Main factors affecting yarn strength and elongation
The main factors affecting the yarn strength and elongation are the fiber properties and yarn structure. The strength and elongation of the blended yarn are closely related to the property difference of the blended fiber and the blended ratio. The external factors such as temperature, humidity and strength test conditions have the same influence on the yarn strength and elongation as the fiber.
Fiber length and linear density:
When the fiber length is longer and the fiber is fine, the friction resistance between the fibers in the yarn is larger and it is not easy to slip off, so the yarn strength is higher.
When the fiber length uniformity is good and the fiber is fine and uniform, the yarn is even and weak rings are few but not significant, which is beneficial to the improvement of yarn strength.
When the strength and elongation of fiber are large, the strength and elongation of yarn are also large; The yarn strength is high if the fiber is strong and the unevenness of elongation is small.
Fiber surface friction properties:
When the fiber surface friction coefficient μ increases, the interfiber sliding resistance increases, the slippage length lc decreases, the proportion of slippage fiber number decreases, and the yarn strength increases. Increasing the fiber crimp number can increase the sliding resistance between fibers.
(1) The influence of staple yarn structure on its strength and elongation is mainly reflected in twist.
When the twist coefficient increases, the friction resistance between wood fibers increases and it is not easy to slip, which is a positive side of the short fiber yarn strength. However, when the twist coefficient increases, along with the increasing fiber tilt, the effective component of fiber strength in the yarn axis decreases, and the fiber fracture heterogeneity intensifies. At the same time, the increase of yarn diameter when the fiber tilts is an unfavorable factor to the relative strength of the yarn.
(2) The impact of joint stock
The combination of single yarns makes the strands of plyyarn uniform, and there is contact between each yarns, so that the binding force between the outer fibers of the single yarn increases. The yarn strength is greater than the sum of the yarn strength.
(3) the arrangement of fiber in staple yarn
The strength of rotary cup yarn is lower than that of ring spun yarn: in rotary cup yarn, there are more irregular arrangement fibers such as fold, curl and ring, but less normal transfer fibers, resulting in poor contact between fibers and fibers, and more slippage fibers during stretching.
(4) bulk yarn
The tensile breaking strength of the expanded yarn is smaller than that of the traditional yarn, while the elongation at break is larger.
Structural characteristics: two kinds of fibers with great difference in thermal shrinkage are blended for thermal shrinkage treatment, so that the fibers with high shrinkage in the yarn are fully retracted, and the normal fibers with small thermal shrinkage are compressed and crumpled along the yarn axis to present the bulk characteristics.
Tensile fracture process: the number of fiber roots under external force is small and the tension of each fiber is not uniform. At the beginning of the stretch, only a small portion of the fibers bear the force, while the rest crumple and relax. After the first fiber is broken, the second fiber is straightened and bears the tensile force until the whole fiber breaks.
(5) Deformation yarn and stretch yarn
Depending on various shaping methods, each fiber has a spiral spring or curly directional wrinkle curve.
At the beginning of a considerable stretch, the fibers are actually straightened gradually with very little increase in tensile force, and they all have very high elongation at break.