Yarn Notes

YARNS
A yarn is a continuous strand of textile fibres, filaments, or materials in a form suitable

for knitting, weaving, or otherwise intertwining to form a textile fabric (American Society
for Testing and Materials [ASTM]). For filament yarns, the process relatively easy and
quick. Spun yarns undergo a series of operations to make the fibres parallel and
cohesive.
YARN CONSTRUCTION
Figure 1: Schematics of yarn construction
LINEAR DENSITY OF YARNS

The linear density of a specific yarn or thread refers to its thickness or size. This
describes the relationship of the yarn to its weight. Over the years several different
methods of calculating the linear density have evolved. These methods are classified
under either direct or indirect systems.
1. Direct system or Fixed length system

This system is based on the weight of a given length of yarn. So the number you see
refer to this weight. It is a metric system which involves much simpler methods of
calculations.
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Tex – is the most commonly used unit. Tex system is based on the weight in grams of
1000 metres of yarn
dTex-dtex is used for very thin threads like machine sewing threads. dtex is Tex
multiplied by ten
Denier
The denier system is used for continuous filament yarns and threads, silk and nylon
for example. Denier is based on the weight in grams of 9000 metres of yarn. Deanier
is used mainly for expressing the size of fibres.
In 1956, the International Organisation for Standardisation, decided that it would

make more sense if there was only one universal system. It was suggested that
the TEX system, which is a fixed length, direct system, should be adopted.
2. Indirect system or Fixed weight system

This is based on the length of yarn that makes up a given weight. The weight is fixed
and the length is variable. So the numbers you see relates0 to the length. This is the
original and traditional method used for calculating the thickness of a yarn. This
method is known as the ‘indirect system’ or count. This method is complex as each
fibre (cotton, wool, worsted, silk, etc) uses a slightly different method of calculation.
Also, some countries have developed their own variations of the system. The fixed
weight or indirect system is divided into 2 sub-systems, namely, yarn count and metric
yarn count.
Yarn count
Yarn count is most often applied to traditional natural fibres and it is based on the
number of hanks of yarn that weigh one pound.
In Yarn count system each fibre has a different given length of yarn in a hank
o Cotton count (Ne c) is based on the number of 840 yard hanks in one pound of
yarn. For example, a cotton count of ‘2’ would mean 1680 yards of yarn weigh
1 pound.
o Worsted count (Ne w) is based on the number of 560 yard hanks in 1 pound of
yarn
o Woolen count (N y) is based on the number of 256 yard hanks in one pound of
yarn.
Metric count (Nm)
The metric count is based on the number of metres that weigh one kilo. This count is
usually used for synthetic yarns.
- All yarn exported to Europe is expected to carry a label stating the metric count
(Nm).
- Cotton count (Ne) = Number of 840 yard lengths per one pound of material
- Metric (Nm) = Number of kilometres per kilogram
For all fixed weight systems the lower the number the thicker the yarn
YARN TYPES
1. Filament yarns
Filament yarns are made from manufactured fibres, except for the tiny percentage
that is filament silk. Manufactured filament yarns are made by extruding a polymer
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solution through a spinneret and solidifying it in fibre form. Then the individual
filaments are brought together with or without a slight twist. The grouping of the
filaments with the addition of twist creates the filament yarn. The spinning machine
winds the yarn on a bobbin. The yarn is then rewound on spools or cones and is a
finished product, unless additional treatments such as crimping, twisting, texturing, or
finishing are required.
1.1 Monofilament Yarns

Monofilament yarns are primarily for industrial uses. These yarns are made of a single
coarse-filament fibre. End uses include sewing thread, fishing line, fruit and vegetable
bags, nets, and other woven or knitted fabrics for which low cost and high durability
are the most important characteristics.
1.2 Tape Yarns
Figure 2. Tape yarn
Tape yarns are inexpensive yarns produced from extruded polymer films. Extrusion
is the standard method of spinning fibres and some films. The split-fibre method is less
expensive than the traditional fibre extrusion process and requires a minimal
investment in equipment. Although some fibre polymers cannot be processed by the
split-fibre method, polypropylene is often processed in this way because it is easy and
inexpensive and produces strong yarns. Pellets of polypropylene with appropriate
additives are melted and then extruded as a film 0.005 to 0.020 inch thick onto a chilled
roll or cooled quickly by quenching in water. The film is slit into tapes approximately
0.1 inch wide and heat-stretched to orient the molecular chains. The stretching can be
carried to a point at which the film fibrillates (splits into fibres), or the film is passed
over needles to slit it. Twisting or other mechanical action completes the fibrillation.
Yarns as low as 250 denier have been made from split fibres. Tape yarns are coarse
and usually used in carpet backing, rope, cord, fishnets, bagging, and furnishing
support fabrics for which ribbon-like yarn is needed. Olefin films are slit into yarns that
are used for the same textile products as split-fibre olefin.
1.3 Bulk Yarns

Bulky Yarns Bulky yarns are formed from inherently bulky manufactured fibres that
are hollow along part or all of their length or from fibres that cannot be closely packed
because of their cross-sectional shape, fibre alignment, stiffness, resilience, or natural
crimp (ASTM). A bulk yarn is one that has been processed to have greater covering
power or apparent volume than that of a conventional yarn of equal linear density and
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of the same basic material with normal twist (ASTM). Often these bulk yarns are
referred to as bulk-continuous filament yarns (BCF). BCF yarns include any
continuous-filament yarn whose smooth, straight fibres have been displaced from their
closely packed, parallel position by the introduction of some form of crimp, curl, loop,
or coil (Figure 10–2). The characteristics of bulk yarns are quite different from those
of smooth-filament yarns. Bulking gives filaments the aesthetic properties of spun
yarns by altering the surface characteristics and creating space between the fibres.
Fabrics are more absorbent, more permeable to moisture, more breathable, and more
comfortable, and they have better bulk, cover, and elasticity. Static buildup is lower.
Bulk yarns do not pill or shed.
Bulking creates air spaces in the yarns, imparting absorbency and improving
ventilation. Bulk is frequently introduced by crimping, imparting waviness similar to the
natural crimp of wool fibre; by curling, producing curls or loops at various intervals; or
by coiling, imparting stretch. Such changes are usually set by heat application,
although chemical treatments are sometimes employed.
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Table 1. Comparison of filament yarns
Characteristic Bulky Yarns Stretch Yarns Textured Yarns
Nature Inherently bulky High degree of yarn High degree of bulk
curl
Fibre type May be hollow or Any thermoplastic Any fibre that develops
crimped fibre crimp with moisture,
heat, or chemical
treatment
Stretch Little stretch 300–500% stretch Moderate amount of
stretch
Characteristics Saw-tooth, Torque and non- Loopy, high bulk,
loops in torque crimped
individual fibres
Processes Stuffer box, air False-twist, knit–de- Air jet, flat-drawn
jet, draw- draw- knit, draw-texturing, textured, draw texturing,
texturing, friction texturing friction texturing
friction texturing
2. Spun Yarns
Spun yarns are continuous strands of staple fibres held together by some
mechanism. Often the mechanism is mechanical twist that uses fibre irregularities and
natural cohesiveness to bind the fibres together into one yarn. The process of
producing yarns from staple fibres by twisting is an old one. Methods of producing
yarns without twist have been developed.
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Table 2. Spun yarns and their characteristics
Yarn Type Characteristics
(a) rotor spun -fuzzy appearance and feel, due to fibre ends protruding from the
surface
-fibres in the sheath more random, and less twisted
-High stiffness
-feels hard due to compact and highly twisted fibres at the core
(b) ring spun -composed of short fibres of definite length

-made from natural fibres or man-made fibres which are cut
-highly twisted
-falls apart when untwisted
-rough to touch
-very compact
(c) Filament -composed of long, continuous fibres
-fine and smooth
-more uniform in diameter
-provides lustrous, shiny or sheen appearance
-softer and more pliable
-loosely twisted
-do not fall apart when untwisted
- Stronger than spun yarn of the same twist
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Table 3. Summary of different yarn types and their characteristics
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YARNS

A yarn is a continuous strand of textile fibres, filaments, or materials in a form suitable

Figure 1: Schematics of yarn construction

LINEAR DENSITY OF YARNS

1. Direct system or Fixed length system

In 1956, the International Organisation for Standardisation, decided that it would

2. Indirect system or Fixed weight system

1.1 Monofilament Yarns

1.2 Tape Yarns

Figure 2. Tape yarn

1.3 Bulk Yarns

Yarn Type Characteristics

(b) ring spun -composed of short fibres of definite length

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