O o d h e a d p u b L i s h I n g L i m I t e d

5.5
Advances, benefits and applications of new
knitting technologies
5.5.1
Structures and constructions in knitted wool
fabrics
Unlike woven fabrics, a knitted fabric shows stretch in all directions. Stitches
can be worked from either side, and various patterns are created by mixing
basic stitches with the purl either in columns (ribs), rows (garter, welting) or
more complex patterns. Each of these fabrics has different properties: a
garter stitch has much more vertical stretch, while ribs stretch much more
horizontally. Using different combinations of knit and purl stitches, along
with more advanced techniques, fabrics of variable consistency, from gauzy
to very dense, from highly stretchable to relatively stiff, from flat to tightly
curled, can be produced. Some more advanced knitting techniques create a
further variety of complex textures like small eyelet holes and ‘knitted lace’
– a very open fabric resembling lace. Changing the order of stitches produces
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a variety of cables, honeycombs, ropes and Aran sweater patterning. Using
entrelac techniques, rich checkerboard textures are formed.
Since knitted fabrics are much more elastic, dresses and lingerie are more
form-fitting than counterparts made from a woven fabric. Knit fabrics can
stretch from 0 to 500%, depending on their material and knitting pattern.
Lace knitting generally produces the most flexible fabric, since it has large
holes that can deform in shape; by contrast, cable knitting generally produces
the least flexible fabric, since the stitches are crossed under tension, which
inhibits deformation. The elasticity of knitted fabrics gives them an excellent
drape, but this is opposed somewhat by their generally greater thickness
compared to wovens. Thus, the turn of the cloth (i.e. the maximum curvature
of a fold of the fabric) is generally finer in woven fabrics than in knitted
fabrics. For this reason, knitted fabrics resist wrinkles better than wovens,
but do not generally take a crease.
The appearance of a construction is also affected by the weight (or fineness)
of the yarn, which is dependent on the fineness of the wool fibre. The thicker
the yarn, the more visible and apparent stitches will be; the thinner the yarn,
the finer the texture.
Knitted fabrics are generally warmer and more comfortable than woven
fabrics, which is why they are worn closer to the body. Moreover, many
knitted fabrics are made from wool, which stays warm even when wet; wool
is preferred since it is more elastic than most fibres and produces more even,
beautiful knits. In general, elasticity and warmth are opposing qualities in a
knitted fabric, since the most elastic knitted fabrics, such as lace, have the
largest holes and are thus less insulating.
5.5.2
Weft knitting
Flat knitting machines
In industrial knitting applications, the terms ‘Flat’ or V-bed knitting machine
refer to two flat needle beds arranged in an upside-down ‘V’ formation.
These needle beds can be up to 2.5 m wide. A carriage, also known as a cam
box or head, moves back and forth across these needle beds, working the
needles to selectively, knit, tuck or transfer stitches. A flat knitting machine
is very flexible, allowing complex stitch designs, shaped knitting and precise
width adjustment. It is, however relatively slow when compared with a
circular machine.
Flat knit or V-bed machines have the ability to produce fully-fashioned
sweaters and cardigans as well as three-dimensional structures and garments.
Fully fashioned knitting machines are flat knitting machines that produce
custom pre-shaped pieces of a knitted garment. Instead of knitting a whole
rectangular sheet of fabric, instructions from a knit pattern on a punch card
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or computer file guide a fully fashioned knitting machine’s needles to add or
drop stitches to create custom two-dimensional shapes appropriate to the
desired finished garment structure like parts of a cardigan. The pieces emerge
from the machine ready to be sewn together.
Fully fashioned knitting cuts down on the amount of material required to
make a garment by eliminating selvage, the remnants that would be left after
cutting from a rectangular fabric sheet. For example, a sweater requires at
least four pieces of fabric: two sleeves, the front piece and the back piece.
Prior to fully fashioned machine techniques, a full sheet of material would
have to be produced, each of the four pieces would be cut out, and the
remaining fabric would be discarded. With full fashioning, the machine
produces only the four required pieces.
The necessary techniques for changing the fabric width or diameter are
achieved by changing the knit structure (e.g. rib to interlock), varying the
structural elements (stitch length, weft insertion, knit, tuck, float), shaping
through loop transfer, wale fashioning by ‘needle parking’, and segmented
takedown for varying rates of takedown across the width of the fabric. These
knit options above may also be used to change the structure of each piece to
create limited curvature (such as convexity at the bust of a sweater) in the
relatively two-dimensional output. Both Shima Seiki of Japan and Stoll of
Germany produce these machines.
Computerised complete garment knitting machines
Complete garment knitting is a next-generation form of fully fashioned knitting
that adds the capability of making a three-dimensional full garment. Unlike
fully fashioned knitting, where the shaped pieces must still be sewn together,
finished complete knitted garments do not have seams. The technology of
knitting seamless garments on V-bed machines has gained significant
commercial acceptance since its introduction in 1995. Besides offering higher
comfort and better fit to consumers by eliminating seams, the innovative
technique creates entire garments with minimal intervention of cutting and
sewing processes, leading to substantial savings in cost and time, higher
productivity, quick response and just-in-time production.
Structures that are most often made with the complete garment technique
are clothing (sportswear to sweaters) or technical textiles (car seat covers
and other three-dimensional shapes such as the therapeutic elastic supports
for foot, ankle, knee, elbow, etc.). These machines can produce a variety of
topologies that were difficult or impossible to create with knitting machines
before, including: connected tubes, circles, open cuboids and even spheres
(for helmet shells).
Complete garment knitting requires two needle beds for three-dimensional
structures (such as clothing). As is the case with all fully fashioned knitting,
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machines require individual single needle selection (through electronic control)
and presser feet (to hold down formed loops). Both Shima Seiki and Stoll
offer comparable solutions for the knitting of complete garments on
computerised V-bed knitting machines. Shima Seiki’s WholeGarment range
of machines has range of gauges from 5 to 18 needles per inch and knitting
widths ranging from 50 to 80 inches (127–203 cm). Stoll’s Knit & Wear
machines have gauges ranging from E2.5 to E9.2 and knitting widths between
72 and 84 inches (182 and 213 cm). Both offer multiple gauge system, which
permits different gauge areas to be knitted in one single course. The technology
allows the combination of many different patterns within one garment, which
cannot normally be accomplished on a traditional knitted garment. For example,
a jersey knit can be placed side-by-side with a mesh knit, which can be
placed side-by-side with a rib knit, which can be placed side-by-side with a
jacquard knit, etc.
Stoll has filed a patent describing a technique for manufacturing seamless
garments using the same needle space as the body width for their Knit &
Wear machines. With the new technique, the sleeves are knitted subsequent
to the body, using the needles previously used in knitting the body. Narrowing
is performed without fashioning, using what Stoll refer to as the ‘gore’
technique. This technique is sometimes also referred to as ‘flechage’ or
‘short-row’ knitting and involves knitting successively shorter rows to narrow
or impart shape into a fabric. Since carriage strokes are shorter compared
with the conventional Knit and Wear technique, knitting time is reduced.
Production time is reduced because the knit and transfer traverses required
to join the sleeves to the body are not required in this case. Joining is carried
out in the gore technique.
One of the most significant by-products of these technological advances
has been mass customisation, i.e. the ability to make one garment of a