Spacer Knitting Machines

Knitted spacer fabrics are derived from one-by-one knits. They consist of two flat fabrics that are connected via pile yarns. These yarns are elastic to pressure and keep the flat fabrics at a constant distance (Fig. 5.15). 

Spacer fabrics can be produced on both flat-bed and circular knitting machines. Between the needle beds (cylinder and rib disc, respectively.), there is a small gap. For the manufacturing of such a structure, three thread systems are required one for each cover fabric and the pile yarn that connects the fabrics (Fig. 5.16). 

The cover fabrics are knitted independently on separate systems. The pile yarns connect the fabrics via loops and are fully integrated into both structures. The loop formation itself occurs alternatingly via cylinder and rib disc, similar to plain fabrics as described above. 

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Figure 6.15 Producing a spacer fabric on a circular weft knitting machine (a) a Terrot double-jersey circular machine and (b) knitting a spacer fabric on the circular machine.

Due to advanced technologies employed in computerised flat knitting machines, it is possible to produce spacer fabrics in which two outer layers are connected by spacer yams or fabric layers. 

Figure 6.19 Spacer fabrics produced using a computerised flat knitting machine Stoll CMS 822, E14 (the coin of a diameter 2.4 cm).

Spacer brics are three-dimensional structures that can be engineered to incorporate a wide range of attributes and hence fulfil specific pre-determined requirements. Knitted spacra fabrics can be produced on both weft and warp kiutting machines. Each of the fabric faces can be designed independently, as well as the middle layer (spacer layer), in terms of yams and structures and this will determine the unique individud properties of each fabric [1,2]. Spacer fabrics have been studied and developed for a few years now but the number of variables that can possibly be input in their constmetion gives such a wide range of possibilities that many are still to be developed and exploited commercially. 

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. 

To this end, the machine building and textile industries have together developed what is known as the Caliweb process in which a warp-knitted spacer nonwoven Multiknit is used instead of the layer of foam. The nonwoven is clearly three-dimensional and is available from 3 mm to 8 mm thick. Fibres are mainly orientated in the third dimension and are integrated into both the meshed surfaces of the nonwoven (Fig. 3.3). Above this, their position is fixed by means of thermosensitive bonding fibres. This structure is as good as the foam which has been replaced. Composite formation between the decorative material and the nonwoven... 

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... 

An article (Anon., 2002b) has reported on the possibility to produce cloth shoes with warp-knitted spacer fabrics on the Raschel machine. Prefabricated products and the application of various functional zones can be realized if the machines are equipped with a Jacquard pattern. The Jacquard pattern is a binding technique in which each warp thread is individually controlled allowing for a maximum range of production possibilities. The subsequent processing, for example, laminating, is easily possible. Examples are shown in Section 14.2.2. 

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