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.
Barré Defects
Visual Characteristic
Repetitive horizontal stripes or bands appearing in the courses of a circular knit or the weft of a woven fabric result from physical or dye-affinity variations in the yarn. These barré defects often remain invisible in the greige state and only become apparent after the fabric is dyed or finished. The pattern repeats at a fixed interval determined by the machine diameter or the number of yarn packages in the creel.
Mechanical Origin
Tension differences at the feeder or irregular stitch lengths across the knitting needles create physical density changes that refract light differently. While barré defects are frequently associated with yarn quality, mechanical faults in the knitting machine like worn needles or misaligned cams also contribute to the phenomenon. Identifying the exact repeat length helps technicians determine whether the issue originates in the yarn supply or the knitting equipment.
Proper diagnosis requires counting the number of courses per repeat to match them against the number of feeders in operation.
Dyeing Verification
Chemical differences between yarn batches can cause varying rates of dye uptake that appear as shaded bands. Systematic testing using a single dye lot on fabric samples containing multiple yarn sources identifies whether barré defects stem from molecular differences in the polymer or the texturizing process.
Mitigation Strategy
Regular maintenance of knitting tension and the use of merged yarn lots from the same production run reduce the risk of visible stripes. Fabric inspection under specific lighting conditions allows for the detection of these irregularities before the material is cut into garments.