Importance Of Yarn Specifications
For sale-ability or for incorporation into various textile structures, yarns should be produced with some yarn specifications. This specification may depend or vary from end-use to end use. For example – The yarn specifications required in the industrial fabric is much different from the yarns of regular fabrics.
There are some specifications of yarn which are common to all types of yarns that is for the purpose of designation or for the purpose of identification.
For identification, important yarn specifications are linear density, structural features, fiber content etc.
1. Specification Of Yarn Linearity
There are many terms which are used to designate the variety of yarn sizes. Yarn count, yarn number, yarn fineness as well as yarn size all are the terms which can be used by the textile industry. Specification of yarn according to linear density is required for designation of yarn.
Linear density is defined as the mass per unit length of material. As the textile yarns are quite flaccid and do not have a dimensionally stable diameter or cross-section shape so that in practical use rather than specifying diameter or volumetric density, it is become reliable to use linear density.
There are two different system of specifying the linear density of yarn.
- Direct system
- Indirect system
The direct system is based on the weight per unit length of the yarn. Examples of the direct system are tex and denier.
It is weight in grams of 9000-meter length of yarn.
It is weight in grams of 1000 meter length of yarn.
Note:- ‘TEX’ system is proposed as a universal system in the world by ASTM.
In case of a direct system, larger the designation number, larger will be the yarn diameter and heavier will be the yarn.
In case of the indirect system, the linear density of yarn is based on the number of standard lengths of yarn per unit weight.
Examples of the indirect system are cotton (Ne), woolen, worsted yarn system for designation of linear density.
The cotton system is based on a number o 840-yard length per pound.
The woolen system is based on the number of 1600 yard length per pound.
The worsted system is based on the number of yard length per pound.
Woolen cut system and linen cut system is based on 300-yard length per pound.
In case indirect system larger is the designation number smaller is the diameter or lighter will be yarn.
In indirect system regardless of fiber content, the yarn numbering is done according to the system of processing (that is cotton, woolen, worsted).
In the indirect system, yarn number is inversely proportional to the linear density of yarn.
2. Specification Of Yarn Structural Features
Yarn structural features are mainly dealt with constructional features.
The major construction features which are must be specified while describing yarn are whether the yarn is the yarn is basically staple or filament in composition, direction and amount of twist and whether the yarn is single or plied.
If the yarn is single and staple spun then the system of spinning should be designated.
In the case of plied yarns, it is necessary to know the resultant yarn number, which is also referred to as singles equipment resultant yarn m=number or singles equipment is the observed linear density of plied yarn.
Plied staple yarns are normally numbered in the indirect system. The resultant is estimated by dividing the singles by the product of the plies.
But this is an estimate because contraction of assemblage during plying is not taken into account and so that the actual results is slightly coarser than the estimated.
Spun yarns always have the higher amount of twist. The twist is expressed by the number of turns per inch or by the number of turns per meter and direction of twist is designated as ‘S’ and ‘Z’ twist. S-twist is referred as the right left hand or anti-clockwise direction of twist.
Twist multiplier is an expression that relates the amount of twist in a yarn to the square root of the yarn count. This indicates the relation degree, level or an angle of twist in the yarn.
TPI = Twist Multiplier * [COUNT (Ne)]^1/2
Twist Multiplier= TPI / [COUNT (Ne)]^1/2
The amount of twist in the filament yarn is substantially less than spun yarn. But the exception for this is the crepe yarns and other novelty yarns. Filament yarns are available in ¼ or ½ TPI in yarn. Filament yarns with zero twist are also available.
In zero twist yarn, some long-term entanglement is brought by filament interchange (radial migration). Which is act as localized pseudo twist or planning phenomenon. This can be understood by running in through the filament yarns in the direction of the yarn axis.
3. Specification Of Fiber Content
In cotton yarns and cotton yarn blends, it is customary to designates. Some information concerning the properties of the constituent fibers. It is important because based on that experienced textile technologist predict yarn quality and performance standards. This same thing is also applicable for wool and wool blends.
When man-made fibers are spun on staple yarn system, at that time follow fiber specification are mentioned.
- Staple length in inches.
- Linear density in denier (den) or milli tex.
- Luster factory is started as bright semi-dull and dull, Which is related to the delustering added to the fiber.
Along with this, there are some other characteristics which are mentioned by the manufactures.
- Cross-sectional shape and surface characteristics.
- Blend compatibility with other fibers.
- Breaking tenacity, modulus, and extension under wet and dry conditions.
- Dyeing behavior.
- Melting and glass transaction temperature.
In case of filament yarn, the generic name of constituent fiber is given. In filament yarn in general practice first, the linear density of yarn is given and followed by the number of filaments per yarn.
4. Specification Of Mechanical And Chemical Treatment
There are various mechanical and chemical treatments available to improve the performance characteristics of textile. Many of these treatments are done in fabric form but several treatments are also carried out on yarn structures.
Among the various yarn treatments major treatments are
- Mercerization and slack mercerization in the case of cotton yarn.
- Shrink resistance of wool yarns.
- Degumming of silk yarns.
- High bulking of spun yarns.
- Texturing filament yarns for stretch.
For industrial yarns, there is treatment range of treatments and coating such as waxing, rubber, thermal plastic, electrically insulating, etc…
The effect of various treatments on industrial product yarn is very stipulated whereas with consumer product yarn, the treatments are specified but an effect on yarn properties are not always stipulated particularly, the effect on treatment on yarn properties such as linear density is not specified.
There should be pre and post-treatment designation for more important yarn properties when significant changes are there.
For example- a designation such as 70-34-0 textured polyester indicates that a 70 denier, 34 filament yarn with ‘0’ twist was textured. The designation does not include the texturing method and resultant linear density because after texturing there is the change in the linear density and extensibility in the relaxed state.
Along with these permanent treatments, there are some varieties of temporary treatments also such as-
- Steaming for twist setting and to overcome internal stresses during spinning and twisting operation.
- Sizing to improve abrasion resistance.
- Application of lubricant to reduce friction and abrasion during processing.
These temporary treatments are removed during dyeing of finishing.