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​The Difference between Spandex covered yarn and Core soun yarn

May 24,2023

01 Structure and classification of covered yarn

Spandex mechanical covered yarn includes an inner elastic core filament(spandex) and an outer synthetic DTY filament / Staple Fibre. Produce an elastic-covered yarn by spiral wrapping the stretched spandex.

According to the number of wrapping layers, covered spandex can divide into single-covered and double-covered, differing in the number of out-covered yarn layers and wrapping degree.

Single-covered yarn is a core spandex outer layer wrapped with an outer covering yarn, with relatively fewer wrapped circles, the spandex core may expose in the final fabric. It doesn’t adapt to make deep colour products, it’s mainly used for socks, weft knitted underwear and other stretch weaving.

The double-covered yarn has two outer layers of filaments or yarns wrapped around the spandex core, and these two layers are generally in opposite directions. The core spandex is covered to a good extent and the core exposure is less, and because the outer wrapped filaments are wrapped with opposite spiral angles symmetrically around the core filaments, the elasticity of the wrapped yarn is well balanced and can generally be processed in the later process without shaping treatment, but the processing cost of double wrapped yarn is higher. It is mainly used for elastic fabrics such as leg guards, elastic belts, sock openings and tights.

Based on different processing equipment can divide mechanical-covered yarn and air-covered yarn.

Mechanical covered yarn is made by continuously twisting and winding the out filaments around a uniformly drafted core spandex yarn. It is twisted and twists are measured in "TPM" (twist per meter). The fabric style is flat is its main feature.

Air-covered yarn, the outer fibre filament and spandex yarn are drawn through a certain type of nozzle at the same time. After high pressed air is regularly sprayed to form a regular network of points in the yarn. The fabric feels soft and smooth.

ACY and SCY have their advantages and disadvantages in downstream weaving factories. When the ACY warps on the air jet loom, usually need sizing, otherwise the fabric is easy to lint, break and so on, but weft is can directing use. Just consider cost, ACY is more productive than SCY, and it can have a lower price than SCY, hence lowering the downstream factories’ cost. Though SCY has lower core exposure, generally less likely to cause quality problems in spinning and weaving, except for uneven twists, however, its production efficiency is low. Thus, the price is more than RMB 5000/T higher than the same routine of ACY. The price of FDY is even more than RMB 10000/T higher than the same routine of ACY. Therefore it greatly increases the cost of using the SCY.

02 Important Process Parameters in Spandex Processing

During the spinning process, spandex stretch is an important process parameter. It affects the flexibility and elongation of covered yarns, evenness and creep properties. when spandex stretch is too small, it can give full use to the advantages of good elasticity of stretch fabric. When the stretch is too high, yarn spinning is more difficult and easy to break, then degradation in quality. In addition, the percentage content of spandex yarns also affects the elasticity of covering yarn, higher spandex content gives better elasticity. The higher the spandex stretch is, the higher the strength and elongation of ACY. After stretching to a certain level, the yarn retraction of spandex yarn makes the outer fibres appear curled. By increasing the spandex stretch, the percentage content of spandex yarns will decrease and cause a large degree of curl in the wrapped fibres. However, when the degree of stretch is too big, the spandex yarn deformation amplitude is close to the critical value of deformation. It will decrease the covered yarn's strength but is conducive to the covered yarn's uniformity.

The phenomenon of deformation with time under the action of a constant draft force is called creep. When the routine spandex yarn is pre-drawn 3.5 times, the creep resistance is best. It should be specifically adjusted according to the usage tone and the style of its downstream fabric.

In addition to the spandex stretch requirement in ACY, SCY has another important process parameter is the twist. Twist can make a difference in quality, elongation and evenness. Increase the twist to raise the force of holding between the outer covering fibre and the spandex yarn, making the covering yarn stronger. when the twist is too low, the outer covering fibre can be loose and affect the covering effect, which may cause the core exposure, so the twist should be high in mechanical wrapping. However, when the twist is too high, the fabric feels stiff and drapes poorly. The general twist level is adjusted according to the number of deniers of the yarn and the style requirements of the fabric.

The elongation of the SCY is also mainly determined by the performance of the spandex core yarn twisting too much, the outer layer of fibre wrapped too closely, and the elastic effect of the spandex yarn can’t give a good performance so that the elongation decreases.

03 The difference between core spun yarn and covered yarn

Spandex-covered yarn is mainly used for fabrics that demand high elasticity and partly for woven fabrics. The fabric woven with covering yarn is thicker and especially suitable for weaving sports tight. Such as swimming suits and ski suits.

core spun yarn and covered yarn

1. The difference between the two, take core spun yarn and covered yarn as an example. Core spun yarn is spandex wrapped with staple fibre with spandex yarn as the core and non-elastic staple fibre outside, and the core yarn is usually not exposed when stretched. Covered yarn is spandex wrapped with a chemical filament fibre, similarly, a core yarn of spandex and outer non-elastic staple fibre or filament spiral-wrapped to the elongated spandex to form the elastic yarn. It may have the core exposed under tension.

2. Core spun yarn is processed on roving and spinning machine; staple covered yarn is processed on roving and twisting machine; Filament covered yarn is processed on twisting machine.

3. The core yarn of core spun yarn is wrapped outside by the staple fibre, you can’t see the corn yarn with a well-wrapped core spun yarn. Staple-covered yarn is preprocessed by one or more yarns patched together and then twisted on the spool by a twisting machine. both the covered yarn and the outer covering yarn can be seen.

4. Core spun yarn, usually processed by the Roving and spinning machine when the roving is drafted, adds the another yarn to be wrapped inside. For example, cotton spun spandex, polyester/viscose spun spandex; cotton spun polyester filament, polyester spun polyester filament, etc. Covered yarn is processed by a twisting machine, one for the core yarn, the other wrapped outside, such as spandex as the core yarn outside wrapped polyester, nylon, etc.

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