Fullwidth weft insertion

When the needles are in the lowered position during the warp knitting cycle, a so-called 'open shed' effect is created at the back of the machine. It is then possible for a weft yarn, laid across the full width of the machine, to be carried forward by special weft insertion bits over the needle heads and deposited on top of the overlaps on the needles and against the yarn passing down to them from the guide bars. In this way, the inserted weft will become trapped between the overlaps and underlaps in the same manner as an inlay yarn when the needles rise but, unlike the latter, the weft will run horizontally across the complete course of loops.

This technique is less restrictive for fancy and irregular yarns than for inlay and, as a weft covers the full fabric width, yarn can be supplied from individual packages. It has the major advantage that weft can be prepared and laid in advance of the timing of the insertion so that it has less effect on the knitting machine speed.

By 1938, a prototype FNF compound needle tricot machine could insert weft whilst knitting at 800 courses per minute. It was, however, Liba who pioneered the modern principles of single reversing weft insertion for coarse-gauge raschels and magazine weft insertion from a stationary package creel for fine-gauge compound needle tricot machines, with their Shussomat [1] and Weftloc models introduced in 1967 and 1970 respectively.

The single traversing weft is laid across the back of the machine by a cable-driven carrier that reciprocates on two parallel rods. At the end of the traverse, the selvedge return loop passes around a vertical pin that holds the weft in place until required, whilst the carrier continues its traverse. The weft pins are attached to the needle bar so that the two descend together, releasing the full-width weft at the moment when

Needle Weft Insertion
Fig. 27.7 Weft insertion principles.

the weft bits, one above every alternate sinker, advance over the lowered needle heads to insert the weft (Fig. 27.7).

This method of weft insertion produces a selvedged effect with the weft rising at the selvedge from one course of insertion to the next. The knitting width is sometimes divided into a number of knitting widths, each having a reciprocating weft carrier. In this way, narrow-width fabrics suitable for dish-cloths can be produced. Insertion of the cotton weft may be interrupted between each piece, triggering a scanning electronic eye that operates a hot wire to melt the empty nylon pillar stitches across the course. Thus, each piece is automatically separated and heat-sealed.

Machines with inlay and knitting bars are used in the production of sun filter curtaining. These employ a pattern chain control of the weft insertion from one end of the machine so that insertion can occur as required from a choice of a number of different wefts. Speeds of about 500 courses per minute are possible with this type of machine.

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