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.
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