What effect will different degrees of twist have on the yarn?

The degree of twisting of the spinning yarn not only affects the appearance quality such as diameter and finish of the spinning yarn, but also affects the intrinsic quality and feel of the spinning yarn such as strength, elasticity, elongation, etc. Therefore, the determination of the twist degree of spinning yarn in fabric technology is also particularly important.

(1) Effect on the diameter and density of spinning yarn

Twisting makes the fibers in the single yarn denser, reducing the gaps between fibers, increasing the density of the single yarn, and reducing the diameter. When the twist coefficient increases to a certain value, the compressibility between fibers in a single yarn becomes very small, and the density does not change much as the twist coefficient increases. On the contrary, the diameter of the yarn may increase slightly because the fibers are too tilted.

The diameter and density of the strands are also related to the twist direction of the strands and single yarns. When the twist direction of the strands is the same as that of the single yarn, the relationship between the twist coefficient, density and diameter is similar to that of the single yarn. When the strands and single yarns are twisted in opposite directions and the twist coefficient of the strands is small, the density of the strands will decrease and the diameter will increase due to the untwisting effect of the single yarn; when the twist coefficient reaches a certain value, the The density of the strands increases with the increase of the twist coefficient, while the diameter decreases with the increase of the twist coefficient. As the twisting continues, the density does not change much, while the diameter gradually increases.

(2) Effect on the strength of spinning yarn

For short fiber yarns, the direct function of twisting is to obtain strength, but it does not mean that the greater the degree of twisting, the greater the strength of the spinning yarn. The reason is that twisting has existing There are factors that are conducive to improving the strength of spinning yarns, but there are also factors that are not conducive to the strength of spinning yarns.

　1． Favorable factors

　(1) As the twist coefficient increases, the centripetal pressure of the fibers on the yarn increases, the frictional resistance between the fibers increases, and the possibility of the spinning yarn breaking due to slippage between fibers decreases.

　 (2) Twisting reduces the strength unevenness of the spinning yarn in the length direction.

When the spinning yarn is under the action of tensile external force, the breakage always occurs at the weak point of the spinning yarn. The strength of the spinning yarn is the external force that the weak link can withstand. As the twist coefficient increases, more twists are allocated to the weak loop, which increases the strength at the weak loop more than other places, thereby increasing the strength of the spinning yarn.

　2． Disadvantages

(1) Twisting causes the fibers in the yarn to tilt, which reduces the axial component of the fiber, thereby reducing the strength of the spinning yarn.

(2) During the twisting process of the spinning yarn, the fibers are prestressed. When the spinning yarn is stressed, the fiber’s ability to withstand external forces is reduced.

The effect of twisting on the strength of spinning yarn is the unity of the above favorable factors and unfavorable factors. When the twist coefficient is small, favorable factors play a dominant role, which is manifested in that the strength of the spinning yarn increases with the increase of the twist coefficient. When the twist coefficient reaches a certain value, unfavorable factors play a dominant role, and the strength of the spinning yarn decreases as the twist coefficient increases, as shown in Figure 2-9. The twist coefficient when the yarn strength reaches a maximum value is called the critical twist coefficient (ak in the figure), and the corresponding twist is called the critical twist. In process design, a twist less than the critical twist coefficient is generally adopted to improve the production efficiency of the spinning machine while ensuring the strength of the spinning yarn.

(3) Effect on elongation at break of spinning yarn

For single yarns, twisting reduces the possibility of fiber slippage in the spinning yarn and increases fiber elongation deformation, which is manifested in a decrease in the elongation at break of the spinning yarn. However, as the twist coefficient increases, the degree of inclination of the fiber in the yarn increases. When stretched, the degree of inclination of the fiber decreases and the spinning yarn becomes thinner, thereby increasing the elongation at break of the spinning yarn. Generally speaking, within the generally adopted range of twist coefficient, the favorable factors outweigh the unfavorable factors, so as the twist coefficient increases, the elongation at break of single yarn increases.

For strands twisted in the same direction, the effect of the twist coefficient on the elongation at break of the spun yarn is the same as that of single yarn. For strands twisted in different directions, when the twist coefficient is small, the twisting of the strand�� means that for untwisting a single yarn, the average twist width of the strand decreases with the increase of the twist coefficient, so the elongation at break of the strand decreases slightly. When the twist coefficient reaches a certain value, the average twist width increases with the increase of the twist coefficient. As the twist coefficient increases, the breaking elongation of the strands also increases.

(4) Effect on the elasticity of spinning yarn

The elasticity of spinning yarn depends on both the elasticity of the fiber and the spinning yarn structure. The spinning yarn structure is mainly formed by the twisting of the spinning yarn. For single yarns and co-twisted yarns, For strands, twisting makes the yarn structure tight, fiber slippage is reduced, and fiber stretchability is increased. Within the general twist coefficient range, as the twist coefficient increases, the elasticity of the yarn increases.

(5) Effect on the finish and feel of spinning yarn

For single yarns and strands twisted in the same direction, the twisting causes the fibers on the surface of the spinning yarn to tilt and makes the surface of the spinning yarn rough and uneven, resulting in poor luster and poor hand feel. harden. For twisted strands in opposite directions, when the ratio of the strand twist coefficient to the single yarn twist coefficient is equal to 0.707, the outer twist width is zero and the surface fibers are parallel to the axis of the spinning yarn. At this time, the strands have good integrity and feel. soft.

AAASDFERHYTJTI

Disclaimer:

Disclaimer: Some of the texts, pictures, audios, and videos of some articles published on this site are from the Internet and do not represent the views of this site. The copyrights belong to the original authors. If you find that the information reproduced on this website infringes upon your rights, please contact us and we will change or delete it as soon as possible.