the modified and conventional ring spinning. Yarn physical properties were evaluated for comparison with conventional yarns at the same twist and the results are shown in Figures 6 –8.

Figure 6.

The strength of (a) 19.4 tex and (b) 14.5 tex modified and conventional yarns with different twists.

Figure 7.

The hairiness of (a) 19.4 tex and (b) 14.5 tex modified and conventional yarns with different twists.

Figure 8.

The evenness of (a) 19.4 tex and (b) 14.5 tex modified and conventional yarns with different twists.

The comparison of the mean difference between properties of yarns produced by the modified and conventional spinning methods at the same counts and twists were conducted using a T-test. The results are given in Table 1, where it is noted that the P-values of the yarn strength and hairiness are smaller than 0.05, except for 19.4 tex at the twist of 900 tpm, indicating that the modified yarns have improved significantly when compared with conventional yarns in these yarn properties. The P-values of the yarn evenness are higher than 0.05, indicating that the evenness of the two types of yarn has no significant difference.

Table 1.

The statistical analysis for the mean values of properties of yarns produced by conventional and modified spinning methods

Yarn type	Twists	P-value
Yarn type	Twists	Strength	Hairiness	Evenness
19.4 tex	700 tpm	0.042	0.006	0.382
	800 tpm	0.000	0.002	0.682
	900 tpm	0.822	0.000	0.747
14.5 tex	700 tpm	0.000	0.002	0.581
	800 tpm	0.000	0.000	0.782
	900 tpm	0.000	0.000	0.625

The strength of 19.4 and 14.5 tex modified and conventional yarns at different twists are plotted in Figures 6(a) and (b), respectively. For both counts, the strength of the modified and conventional yarns linearly increases with the increase of the twist. It is noted that when compared with the conventional yarns at the same twist, the modified yarns show a marked increase at both yarn counts, but the yarn of 19.4 tex at 900 tpm possesses slightly better strength. For 19.4 tex yarns, larger differences are present between the two types of yarn in the region of the lower twist.

Figures 7(a) and (b) show the hairiness of 19.4 and 14.5 tex conventional and modified ring-spinning yarns, respectively, at different twists. It is clear that the modified yarns possesses much less hairiness than the conventional yarns at the same twist. As shown in Figures 7(a) and (b), with the increase of twist, the hairiness of the modified and conventional yarns decreases steadily.

Figures 8(a) and (b) show the comparison of the evenness of 19.4 and 14.5 tex yarns spun by the modified and conventional ring spinning, respectively, at different twists. It can be seen that the evenness of the modified and conventional yarns has a similar value at different twists, and the effect of the modified unit on the yarn evenness is not significant.

From the above results, the modified yarn shows relative advantages in strength and hairiness. That is, the comprehensive qualities of the yarns are improved. In the following section, the experimental results will be explained in detail by analyzing the mechanism of the effect of the dynamic twist-resistant device on yarn qualities.

Discussion

The main difference between the modified and conventional ring-spinning systems is the employment of the dynamic twist-resistant device. The function of the device is to produce resistant torque on the yarn so as to reduce the twisting torque at the twist point. Thus, the geometry of the spinning triangle will be changed correspondingly. The image of the yarn twist between the front roller nip and the device verified that the modified unit has a certain effect on the propagation of twist because it acts on the cylinders on the yarn body. The lower twist angle of the modified yarns indicates the reduction of the twisting torque at the twist point, which leads to the twist point C moving down to $C'$ , as shown in Figure 9. Therefore, the spinning triangle becomes longer compared with conventional ring spinning. The fiber tension distribution in the longer spinning triangle can be analyzed using the energy method¹⁵ by the spinning triangle model shown in Figure 9.

Figure 9.

The model of the spinning triangle with different heights.

In this model, it was assumed that both ends of the fiber in the spinning triangle were gripped by the front roller nip and the twist point, respectively. In addition, the spinning tension applied to the spinning triangle at the twist point was constant. In addition, the fiber stress–strain behavior was assumed to follow Hooke’s law at small strain, and the fibers were distributed uniformly in the spinning triangle. The friction between the fibers and the bottom roller, fiber migration and slippage were not taken into account. Moreover, the geometry of the spinning triangle was symmetrical, ignoring the horizontal deviation of the twist point caused by the twisting torque.

The total energy of the spinning triangle is the sum of the fiber strain energy and the work done by the spinning tension. Solving the minimization of the total energy formula, the distribution of the fiber tension in the spinning triangle can be given, which is similar to the results of Feng et al.¹⁶

\begin{matrix} F_{i = 0 \dots n} = \frac{F - AE {\sum_{i = 0}^{n} [cos θ_{i}^{- 1} (cos θ_{i}^{- 1} - 1) + \sum_{j = 0}^{m} [cos θ_{j}^{- 1} (cos θ_{j}^{- 1} - 1)]]}}{\sum_{i = 0}^{n} cos θ_{i}^{- 2} + \sum_{j = 0}^{m} cos θ_{j}^{- 2} - 1} M + AE (cos θ_{i}^{- 1} - 1) \end{matrix}

\begin{matrix} F_{j = 0 \dots m} = \frac{F - AE {\sum_{i = 0}^{n} [cos θ_{i}^{- 1} (cos θ_{i}^{- 1} - 1) + \sum_{j = 0}^{m} [cos θ_{j}^{- 1} (cos θ_{j}^{- 1} - 1)]]}}{\sum_{i = 0}^{n} cos θ_{i}^{- 2} + \sum_{j = 0}^{m} cos θ_{j}^{- 2} - 1} M + AE (cos θ_{i}^{- 1} - 1) \end{matrix}

where A is the cross-section of the fiber, E is the fiber Young’s modulus, F is the spinning tension, m and n are the number of fibers on both sides of the spinning triangle, $θ_{i}$ is the angle of the ith fiber and center fiber, $θ_{i}$ is the angle of the jth fiber and center fiber and m + n + 1 is the number of total fibers in the spinning triangle.

According to the energy method, the fiber distribution in the spinning triangle can be calculated by MATLAB software. The yarn and fiber parameters used in the simulation were as follows: number of fibers: 123; fiber tension: 20cN; fiber linear density: 2 dtex; fiber Young’s modulus: 30cN/tex; fiber radius: 3 µm. As for the spinning triangle parameter, taking 19.4 tex, 700 tpm modified and conventional ring spinning as an example, the width of both spinning triangles is 2 mm, the height of the modified spinning triangle is 2 mm and that of conventional spinning is 1.5 mm. The distribution of fiber tension in the different heights of the spinning triangle is shown in Figure 10.

Figure 10.

Fiber tension in the different heights of the spinning triangle.

From Figure 10, it can be seen that the increase of the height of the spinning triangle leads to more uniform fiber tension distribution compared with the spinning triangle of conventional ring spinning. In addition, the tension of the outer fibers is reduced.

From the measured results shown in Figures 6 –8, the qualities of modified yarns, under the effects of the dynamic twist-resistant device, are improved. For fiber strength, the modified yarns are significantly different from the conventional yarns. This is because the magnitude of the fiber tension in the spinning triangle tends to decrease with the increase of the height of the spinning triangle, which leads to uniformity of fiber tension. Therefore, the yarn torque is improved due to the uniformity of fibers in the spun yarn,¹⁷ which is beneficial for increasing the lateral pressure between the fibers^12,17 in the yarn and reinforces the yarn strength correspondingly.¹⁸ The effect of the dynamic twist-resistant device on the yarn is not significant at 900 tpm, 19.4 tex. This is because the action of the device on the yarn is relatively small when the twisting torque is increased in the region of high twist.

Hairiness is another significantly improved property of the spun yarn. From the research conducted by Cheng and Li¹⁹ and Kalyanaraman,²⁰ the larger tension forces acting on the outer fibers in the spinning triangle would increase the wrapping of the surface fibers and lead to the reduction of hairiness, correspondingly. However, in the modified ring-spinning system, the fiber tension of the outer fibers is decreased and the hairiness is reduced. This is because the action applied by the device on the yarn body makes the hairiness adhere to the surface of the yarn, which results in the reduction of hairiness. In addition, the adhered hairiness may be partly rolled in the yarn body by the subsequent twist.

The modified ring-spinning system has no significant effect on the yarn evenness for each type of yarn. This is because the dynamic twist-resistant device has no effect on the fiber in the yarn, but on the tension of fibers and yarn torque.

Conclusion

This paper presents a modified ring-spinning system using the dynamic twist-resistant device. This device can produce resistant torque, which prevents the twist propagation process, thus reducing the twisting torque at the twist point, which leads to the increase of the height of the spinning triangle. The high-speed camera i-speed was used to capture the yarn between the front roller nip and the dynamic twist-resistant device, and the conventional yarn in the same area. PFC software was used to simulate the effects of the cylinders in the device on the yarn. The results of the images show that the twist angle of the modified yarn is lower than that of conventional yarn, which verified the resistance effect of the dynamic twist-resistant device on the yarn body.

The cotton yarns of 19.4 and 14.5 tex were spun by modified and conventional ring spinning with different twists, 700, 800 and 900 tpm, and comparison of both yarns at different twists was conducted; the results were analyzed by considering the distribution of fiber tension in the spinning triangle. The experimental results show that, compared with the conventional yarns, the modified yarns have a better performance in terms of strength and hairiness, and the effect of the modified ring-spinning system on the evenness is not significant. This is because the dynamic twist-resistant device affects the geometry of the spinning triangle and makes the height of the spinning triangle increase, which leads to uniform fiber tension in the spinning triangle. According to the simulation of fiber tension in the spinning triangle, a longer spinning triangle presents a more uniform fiber tension distribution, which is of benefit for the yarn torque and yarn strength. The reduction of yarn hairiness is due to the action applied by cylinders, which makes the hairiness adhere to the surface of the yarn. The adhered hairiness may be partly rolled in the yarn body by the subsequent twist.

This paper analyzed the mechanism of the dynamic twist-resistant device and its effect on yarn qualities. However, we have not investigated the effect of the device parameters on yarn twist propagation quantificationally, which will be investigated in future studies combining with the twist transfer equation and its effect on the spinning triangle.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by National Key R&D Program of China (Grant No. 2017YFB0309100), College of Textile, Donghua University, Shanghai, China.

References

Hua

Tao

Cheng

KPS

et al.

Effects of geometry of ring spinning triangle on yarn torque part I: Analysis of fiber tension distribution. Text Res J 2007; 77: 853–863.

Alamdar-Yazdi

. Effects of directed movement of fibres in a twist triangle on yarn quality. J Text Inst 2011; 102: 263–271.

Feng

Tao

et al.

Theoretical study of spinning triangle with its application in a modified ring spinning system. Text Res J 2010; 80: 1456–1464.

Yang

Tao

et al.

Structure and properties of low twist short-staple singles ring spun yarns. Text Res J 2007; 77: 675–685.

Fujino

Uno

Shiomi

et al.

A study on the twist irregularity of yarns spun on the ring spinning frame. J Text Mach Soc Jpn 1962; 8: 51–62.

Klein

. Spinning geometry and its significance. Int Text Bull Yarn Fabric Forming 1993; 139: 22–26.

Wang

Chang

. Reducing yarn hairiness with a modified yarn path in worsted ring spinning. Text Res J 2003; 73: 327–332.

. Dynamic model of sirospun process. Part I: Theoretical dynamic model. J Text Inst 2010; 101: 805–811.

Cheng

. Relationship between hairiness and the twisting principles of solospun and ring spun yarns. Text Res J 2004; 74: 763–766.

10.

Tao XM and Xu BG. Manufacturing method and apparatus for torque-free singles ring spun yarns. Patent 6860095, USA, 2005.

11.

Nikolić

Stjepanovič

Lesjak

et al.

Compact spinning for improved quality of ring-spun yarns. Fibres Text East Eur 2003; 11: 30–35.

12.

Liu

. Research on spun yarn qualities in a modified ring-spinning system using airflow-twisting device. J Text Inst 2013; 104: 1258–1267.

13.

Hua

Tao

Cheng

KPS

et al.

Effects of geometry of ring spinning triangle on yarn torque. Part II: Distribution of fiber tension within a yarn and its effects on yarn residual torque. Text Res J 2010; 80: 116–123.

14.

Bennett

Postle

. A study of yarn torque and its dependence on the distribution of fiber tension in the yarn. Part I: Theoretical analysis. J Text Inst 1979; 70: 121–141.

15.

Shaikhzadeh NS. An analysis of the twist triangle in ring spinning. PhD Thesis, University of New South Wales, Australia, 1996.

16.

Feng

Tao

et al.

Performance of cotton single yarns and knitted fabrics produced by a 2-step spinning method. Fibers Polym 2014; 15: 882–890.

17.

Bennett

Postle

. A study of yarn torque and its dependence on the distribution of fibre tensile stress in the yarn part II: Experimental. J Text Inst 1979; 70: 133–141.

18.

Yang

Tao

et al.

Structure and properties of low twist short-staple singles ring spun yarns. Text Res J 2007; 77: 675–685.

19.

Cheng

KPS

CHL

. JetRing spinning and its influence on yarn hairiness. J Text Inst 2002; 72: 1079–1087.

20.

Kalyanaraman

. A process to control hairiness in yarn. J Text Inst 1992; 83: 407–413.