Yarn Manufacturing

Fiber Properties

Annual world consumption of fiber was 96.o million tons in 2014

( MMF growth 4.9%. Natural   fibers 0.7%)

Current ratio of   cotton : MMF = 28 : 72

Yarn types

I. Spun yarn (80%)-cotton, viscose, polyester, acrylic etc.

II. Continuous filament (20%) polyester, nylon etc.

Staple fiber Spinning        Spun yarn

Filament Drawing, Texturising                Filament yarn

Spinning Systems: (i) Short staple spinning (<60mm)

(Cotton, man-made fiber)

        (ii) Long staple spinning (>60 mm)

(Worsted, Woolen, Jute, Flax, manmade fiber etc)

Definition of spinning:

Spinning is the process where fibers are converted into yarn. Or,

Spinning refers to the conversion of a large quantity of individual unordered fibers of relatively short length into a linear, ordered product of very great length and sufficient strength by using suitable machine and devices.

Short staple spinning:

Cotton Spinning:

· Raw material represents about 50-75% of the manufacturing cost of short staple yarn.

· Raw material accounts for about 80% of yarn quality

Cotton harvesting          Seed cotton.

      Seed Cotton ginning (i) Lint (good fiber)

(ii) Linters (short fiber)

(iii) Seeds/Bale (variable)

      Ginning- separation of fibers and seeds from the seed cotton.

Types of ginning:

       -  Saw ginning   

       -  roller ginning etc.

Cotton is available commercially in:

· bale form

· highly compressed

· bale weighing around 225 kg/500 lb

· Wrapping with polyethylene, polypropylene, jute etc.

Grading of cotton:

Cotton is generally grading according to (a) color (b) amount of foreign matters (c) preparation of cotton.

 Assessment of grade varies from country to country.

Classification of cotton:

Cotton is classified on the basis of two features:

(a) Staple length

(b) Grade

The universal grade standard for upland cotton from high to low are:

1. Strict Good Middling     - SGM

2. Good Middling               -  GM

3. Strict Middling               -  SM

4. Middling    -  M

5. Strict Low Middling        - SLM

6. Low Middling                  - LM

7. Strict Good ordinary       -  SGO

8. Good Ordinary                 -  GO

Cotton fiber growing countries:

(a) Egypt, (b) USA

(c) CIS: Commonwealth of independent states (CIS) is the international organization or alliance consisting of eleven former Soviet Republics- Armenia, Azerbaijan, Belarus,  Kazakhstan, Kyrgyzstan, Moldova, Russia, Tajikistan, & Uzbekistan(1). (cotton growing countries underlined)

(d) China, (e) India, (f) Sudan, (g) Australia, (h) Pakistan, (I) Burkina Faso

Commercial name of cotton fiber:

a] Pima (USA), b] Arizona (USA),c] SJV (USA), d] Elena (CIS),e] Parvee (CIS), f] Ronda (CIS), h] Giza (Egypt), i] Andy (Australia), j] Suvin (india), (k) Delta (Bangladesh), (l) Barakat (Sudan)

Characteristics of cotton fiber influencing spinning:

Raw material represents about 50-75% of the manufacturing cost of a short-staple yarn. This fact alone is sufficient to indicate the significant of the raw material for the yarn producer.

Optimal spinning condition can be obtained only through mastery of the raw material. Excessive economy in relation to raw material usually does not reduce costs and often increases them owing to deterioration of process ability in the spinning mill.

The following cotton fiber characteristics are considered for spinning process:

(1) Fiber length and uniformity of length, (2) Fiber strength, (3) Fiber Fineness, (4) Maturity, (5) Cleanliness, (6) Fiber elongation, (7) Stiffness, (8) Chemical Deposits.

1] Fiber length and uniformity of length:

Fiber length is one of the most important fiber characteristics. It influences:

· Spinning limit(minimum number of fibers in the yarn cross-section)

· Yarn strength

· Yarn evenness

· Handle of the product

· Luster of the product

· Yarn hairiness and

· Productivity

In the case of cotton, the longer types are generally also the finer ones. It is length of the cotton that determines the adjustment and detailed construction of the machinery that is used to process it. Length is important because of the fact that it determines the amount by which the fibers overlap one another in the yarn. The greater the overlap, the more easily can the fibers be bound together by twist. From this it follows that the longer cotton makes it possible to spin either stronger yarn or alternately finer ones.

Productivity is influenced via the end-breakage rate, the quality of waste, the required turns of twist (which affects the handle and general spinning conditions).

Staple lengths are needed in setting machines especially roller spacing. The following length groupings are currently used in stating the trade staple.

Short staple:         1 in or less

Medium staple:    1 1/32-1 1/8 in

Long staple:          1 5/32- 1 3/8 in

Extra-long staple:  1 13/32 in. and above

The proportion of short fibers:

The proportion of short fibers has an extremely great influence on the parameters listed for length (expect in the case or rotor spinning, where this influence is less). The uniformity or variability of the cotton is very important because it causes difficulties in roller setting and cause irregularities in the yarn. Besides the influence, a large proportion also leads to strong fly contamination (among other problems), and also to extreme drafting difficulties.

2] Fiber strength:

Strength is very often the dominating characteristics. This can be seen from the fact that nature produces countless fibers, most of which are not usable for textile because of inadequate strength. The minimum strength for a textile fiber is approximately 6 cN/tex (about 6 km breaking length). Since binding of the fibers into the yarn is achieved mainly by twisting, and thus can exploit at most 30-70% of the strength of the material, a lower limit of about 3 cN/tex is finally obtained for the yarn, the minimum strength of a yarn. Some significant breaking strengths of fibers are :

A] Polyester fiber: 35-60 cN/tex;         B] Cotton:15-40 cN/tex;                      C] Wool:12-18  cN/tex

In relation to cotton, the strength of fiber bundles is measured and stated as the Pressley value. The following scale of values is used:

93 and above = excellent;

87-92 = very strong;

 81- 86 = strong;

75-80 = medium;

70-74 = fair;

under 70 = weak.

3. Fiber fineness:

Fineness is one of the most important fiber characteristics. The fineness determines how many fibers are present in the cross-section of a yarn . Additional fibers in cross-section provide not only additional strength but also a better distribution in the yarn. In Ring spinning thirty fibers are needed at the minimum in the yarn cross-section, but there are usually over 100. One hundred is approximately the lower limit for almost all new spinning processes. This indicates that fineness will become still more important in the future. Fiber fineness influences primarily:

spinning limit; drape of the fabric product;

yarn strength; luster;

yarn evenness; handle;

yarn fullness; productivity of the process.

Productivity is influenced via the end-breakage rate, the number of turns per inch required in the yarn (giving improvement of the handle), and generally better spinning conditions.

Specification of fineness:

With the exception of wool and hair fibers, fiber fineness cannot be specified by diameter as in the case of steel wire, because the section is seldom circular and is thus not easily measurable. As in the case of yarns, fineness is usually specified by the relation of mass (weight) of length:

tex       or militex          dtex 

 Whereas for synthetic fibers dtex (or militex) is used almost exclusively, the Micronaire value (microgram/inch) is used worldwide for cotton. The fineness scale is as follows.

Mic value	Fineness
Upto 3.1	Very fine
3.1-3.9	fine
4.0	medium
5.0-5.9	Slighty coarse
above 6	coarse

Conversion factor dtex = Mic x 0.394 (mic. is largely dependent on degree of maturity).

It should be remembered, however, that the micronaire value not always represents the actual fineness of the fibers due to the presence of excessive immature fibers.

4] Fiber Maturity:

The cotton fiber consists of cell wall and lumen. The maturity index is dependent upon the thickness of the cell wall. Fiber is to consider as ripe when the cell wall of the moisture-swollen fiber represents 50-80% of the round cross-section, as unripe when it represents 30-45% and as dead when it represents less than 20%. Since some 5% unripe fibers are present even in a fully ripened boll, cotton stock without unripe fibers is unimaginable..

Unripe fibers have neither adequate strength nor adequate longitudinal stiffness. They therefore lead to:

· Loss of yarn strength

· Neppiness

· A high proportion of short fibers

· Varying dye ability and

· Processing difficulties, mainly at the card.

5] Fiber cleanness:

 A] Impurities: in addition to usable fibers, cotton stock contains foreign matters of various kinds;

i. Vegetable matter: Husk portions, seed fragments, stem fragments & leaf fragments

ii. Mineral material: Earth sand, ore dust picked up in transport & coal dust picked up in transport

iii. Other foreign matter: Metal fragments, cloth fragments & packing material (mostly polymers)

iv. Fiber fragments: Fiber particles (with finally make up the greater portion of the dust)

These foreign materials can lead to extreme disturbances during processing:

· Metal part can cause fires or damage card clothing. Cloth fragments and packing material can lead to foreign fibers in the yarn and thus to its unsuitability for the intended application.

· Vegetable matter can lead to drafting disturbances, yarn breaks, filling up of card clothing, contaminated yarn etc.

· Mineral matter can cause deposits, high wear rates in machines (grinding effects, especially apparent in rotor spinning) etc.

 The new spinning processes are very sensitive to foreign matter. Foreign matter was always a problem but is becoming steadily more serious from year to year. This is due primarily to modern high-performance plucking methods; hard ginning and cleaning; pre-drying; careless handling during harvesting, packing and transport; modern packing materials.

The scale below represents the degree of trash:

upto 1.2%            =   very clean

1.2-2.0%               =    clean

4.0-7.0%               =     dirty

7.0% and more    =  very dirty

B] Neps:

Neps are small entanglements or knots of fibers. In general, two types of neps can be distinguished. Fiber neps and seed-coat neps, that is, small knots that consist only of fibers and others are containing foreign particles such as husk, seed. It is clear that there is a relationship between maturity index and neppiness. Neppiness is also dependent, exponentially, on the fiber fineness because fine fibers have less longitudinal stiffness than coarser fibers.

The  processing method also has a considerable influence. A large proportion of the neps in raw cotton are produced by plucking and hard ginning and the nep count is substantially increased in the blowroom.

C] Dust:

Dust consists of small and microscopic particles of various substances, which are present as suspended particles.

Microdust consists of 50-80% fiber fragments, leaf and husk fragments. 10-25% sand and earth, and 10-25% water soluble materials. Dust creates environmental problem and affects quality.

6] Fiber Elongation:

The elastic elongation is of decisive important since textile products without elasticity would hardly be usable. They must be able to deform (e.g. at knee or elbow) in order to withstand high loading (and also during processing), but they must also return to shape. The fiber elongation should therefore be at least 1-2% (glass fibers), and preferably slightly more.

The greater crease resistance of wool compared with cotton arises, for example, from the difference in their elongation: cotton = 6-10%, wool = 25-45%.For normal textile goods, higher elongations are neither necessary nor desirable. They make processing in the spinning mill more difficult, especially in drawing operations.

7] The slenderness ratio (Stiffness):

Fiber stiffness plays a significant role, mainly when rolling, revolving and twisting movements are involved. A fiber that is too stiff has difficulty in adapting to the movements. For example, it is not properly bound into the yarn, produces hairiness or is even lost. Fibers that are not stiff enough have too little springiness. They do not return to shape after deformation.

8] Chemical Deposits (Sticky Substance):

The  best-known sticky substance on cotton fibers is honeydew, Strictly, this is a secretion of the cotton louse, but today all sticky substance are incorrectly called honeydew, sticky substances are as follows:

Secretions: honeydew;

Fungi and bacteria: decomposition products;

Vegetable substances:               sugars from plant juices; leaf nectar;

Overproduction of wax;

Fats, oils: seed oil from ginning

Synthetic substances: defoliants; insecticides; fertilizers

oil from harvesting machines.

The Sudanese cotton is noted for its stickiness due to presence of some saccharins. These saccharine are mostly, but not always, produced by insects or the plants themselves. During spinning of sticky cotton, however, the relative humidity of the air in the production area should be held as low as possible.

Fiber characteristics which affect yarn breaking force properties:

Fiber characteristics	Ring spun yarn (Ne-26)	Rotor spun (Ne-26)
Length	22%	12%
Length Uniformity	20%	17%
Strength	20%	24%
Microraire	15%	14%
Elongation	5%	8%
Color	3%	6%
Trash content	3%	6%
Unexplained	12%	13%