DRAW TEXTURISING

 DRAW TEXTURISING 

DRAW TEXTURISING MACHINE

• Theory: 

1. Texturising is the process of introducing permanent waviness, loops, coils and wrinkles by modifying the geometrical and structural characteristics of constituent filament yarns.
2. The production of textured filament yarns by false twisting is an important commercial method.
3. The false twist texturising process consists of softening a continuous filament yarn by heating to make it more pliable, deforming the softened yarn by twisting, cooling the yarn in the twisted state to set the deformation, and then removing the inserted twist.
4. In the industry textured yarn is also known as DTY that stands for Draw Textured Yarn. Only thermoplastic filament yarns can be false twist textured.
5. In principle, enhanced textile properties both tensile and tactile are given to continuous filament yarn by the simultaneous action of drawing, heating and twisting the filament yarn, this subsequently is untwisted.

•         Principle: 

1) Filament yarns like polyester and nylon and thermoplastic. They soften and can be easily deformed with the application of heat and upon cooling, the filaments remain in their deformed state (i.e. the filaments become heat-set).
2) Normally if filaments are twisted, torsional stress develops in the filaments and the filaments will want to untwist to release the stress.
3) However, if such filaments are twisted and heat-set (i.e. heated above their glass transition temperature and then cooled below their glass transition temperature), their torsional stress will be relaxed and the filaments will remain twisted even though the external force is removed.
4) If these filaments are then untwisted, stress will develop again in the individual filaments. If these stressed filaments are allowed to relax, they will seek the minimum-energy-state (or least stressed state) by forming adjacent helices and snarls.
• These helices and snarls prevent the individual filaments from staying as closely packed as before and the filaments will occupy a much greater volume than before. In other words, the filaments become bulky and textured.

Yarn after Texturising

•  Principle of filament texturing by twisting, heat-setting and untwisting:

The false twist process can be divided into three fundamental elements. It is the way in which these elements are employed and controlled that when they are used in combination with each other gives the resulting product its desired properties. By controlling these three fundamental variables a wide variety of different textured yarn can be made from one POY feedstock.

1. Creel: 
The creel itself should be of robust construction and be large enough to accommodate a variety of feed yarn package sizes. it should also be able to accommodate a reserve package from which transfers can be made for a continuous process. To this end it is a decided advantage if the creel is of a rotary design so that POY can be loaded on to all arms within the creel from one position. This reduces the risk of POY damage. All ceramic surfaces within the creel should be in good condition and of low friction surface.

2. Yarn transport system: 
The input shaft, which transports the yarn from the creel into the draw zone. Obviously all the shafts of the machine are usually of a similar type. The prime consideration is that the yarn is transported through the machine with no slippage. Normally the transport or feed unit will consist of a bright chrome metal surface and a rubber apron or a nip roll.

3. Twist stops: 
The functions of the twist stops are twofold:

i. The twist stop prevents the twist developed in the yarn by the twist insertion device, running all the way back to the input shaft and hence causing yarn instability between the input the shaft and the entrance to the primary heater and therefore increased yarn breaks.

ii. The twist stop effectively traps all of the twist generated in the yarn between the top of the twist insertion device and the entrance to the heater. This allows the twist to have maximum effect within the heater and hence to generate the maximum possible bulk in the textured yarn.

4. Primary heater: 
Contact heaters have been used for many years on texturing machines. Primary contact heaters are usually liquid filled and work on the vapor phase principle. They have an electrical heating element in the base of the heater, controlled by a thermocouple. To regulate the temperature, the liquid is a diphase mixture of two components, mixed in such a way that they  produce vapor with a comparatively low pressure at the heater operating temperature. The heater is sealed and all air is exhausted so that a condition of vacuum applies internally. This allows the vapor to condense on the inside surface of the heater track once the heaters have brought the liquid to the operating temperature. The condensation causes the vapor to give up its latent heat and this enables the heater track to be held with an almost constant temperature profile.

5. Fume exhaust: 
The main function of the fume exhaust is to help maintain the machine, and particularly the primary heaters in a clean condition. Basically low velocity air is drawn across the yarn path at the entrance and exit to the primary heater.

6. Cooling plates: 
The cooling plate is situated between the exit of the first heater and the entrance to the twist insertion device. It has two major functions:

i. It allows yarn bundle to cool, while still in a highly twisted state between leaving the primary heater and entering the friction aggregate. Yarn temperature at the entry to the twist insertion device is ideally in the range 86-90 C for polyester.

ii. It gives stability to the high twisted yarn bundle between exit from the primary heater and entry into the friction unit.

7. Twist insertion: 
The heart of the draw-texturising process is the twist insertion device. The action of twisting the drawn heated filaments and then subsequently detwisting them are what gives the crimp character and bulk to the yarn. In principle the yarn is twisted at high speed by the discs of the friction unit. The twist is transmitted back up the yarn path on to the primary heater whereas the heater has softened the yarn and cooled on the plate; it is set into its molecular structure. This is why the yarns that are processed by the false twist texturising process must be thermoplastic in nature. As the yarn exits the friction unit, it untwists in the opposite direction to that above the unit but as the yarn is now cold, it does not affect the sense of twist or torsion set in the yarns memory. The amount of twist inserted into the yarn is governed by two main factors:

The amount of contact between the yarn and friction discs

The speed of the friction discs relative to the speed of the yarn (D/Y).

Himson HDS –CX2 m/c is equipped with HI TWIST Friction twist unit. It comprises three stacks of overlapping friction discs. The units can be assembled with ceramic coated or polyurethane discs of varying configurations. The discs are fitted to fixed center spindles. A toothed belt drives the three spindles. An endless flat section belt drives each unit tangentially.

False twist devices:
i.   Pin-spindle false twister
ii.  Stacked disk type false twister
iii. Crossed-belts false twister
iv.  Ring false twister

8. Secondary heater: 
After the yarn has passed through the center shaft, it is passed through a heater tube between 1.0 and 1.3 m in length, where it is heated under controlled relaxation. The reason for subjecting for
yarn to this is to reduce the amount of skein shrinkage or crimp and stretch left in it after exiting the twist insertion device. If this is not done, i.e. no secondary heat is applied, it is known as either single heater or high extension yarn. To reduce the amount of crimp, the yarn is heated to temperatures of 150–235 degreeC.

9. Coning oil application: 
Coning oil is applied to the yarn to enable it to be processed more efficiently during knitting and weaving. The rate at which the oil is added to the yarn with a roller and trough is governed by following factors:
i)   The speed of the oil application roller
ii)  The area of contact between the yarn and the oil roller.
iii) The viscosity of the oil
iv) The type of surface of the oil application roller

The amount of oil applied to the yarn depends upon its end uses but values typically lie between 1 and 3 %.

10. Take –up system: 
Take system consists of a package support, a drive for the package and a traversing system to for laying the yarn on to the package.

• Published By:

Harshad Bisale.
Dept. Of Textile Technlogy,
DKTE Textile and Engineering Institute.
harshadsb.a03@gmail.com