Introduction of Covered Yarn
Covered yarn is a new type of yarn, which uses filament or staple fiber as the core, and wraps another filament or staple fiber yarn. The outer yarn covers the core yarn in a spiral manner. It is characterized by uniform evenness, bulk and plumpness, smooth yarn with less hairiness, high strength and less broken ends.
Covered yarns are mostly used for knitted fabrics that require high elasticity, and some are used for woven fabrics. They are ideal yarns for high-grade and thin wool, hemp fabrics, jacquard double-layer weft knitted fabrics and warp knitted fabrics. Covered yarn can be spun for both thickness and fine yarn, among which elastic yarn is the most suitable for weaving sports tights, such as swimming suits, ski suits, women’s underwear, etc. According to the purpose of the covered yarn, the appropriate core yarn and outer yarn are selected, and its strength is higher than any single yarn.
The common methods of covered spinning are: one is that the core and the outer fibers are short fibers; one is that the filament is used as the core, and the short fibers are the outer fibers; the other is that the short fiber bundle is the core, The outside is wrapped with filament; the other is that both the core and the outer fiber are covered with filament. The yarn strength of the synthetic filament covered yarn is higher than that of the general staple fiber covered yarn, but the yarn surface lacks the characteristics of natural fibers. In addition, in the production process of the covered yarn, the weight of the core yarn bobbin is reduced due to the reduction of the core yarn, and it is easy to be separated from the fixing rod, which affects the production.
Characteristics of Air Covered Yarn and Mechanical Covered Yarn
According to the different processing equipment of covered yarn, covered yarn can be divided into air covered yarn and mechanical covered yarn.
Air-covered yarn (ACY) is a yarn that draws the outer fiber filament yarn and the core yarn through a certain type of nozzle at the same time, and is regularly sprayed by compressed air to form rhythmic network points. The resulting fabric feels soft and smooth.
Mechanical Covered Yarn (SCY) is to continuously rotate and wrap the outer fiber filament yarn on the core yarn that is drawn at a constant speed, and has a twist after twisting. crisp.
Air-covered yarn generally needs sizing when warping on an air-jet loom, otherwise the fabric is prone to fluff and broken threads, but it can be used directly by beating up. The production capacity of air-covered yarn is much higher than that of machine-covered yarn, so its price is lower than that of mechanical covered yarn, which is convenient to reduce the cost of downstream weaving mills.
The advantage of mechanically covered yarn is that the core yarn is not exposed, and generally, it is not easy to produce quality problems during spinning and weaving except for uneven twist. The disadvantage is that the output is low, and the price is therefore much higher than that of the air-covered yarn of the same specification, which is especially reflected in the fine-denier covered yarn.
Main process characteristics of covered yarn
Air-covered yarn pre-draft ratio
In the production process of covered yarn, the pre-draft ratio of the core yarn is an important process parameter, which affects the elasticity of the covered yarn and the fabric, as well as the strength and elongation, evenness and creep of the covered yarn. performance.
If the pre-draft ratio of the core yarn is too small, it cannot give full play to the advantages of good elasticity of the elastic fabric. When the pre-draft is too high, spinning is difficult, and it is easy to cause broken threads, and the product quality will decrease accordingly.
In addition, the content of the core yarn also affects the elasticity of the covered yarn. High content means better elasticity. In the case of a certain core yarn specification, increasing the draft ratio will reduce the percentage content of the core yarn, that is, the pre-processing of the core yarn. The draft ratio is inversely proportional to the percentage content of the core yarn.
The strength and elongation of the covered yarn increases with the increase of the pre-drafting ratio of the core yarn. After the drafting reaches a certain value, the retraction of the core yarn makes the outer fibers in a crimped state, and the core yarn of the core yarn is straightened. Increasing the pre-draft ratio, the percentage content of the core yarn decreases, and the curling degree of the outer fiber is large, but when the draft is too large, the deformation amplitude of the core yarn is close to the critical value of deformation, which will reduce the strength and elongation of the covered yarn, but there are some Conducive to covering yarn evenly.
The phenomenon that the deformation changes with time under the action of constant drafting force is called creep. It is generally believed that the creep resistance of the covered yarn is the best when the core yarn is pre-drafted by 3.5 times.
Twist of mechanically covered yarn
For mechanical covered yarns, the twist also affects the quality, elongation and evenness of the yarn. Increasing the twist can increase the cohesion between the outer fiber yarn and the core yarn, which improves the strength of the covered yarn.
The elongation of the machine package is mainly determined by the performance of the core yarn. If the twist is too large, the outer fiber wrapping is too tight, and the elastic effect of the core yarn cannot be fully exerted, which reduces the elongation. During the spinning process, the fibers will move slightly along the yarn axis due to friction and other reasons, resulting in poor evenness. With the increase of twist, the evenness will also improve.
The existence of the core yarn in the mechanically covered yarn will weaken the cohesion between the outer fibers. If the twist is too low, the outer fibers will be loose, which will affect the coating effect and cause the core to be exposed. Therefore, the twist should be appropriately high during mechanical coating. In order to reduce production costs, small spinning mills will reduce twist or increase equipment speed to increase output, which is not conducive to the quality of covered yarn.
