The influence of twisting degree on the yarn

The degree of twisting of the yarn not only affects the appearance quality of the yarn, such as the diameter and gloss, but also affects the inherent quality and feel of the yarn such as strength, elasticity, and elongation. Therefore, the determination of the degree of yarn twisting in the textile process is also of particular importance.

(a) Impact on yarn diameter and density

Twisting increases the density of fibers in the single yarn, reduces the gap between the fibers, increases the density of the single yarn, and decreases the diameter. When the twist factor increases to a certain value, the compressibility between the fibers in the single yarn becomes very small, and the density does not change much with the increase of the twist coefficient. On the contrary, since the fiber is inclined too much, the diameter of the yarn may slightly increase.

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

(b) Impact on yarn strength

For short fiber yarns, the most direct effect of twisting is to obtain strength. However, the greater the degree of twisting, the greater the strength of the yarn. This is due to the fact that twisting has both positive and negative effects on the strength of the yarn. There are also factors that are detrimental to the strength of the yarn.

1. Favorable factors

(1) Increasing the twist factor increases the centripetal pressure of the fiber on the yarn uranium, increases the frictional resistance between the fibers, and decreases the likelihood of the yarn breaking due to slippage between the fibers.

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

Under the action of tensile force, the yarn always occurs at the minimum strength of the yarn. The strength of the yarn is the external force that the weak loop can withstand. As the twist factor increases, more roundabouts are assigned to the weaker loops, which makes the weaker loops stronger than anywhere else, thus increasing the yarn strength.

2. Unfavorable factors


(1) Twisting causes the fibers in the yarn to tilt, so that the axial component of the fiber is reduced, and the strength of the yarn is reduced.

(2) The fibers are prestressed during the yarn twisting process. When the yarn is stressed, the fiber's ability to take on external forces is reduced.

The effect of twisting on yarn strength is the unity of opposites between the above favorable factors and unfavorable factors. When the twist factor is small, the favorable factors play a dominant role, as the yarn strength increases with the increase of the twist factor. When the twist factor reaches a certain value, it appears that unfavorable factors play a leading role, and the yarn strength decreases with the increase of the twist factor, as shown in Figure 2-9. The twist coefficient at the maximum yarn strength is called the critical twist coefficient (ak in the diagram), and the corresponding twist is called critical twist. In the process design, the twist factor less than the critical twist factor is generally used to improve the production efficiency of the spinning frame under the premise of ensuring the strength of the spun yarn.

QQ picture 20150729095443

(c) Effect on yarn elongation at break

For single yarns, twisting reduces the possibility of fibers slipping in the yarn and increases fiber elongation and distortion, which is reflected in a decrease in elongation at break of the yarn. However, as the twist coefficient increases, the degree of inclination of the fibers in the yarn increases, and the tendency of the fibers to be inclined decreases and the yarn becomes thinner as the fibers are stretched, so that the yarn elongation at break increases. In general, in the range of commonly used twist factors, the favorable factors are greater than the adverse factors, so as the twist factor increases, the elongation at break of the single yarn increases.

For strands twisted in the same direction, the influence of the twist factor on the elongation at break of the yarn is the same as that of the single yarn. For strands twisted in different directions, when the twist factor is small, the twisting of the strands means the retraction of the single yarn. The average twist of the strands decreases with the increase of the twist coefficient, so the elongation at break of the strands The rate has declined slightly. When the twist coefficient reaches a certain value, the average rate increases with the increase of the twist coefficient, and the elongation at break of the strand also increases.

(d) Impact on yarn elasticity

The elasticity of the yarn depends on the elasticity of the fiber and the structure of the yarn. The yarn structure is mainly formed by twisting the yarn. For the single yarn and the same twisted strand, twisting makes the yarn structure compact. As the fiber slip decreases, the stretchability of the fiber increases. Within the general twist coefficient range, the yarn elasticity increases as the twist coefficient increases.

(e) Effect on yarn luster and feel

Single yarns and strands twisted in the same direction, due to twisting, tilt the fibers on the yarn surface and roughen the surface of the yarn, resulting in poor yarn gloss and harder feel. For twisted twisted strands, when the ratio of the strand twist factor to the single yarn twisting coefficient is equal to 0.707, the outer strand width is zero, and the surface fibers are parallel to the yarn axis. At this time, the strands have the best gloss and soft touch. .


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