Knitting

Knitting is fabric-or garment-making by forming a series of interlocking loops in a continuous yarn or a set of yarns. In production situations, the work is carried out through the movement of hooked needles. (Hand knitting is normally performed with straight needles.) Each row of loops is vertically interlocked with the preceding row. With a sufficient number of loops, the yarn becomes a fabric. Knitted fabrics have the advantage of stretchability, a property not possessed by woven fabrics. Stretching can be in any direction even if the yarn used has little elasticity. Fig. 10D illustrates two types of knitted fabric. Mechanized production knitting utilizes a series of needles commonly operated by cams.

Figure 1A: Two examples of knit fabrics made by interlocking continuous strands of yarn—a) a plain knit made on a weft or filler knitting machine. The path of each crosswise yarn is called a course. b) a single-warp tricot knit.

somewhat more common. In weft knitting, the courses (crosswise rows of loops) are composed of continuous yarns. Weft knitting can be done by hand or machine but production weft knitting is a machine operation. The individual yarn is fed to one or more needles at a time. In warp knitting, the wales (predominantly vertical columns of loops) are continuous.3 Separate yarns are fed to each needle. The warp knitting operation is always produced by machine.

Knitted fabrics can be either flat or tubular in form. Warp knits are usually flat; weft or filling knits are most often tubular.

1 Two types of hooked needles are used in production knitting machines, the bearded or spring needle and the latch needle. They are illustrated in Fig. 1B. With both designs, the needles draw new loops through the previous loops that they have retained. Once the needle head and new loop have gone through the old loop, the old loop is cast off. The latch needle is most often used. It operates more automatically than the bearded needle which requires other machine elements to present the loop and close the hook. Fig. 1A illustrates stitch formation with a latched needle in a circular machine.

Figure 1B Production knitting needles. a) the bearded spring needle used for fine knitted fabrics and b) the more common latch needle.

Figure 1C: Stitch formation in weft knitting with latch needles in a circular machine. (from Knitting Technology by David J. Spencer. Reprinted by permission of Elsevier Science.)

Weft or Filling Knitting:Can be produced on either flat or circular knitting machines. In weft knitting, one continuous yarn runs crosswise in the fabric and makes up all the loops in one course. The needles either act in succession or the yarn is fed in succession, so that loop formation and interlocking is not simultaneous. Fig. 1C, view (a), illustrates a basic weft knit jersey cloth. Fig. 1C illustrates weft knitting with latch needles and shows that the multiple, evenly-spaced, needles have hooks with latches at the end. The needles are moved upward or downward by cams. As each needle rises, the needle hook loops over the yarn which it hooks on the down stroke, and the yarn is held in place by the needle latch. At the bottom of the needle stroke, a previous loop slips off the needle, and the new loop is held in place with the latch. On the next cycle,the loop is released from the latch as the needle rises, another loop is formed and the process is repeated.3 Fig. 1D shows six stages of weft knitting with bearded needles.

Figure D: Six stages of stitch formation in weft knitting with bearded needles. In this example, all stitches in one row are formed at the same time. (from Knitting Technology by David J. Spencer. Reprinted by permission of Elsevier Science.)

Figure E: Warp knitting with bearded needles. Loop forming is performed simultaneously with separate yarns fed through warp guides.

Several different stitches can be formed in weft knitting. In the knit stitch, the loop is drawn from the back and passed through the front of the preceding loop to the front of the cloth. In the purl stitch, the loop is drawn from the front through the back of the preceding loop to the back of the cloth. In the miss stitch, no loop is formed. In the tuck stitch, two courses on one wale are looped over a third. The stitches, and various combinations of them, make all the patterns of knit and double knit cloth. Distinct patterns can be made from combinations of the knit and purl stitches since the knit tends to advance and the purl to recede.1 Double knits are made by machine only, using two yarns and two sets of needles. These knits use a variation of the rib and interlock stitches, drawing loops from both directions.1 Jersey is a common knitted
cloth, made from only knit or only purl stitches.
Circular weft knitting machines are used to make hosiery, underwear and simulated furs. They can knit shaped garments. Jacquard effects are possible, and are now generally controlled electronically. Flat knitting machines can also produce shapes by increasing or decreasing loops. Full-fashioned garments can be made on flat knitting machines.

Warp Knitting:

The previous loop to slip off the hook while a new loop is held.3 If bearded needles are used, a yarn guide, called a sinker, positions the yarn across ascending needles and then retracts as the needles descend. Fig. E illustrates warp knitting.
Warp knitting is a versatile process, but standard warp knitting machines make just three basic stitch variations: open loop, closed loop or no loop. Various fabric patterns are created from different combinations of these stitches. One simple pattern produces tricot knit, which consists of a zigzag pattern of closed loops of parallel wales. Tricot fabrics are run-resistant. Other warp-knit patterns are simplex, milanese and raschel. Milanese knitting produces run resistant fabrics with a diagonal rib pattern. Several sets of yarn are used. The raschel knit is made with latched needles rather than the spring beard needles used for other knits. One or two sets of latch needles are used. Raschel knit fabrics are used frequently for underwear. Warp knitting is used to produce fabric for dresses, lingerie, upholstery and draperies. among other products.