Weft-Knitted NCF

The weft-knitting process has a loop formation perpendicular to the production direction. Therefore one yarn system is sufficient for the manufacturing of weft-knitted fabrics. In weft-knitted NCF, reinforcing threads are fixed within the loops (Fig. 8.15). 

Weft-knitted NCF can be produced as biaxial and multiaxial fabrics or as two- and three-dimensional near-net-shape textile structures. Warp and weft threads out of rovings are superposed and fixed together with loop systems. Due to the course-wise weft insertion the reinforcing threads remain noncrimped. Through the combination of weft insertion over the entire width or part of the width with or without support of a stitch-transferring device and by changing loop sizes on individual needles, three-dimensional near-net-shape preforms can be produced (Hufenbach, 2007). 

Exact control of yarn tension force of inserted threads. 

Reduction of set-up times and increase of automation in order to increase machine efficiency 

Insertion of 0 -thread layers in any position (not only a top layer). 

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Figure 8.15 Biaxial (left) and multiaxial (right) weft-knitted NCF...

Figure 8.16 Multi-ply, weft-knitted NCF (according to Hufenbach, 2007)...

Multiaxial warp-knitted NCFs with noncourse-wise weft insertion consist of a current maximum of seven iayers of rovings or spread fiber tows oriented in paral-lei. The orientation of the single-fiber layers can be freely adjusted between -20 to +20° relative to the production direction (angle specification analogous to ENl 3473-1). On the top side of the fabric, an additional 0° layer can be attached. The introduction of two surface fabrics, for example nonwovens, is also possible (Fig. 8.10). The mass per unit area, the structure (closed or open) of the fabric, the material, and the thread count of each layer can be varied individually for each layer. The single-fiber layers are fixed together with a warp yarn. 

Unidirectional NCFs can also be produced with this technology. Then, only weft threads are inserted and connected via warp knitting. 

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