Individual stitch selection is the most versatile and widely-employed method of knitting designs in colour, or different types of stitches in self-colour. It is based on the relative positioning of an element during a knitting cycle determining which stitch, from a choice of two or more, is produced in its corresponding wale at a particular feeder course of a machine revolution or traverse.
Latch needle weft knitting machines are especially suitable because their individually tricked and butted elements offer the possibility of independent movement. Depending upon machine and element design, and cam arrangement, one or more of the following stitches may be produced - knit, tuck, miss, plated, plush, inlay, loop transfer and purl needle transfer.
The following rules apply to individual element selection of stitches:
1 If each set of elements has butts of identical length and position, and the camtrack is fixed, each element will follow the same path and produce an identical stitch in its corresponding wale at that feeder course (Fig. 3.4).
2 If each feed in the machine has the same arrangement of fixed cams, identical stitches will be knitted in each wale at every feeder course (Fig. 7.1).
3 When the butts of adjacent elements are caused to follow different paths through the same cam system, different stitches may be knitted in adjacent wales of the same feeder course (Fig. 9.11).
4 When butts of the same element are caused to follow a different path through successive cam systems in the same machine, more than one type of stitch may be produced in the same wale (Fig. 9.4).
5 Unless the device is of the variable type that can present a different selection commencing in the first wale of each traverse or machine revolution, the design depth in feeder courses will be the number of operative feeds on the machine.
If the device is variable, the design depth will be increased by a multiple of the number of different selections available per device (see Chapter 11).
Weft knitted jacquard designs are built up from face loops in selected colours on a base fabric of either single jersey, 1 x 1 rib, or links-links (purl). The face loop needles are individually selected, usually each only once per pattern row, to rise and take one yarn from a sequence of different coloured yarn feeds on a knit or miss basis.
In two-colour jacquard, certain needles will be selected to knit colour A from the first feed and, at the next feed, there will be a negative selection with the remaining needles being selected to knit colour B. The face loops of two feed courses thus combine to produce one complete row of face pattern loops.
In three-colour jacquard, each needle will be selected to knit once and miss twice at a sequence of feeds, so that three feeder courses will produce one design row. The greater the number of colours in a design row, the lower the rate of productivity in design rows per machine revolution or traverse, assuming striping is not employed.
If striping is employed with jacquard selection, different colours can be selected at different design rows so that there are more colours in the total design than in one design row. For example, a four-feed machine with four-colour striping at each feed could knit 4 colours per design row but have a total of 16 colours in the design depth.
Single-jersey jacquard (Fig. 10.4) in knit and miss stitches produces clear stitch definition, exemplified by the fair isle designs used in woollen cardigans and pullovers. The floats to some extent reduce the lateral extensibility of the garments and, when continuous filament yarns are used in gauges of E 18 or less, the floats on the technical back can create problems of snagging. Single-cylinder sock machines may knit 1 x 1 float stitch jacquard. Odd needles are selected to knit and miss whilst even
needles knit at every feed, thus reducing the coloured yarn floats on the technical back to a single wale. The clarity of the coloured pattern area is only slightly impaired.
Accordion fabric (Fig. 10.5) is single jersey with the long floats held in place on the technical back by tuck stitches. It was originally developed using knit and miss pattern wheel selection (Section 11.11). Needles required to tuck (if not selected to knit) were provided with an extra butt, in line with a tuck cam placed immediately after the pattern wheel selection.
In straight accordion, every odd needle was of this type, so every odd needle tucked when not selected to knit.
Alternative accordion provides a better distribution of tuck stitches; odd needles had a tuck butt position in line with cams placed at odd feeders, and even needles had another butt position for cams at even feeders. With both these types of accordion, tuck stitches occur close together, causing distortion of face loops and allowing unselected colours to 'grin' through between adjacent wales onto the face.
The third type of accordion - selective accordion - is most widely used, but it requires a three-step pattern wheel or other selection device that can select the tuck loops so that they are carefully distributed to create the minimum of stitch distortion on the face of the design.
Rib jacquard designs are achieved by cylinder needle selection. The dial needles knit the backing and eliminate floats that occur when cylinder needles only are selected to miss (Fig. 10.6). Tuck stitches are therefore unnecessary. There are two groups of these fabrics - flat jacquards and relief designs.
Flat jacquards are described by the size of the design area followed by the number of colours in one complete pattern row of loops and the type of backing.
On circular machines, the selection is on the cylinder needles only and the dial
Fig. 10.6 Rib jacquard.
Fig. 10.6 Rib jacquard.
needles knit the backing loops, whereas on flat machines both beds may have selection facilities.
With horizontally striped backing, all dial needles will knit at every feeder, thus producing an unbalanced structure with more backing rows of stitches than design rows. In the case of three-colour jacquard, there will be three times as many backing rows as design rows. This type of backing ensures that the maximum yarn floats are only across one needle space and there is thus little loss of lateral extensibility - a prerequisite for garment-length and hosiery structures.
For double jersey fabrics, birds eye or twill backing (Fig. 10.7) is preferred as this is a more stable structure which is better balanced and has a pleasing, scrambled-colour appearance on the backing side. It is achieved by knitting the backing on alternate needles only and arranging for each colour to be knitted by odd backing needles at one feed and even needles at the next. The optimum number of colours is usually three.
On flat machines, it is possible to select only certain needles to remain in action to knit the backing; for example, 1 in 3 or 1 in 5. This is termed ladder backing. The backing needles virtually chain knit the floating threads in the back of the fabric. This produces a lighter fabric but there is less connection between the design and the backing sides of the fabric.
Whereas flat jacquard patterns have equal numbers of loops in each wale of the pattern repeat, blister and relief patterned fabrics do not. Links-links purl machines (particularly hosiery machines) may have facilities for knitting combined colour and stitch effects. Usually, the needles in one bed knit continuously so that the lateral extensibility of the structure is not too adversely affected. Float bolt patterning is more restricted. At the first feed, needles selectively transferred to the bottom cylin-
der knit together with those remaining in the top cylinder. At the second feed, the latter knit alone with the miss stitches floating at the back of the plain loops of the previous course. In combined links-links and three colour float jacquard, needles may be selected to knit in the bottom cylinder at any one of the three feeds. The needles which remain in the top cylinder knit at each of the three feeds, producing floats behind held plain loops (Fig. 10.8).
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