KNITTED FABRICS

The looping of a yarn is the basis of the knitted structure, each loop depending on its neighbours. In England, the term hosiery covers all types of knit-wear, but this is not so elsewhere, and confusion is because of the differences between circular knit fabrics, flat knit goods, and knitted garments.

The manufacture of stockings was the purpose of the first knitting machine, and it is to be noted that the knitting industry is the only section of the textile industry where the manufacture of a garment from yarn is commonly conducted in one factory.

The chief outlet for knitted fabrics is in underwear; this may be made in three main ways, fully-fashioned, cut, and seamless. Fully-fashioned underwear is made from pieces of knitted fabric, the cut garments from pieces cut and seamless material is made from tubular-knit fabric.

Knitted fabrics may be divided into two great classes, (a) tubular knit, and (b) flat knit, with selvedges. The former are capable of very high-speed production.

Weft-knitted Fabrics

The plain stitch is the fundamental structure of knitted fabrics, and in its simplest form it is produced by a single thread running crossways in a series of loops, one row of which is drawn into the next until a coherent fabric is formed. Looped structure possesses considerable elasticity and is suitable for underwear, as it maintains close contact with the body without crumpling. The disadvantage of looped structure is that if one thread is broken, a hole appears which rapidly extends in the runs or ladders. The common knitted structure is formed by a yarn making a series of loops across the fabric gives rise to the term “weft-knitted”.

Stitches: Knitted fabrics may be classified according to the type of stitch or connection of loops. There are three basic stitches, namely plain, rib, and purl.

The plain stitch is characterised by the fact that all the loops are drawn to the same side of the fabric. A plain knit has all the loops intermeshed and situated in the same direction.

The rib stitch uses the same type of loop as the plain knit, but the interlooping is different in that loops of the same course are drawn to both sides of the fabric; hence a line of wales or rib, produced on both sides, and they appear alike. The rib stitch suffers contraction in knitting and gives great elasticity across the width because the plain loops and the rib loops are in parallel planes; ribs are therefore popular because their concertina-effect is useful for the cuffs of sleeves, the tops of hose and the wefts of other garments, where a close fit is required.

The purl stitch again utilises the same type of loop, but successive courses of loops are drawn to opposite sides of the fabric producing ridges running across the fabric. Whereas in the rib stitch the wales are meshed in opposite directions, namely front to back, in purl stitch, the loops of the courses are meshed in opposite directions. The simplest purl stitch consist of one row of loops connected on one side of the fabric and the next row connected on the other side; this brings about a contraction in length and the formation of parallel courses in two planes with ridges across the material. As with the rib stitch, the simple purl stitch appears the same on both sides of the fabric, and resembles the back of the plain stitch.

                

Plain knit (Back)  Plain Knit (Front)        Rib                      Purl

Figure 3: Diagram of some weft-knitted structure.

The knitted fabric may be decorated either by variation in loop formation, or by selection of yarns, colours and loops.

Needles: Unlike domestic hand-knitting, which is straight, machine knitting utilizes needles with hooked tops; there are two types of knitting needle, latch needle and spring or bearded needle.

Figure 4: Latch needle.

The latch needle bent round at the top into a semicircle to form the hook. 

Figure 5: Spring or bearded needle.

The spring or bearded needle does not contain a moving part; it resembles a crochet hook with an elongated point, but opposite the tip of the point is a recess or eye on the shaft into which the tip may be pressed to close the hook.

The latch is the older and is commonly used on circular machines for the production of the more popular types of knit-wear; the bearded needle is used for goods of higher quality.

Warp-knitted Fabrics

The weft-knitted material is formed from a single yarn which makes a horizontal row of loops on which the next row depends. But in case of warp-knitting requires a number of yarns, one for each vertical row of loops. In warp-knitting a series of loops makes a series of longitudinal chains; the chains must be connected together laterally to form a fabric, and the simplest method is that which connects the odd threads at one course with the even threads at the next course, and so on. In this manner, it is possible to create a fabric consisting entirely of warp yarns; one warp thread is required for every needle and hence for every wale. The warp-knitted fabrics are of two chief types, according to whether the threads are connected sideways after each course or at intervals: the two types are termed close and open respectively.

The simplest knitted texture is 1×1 warp, in which the sequence of movements is rise, fall; fall, rise. In warp-knitting, it is essential to have a series of guides to move the threads from one needle to another, and also to pass the yarns around the needles and under the needles. The lateral movements may be termed rises or fails according to whether the movement is to the left or right.

The elasticity of the warp-knitted structures is inferior to that of weft-knitted fabrics.

Tricot is a double-knitted fabric which is ladder proof.

Locknit requires one needle bar and two guide bars ladder proof.

Atlas fabric is knitted from a set of threads which lap continuously in one direction and then reverse; zig-zag is formed, ladders readily.

Milanese is knitted in a somewhat similar structure, but the return is not made until the selvedge is reached.

Figure 6: Diagram of warp-knitted structure.