Anwar Abdkader

Superconducting Magnetic Bearing as Twist Element in Textile Machines

Superconducting magnetic bearings (SMBs) enable the levitation of a magnet in a stable position over a cooled superconductor without the need for an additional positioning system. These passive bearings are being investigated for applications wherever a stationary levitation or a contact-free rotary or linear motion is desired and cannot be realized by simpler means. Ring spinning is the most widely used technique for the production of short staple yarn in the textile industry. The productivity of the ring-spinning process depends on the rotational speed of the spindle. It is limited by friction in the so-called ring-traveler twist element. During the spinning process, the traveler is dragged along the ring by the yarn with up to 30000 r/min. The resulting friction causes wear of the twist element and melting of synthetic yarn at high spindle speeds due to strong heat generation. Recently, an SMB was implemented as a contact-free twist element in a ring-spinning machine up to 11000 r/min. This prototype SMB consists of a rotating permanent-magnetic (PM) NdFeB ring acting as a yarn-driven traveler and a stationary bulk YBCO ring at 77 K in an open LN2 bath. In this paper, we investigate the bearing properties of this SMB with regard to the special requirements of the ring-spinning process. Dynamics of the spatially vibrating and rotating PM ring are analyzed including the forced vibration due to interaction with the yarn. For the expected yarn forces, the displacement amplitude at the resonance frequency remains below the field-cooling height. In addition, the possibility of realizing higher rotational speeds by mechanically reinforcing the NdFeB ring with a shrunk-on steel shell is discussed.

Innovative twisting mechanism based on superconducting technology in a ring-spinning system:

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.

Dynamics of rotating Superconducting Magnetic Bearings in Ring Spinning

A superconducting magnetic bearing (SMB) consisting of a stationary superconductor in a ring-shaped flowthrough cryostat and a rotating permanent-magnetic (PM) ring is investigated as a potential twist element in the textile technological process of ring spinning. Since the dynamic behavior of the rotating PM influences the yarn and the stability of the spinning process, these factors are studied in this paper considering the acting forces of the yarn on the PM-ring, its vibration modes, and the resulting oscillation amplitudes. For the assessment of a safe field-cooling distance during the operation of the rotating SMB in a ring-spinning machine, a correct calculation of the resonance magnification is particularly important. Therefore, the decay constant δ of the damped oscillation was measured as a function of the field-cooling distance (FCD) and the displacement. The observed increase of the decay constant δ with the initial lateral displacement and decreasing FCD is discussed in correlation to the number of depinned flux lines.

Mathematical modeling of the dynamic yarn path depending on spindle speed in a ring spinning process

This paper presents a mathematical model to predict the distribution of yarn tension and the balloon shape as a function of spindle speed in the ring spinning process. The dynamic yarn path from the delivery rollers to the winding point on the cop has been described with a non-linear differential equation system. These equations have been integrated with a Runge–Kutta method using MATLAB software. Since the numerical solution of the equations strongly depends on initial values, an algorithm of sensitivity analysis has been developed to predict the right choice of initial values in order to find a stable solution. For model validation purposes, the yarn tension has been measured between delivery rollers and yarn guide. Furthermore, a high-speed camera has been used to capture the balloon shape at different spindle angular velocities in order to compare the theoretically determined balloon shape with the one that actually occurs on the machine.

Development of new hybrid yarn construction from recycled carbon fibers for high performance composites. Part-I: basic processing of hybrid carbon fiber/polyamide 6 yarn spinning from virgin carbon fiber staple fibers

The availability of a considerable amount of waste carbon fiber (CF) and the increased pressure to recycle/reuse materials at the end of their life cycle have put the utilization of recycled CF (rCF) under the spotlight. This article reports the successful manufacturing of hybrid yarns consisting of staple CF cut from virgin CF filament yarn and polyamide 6 fibers of defined lengths (40 and 60 mm). Carding and drawing are performed to prepare slivers with improved fiber orientation and mixing for the manufacturing of hybrid yarns. The slivers are then spun into hybrid yarns on a flyer machine. The investigations reveal the influence of fiber length and mixing ratio on the quality of the card web, slivers and on the strength of the hybrid yarns. The findings based on the results of this research work will help realize value-added products from rCF on an industrial scale in the near future.

Cryogenic System for the Integration of a Ring-Shaped SMB in a Ring-Spinning Tester

A liquid nitrogen cryostat has been developed for experiments with a Superconducting Magnetic Bearing (SMB) in a ring spinning machine. The use of an SMB without friction instead of the common friction afflicted twist element is a promising approach leading to increased productivity and material variety. Here, an SMB designed as an axial ring system consisting of a liquid nitrogen (LN2)-cooled high-temperature superconductor ring YBa2Cu3O7-x and a permanent-magnet ring at room temperature is investigated. To assure the high quality of the yarn, the process has strong edge conditions concerning the air moisture and the ambient temperature. To protect the yarn from LN2 temperature, a continuous-flow cryostat was designed, tested, and integrated in the ring spinning tester. The geometric requirements of the spinning process lead to a ring-shaped vessel with a hole in the middle for the rotating spindle. First spinning experiments running at rotations in the range of 20 000 rpm show a reliable operation of the continuous flow cryostat in the SMB-based spinning process. In addition, easy process handling and low LN2 consumption are demonstrated.

Measurement Methods of Dynamic Yarn Tension in a Ring Spinning Process

The most common measuring method to characterise the dynamic yarn path in the ring spinning process is to measure the yarn tension, where the yarn path is almost straight. However, it is much more complex to measure the yarn tension at the other positions, for example, between the yarn guide and traveller (balloon zone) and between the traveller and winding point of the cop (winding zone), as the yarn rotates continuously around the spindle axis. In this paper, two new methods of yarn tension measurement in the balloon zone are proposed. In the first method, the balloon shape was first recorded with a high speed camera. The balloon tension was then calculated by comparing the yarn strain (occurring in the balloon zone) measured by a digital image analysis program with the stress-strain curve of the yarn produced. In the second method, the radial forces of the rotating balloon were measured by using modified measurement techniques for measurement of yarn ten sion. Moreover a customised sensor was developed to measure the winding tension between the traveller and cop. The values measured were validated with a theoretical model and a good correlation between the measured and theoretical values could be revealed.

Development of a new hybrid yarn construction from recycled carbon fibers (rCF) for high-performance composites. Part-II: Influence of yarn parameters on tensile properties of composites:

This article reports the successful manufacturing of hybrid yarns from virgin staple CF (40 or 60 mm) or recycled staple CF (rCF) by mixing with polyamide 6 (PA 6) fibers of defined length. The hybrid yarns are produced using an optimized process route of carding, drawing, and flyer machine. Furthermore, the influence of CF length, CF type (i.e. virgin or rCF), CF volume content, and twist of the yarn are also investigated regarding the tensile properties of unidirectionally laid (UD) thermoplastic composites. The results show that CF length, yarn twist, and CF content of composites play a big role on the tensile properties of thermoplastic composites. From the comparison of tensile strength of UD composites produced from 40 and 60 mm virgin staple CF, it can be seen that the increase of yarn twist decreases the tensile strength. However, the effect of twist on the tensile properties of UD composites manufactured from 40 mm virgin staple CF is insignificant. The tensile strength of UD thermoplastic composites manufactured from the hybrid yarn with 40 and 60 mm virgin staple CF and rCF is found to be 771 ± 100, 838 ± 81, and 801 ± 53.4 MPa, respectively, in the case of 87 T/m containing 50 volume% CF.

Influence of process parameters on the tensile properties of DREF-3000 friction spun hybrid yarns consisting of waste staple carbon fiber for thermoplastic composites:

Due to their excellent strength, rigidity, and damping properties, as well as low weight, carbon fiber reinforced composites (CFRCs) are being widely used for load bearing structures. On the other hand, with an increased demand and usage of CFRCs, effective methods to re-use waste carbon fiber (CF) materials, which are recoverable either from process scraps or from end-of-life components, are attracting increased attention. In this paper, hybrid yarns consisting of waste staple CF (40 and 60 mm) and polyamide 6 staple fibers (60 mm) are manufactured on a DREF-3000 friction spinning machine with various process parameters, such as spinning drum speed, suction air pressure, and core–sheath ratio. The relationship between different textile physical properties of the hybrid yarns, such as tensile strength, elongation, and evenness with different spinning parameters, core–sheath ratio, and input CF length is revealed.

Influence of Fibre Length and Preparation on Mechanical Properties of Carbon Fibre/Polyamidea 6 Hybrid Yarns and Composites

The aim of this paper was to investigate the effect of carbon fibre (CF) length and preparation prior to carding on the mechanical properties of hybrid yarns as well as composites consisting of CF and polyamide 6 (PA 6). The hybrid yarns are manufactured using an optimised process route of carding and drawing with a flyer machine from virgin staple CF (40/60/80/100 mm) and PA 6. In order to explore the effect of fibre preparation on the mechanical properties of hybrid yarns as well as composites, virgin staple CF and PA 6 fibres were prepared by varying the mixing type prior to the carding process. For this purpose, the fibres were mixed either by a fibre-opening device or supplied directly to the carding machine without prior mixing. The CF content of the card webs produced is kept at 50 volume %. Hybrid yarns were produced with a twist of 102 twist/m and then thermoplastic unidirectional (UD) composites were manufactured from them. The investigations revealed the influence of the input CF length and mixing type on the mechanical properties of hybrid yarns and thermoplastic UD composites.