Masaaki Okamura

Effect of Suction Air Pressure in Friction Spinning on Yarn Properties

We have studied the effects of suction air pressure on the structural parameters and mechanical properties of yarn. Changing the amount of suction air pressure improves the fiber extent in yam and yarn appearance. Therefore, photographic and fiber tracing methods are used to evaluate, respectively, yam appearance and fiber extent in the yam. To consider the effect of suction air pressure on yarn diameter, yam tension at the yarn-forming zone and yam diameter are measured simultaneously on a friction spinning machine using various levels of suction air pressure, and then the relationship between them is considered using the cross correlation method. The results show that at high suction air pressure, yarn di ameter, yarn unevenness, and yam irregularity decrease, while fiber extent in the yarn and twist efficiency increase. On the other hand, the value of the correlation coefficient demonstrates that there is a high correlation between variations in yam tension and yarn diameter. The results of yam mechanical property measurements show that at high suction air pressure, yam tenacity increases and yarn elongation decreases. Results are reported from experiments on 100% cotton yams.

Filament Pre-tension in Core Yarn Friction Spinning

Core yams are known to improve cotton yam properties. In this research, core yarns are spun by introducing filaments under tension into the yarn-forming zone of an ex perimental friction spinning apparatus. A 30-denier (3.3 tex) nylon monofilament and a black 75-denier (35f) nylon multifilament make up the core, and cotton fibers are used as the sheath. The effect of filament pre-tension on the structural parameters and mechanical properties of the core yarn is examined, and core yarn properties are com pared with those of equivalent 100% cotton yarns. The photographic and fiber tracing methods are used to consider the appearance of the yarns and the geometric position of the core in the core yarns. The results show that the appearance of the core yarn is similar to that of regular cotton yarns, with the exception of core yarns produced with 00 gf/fil pre-tension. Core yarn irregularity does not change with filament pre-tension, and it is less than that of cotton yam. Core yam strength significantly increases as filament pre-tension and filament percentage increase, and it is greater than that of cotton yarn. Core yarn elongation is less than that of cotton yarn at a low filament percentage and greater than that of cotton yarn at a high filament percentage.

ANALYSIS OF YARN TENSION IN THE YARN-FORMING ZONE IN FRICTION SPINNING

We have analyzed the tension distribution along the yarn tail in the yarn-forming zone of a friction spinning machine by considering the effective parameters of the torque applied to the yarn tail. Tension is applied to the yarn tail by suction air pressure and rotation of friction rollers. The yarn tension in the yarn-forming zone is measured for various yarn counts and suction air pressures. The effects of the parameters on yarn tension are considered in a theoretical analysis based on tension distribution along the conical yarn tail. Theoretical results are compared with me experimental data. The results of this research show that yarn tension increases with increasing suction air pressure and yarn size in tex, and yam diameter decreases with increasing suction air pressure for the same yarn size. Therefore, because of the low tension experienced with fine yarns, it is difficult to properly produce such yarns through friction spinning.

False Twist in Core Yarn Friction Spinning

We have analyzed false-twist distribution in filaments along core yams produced on a friction spinning machine, considering the effective parameters for imparting twist to the filaments and yarns. The theoretical analysis is based on twist distribution along the conical yarn tail. Twist is applied to the yam tail by suction air pressure and rotation of the friction rollers. The theoretical results are compared with the experimental data. The results show that although, theoretically, the twist imparted to a filament is zero, there is still some twist in the filament in both directions (S and Z) in a short yarn length. As the sample length increases, these twists combine and cancel each other. The resulting twists tend toward zero in longer yam samples. Filament pre-tension also affects the false twist of the filament. The results show that the remaining twist in filaments in non-pre-tensioned yams is greater than that in pre-tensioned yams.

Hollow Yarn in Friction Spinning. Part II: Yarn Structure and Deformation Under Axial Tension and Lateral Forces

In Part I of this study, we explained the method of producing a hollow yarn on a friction spinning machine and then considered its tensile properties. In this part of our study, we consider the structural properties of that yarn and the effect of axial and lateral forces on its structure, such as diameter changes, ellipticity, compressibility, and volume. We compare the properties of hollow yarns with those of equivalent 100% cotton yarns. The results indicate that stretching tension may affect the yarn diameter variation but not its linear density. The yarn diameter is bigger than that of conventional cotton yarn, and it decreases with increasing axial tension, which also happens to a conventional cotton yarn. Other results show that the yarn ellipticity ratio is greater than that of the cotton yarn and that it increases with increasing PVA percentage in the hollow yarn. In addition to higher compressibility, the hollow yarn shows better recovery. The volume of hollow yarn after compression is also greater than that of conventional cotton yarn.

Fiber Speed and Yarn Tension in Friction Spinning

To investigate fiber speed inside the transport channel, fiber flow and yarn tension are measured at the same time on a friction spinning machine. Fiber speed at the fiber flow detection point is calculated using the number of fibers in a cross section of the channel at the detection area, the number of fibers in the cross section of sliver, and the speed of sliver feeding. The cross correlation method is used to obtain the time lag between the variation of yarn tension and the number of fibers in the channel cross section. The mean fiber speed between the fiber flow detection point and the yarn-forming zone is calculated from the time lag. Fiber speed in both cases is calculated for various levels of suction air pressure. The results of this research show that fiber speed decreases from the beginning to the end of the transport channel, and increases with increasing suction air pressure in the yarn-forming zone. On the other hand, calculating the value of the correlation coefficient demonstrates that there is a high correlation between yarn tension variation in the yarn-forming zone and the number of fibers in the channel cross section.

Limits of Hollow Yarn in Friction Spinning

In hollow yarn spinning, the yarn is spun with a PVA filament in its core in the yarn-forming zone, which provides enough dynamic strength to the yarn during spinning. Therefore, the dynamic strength of the yarn is not so important a factor in spinning. In order to measure the spinning limit of a hollow yarn, we measure the strength and irregularity of the hollow yarns after extracting the PVA. The results show that the high PVA percentage hollow yarns do not show good tensile properties and irregularity. Both spinning and PVA extraction increase the irregularity of the cotton component in the yarns or hollow yarn products, while the effect of PVA extraction can be minimized by treating the yarns when they are formed into fabrics. We conclude that the PVA percentage should not exceed 40%. We also conclude that the middle count yarns (20 tex and thinner), which are not spinnable as conventional yams, can be spun on a friction spinning machine using the hollow yarn spinning technique.

Producing Medium Count Yarns from Recycled Fibers with Friction Spinning

Yams production from recycled fibers (RF) is limited, and spinners often prefer to produce coarse yams from these fibers. In this research, we attempt to produce middle- count twp-component and three-component yams from RF in such a way that the RF in the yarn core are completely covered by virgin cotton fibers. To improve the tensile properties of such yams, we produce a three-component yarn with a continuous filament in its core, RF in the middle layer, and virgin cotton fibers in the sheath, using a friction spinning machine modified for this purpose. The results show that the appearance of the 51/49 cotton/RF two-component yams is like that of a 100% cotton yarn, and the imperfections of the RF sliver have no significant effect on yarn appearance. The results also show that the strength of a two-component yarn is greater than that of a 100% RF yarn. Spinning a 30 tex yarn from 100% RF is very difficult, and the end breaks are extremely high. In practice, it is impossible to produce yarn from RF. However, producing a 30-tex two- component yarn using RF with new fibers in the sheath is easy and trouble-free, but the yarn is weak. The tensile properties of the yarn show that the strength and elongation of a 30-tex three-component core yarn are greater than those of an equivalent 100% cotton yarn, a cotton/RF yarn, and a 100% RF yarn. Also, the irregularity of the three-component core yarn is less than those of cotton/RF and RF yams. Thus, we show that medium count yams of acceptable appearance and tensile properties can be produced from RF.

Fiber Feeding onto the Yarn Tail in Friction Spinning Part II: Convergent Fiber Transport Channel

The divergent channel in friction spinning causes fiber deceleration and inferior orientation in the transport channel. A convergent channel is designed, and the properties of yarns made by it are compared with conventional channel yams. The position of the convergent transport channel relative to the suction slit is a very important factor in improving yarn properties. The results of our research show that yams made by the convergent channel positioned 15 mm from the beginning of the suction slit are the strongest. The mechanical properties and structural parameters of friction-spun yams made by conventional and convergent channels are investigated at various suction air pressures. The results clearly indicate that the strength of yams made by the convergent channel is about 22% higher with no significant difference in elongation compared with yams made by the conventional channel at a suction air pressure of 2000 mmAq. Yarn twist at the various suction air pressures has no significant impact on yarns made by the two channels, meaning that the convergent channel provides the same twist efficiency as the conventional channel. We also find that yarns made by the convergent channel have a higher proportion of long effective fiber lengths and a lower proportion of short effective fiber lengths in which the total fiber extent is about 54.1 % compared to about 48.6% for conventional channel yams. We conclude that the superior strength of yarn made by the convergent channel is due to differences in its structure.

Yarn Tail Structure in Friction Spinning

We have analyzed the yarn tail structure in the yarn-forming zone of a friction spinning machine by considering the shape of individual fibers in the yarn. We use photographic and fiber tracing methods to consider the shape of individual fibers in the yarn structure. In this research, we try to demonstrate that the shape of the yam tail in friction spinning can be obtained from the fiber configuration in the yarn structure. The results of our research indicate that the yarn tail in the yarn-forming zone has a complex shape. The tip of the yarn tail is thicker than in theory, not only because of the volu minous structure in this part of tail in the yarn-forming zone, but also because it may be affected by the quality of fibers feeding in to the yarn tail through the outlet of the transport channel. The experimental results of the twist imparted to the yarn tail also show that the twist in the inner and outer layers of the yarn is different and increases in the yarn center 2-2.5 times compared with twist in the yam surface.