Elastomeric fabrics warp knitting

Commercially, elastomeric fibers are almost always used in combination with hard fibers such as nylon, polyester, or cotton. Use levels vary from a low of about 3% in some filling stretch cotton fabrics to a high of about 40% in some warp-knit tricot fabrics. Raschel fabrics used in foundation garments normally contain 10—20% spandex fiber. 

Actually, elastomeric knitted fabrics account for the highest proportion of commercial sportswear. The knitting technology involves warp knitting and circular knitting. The former relates to tricot, raschel, and double-needle-bar raschel the latter involves single knit, interlock, double knit, and rib knits. 

Raschel Warp knit raschel fabrics are produced in a similar way as tricot fabrics except for their stitch motions. The motion results in elastic yams being put into raschel construction as lay-in-yams versus knit-in yams on tricot constractions as shown in Figure 3.7. This lay-in stmcture leads to the raschel fabrics with elastic stretch in the length direction. Other elastic bar movements are possible to increase stretch and modulus in width. Raschel machines can have up to 64 yam guide bars to produce fabric patterns as extensive as jacquard lace. Elastomeric fabrics made by raschel showed good elastic stretch, recovery, and modulus in both length and width directions as elastic yam lap increases. 

Special requirements for warp knitting include the following (1) a device is required for proper density and even tension of elastomeric yams in producing elastomeric fabrics with repeatable results in stretch, recovery, modulus, shrinkage, and elastic fiber content (2) yam let-off must be electronic or electromechanical for best fabric control and reproducibility (3) special selvage holders (pullers), fabric hot-wire slitters. 

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