Covered spandex yarn
Spandex covered yarn is an elastic yarn formed by covering spandex filaments with filaments or short fiber yarns in a spiral manner to cover the stretched spandex filaments.
Classification of spandex covered yarn
1. According to the number of coating layers, it can be divided into two types: single-covered yarn and double-covered yarn. Among them, nylon and polyester are mostly covered by single-wrap.
2. According to different equipment, it can be divided into two types: mechanical covered yarn and air covered yarn.
Features of Spandex Covered Yarn
1. Air-covered yarn (abbreviated as empty bag, English abbreviation is acy) is the process of drafting the outer fiber filament and spandex yarn at the same time through a certain type of nozzle, and forming a rhythmic network point by the regular spray pressure of high-compressed air Yarn. The fabric feels soft and smooth;
2. Mechanically covered yarn (abbreviated as machine bag, English abbreviated as scy) is the continuous rotation of the outer fiber filament and winding it on the core spandex drawn at a constant speed. It is twisted and has a twist (English abbreviation is tpm) ), the fabric style is flat and crisp is its main feature.
Both empty and machine-wrapped yarns have their own advantages and disadvantages in the downstream weaving mills. When the empty bag is warped on the air-jet loom, sizing is generally required, otherwise the fabric is easy to be fluffed and broken, but the beating can be used directly. From the perspective of cost alone, the empty package production capacity is much higher than the machine package production capacity, making the price lower than the machine package, which is convenient for reducing the cost of downstream weaving factories.
Although the core yarn is not exposed in the machine package, except for the uneven twist, it is not easy to produce quality problems during spinning and weaving, but the output is low, and the price is higher than that of the empty package of the same specification. The price is more than RMB5000/t. The price is even higher than that of the empty package of the same specification above RMB10000/t, so the cost of using the machine package is greatly increased.
Main process
In the spinning process, the spandex stretch is an important process parameter, which affects the elasticity of the covered yarn and the fabric, and also affects the strength and elongation of the covered yarn. Uniformity and creep performance. The pre-draft ratio of spandex is too small to give full play to the good elasticity of the elastic fabric. When the draft is too high, spinning is difficult, and it is easy to cause yarn breakage, and the quality of the product decreases; in addition, the percentage of spandex yarn also affects The covered yarn has high elasticity, high content and good elasticity. In the case of a certain spandex yarn specification, increasing the drafting ratio will reduce the percentage of spandex yarn, that is, the pre-drafting ratio of spandex is inversely proportional to the percentage of spandex yarn.
The strength and elongation of the air-covered yarn increases with the increase of the spandex pre-draft ratio. After the spandex yarn is drawn to a certain value, the shrinkage of the spandex yarn makes the outer fiber curled; appropriately increase the pre-draft ratio, and the spandex The percentage content is reduced, and the degree of curling of the outer fiber is large. However, when the draft is too large, the deformation range of the spandex yarn is close to the critical value of deformation, which will reduce the strength and elongation of the covered yarn, but it is beneficial to the evenness of the covered yarn.
The phenomenon that the deformation changes with time under the action of a constant drafting force is called creep. Conventional covered yarn has the best creep resistance when the spandex yarn is pre-drawn 3.5 times. Specifically, it should be adjusted appropriately according to the purpose and the style of downstream fabrics.
In addition to the requirements of the spandex draft ratio in the air-covered yarn, the mechanical covering yarn has another important process parameter that is the twist. The twist affects the quality of the yarn, the strength and the evenness of the evenness. Increasing the twist can increase the cohesive force between the outer fiber and the spandex yarn, so that the strength of the covered yarn is improved. If the twist is too low, the outsourcing fiber is loose, which affects the coating effect, and the core is exposed. Therefore, the twist should be high during mechanical coating. However, the twist is too high, the fabric feels hard, and the drape is poor.
Generally, the twist should be adjusted accordingly with the change of yarn denier and different fabric style requirements, such as n40d+20d machine package, the twist is about 600 twists, and the twist of n70d+40d or t150d+40d machine package is controlled at 480 Left or right is fine. The elongation of the machine bag is also mainly determined by the performance of the spandex core yarn. If the twist is too large and the outer fiber is wrapped too tightly, the elastic effect of the spandex yarn cannot be fully exerted, which reduces the elongation.
As the twist increases, the evenness of the evenness improves. If the twist is too small, the outer fiber is loose. In the spinning process, the fiber will move slightly along the axis of the yarn due to friction and other reasons, so the evenness is deteriorated.
Scope of application
Mainly used in: weaving, stretch denim, webbing, socks, underwear, lace and sporting goods, etc
