Thermal Fixation Dwell Time Calibration for Micro Polyamide Spandex Knits
Calibrate stenter line speed to effective core dwell time above 190°C rather than total chamber residence to prevent spandex degradation and knit shrinkage.
Air Quenching
Cooling Mechanism
Solidification of molten polymer filaments occurs through the controlled application of directed airflow immediately following the spinneret. This air quenching determines the rate at which the fibre transitions from a liquid state to a semi-crystalline solid. A steady stream of air absorbs heat from the extrudate to prevent the individual strands from sticking together while they are still in a plastic state.
Filament Uniformity
Consistency in the air velocity and temperature ensures that every filament across the spinneret face undergoes the same cooling profile. Variations in air quenching lead to differences in molecular orientation and crystallinity which later appear as uneven dyeing properties or physical strength discrepancies in the finished yarn. Precise control of the laminar flow is required to avoid turbulence that could cause mechanical damage or tangling of the fine filaments.
Production Speed
Higher extrusion rates require more intense cooling to achieve full solidification before the yarn reaches the take up mechanism. Increasing the volume of air or lowering the temperature allows for faster throughput but requires careful balancing to avoid excessive tension on the molten polymer.
Airflow Velocity
Monitoring the pressure and distribution of the cooling air remains the primary method for maintaining quality in a melt spinning plant. Efficiency depends on the configuration of the quench cabinet and the stability of the ambient environment.