Texturizing

After stretching, all the synthetic fibers can be represented as the fibers with smooth glass-like cylindrical surface, strong gloss, low hygroscopicity. This renders difficult for the fibers for their application with better hygienic and aesthetic properties.
Owing to this, the fibers or the filaments are processed further, which is known as 'texturization' or simply *texturing'. Texturization is defined as the means by which luxurious bulk, greater absorbency and improved hand are combined with rugged performance, through the permanent introduction of crimps, loo,s, coils or crinkles into otherwise continuous filaments.

Yarns after texturization differ from the initial yams by high bulkiness, crispiness, porosity, softness and maybe high elastic extensibility. So the fabrics made from these textured yarns exhibit the following advantageous properties :
  1.  higher bulk
  2.  greater water sorption
  3.  increased warmth
  4.  higher covering power
  5.  better air permeability
  6.  better dimensional stability
  7.  good draping capacity
  8.  higher hygienic characteristics
  9.  Pleasing hand and appearance



Texturiztion process

Stretch yarn
These yarns show high stretch, moderate bulk per unit weight and helical crispiness. The elastic extensibility can be as high as 400%. These yarns are mostly used for the stretch-to-fit type fabrics.

Modified stretch yarns
These yarns exhibit moderate degree of stretch, high bulk per unit weight, helical or planner crispiness. The yarns are used in shirtings, suitings, etc.

Bulk yarn
These yarns exhibit increased bulk with little or no stretch, loopy structure and common extensibility. These yarns are also used in shirting, suiting, etc. The exact classification of the process can be summarised as follows:

TEXTURIZATION BY MECHANICAL METHODS


Stretch yarn
This yarn can be produced by discontinuous i.e., twist-de-twist method or by continuous method i.e., false-twist method.

MODIFIED STRETCH YARN
This yarn can be produced by the following methods:
  1.  Modified false-twist method
  2.  Edge crimping method
  3.  Stuffer-box method
  4.  Gear-crimping method
  5.  Knit-de-knit method


Bulk yarn
The bulking can be introduced in a parallel direction with respect to the yam i.e., air-texturing method. Bulking can also be done perpendicularly to the yam direction. In the case, the texturization is generally referred to as "cross-sectional texturization" or "Non-circular fibers".

TEXTURIZATION BY CHEMICAL METHOD

Solvent texturization is the process, where the thermoplastic or thermosetting yams can be texturized by chemical means. Details of this process will be discussed afterward.


TEXTURIZATION PROCESSES


Details of the different texturization processes are discussed below.

TWIST-DE-TWIST METHOD
The production of textured yarn by conventional method consists of the following operations:
(1) The initial yam is rewound from bobbins into flanged spools in the winding machine.
(2) The yarns must be twisted by twisting up to 2000 to 3000 t.p.m in up twister or in machines with double twist spindles. Some yarns should be twisted in 'S' direction and the others in 'Z' direction.

(3) The yarns with both S and Z twist is steamed in an autoclave by means of hot air, hot water or saturated steam. The torque caused by twist forces the filament to follow a helical line but internal a stresses tend to untwist the yam, To relieve these internal stresses and to have a balanced structure, the yarns are subjected to heat treatment.

(4) After steaming, the yarns are wound onto flanged bobbins in a rewinder.

(5) For high dense packages, the yarn should be again steamed and "panoramas

(6) The twisted yarn is then untwisted in a twister, where untwisting can be done by twisting in an opposite the direction of the first twist.

(7) Doubling of the two yarns with an opposite twist can be done in any folding machine or in ring twisting machine with a ply twist of 50-150 t.p.m.

(8) The plied yarn is then transferred to a suitable package. These yarns show remarkable crimp, bulk, elasticity, and elongation. They can be stretched up to 500% depending upon the denier and twist imparted with excellent recovery from stretch. The yams will have a former and crisp hand.


FALSE TWIST METHOD

The false-twist method is a continuous method to produce high stretch yam. In this single-process machine, the three operations i.e., twisting, heat- setting and untwisting recombined. The yam is taken from the supply package  It is

 False-twist texturization method fed by feeding arrangement to the heater  and then it enters in the false twist mechanism for twisting. After the yarn emerges from the false twist mechanism it is untwisted and forwarded by the delivery unit to take-up package  

The false twist mechanisms consist of a false twist spindle, rotating at a speed of 50,000 rpm to 1,00,000 rpm. The spindle is basically a thread guide hook. However, this type of false twist spindles is gradually replaced by friction type false twist mechanisms. Endless belts, bushings, rings, disks, and other rotating bodies are generally used as twisting elements.

MODIFIED STRETCH YARN FROM FALSE TWIST METHOD

The stretch yarn produced by the false twist method is characterized by high stretch with moderate bulk per unit weight. The process can be modified to reduce their stretch and to increase their bulk. This can be done by the following processing operations: High stretch yarns can be further treated with steam in an autoclave or can be steamed in a yarn dyeing machine. The stretch will be reduced to 20-50%.

Additional heat treatment in heater boxes present on double twisters, twisters or winders. In this process, doubling winding and heat treatment can be combined.  Low stretch yarns can also be manufactured in a continuous manner in the false twist machine modified with an additional heater after a false twist spindle. It is one of the efficient processes.


STUFFER-BOX METHOD

The yam is taken from the supply package  to heated stuffer box through the yam guide and tension roller  The pressure roller compresses the filament. After passing through the stuffer box, the yarn is withdrawn from it and is collected on the take-up bobbin  by passing through the yarn guide and traversing guide. The process consists basically of compressing the filaments into confined space of a heated


the chamber is known as "Stuffer box", where the yarns are heat-set in their crimped configuration. This may be done either by feeding multiple ends in a warped form, where the process is known as 'supine'. In this process, all the ends are simultaneously crimped and heat-set. Alternately, single filament is crimped and heat-set in their crimped configuration. This process is known and 'texturized'.



EDGE-CRIMPED METHOD


The yarn is taken from the supply package to the edge-crimping unit through the guide rollers  The crimping unit consists of the input rollers output rollers. separated by heater and knife for crimping. After the crimping, the yarn is collected at the bobbin by means of the traversing guide. The yarm, drawn over the edge of a knife or steel plate is strained by different types of bending strains. The yarn side contacting the knife is compressed while the opposite side is stretched.

During the movement of the yarn, the point of bending is constantly changing its position, both in parallel and radial direction of the yarn. As a result, the yarn after cooling acquires a coiled spring configuration. In addition to crispiness, due to bending, the yams are also given crimp due to change in orientation of the molecules, induced during bending


GEAR-CRIMPING METHOD


The yam comes from the supply package to the heated gears through the yarn guide and tension guide. The gears are heated and enameled with each other. The yam passes through the enmeshed teeth of these two rollers, after which it is deflected by the guide roller and collected on the take-up bobbin. The texturing of thermoplastic yarns may be affected by the action of saw-toothed gears or toothed surfaces. The crimp
A textbook of fiber science and technology is formed when the yarn is trapped between enmeshing sinkers in a rotating head. This head is heated so that the crinkle deformation can be permanently set. The amplitude of the crimp and the number of crimps per unit space is dependent upon the configuration and the number of teeth present in the gear per unit space. This can be varied over a wide range to suit the desired end-use.

KNIT-DE-KNIT METHOD

This is a no torque texturization process. This technique consists of knitting the continuous filament and then stabilize the loop in an autoclave or in a single process by heat setting. After heat-setting, the yarns can be' unraveled and back wind. Heat-setting can also be done with the knitted fabric in a tensioned state to have the desired crimp configuration.
Knitting and heat-setting can be done in the knitting head. The yarns are fed to the knitting head from the supply package through the guide rollers. After knitting, the fabric is taken up by the input roller. The yam configuration is heat-set bypassing through the heater (f) in a tensioned state by means of the input and output rollers. Finally, the set fabric is collected on the take-up package. The set fabric can be knitted in a high-speed rewinding machine. The yarn is unraveled from the set fabric  by means of the

tension rollers moving with high speed. Finally, the crimped yam is collected on the take-up bobbin. The extensibility of the crimped yarn depends upon the loop length, yam thickness, knitter grade, tension applied,

AIR TEXTURIZATION METHOD

The yam passes from the supply package to the air jet device by means of the yarn guides, tension guide, and overfed rollers. The yam is bulked inside the air-jet device by means of the compressed air. This method consists of overfeeding the yam through a turbulent air stream which transforms the excess length of the yam fed into random loops. The loop structure can be locked by stabilization and the structure resembles a spun yam. After bulking the yarn is collected on the take up bobbin by means of traverse guide. This yan is characterized by greater bulk, better covering power and more subdued luster without stretch.

CROSS-SECTIONAL Texturization

Cross-sectional texturization may be carried out by using different types of non-circular spinnerettes. Such yarns are referred to as 'profile-extruded yam'. Depending upon the type of spinnerette, the cross-section may be hedral, profile, hollow, or any other shape. Some of the spinnerettes. Further processing may induce complementary crimp properties with selected spinnerettes. These yams exhibit properties like lower volume weight, high coverage, good draping properties.


 SOLVENT TEXTURISATION


The crispiness in non-thermoplastic yarns can be induced in two ways. The spinning conditions can be properly selected so that a crimped yarn can be manufactured eg- crimp viscose rayon can be manufactured by a proper selection of spinning conditions. Alternately, these yarns can be crimped by means of solvents.
Treatment with solvents modifies the structure, which can be changed to any desired configuration. The new configuration can be stabilized by the removal of the solvent. This process can be use1 for texturization of cellulosic, protein and other synthetic fibers including thermoplastic fibers like nylon and polyester. 



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