The term knitwear includes two main textile techniques, weft and warp knitting (Spencer, 2001; Weber and Weber, 2008) (Table 7.1). After weaving, it is the most common method of manufacturing textile fabrics. Because of the interlooped structure of the knitted fabric, the properties are completely different to woven fabrics. The difference in weft and warp knitting originates in the way the needles move during the production and in the way the yarn is supplied. Weft knitting is a one fibre technique, which means that only one fibre is needed to build the stitches. The needles are moved separately, whereas the warp knitting needles are moved simultaneously. Therefore, all needles need the fibre material at the same time. For this reason, the yarn is supplied with the help of warp beams. The most important knitwear fabrics are circular knitted, warp knitted, flat-knitted fabrics and fully-fashioned fabrics.
The specific features influencing yarn delivery on large-diameter single jersey circular knitting machine are high productivity, continuous knitting and a great number of simultaneously processed yarns. Some of these machines are equipped with a striper (yarn guide exchange), but only a few enable reciprocated knitting. Small diameter hosiery machines have up to four (or occasionally eight) knitting systems (feeders) and an important feature is the combination of rotary and reciprocal movement of the needle bed (beds). Between these extremes are the middle diameter machines for ‘body’ technologies.
Figure 4.15 shows the simplified yarn supply system on a large-diameter double jersey circular knitting machine. Yarns (1) are brought from the bobbins (2), passed through the side creel to the feeder (3) and finally to the yarn guide (4). Usually the feeder (3) is equipped with stop-motion sensors for yarn checking.
In small diameter circular knitting machine spare parts as well as flat bed knitting machine, generally one yarn is fed at a time to the needle for loop formation through the desired feeding system or feeder. However, in medium to larger diameter circular knitting machines, more number of feeders are arranged/accommodated at regular intervals for supplying more number of yarns to the needles simultaneously for achieving higher production. Each feeder produces separate course in each revolution of the machine. Production can also be increased by increasing the machine speed. But there is a limitation in increasing the machine speed as vibration, jerk, noise, yarn breakage and ultimately power consumption increase to a great extent at higher speed. So instead of increasing the machine speed, attempts are being made to increase the number of feeders in the machine. Machines are available with up-to 152 feeders for 42 inch diameter [2]. Number of feeders on a circular machine depends on machine diameter, type of machine (plain, rib etc.), patterning facility and machine gauge. Number of feeder is mostly even number.
Traditionally, loop cut circular knitting machine were used for producing pantyhose [25]. In 2002 Karl Mayer introduced the RDPJ 6/2 warp knitting machines for making seamless, jacquard patterned tights and fish-net pantyhose. Karl Mayer’s MRPJ43/1 SU and MRPJ25/1 SU jacquardtronic raschel knitting machines can manufacture pantyhose with relief-like and lace patterns [26]. Other developments in machinery were aimed to increase the efficiency, productivity [27, 28] and quality of pantyhose [29].
Matsumoto et al. have also carried out some studies on the control of sheerness in pantyhose fabrics [18,19,30,31]. They produced an experimental hybrid knitting system composed of two experimental covering machines and a circular knitting machine. Each covering machine had two sections of single covered yarn. The pantyhose samples were knitted under a constant condition, while the single covered yarns were produced by controlling the covering levels of 1500 turns per metre (tpm) and 3000 tpm in nylon yarn with a draw ratio of 2 = 3000 tpm/1500 tpm for the core polyurethane yarn. The lower covering level produced a higher sheer in the pantyhose. Four different pantyhose samples were produced with different covering levels of tpm in different leg regions. The results showed that the aesthetics and sheerness of pantyhose fabric were greatly influenced by changing the covering level of the single covered yarn in the leg parts, and the mechanical hybrid system could improve the aesthetic properties of pantyhose fabric.
Weft knit fabrics are produced predominantly on cut pile circular knitting machine. The simplest of the two major weft knitting machines is a jersey machine. Generally, the terms circular knit and plain knit refer to jersey goods. The loops are formed by knitting needles and the jersey machine has one set of needles. Typical fabrics are hosiery, T-shirts, and sweaters.
Rib knitting machines have a second set of needles at approximately right angles to the set found in a jersey machine. They are used for the production of double-knit fabrics. In weft knits, design effects can be produced by altering needle movements to form tuck and miss stitches for texture and color patterns, respectively. Instead of a single yarn, several yarns can be used in the production of these structures. This increases the design possibilities.
