The global competitive situation has forced the modern textile market to focus vigorously on issues like productivity and cost reduction in manufacturing yarn and fabric while maintaining the quality at a high level. Yarn is the prime raw material in fabric manufacturing, like weaving, knitting, and narrow weaving. For maximizing yarn productivity, an increase in the production rate of the spinning machine is necessary. During spinning, the yarn is spun in a simplex machine and ring frame sequentially. The produced material from simplex is fed into the ring frame. Generally, the production rate in the ring frame determines the production output [1] [2]. Textile industries have come out from the concept of conventional ring spinning to enhance productivity and modify the yarn with different structures and properties. Ring-spun yarn, however, has always been the acknowledged quality benchmark within the spun yarn sector [3]. The ring and rotor are two basic spinning systems. In the case of ring spinning, the twist is inserted into yarn by the aid of a rotating traveler. Twisting and wind-up take place simultaneously. The structure of ring yarn is generally assumed as the basic structure in spun yarn technology. Nevertheless, in compact spinning, tension differences between fibers during the twist insertion are smaller than those in-ring spinning due to the reduction of the spinning triangle [4]. It has been claimed that compact spinning has the possibility of attaining yarn strength identical to that in typical ring yarn with approximately 10% lower twist [5]. Many open-end (OE) spinning has been invented, but none can replace the rotor spinning. In rotor spinning, the sliver (fibers bundle) is separated into individual fibers with an opening roller in an air stream, and separated fibers are re-collected in the rotor. The production rate of open-end rotor spinning (OERS) is up to 200 meters per minute for up to 20 Tex linear density [6].

This work endeavors to analyze and compare the parameters of cotton yarn spun on the Suessen EliTe^® compact spinning frame and the open-end rotor spinning frame. Yarns spun on compact spinning have better advantages when compared to open-end rotor spinning in terms of tensile strength and elongation%, mass irregularity on short segments, hairiness, and imperfection index. The analysis allows us to assume the quality parameters of spun yarns for any given linear mass and enables the modeling of yarn parameters for different carded yarn, spun with the use of the compact and rotor to avoid probable faults during spinning.

Textile yarns can be classified according to spinning systems like the ring, compact, rotor, air-jet, friction, and spun yarn. Ring spinning is a universal system, although it has some limitations like small yarn package size, limited spindle speed, traveler speed, ballooning, and the spinning triangle resulting in higher cost and less productivity [7]. So, bound to try a new spinning system, aerodynamic compact and open-end rotor spinning are two of the most established methods. These spinning systems undoubtedly have a distinctive production edge over the ring spinning system. Alternatively, researchers have also focused on enhancing the production of ring yarn by overcoming those limitations [3] [8] [9].

1) Aerodynamic compact spinning

Ring yarn has a high amount of fibers, which not only fail to contribute to yarn strength but also increase yarn unevenness. Compact spinning is a novel approach through the re-engineering of a typical ring spinning process by attaching a pneumatic zone [10]. It eliminates the spinning triangle by condensing the fibers pneumatically or mechanically [11]. It can be achieved by condensing the fiber sheet in the drafting zone. The condensation can be achieved by the three ways [10]:

a) Roving twist: The twist in roving has a 2-fold objective. Firstly, it prevents the roving from being disturbed before it enters the ring frame drafting. Secondly, the twist contains the spreading of the fiber sheet during the drafting process.

b) Mechanical condensing: Condensation of the fiber flow can be enhanced by a funnel-shaped condenser, located between the aprons and delivery rollers. However, it deteriorates the actual drafting by exerting unavoidable frictional forces on the fiber flow.

c) Aerodynamic condenser: An aerodynamic condensation happens by gentle aerodynamic forces after the drafting but before the yarn formation. The fiber flow reaching the spinning triangle is so narrow that all fibers can be caught uniformly. The small-sized spinning triangle allows for excellent yarn formation [12]. In the Suessen EliTe^® compacting machine [13], an aerodynamic condensing zone is used, as shown in Figure 1.

An additional drafting zone [14] [15] is introduced in the 3/3 double apron standard drafting system. A perforated lattice apron closely embraces a tubular profile. The delivery top

roller, fitted with rubber cots, presses the lattice apron against the hollow profile and drives the apron, forming the nipping delivery line. The tubular profile has a small slot towards the fiber flow direction, which commences at the immediate vicinity of the front roller, nipping line, and ends in the region of the delivery nipping line 1(b). An air current is created through the lattice apron via the slot towards the inside of the profile tube, which seizes the fibers immediately after they leave the front roller nipping line and condenses the fiber strand, which is conveyed by lattice apron and transported to the delivery path. As the slot is under negative pressure, it reaches right up to the nipping delivery line,

and the fiber assembly remains compacted [1] [12] [13] [16]. Over 330,000 spindles of ring spinning with the EliTe compact drawing apparatus from Suessen are currently operating in spinning mills all over the world [17]. However, the first compact spinning frame for industrial use was built in 1995 [18].

2) Open-end rotor spinning

In rotor spinning, a conical sliver is continuously formed in a rotor groove, from staple fibers opened in the opening roller, and oriented employing centrifugal forces. At the thickest point of the conical sliver, fibers are twisted into the open yarn end rotating in the rotor, with the twists spreading to the delivery rollers. The fibers located in the yarn core cannot evade the imparting of twists, which results in higher yarn twist and the corresponding higher packing density in the yarn core. In the outer yarn structure, fibers can evade the twist impartation, making the yarn more voluminous. The wrapping fibers are wound around the yarn core in the form of a band. Underneath this is a thin fiber layer with few or partially opposing twists. If the fibers being applied to well-twisted yarn feature fewer permanent than false twists, the fibers are twisted in the opposite direction of the yarn twisting direction [19].

Both compact and rotor spinning were introduced to enhance spindle speed. It was observed that for compact spinning, with increased spindle speed, end breakage rate as well as yarn imperfection increases, and the yarn breaking extension decreases [2]. However, the spindle speed does not affect the yarn hairiness index compared to other factors [2]. Nevertheless, in the case of rotor spinning, maximum spindle speed depends on the rotor diameter and yarn strength. P. Grosberg and S. Mansour experimented on the rotor frame to enhance its speed up to 100,000 revolutions per minute (rpm) [20]. The spindle was modified slightly by reducing the rotating weight and overhanging length. Technologically, the main effect of increasing rotor speed is to increase the spinning tension, which will ultimately cause end breakage. However, there is a limitation for rotor spinning on the range of twists and linear densities that can be spun at different spinning speeds [20].

Mechanical properties of spun yarns depend on not only the physical properties of the fibers but also the yarn structure characterized by the arrangement of the individual fibers in yarn cross-section. Therefore, properties (yarn strength, extensibility, appearance, compactness, packing density) of a compact yarn and open-end rotor yarn are related to fiber distribution along yarn cross-section [21]. Fiber arrangements in open-end rotor yarns (Figure 2) are complicated because of their non-uniform appearance in comparison with ring-spun yarn, which has a uniform fiber core [4].

The number of belly-band fibers is highest in rotor yarn. Belly-band fibers are created when a fiber under high air pressure at the rotor surface is not able to blend with the common twisted strand and winds itself onto the yarn axis as it exits through the navel [4]. Rotor spun yarns have a densely packed core of fibers aligned with the central axis, loosely packed fibers twisted around the core at a considerable angle, and wrapper fibers on the outside. This type of structure

makes rotor spun yarns successful in the commercial manufacture of coarser yarns. A scanning electron microscopic view shows (Figure 3) that a more compact yarn structure would be obtained as the yarns get finer [21]. The compact structure also shows less protruding fibers on the outer surface of the yarn, which will lead to less hairiness, increased uniformity and yarn strength [8] [9] [22] - [26].

Earlier it was found that packing densities of compact yarn is not always uniform in yarn cross-section, although compact yarns had approximately 30% higher packing density compared to that of ring and rotor spun yarns [21]. Considering the idealized helical yarn geometry and it was ascertained that the higher the twist level, the larger the helix angle θ, resulting in a more prominent compressive load [27]. Higher the compressive load, the more compact the yarn structure is. Again, the justified, thicker yarns have more fibers in their cross-sections, which results in a rise in total load (P), and hence the total compressive load acting on the yarn leads to increased packing density [27]. At the same yarn linear density, the rotor yarn is found bulkier than the ring-spun yarn [4].

Structural characteristics of Lyocell rotor yarn were observed by the tracer fiber method [28], which showed that a certain amount of fibers was transferred from the internal to external layer during rotor spinning. Moreover, there were more fiber reversal fragments inside of rotor yarn. The single yarn wet snarling counts were decreased due to those structural properties [28]. Nevertheless, while noticing the configurations of tracer fibers of the ring-spun yarn, it was assumed that ring yarn has an ideal cylindrical average helix angle of 17.2˚ [29].

The main advantages of compact yarns are lower yarn hairiness, higher strength, and elongation values depending on their compactness [21]. The fibers in compact yarns are almost entirely integrated into the yarn body [3] [21] [30] [31]. The spinning speed does not affect the compact yarn strength variability [20]. The compact yarn has reduced the breakage rate of warping and weaving machines. The size consumption of the sizing machine is reduced by up to 50%. It also provides good bursting strength in knitted fabrics [6]. The low hairiness index eliminates the singeing process, and dye consumption is also reduced. Fabric woven from compact yarn has improved tensile strength, pilling and abrasion resistance [18] [23] [32]. Open-end rotor spinning has several advantages

like increased production rate, separation of twisting and winding, and elimination of speed frame and winding. The effect of fiber fineness on the hairiness of yarns made using different spinning techniques is significant. Rotor spun yarn shows the highest deviation from ideal unevenness [33]. Rotor Spun yarns found with frequent breakage during knitting [6] and more irregular than ring yarn [34]. 100% desirability satisfaction can be achieved for specific yarn quality parameters by process optimization, following USTER^® benchmarks, at a rotor speed of 77,800 rpm and 700 twists per meter [35]. Rotor yarn of coarser count is used for denim fabric and tends to show a starting mark due to the creep behavior of yarn [36]. Rotor yarn has a lower maximum tensile load than a ring-spun yarn [19]. Advancements through the compact spinning and how it lacks from the rotor spinning, is the main purpose behind this work.

The above study was carried out to determine the significant differences in the properties of compact and open-end rotor spun yarns, which were influenced by the inner structure of the yarns and their linear density. This was demonstrated in the current work by an analysis of experimental and theoretical assumptions of the geometrical arrangement of fibers in the yarn structures, which indicated a better performance of compact yarns compared to rotor yarn. The study has shown that open-end rotor yarns being composed of core fibers are less parallel compared to aerodynamic compact yarns, which are highly oriented in parallel and also have higher twists. This uniformity makes compact yarn the least hairy between these two. In this regard, the compact spinning effectively controlled the fibers by the condensing process compared to rotor spinning. However, this effectiveness decreased with yarn fineness because the aerodynamic condensing system of the compact spinning technology had better fiber control of finer counts. Again, compact spun yarn shows higher strength, which is a reflection of better fiber migration. Compact yarns are, therefore, stiffer than open-end rotor spun yarns. It can be concluded that compact spun yarn is more effective in terms of irregularity, CV% of irregularity (CV_m), imperfection, hairiness, strength, and elongation as compared to rotor spinning. Though in the case of coarser yarn, the difference is higher, the difference decreases with the fineness of the yarn. Compact yarn assures better economic benefits for both yarn producers and customers, though its manufacturing cost is higher. On the other hand, the open-end rotor spinning ensures significantly less waste generation.

The authors would like to express thanks and gratitude towards Multazim Spinning Mills Ltd., Valuka, Mymensingh, Bangladesh, for providing machinery and equipment on time during this research work and the Zubair Spinning Mills Ltd., Gazipur, Bangladesh, for other assistance that made this work possible. The authors declare that they have no conflict of interest.

The authors declare no conflicts of interest regarding the publication of this paper.

Islam, Md.R., Ahmed, S., Siddik, Md.A. and Ashique, S.M. (2021) Analysis of Cotton Yarn Properties Spun on Aerodynamic Compact and Open-End Rotor Spinning. Journal of Textile Science and Technology, 7, 22-40. https://doi.org/10.4236/jtst.2021.71003