Innovative Twisting Mechanism Based on Superconducting Technology in a Ring-Spinning System

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Mahmud Hossain, Anwar Abdkader, Chokri Cherif, Maria Sparing, Dietmar Berger, Günter Fuchs, Ludwig Schultz Innovative twisting mechanism based on superconducting technology in a ring-spinning system

Erstveröffentlichung in / First published in: Textile Research Journal. 2014, 84(8), S. 871 – 880 [Zugriff am: 07.08.2019]. SAGE journals. ISSN 1746-7748.

DOI: https://doi.org/10.1177/0040517513512393

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Original article Textile Research Journal 2014, Vol. 84(8) 871–880 ! The Author(s) 2014 Innovative twisting mechanism based Reprints and permissions: sagepub.co.uk/journalsPermissions.nav on superconducting technology in a DOI: 10.1177/0040517513512393 ring-spinning system trj.sagepub.com

Mahmud Hossain1, Anwar Abdkader1, Chokri Cherif1, Maria Sparing2, Dietmar Berger2,Gu¨nter Fuchs2 and Ludwig Schultz2

Abstract Twist plays an important role to impart tensile strength in yarn during the spinning process. In the most widely used ring-spinning machine for short staple yarn production, a combination of ring and traveler is used for inserting twist and winding the yarn on cops. The main limitation of this twisting mechanism is the friction between the ring and traveler, which generates heat at higher speed and limits the productivity. This limitation can be overcome by the implementation of a magnetic bearing system based on superconducting technology, which replaces completely the existing ring/traveler system of the ring-spinning machine. This superconducting magnet bearing consists of a circular superconductor and permanent magnet ring. After cooling the superconductor below its transition temperature, the permanent magnet ring levitates and is free to rotate above the superconductor ring according to the principles of superconducting levitation and pinning. Thus the superconducting magnetic bearing (SMB) ensures a friction-free operation during spinning and allows one to increase spindle speed and productivity drastically. The yarn properties using the SMB system have also been investigated and they remain nearly identical to those of conventional ring yarns.

Keywords yarn, ring spinning, twisting, ring/traveler system, superconducting magnetic bearing, permanent magnet ring, high-temperature superconductor, pinning effect

The ring-spinning process is the most widely used following equation: spinning method for short staple yarn production. It nspi is due to the high quality of the yarn and the ﬂexi- T ¼ ð1Þ V bility that the ring-spinning process is still dominating over unconventional spinning technologies such as where T is the actual twist in turns per meter, nspi is the rotor spinning, air jet spinning, etc. According to spindle speed in rpm and V corresponds to the delivery the principle of the ring-spinning process, as shown speed of the front drafting roller in m/min. in Figure 1(a), the ﬁbrous material roving to be spun is fed to the drafting system to be stretched according to required yarn count. Then the drafted roving is 1Institute of Textile Machinery and High Performance Material delivered in the ring/traveler system through the Technology (ITM), Technische Universita¨t Dresden, Germany yarn guide to impart twist to the yarn and winds it 2IFW Dresden, Institute for Metallic Materials, Germany on cops. The traveler rotates on the ring and is dragged with the spindle via the yarn attached to it. Corresponding author: Mahmud Hossain, Institute of Textile Machinery and High Performance Each rotation of the traveler along with the ring Material Technology (ITM), Technical University of Dresden, inserts one turn of twist in the yarn. The amount Breitscheidstrasse 78, Tor 3, Dresden 01237, Germany. of twist in yarn can be estimated from the Email: [email protected] 872 Textile Research Journal 84(8)

1 Figure 1. (a) Principle of ring-spinning process. (b) Forces acting on traveler in the ring/traveler system. FR: frictional force; Fz: centrifugal force; Fw: winding force; Fv: force component of Fw; Q: air resistance.

The rotation of the traveler lags somewhat behind problem in the existing ring and traveler. It limits the that of the spindle due to the relatively high friction of productivity particularly when spinning high twist the traveler on the ring and the atmospheric resistance cotton yarn and even melts synthetic yarns. That is of the traveler, as well as the thread balloon between why the production rate of ring-spinning machine is the yarn guide and traveler. This difference in speed lower, for example, approx. 1/10th of rotor spinning between the spindle and the traveler enables the wind- and 1/20th of the air jet spinning machine.5 In order ing of yarn onto the cops. to reduce or eliminate the wear and damage of the ring/ The length of yarn wound up on the cops must cor- traveler system, either the friction between the ring and respond over time to the length delivered at the front traveler has to be reduced or the existing ring/traveler delivery rollers. Thus, the length of yarn Lw wound on system should be eliminated. the cops per minute can be calculated according to fol- Many concepts have been developed to reduce or lowing equation: eliminate the friction between ring and traveler and are summarized briefly as follows:6–11 Lw ¼ dsðnspi À nTÞð2Þ . different materials of the ring/traveler system (such where ds is the actual winding diameter in m and nT is as synthetic, steel, ceramic, etc.); the rotational speed traveler in rpm. . different forms of ring and traveler (such as C, N, However, the ring/traveler system limits the product- Elliptic and SU Traveler, T-flange, S-shaped angular ivity of the ring-spinning machine. The friction between flange, etc.); the ring and traveler increases sharply at higher spindle . implementation of coatings of nitrogen, chromium, speed. As shown in Figure 1(b), the main forces acting nickel, etc. on the traveler are the frictional force between the ring and traveler, the centrifugal force of the rotating trav- However, these developments have improved the ring- eler and the winding force. During spinning, high con- spinning productivity only to a minor degree. tact pressure occurs between the ring and traveler. This Further developments,12–24 such as pressure includes strong frictional forces, which in turn lead to heat generation. This heat has to be dissipated . a rotating ring; at a faster rate to avoid quicker wear-out of the ring . an electromagnetically controlled ring; and traveler. The low mass of the traveler does not . the Nova-spinning process; permit dissipation of the generated heat in the short . the TLS (Traveler-less-system) process; time available, which leads to a high temperature in the contact zone, causing breakouts and unstable run- have not been industrially implemented yet due to their ning of the traveler, as well as premature wear of the complexity. ring, which ultimately influences yarn quality.2,3 Thus, Recently, an active magnet bearing system, in which the maximum production of ring spinning is limited by the rotating magnetic ring is suspended in space by the the traveler speed of about 40 m/s.4 This is the central magnetic levitation system, has been developed as a Hossain et al. 873 replacement of the existing ring/traveler system.24 This development provides a ring-spinning system character- ized in part by the replacement of the ring/traveler system with only one rotating, floating ring that has an eye on its inner middle surface. The yarn passes through this eyelet on the bobbin and due to the rotation of the spindle, the floating ring revolves with the yarn tension and thus imparts twist on yarn. The ring is kept suspended in space by the active magnetic levitation system.24 However, this type of bearing is rather complex with many sensors, requires high maintenance and also occupies more space in the ring-spinning machine. In this paper, an innovative high-performance twisting and winding mechanism based on superconducting technology is presented, taking into account the Figure 2. Levitated magnet over superconductor (HTSC). dynamics of yarn in order to overcome the main limi- HTSC: high-temperature superconductor. tation of the existing ring-spinning process. The implementation of superconducting magnetic bearings temperature. Figure 2 illustrates magnetic flux lines of (SMBs) offers a friction-free twist element and no a PM, which are emerging from the north pole to the sensor or complex control system is necessary, in con- south pole. Some of the flux lines penetrating through trast to the aforementioned active magnetic levitation the superconductor are pinned by nano-crystalline system. The concept of applying a suitable SMB for defects within the superconductor, the so-called ‘pin- twisting the yarn in the ring-spinning machine has ning centers’. been internationally patented.25 Designs of superconductor magnet Superconducting magnetic bearing bearing ring The SMB is a very promising application of high- The SMB is comprised of superconducting material and temperature superconductors (HTSCs). It is based on a magnetic component. In general, the well-known two the interacting force between an agent system (such as a designs of SMB27–30 can be applied as twisting and permanent magnet (PM)) and HTSC elements. The winding devices in the conventional ring-spinning unique concept of these bearings is that they possess a machine: self-stabilizing behavior, that is, they remain fully passive devices without any necessity for position sensing 1. SMB1, where a magnetic ring rotates coaxially over and control. Contactless, self-stabilizing levitation from a superconductor ring; standstill up to the highest relative velocities are the 2. SMB2, where a magnetic ring rotates coplanarly advantages of this bearing. This results in benefits inside the superconductor ring. such as being wear-free, redundancy of the control and sensor units, high reliability and the absence of EMC (electromagnetic compatibility). Superconducting magnetic bearing, SMB1 Principle of superconducting magnetic bearing As shown schematically in Figure 3(a), the PM (rotor) and the superconducting ring (stator) are arranged To construct a SMB, a PM can be placed over a super- coaxially with the spindle axis in place of the conven- conductor at some millimeters distance (by means of a tional ring/traveler system. The PM is levitated and free non-magnetic spacer). By cooling the superconductor to rotate, while the superconductor ring remains sta- to À196C with, for example, liquid nitrogen, the flux tionary. The weight of the PM has to be minimized lines of the PM penetrating the superconductor are for two reasons: (1) in order to reduce the moment of pinned by nano-crystalline defects within the supercon- inertia during its rotation and (2) in order to avoid ductor, which is known as the ‘flux pinning effect’.26 overloading of the bearing in which the weight of the When the spacer is removed, the superconductor gen- PM has to be compensated by the bearing force. erates a restoring force due to induced super-currents, Figure 3(b) shows schematically the flux lines of the which keep the magnet in a stable levitated position as PM (rotor) that penetrate the superconducting material long as the superconductor stays below its transition of the stator. Before cooling, the stator and rotor are 874 Textile Research Journal 84(8)

Figure 3. Superconducting magnetic bearing, SMB1: (a) topology; (b) cross-sectional view of SMB1, where magnetic fluxes are trapped in the pinning center during levitation.

Figure 4. Superconducting magnetic bearing, SMB2: (a) topology; (b) cross-sectional view of SMB2 where magnetic fluxes are trapped in the pinning center. held at a fixed axial distance. After the superconductor force (pinning force) of magnetic fluxes penetrating ring is cooled below the transition temperature of the into the superconductor for both designs can be superconducting material, the PM keeps a stable levi- expressed as31 tated position, due to the principle of the ‘flux pinning effect’ already described in section Principle of super- Fp jc Á A Á dB=dz ð3Þ conducting magnetic bearing of this paper. The PM (rotor) is rotated above the superconducting (stator) where jc is the critical current density of super-currents, through the yarn winding on the bobbin. A is the effective area between superconducting and magnetic ring, and dB/dz is the magnetic field gradient. Superconducting magnetic bearing, SMB2 SMB2 has the advantage of a larger stiffness than SMB1, if a sufficiently long yttrium barium copper In the second proposed design, a PM ring levitates oxide (YBCO) hollow cylinder is used. However, the coplanarly inside the superconducting ring. After cool- preparation of such a hollow cylinder is much more ing down the superconductor, the permanent magnetic complicated than the preparation of the YBCO ring ring will be levitated, surrounding the bobbin as shown required for SMB1. Taking into account that only in Figure 4(a). moderate bearing forces are required in a ring-spinning Figure 4(b) shows a cross-sectional view of the bear- machine, SMB1 has been investigated in this work. ing in which the magnetic flux lines of the PM ring are The ring-spinning machine using SMB1 is shown trapped by the pinning centers within the supercon- schematically in Figure 5. ductor, after the superconductor is cooled below its transition temperature. Thus, the PM ring levitates Technical data of superconducting inside superconductor ring. magnetic bearing (SMB1) The most important parameters of the SMB are the static bearing force and the stiffness for vertical and SMB1 has been already implemented in a ring-spinning lateral displacement (SMB1), as well as axial and tester of the Institute of Textile Machinery and High radial displacement (SMB2). The attainable bearing Performance Material Technology (ITM) in order to Hossain et al. 875 investigate whether this type of bearing is principally strong as possible. Strong pinning forces can be realized suitable for using as a twist inserting element. in melt-textured bulk YBCO material.32–34 It is possible SMB1 is composed of a neodymium-iron-boron to manufacture superconducting YBCO magnets that (NdFeB) magnet ring provided by IBS Magnet and a can produce magnetic fields of 16 Tesla at À249C and superconductor ring from YBCO provided by evico attractive or repulsive levitation forces up to GmbH. NdFeB is one of the strongest PMs with very 5000 N/cm2.35 good magnetic properties. The density of NdFeB is 3 7.4 g/cm and the fracture strength is 80 MPa. For a Assembling the superconducting magnetic bearing magnet with a diameter of 10 cm, a maximum rotation speed of ca. 28,400 rpm is possible, taking into account As shown in Figure 6(a), the superconducting ring has the tensile stress and the fracture strength. In order to been placed on a non-magnetic brass pot, which is used realize higher rotation speeds, the PM ring has to be as a container for liquid nitrogen in order to cool down reinforced. YBCO (YBa2Cu3O7-x), on the other hand, is the superconductor. a crystalline chemical compound and a popular high- The magnetic flux lines of the PM act as an excita- temperature superconductor, achieving superconduct- tion system in the SMB. A metal eyelet (yarn guide) has ivity at transition temperature, Tc ¼ –184 C above the been fixed on the surface of the PM so that the yarn can boiling point of liquid nitrogen (À196.15C). For the be twisted and wound up on the bobbin from the spin- technical application, the pinning force must be as ning zone. The whole system is surrounded with poly- styrene for insulation purposes. In order to avoid additional magnetic forces between the PM and the ring-spinning machine, the existing metallic ring rail is replaced with a wooden one. In Figure 6(b), the com- plete SMB system is shown after its placement in the ring-spinning tester.

Ring spinning with SMB Before the start of the yarn production in the SMB, the YBCO superconductor is cooled on À196C and kept at this temperature throughout the whole spinning process. A non-magnetic spacer has been used between the PM ring and superconductor to ﬁx the levitation distance. The ﬂux lines of the PM ring penetrate the superconductor ring, as shown schematically in Figure 7. At the beginning of spinning in the SMB, the rotational speed of the PM has to be controlled, or rather Figure 5. New concept of ring-spinning using SMB1. increased slowly. Otherwise, the higher moment of

Figure 6. Superconducting magnetic bearing: (a) construction; (b) implementation in the ring-spinning tester. 876 Textile Research Journal 84(8)

Figure 7. Schematic diagram of superconducting magnetic bearing SMB1 before cooling.

Table 1. Spinning parameters

Parameters Values

Material 100% PES Staple length (mm) 38 Roving count (tex) 678 Yarn count (tex) 31 Twist (t/m) 475

Twist coefficient, atex 26.45 Spindle speed (rpm) 3640 Delivery speed (m/min) 7.66 Ring diameter (mm) 38 Total draft 22.8

PES: polyester. Figure 8. Spinning with the superconducting magnetic bearing in the ring-spinning machine. inertia of the PM would lead to yarn breakage. Starting The spinning process using a SMB in a ring-spinning with a low spindle speed it is possible to spin yarn with- tester is shown in Figure 8. out an additional brake system. Each rotation of the PM imparts twist in the yarn. Investigation of yarn properties The vertical stiffness of this SMB1 is 60 N/mm, compensating for the weight of the PM ring already The yarn properties, such as microscopic appearance of at a small vertical displacement of 0.02 mm. Thus, levi- the yarn, the yarn tenacity, the yarn twist and the yarn tation is no problem. The lateral stiffness of this SMB1 irregularity, of conventional ring spun yarn and SMB is 30 N/mm, which is sufficiently large for a stable yarn have been investigated under standard atmos- rotation of the PM ring above the YBCO ring, as was pheric conditions and according to the standard confirmed experimentally up to 10,000 rpm. Besides, norm. The testing equipments used to carry out the the rotating PM ring is self-stabilizing at high rotary yarn tests are Zeiss microscope AXIOImager.M1m, speeds. Uster Tensorapid 3, Zweigle twist tester D 312 and Yarn was produced in a SMB (SMB1) and by con- Uster Tester 3. The microscopic view of the yarns is ventional ring spinning with the ring/traveler system. In shown in Figure 9. As shown in the figure, the SMB- both cases the same material and spinning conditions ring yarn is smoother and twisted uniformly compared were used. In this experiment, the yarn count of 31 tex to conventional ring spun yarn. There are more pro- has been produced from 100% polyester (PES) mater- truding fibers in the structure of conventional ring yarn. ial. The following spinning parameters (Table 1) have As the friction as well as the frictional heat in the ring/ been used for this experiment. traveler has been eliminated, fewer protruding fibers in Hossain et al. 877

Figure 9. Microscopic investigation of conventional ring yarn and superconducting magnetic bearing (SMB)-ring yarn.

yarn have been found when implementing the SMB system. Table 2. Yarn properties of superconducting magnetic bearing The other yarn properties are summarized in (SMB) yarn Table 2. Conventional SMB-ring According to Table 2, the SMB-ring yarn has a simi- Yarn properties ring yarn yarn lar strength to conventional ring yarn. The better align- ment of the fibers improves the yarn strength in the case Yarn tenacity (cN/tex) 35.86 36.50 of SMB-ring yarn. The yarn elongation of conventional Yarn elongation (%) 11.56 11.73 ring and SMB-ring yarn has no significant difference. Yarn irregularity (CV %) 11.93 10.00 Since the spinning parameters are the same, these yarns Yarn twist (TPM) 467.75 467.58 show similar types of load–elongation curve (Figures 10 and 11). 878 Textile Research Journal 84(8)

The yarn properties of SMB-ring yarn show the sat- isfactory results compared to conventional ring spun yarn. After further modiﬁcation of the SMB, the yarn properties might improve to a certain level. However, the main advantages of this SMB over the conventional ring/traveler system can be summarized as follows:

. the SMB is a type of passive magnetic bearing system; . no extra control system and sensor is necessary to run a SMB; . no optimization is necessary during rotation of the PM ring; . this bearing system can be implemented as a radial, axial, linear bearing system for high-speed applications such as in linear transport systems, turbo machines, rotating energy storage (ﬂywheel), etc.; . the construction of this type of bearing is simple compared to active magnetic bearing systems; Figure 10. Load-elongation curve of conventional yarn. . the SMB is a stable bearing system, which is important to avoid tension variation of yarn during the spinning process; . the friction-free SMB can rotate stably at a higher speed, which helps to increase the productivity of the ring-spinning machine.

Conclusion and outlook Several twisting mechanisms have been developed in the 150-year-old ring-spinning technology in order to achieve a higher production rate. Mechanical developments of the spindle, a lower spinning ring diameter, automation of doffing, etc., were the vital developments in this time. However, those developments have created only a modest advancement in terms of productivity. In this regard, friction-free SMB offers a high potential to replace the existing ring traveler system. In addition, the construction of this bearing system is very simple compared to other bearing systems, such as active Figure 11. Load-elongation curve of superconducting magnetic magnet bearing. Two main SMB designs have been bearing-ring yarn. analyzed theoretically to implement in the ring-spinning system. One of them has already been applied in a ring-spinning tester and the yarn has been spun suc- The unevenness of SMB-ring yarn has been signifi- cessfully, which proves the suitability of this bearing cantly reduced compared to conventional ring yarn. system in the existing ring-spinning machine. The presence of fewer protruding fibers might result Moreover, the yarn properties of SMB-ring yarn and in more uniform yarn in the SMB system. The yarn conventional ring yarn have been investigated. The twist has been measured according to the twist contrac- SMB yarn has fewer projected fibers and seems more tion method. No significant difference of twist has been even compared to conventional ring spun yarn. The found between conventional ring spun yarn and SMB- yarn irregularity has also been significantly reduced. ring yarn. 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