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.

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.

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.

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.

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.