Double-bar Raschel machines

The Cetex Institut fur Textil- und Verarbeitungsmaschinen gemeinniitzige GmbH based in Chemnitz, Germany, has been developing new areas of application for the 3D contour warp knitting process oti double-bar Raschel machines since 1997. The objective, to enable the incorporation of directly oriented thread systems into the base fabric (filler thread, weft thread), was reached (Anmi., 1997b). 

Production of flat fabrics and branched tubular structures with various geometries can be produced at the RWTH-ITA with the help of a special double-needle-bar Raschel Machine (Figure 3, Type DR 16 EEC/EAC Karl Mayer Textilmaschinenfabrik GmbH, Oberfaausen, Germany). Fields of application are e.g. keratoprosthesis (artificial cornea), vascular grafts, heart-valves, hernia-meshes and stents. 

Figure 6.4 A double-needle bar Raschel machine (Jakob Miiller MDK80).

Both weft and warp knitting machines are able to construct tubular structures. Although circular weft knitting machines can only be used in producing single tubes, flat weft knitting machines with two needle beds and double-needle bar Raschel machines are able to produce single, bifurcated and multibranched tubes. 

Similar to a computerised flat knitting machine with two needle beds, a double-needle bar Raschel machine has two needle bars. It is possible to knit tubes of different sizes on such a machine with a set of fully threaded guide bars to knit two separate fabrics... 

Figure 6.22 Principle of producing spacer fabrics on a double-needle bar Raschel machine (a) a schematic illustration and (b) RD 6 by Karl Mayer.

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... 

Spacer warp-knitted NCFs are produced with double-needle bar raschel machines. The machine has symmetric build-up warp-knitting elements (Fig. 8.14). 

Double-needle-bar raschel Special support, brace, athletic shoe, and medical brace fabrics are produced on raschel double-needle-bar machines. By using different elastic yams, fabrics can be produced with different properties on each fabric surface. These fabrics use elastic yams on the pattern or surface bars to create two-layer fabrics with space between the layers that show stretch with powerful recovery. 

The tubular vascular graft is generally knitted on a double needle bar Raschel warp knitting machine of fine gauge ( 56), preferably with a tricot stitch. The needle beds are straight and occupy the width of the machine. The machine has a number of guide bars, which move relative to the needles to facilitate interlooping of adjacent yarns as the fabric is knitted. The number of bars can be as many as 20, but the usual number is between 4 and 10. 

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. 

This kind of fabric is produced on double-Raschel machines consisting of two machine sides that work independently. Each machine side produces one basic fabric that is then connected to the other basic fabric via pile threads supplied by one or more additional guide bars. The fabric is taken up inside the machine. 

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