Warp knitting principles

Figure 21.33 The principle of warp knitting with weft inserts (Karl Mayer machine). Source Reprinted from Raz S, Knitted Fabrics—Guide to Technical Textiles, Karl Mayer, Obertshausen, 1988, with kind permission.

In most load-bearing medical applications, however, warp-knitted structures, which include both weaving and knitting features, will generally be preferred. Specially constructed Raschel machines that have two needle bars and several guide bars are commonly used. The two needle bars, working alternately, contribute to the versatility of the products. The basic principle is that each needle bar produces a flat fabric the two fabrics are simultaneously connected to each other to form a three-dimensional structure. Examples of structures that can be produced are a double-sided, double thickness structure two separate fabrics with different structures and yarns, joined as needed tubular structure, straight or tapered, and with branches and a sandwich or a spacer fabric with filler yarns. 

Warp-knitted spacer fabrics are produced on double-needle bar Raschel machines the principle is schematically shown in Figure 6.22(a). While the guide bars 1 and 2 lap the front-needle bar, and the guide bars 5 and 6 lap the back-needle bar, to knit the top outer layer and the bottom outer layer, respectively, the guide bars 3 and 4 lap the spacer yams around both the needle bars in succession. A spacer fabric being produced on a double-needle bar Raschel machine RD 6 by Karl Mayer is shown in... 

Figure 15.5 (a) Schematic diagram of translational warp yam manipulation unit, (b) functional principle (schematic) and (c) realized looped stmcture in 0° direction by CFY in a multiaxial warp knitting machine MALIMO 14024. 

Furthermore, warp-knitted carpets belong to the group of carpets produced according to the principle of knitwear production. They are so-called warp-knitted fabrics in which the pile threads are bound in a ground material as pile thread end or a pile loop. 

The conventional principle for the production of warp-knitted fabrics has been explained in Chapter 5. Such warp-knitted fabrics are characterized by, among other things, their extremely elastic and direction-dependent behavior when subjected to tensile stress (Fig. 8.2). 

The reinforcement threads either run in the production direction (0°, pillar threads) or perpendicular (90°, weft threads). The distance between those threads is variable. The warp-knit yarns normally consist of thermoplastic materials such as PE or PA. Figure 8.6 shows the resulting structure schematically for both principles described above (1) indicates that thread distance and stitch length coincide (course-wise), and (2) that it does not (noncourse-wise). 

This summary relates to woven structures but the principles also apply to knitted, especially of warp constructions. The primary materials considered are polyester and elastomeric yams. 

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