The direction of lapping at successive courses

When using either open or closed laps there are three possible arrangements of lapping at successive courses, which may be used alone or in combination:

1 The pillar stitch. In the pillar or chain stitch, the same guide always overlaps the same needle. This lapping movement will produce chains of loops in uncon nected wales, which must be connected together by the underlaps of a second guide bar.

Generally, pillar stitches are made by front guide bars, either to produce vertical stripe effects or to hold the inlays of other guide bars into the structure.

Open-lap pillar stitches are commonly used in warp knitting. They can be unroved from the end knitted last.

Closed-lap pillar stitches are employed on crochet machines because the lapping movement is simple to achieve and is necessary when using self-closing carbine needles, which must always be fed with yarn from the same side

2 Balanced advance and return lapping in two courses (23.5a). Many tricot structures are based on this type of lapping movement. Its extent may be described by indicating the number of needles underlapped, followed by the number of needles overlapped (usually one). With a fully-threaded guide bar every one-needle space increase in the underlap movement will cause an extra warp thread from that bar to cross between each wale.

Tricot lapping or 1 x 1 is the simplest of these movements, producing overlaps in alternate wales at alternate courses with only one thread crossing between adjacent wales. Two threads will cross between wales with a 2 x 1 or cord lap, three threads with a 3 x 1 or satin lap, four threads with a 4 x 1 or velvet lap, and so on.

Each increase in the extent of the underlap tends to make the structure stronger, more opaque and heavier. The increasing float of the underlap has a

Open Pillar Stitch

Fig. 23.6 Open and closed lap pillar stitches.

Fig. 23.6 Open and closed lap pillar stitches.

more horizontal appearance, whilst overlaps produced by the same thread will be separated from each other at successive courses by an extra wale in width.

3 Atlas lapping (Fig. 23.7). This is a movement where the guide bar laps progressively in the same direction for a minimum of two consecutive courses, normally followed by an identical lapping movement in the opposite direction. Usually, the progressive lapping is in the form of open laps and the change of direction course is in the form of a closed lap, but these roles may be reversed. From the change of direction course, tension tends to cause the heads of the loops to incline in the opposite direction to that of the previous lapping progression. The change of direction course is normally tighter and the return progression courses cause reflected light to produce a faint, transverse shadow, stripe effect.

The underlaps on the technical back give the appearance of sinker loops in a spirally weft knitted structure. With a single guide bar having different coloured warp threads, zigzag effects can be produced. This is sometimes termed single atlas or vandyke. More elaborate geometrical patterns can be achieved with patterned warps using atlas lapping on two or more guide bars. Atlas is also the base for many simplex and all Milanese fabrics.

Cohesive single guide bar structures (Fig. 23.8a, b) may be knitted using a single, fully-threaded guide bar producing underlaps and overlaps. However, these are seldom commercially viable because of their flimsiness, low strength, lack of stability, poor covering power, distortion caused by loop inclination, and limited patterning potential.

Loop inclination is caused by the underlaps of the guide bar entering and leaving the head of the needle loop from the same side and thus producing an unbalanced tension from that direction (unlike weft knitting where the sinker loops enter and leave from opposite sides of the head of the loop).

A more balanced tension is achieved by having two sets of warp threads under-lapping in opposition to each other so that the underlaps of each enter and leave

Marquisette PatternKnitted Structure

(b) Technical Back Fig. 23.8 Face and back of single guide bar warp knitted fabric.

from opposite sides of the head of the loop. For these reasons, the simplest warp knitted structures are usually composed of two sets of warp threads, and most machines have a minimum of two guide bars.

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