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Newsflash |
Knit is a medium that crosses all generations and is often learnt from
the lap of mothers and grandmothers who teach their children and
grandchildren the basic technique and introduce them to knitting.
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An introduction to textile technology |
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Written by Erin
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Saturday, 23 February 2008 |
Textile fabrics can be produced directly from webs of fibres by bonding, fusing or interlocking to make non-woven fabrics and felts, but their physical properties tend
to restrict their potential end-usage.The mechanical manipulation of yarn into fabric
is the most versatile method of manufacturing textile fabrics for a wide range of
end-uses.
There are three principal methods of mechanically manipulating yarn into textile fabrics: interweaving, intertwining and interlooping.All three methods have evolved from hand-manipulated techniques through their application on primitive frames into sophisticated manufacturing operations on automated machinery.
1 Interweaving is the intersection of two sets of straight threads,
warp and weft, which cross and interweave at right angles to each
other.Weaving is by far the oldest and most common method of producing
continuous lengths of straight-edged fabric.
 Interweaving
2 Intertwining and twisting includes a number of techniques, such as
braiding
and knotting, where threads are caused to intertwine with each other at
right angles or some other angle. These techniques tend to produce
special constructions whose uses are limited to very specific purposes.
 Intertwining and twisting
3
Interlooping consists of forming yarn(s) into loops, each of which is
typically only released after a succeeding loop has been formed and
intermeshed with it so that a secure ground loop structure is
achieved.The loops are also held together by the yarn passing from one
to the next. (In the simplified illustration this effect is not
illustrated.)
 Interlooping
Knitting is the most common method
of interlooping and is second only to weaving as a method of
manufacturing textile products. It is estimated that over 7 million
tons of knitted goods are produced annually throughout the world.
Although the unique capability of knitting to manufacture shaped and
form-fitting articles has been utilised for centuries, modern
technology has enabled knitted constructions in shaped and unshaped
fabric form to expand into a wide range of apparel, domestic and
industrial end-uses.
Textile yarns and fibres
Yarns
are the raw materials manipulated during knitting. A yarn is defined as
‘an assembly, of substantial length and relatively small cross-section,
of fibres or filaments, with or without twist’. The term ‘thread’ is
loosely used in place of yarn and does not imply that it is as smooth,
highly twisted and compact as a sewing thread.
Textile fibres
are the raw materials of the yarns into which they are spun. There are
two configurations of fibres: staple fibres and filament fibres.
•
Staple fibres are of comparatively short length – for example, cotton
and wool fibres, which require spinning and twisting together in order
to produce a satisfactory length of yarn of suitable strength.
• A filament is a fibre of indefinite length – for example silk, which requires combining
with other filaments, usually with some twist, in order to produce a yarn of sufficient bulk.
Originally, all textile fibres occurred naturally – for example, animal fibres such as
wool and silk, and vegetable fibres such as cotton and flax. The first artificiallyproduced
fibres
were the rayons, developed by the regeneration of long-chain cellulose
polymers that occur naturally in wood pulp and cotton linters.
Derivatives such as cellulose acetate and triacetate were later
produced by the acetylation of cellulose polymers.
Nylon, the
first truly synthetic fibre, was invented by Wallace H. Carothers in
1938. It is based on a synthetically-built, long-chain polyamide
polymer that previously did not occur naturally. A wide range of
synthetic fibre polymers, including polyesters and polyacrylics, has
since been developed.
Many of the synthetic polymers may be
converted into yarns in continuous filament form (in which state they
were extruded during manufacturing). The filaments may also be cut or
broken into staple fibre form, to be later spun on systems originally
developed for natural fibres such as wool or cotton.
The
properties of more than one type of fibre may be incorporated into a
fabric as the result of blending the fibres during spinning, or by
knitting two or more types of yarn.
Knitting requires a
relatively fine, smooth, strong yarn with good elastic recovery
properties. The worsted system has proved particularly suitable for
spinning yarns used for knitwear, outerwear and socks, and the combed
cotton system for underwear, sportswear and socks.
The
introduction of synthetic fibres, which can be heat set in a permanent
configuration, has led to the development of texturing processes that
directly convert
these filaments into bulked yarns, thus bypassing the staple fibre spinning process.
During
texturing, the filaments are disturbed from their parallel formation
and are permanently set in configurations such as crimps or coils that
help to entrap pockets of air and confer properties such as bulkiness,
soft handle, porosity, drape, cover, opacity and (if necessary)
elasticity to the resultant yarn. Examples of yarns of this type
include false twist nylon and Crimplene, the latter being a registered
trade name for a technique whereby the properties of the textured
polyester yarn are modified during a second heat-setting operation so
that the stitch clarity, handle and stability of the fabric are
improved.
The development of synthetic fibres and of their
texturing processes has proved particularly beneficial to the knitting
industry and has resulted in a close association between the two
industries. The most recent development is the widespread use of the
elastane fibre Lycra to support the elastic properties of knitted
garments.
The period from the mid-1960s to 1973 is often
regarded by knitters as a ‘golden age’ because fashionable demand for
textiles composed of synthetic fibres reached
a peak during that period.
Yarn count numbering systems
A
yarn count number indicates the linear density (yarn diameter or
fineness) to which that particular yarn has been spun. An important
consideration in choosing a yarn count is the machine gauge which
defines the spacing of the needles in the needle bed (usually as
needles per inch).
Obviously, the finer the machine gauge, the
finer the required yarn count. Choice of yarn count is also restricted
by the type of knitting machine employed and the knitting construction.
The
count, in turn, influences the cost, weight, opacity, handle and
drapability of the resultant structure. In general, staple spun yarns
tend to be comparatively more expensive the finer their count because
finer fibres and a more exacting spinning process are necessary in
order to prevent the yarn from showing an irregular appearance.
Unfortunately,
a number of differently based count numbering systems are still
currently in use. Historically, most systems are associated with
particular yarn-spinning systems. Thus, a yarn spun on the worsted
system from acrylic fibres may be given a worsted count number.
The
worsted count system is of the indirect type based on length per fixed
unit mass, i.e. the higher the count number, the finer the yarn. The
weight is fixed (1 lb) and the length unit (number of 560-yard hanks)
varies. A 1/24’s worsted yarn (24 ¥ 560-yard hanks weighing 1 lb) will
be twice the cross-sectional area of a 1/48’s worsted yarn (48 ¥
560-yard hanks weighing 1 lb).
The designation 2/24’s worsted
indicates that the yarn contains two ends of 1/24’s so that the
resultant count is twice the cross-sectional area (24/2 = 12’s).
The
denier system is used in continuous filament silk spinning, and when
the silk throwsters began to process textured synthetic continuous
filament yarns, these nylon and polyester yarns were given denier count
numbers.
The denier system is of the direct type based on mass
per fixed unit length, i.e. the lower the number, the finer the
yarn.The length unit is fixed (9000 metres) and the
weight unit (in grams) is variable. A 70 denier yarn (9000 metres weigh 70 g) will be
twice as fine as a 140 denier yarn (9000 metres weigh 140 g). A 2/70 denier yarn will
give a resultant count of 140 denier.
The
tex system was introduced as a universal system to replace all the
existing systems. As tex sometimes produces a count number having a
decimal point, it has been found more satisfactory to multiply the
count number by 10 to give a deci-tex number. The tex system has not
been universally accepted, particularly for spun yarns, and on the
continent of Europe the metric system is used for these yarns.
Common
commercial practice has been followed, with decitex being used for
filament yarn counts and the metric system for spun staple yarn counts.
The main count systems, with their continental abbreviations, are as follows:
Indirect Systems
Bradford Worsted System (NeK) – the number of 560-yard hanks that weigh 1 lb
(453.6 g).
English Woollen System (NeW) (Yorkshire Skeins) – the number of 256-yard hanks
that weigh 1 lb.
English Cotton System (NeB) – the number of 840-yard hanks that weigh 1 lb.
Continental Metric System (Nm) (Cotton System) – the number of 1000-metre
hanks that weigh 1000 g (1 kg).
Direct Systems
Denier System (Td) – the weight in grams of 9000 metres.
Tex System (Tt) – the weight in grams of a 1000 metres.
Decitex System (dtex) – the weight in grams of 10 000 metres.
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Last Updated ( Saturday, 23 February 2008 )
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