It is a Thermo mechanical Process of introducing crimpiness / waviness in filament. Thus it creates voids & helps mechanical absorption of moisture. This is how it helps in improving the warmth & comfort feel of Polyester although moisture regain remains low.
This is a process of value addition & not essential but a desirable process.
Line diagram of DTY Yarn Path & Illustration of Process Parameter
- Yarn Speed : It is the speed of FR2 in mtr per min. Setting of this speed is governed by surging speed, DTY product quality & DTY performance.
- Draw Ratio (D.R) : It is the speed difference between FR1 & FR2. FR2 speed > FR1 speed, hence drawing operation takes place. Setting of this parameter is governed by tension on yarn ( T1), final yarn properties with respect to Tenacity, Elongation, shrinkage, crimp stability, broken filament level & dyeability.
- Velocity Ratio / DY ratio : It is the ratio of surface speed of nip twister belt/ disc to the linear speed of yarn. Setting of this is governed by tension after false twisting mechanism ( T2). Ideally tension after false twisting (T2)should be same as before ( T1), that means T2/T1 =1. This ensures complete untwisting. But optimisation of this depends on tight spot( spot of incomplete untwisting/ slippage),broken filament, loop,crimp properties & DTY performance.
- Primary Heater Temperature : This temperature facilitates drawing – as Polyester needs hot drawing. For this purpose yarn temperature above glass transition ( Tg @ 80degC) is enough. But texturising requires recrystallisation & hence yarn residence time of @0.2 sec at a temperature of @ 190degC is required.. Thus optimisation for Texturising serves both purposes. Also yarn before reaching F.T must be below Tg .Setting of this is governed by above, Crimp properties & stability & bf on yarn, dyeing uniformity.
- Stabilising overfeed / OF2 : It is the overfeed in second heater & is controlled by speed difference of FR2 & FR3 – FR3 speed is changed. Speed of FR2 > speed of FR3 causing this overfeed.It causes relaxation in second heater while bulk setting. Ideally it should be as high as possible till the yarn starts dangling. Its setting is governed by final bulk, loop on dty package, dyeing uniformity etc.
- Stabilising overfeed / OF2 : It is the overfeed in second heater & is controlled by speed difference of FR2 & FR3 – FR3 speed is changed. Speed of FR2 > speed of FR3 causing this overfeed.It causes relaxation in second heater while bulk setting. Ideally it should be as high as possible till the yarn starts dangling. Its setting is governed by final bulk, loop on dty package, dyeing uniformity etc.
- Take up overfeed / OF3 : It controls the package winding tension. It is controlled by speed difference between FR2 & Take up bowl – by changing the take up bowl speed. Speed of FR2 > Speed of take up bowl but speed of FR3 < speed of take up bowl – this underfeed between FR3 & Take up bowl causes winding tension. Its optimisation is governed by requirement of winding tension for specific deniers.
- Winding Parameter : There are various parameters for proper package winding. These parameters are aimed for proper package formation so that it gets transported to customers place without deformation & gets smoothly unwound at a speed upto 1000 mpm.
