High Efficiency of Elastic Yarn Production
Although the quality of conventional covered yarn (CCY) is still unmatched, the main issue is the low production speed and limited versatility of the process. Air covering appears to be a good alternative to the high cost of the CCY process with its high production speed and flexibility while providing excellent elastic yarn quality.
Air covering produces elastic yarn by combining textured yarn with elastane. Both threads are interlaced by running them through an intermingling jet where air pressure is applied. One or more drawn textured yarns (DTY) are overfed to enter the air jet with minimal tension and create intermingling points. A specific draw ratio is applied to the elastane during the air covering process and creates the required elasticity for the final product. The structure of air-covered yarn (ACY) is quite different from the conventional covered yarn. ACY alternates intermingling points and open lengths (Fig. 1), whereas filament yarn is wrapped around the elastane for CCY (Fig. 2).
The conventional covering process provides the best evenness and covering quality by wrapping a cover thread around a core thread. However, the process speed is very slow and the cost of production is very high, especially for apparel applications with fine yarn counts.
The efficiency of the air covering process is much higher than conventional covering since DTY and elastane are interlaced and not twisted together. The air covering process eliminates the need for high rotational speed, which is the limiting factor of the conventional covering process. The production speed for air covering is typically 30 to 50 times higher than conventional covering (Fig. 3).
Due to the high rotational speed and low efficiency of the CCY process for fine counts, the power consumption needed to produce 1 kg of yarn is much higher, resulting in higher process costs compared to ACY (Fig. 4, calculation based on PA DTY 20D + Elastane 20D draft 3.0 from China; ACY produced on SSM XENO-AC; CCY produced on SSM NOVA-CS and prepared on SSM FM1).
Moreover, the CCY process requires the covering yarn to be wound on flanged bobbins in advance. Therefore it is a two-step process. Air covering is a one-step process and there is no need for extra preparation. The SSM auto-doffing system increases productivity, and the individual spindle setup with single driven feeders provides the highest cost-efficiency and flexibility to produce small lots. SSM air covering machines offer the most accurate quality control with regulated pretension and winding tension, providing the best option for yarn producers to ensure the highest yarn performance. The SSM air covering process is a proven technology, with more than 800 air covering machines and more than 22 000 spindles running at customers worldwide.
Air-covered yarn is widely used in the production of elastic denim (Fig. 5), especially in the weft, for its excellent stretch recovery properties. SSM developed the possibility to integrate Lurex with ACY or use two elastane in the same yarn for even more recovery in super-stretch denim. These yarns meet the requirement for high stretch recovery under constraint for technical applications such as elastic ribbons. When used in hosiery, ACY also delivers balanced compression and the premium comfort required by the user.
While conventional covering machines can only combine one or two threads with elastane by single or double covering, air covering can run up to eight plies together with elastane. The air covering process can mix a large variety of colors, especially to create the so-called “heather” effect famous in sportswear and seamless fabrics (Fig. 6). There are even more opportunities to create unique fancy fabrics with the recent introduction of the innovative fancyflex technology on the SSM XENO-AC air covering machine (Fig. 7).
Air covering is not only economically interesting for its superior efficiency, but the high quality and the excellent ACY properties also make it an attractive solution whenever production of elastic yarn is needed. SSM is also offering a modern range of conventional covering machines for the highest covering quality: NOVA-CS (Fig. 8) for single covering and NOVA-CD for double covering.