Hydrodynamic Shear Controls and Dyebath Exhaustion Rates in Jet Dyeing
Hydrodynamic shear controls dyebath exhaustion by thinning the liquid boundary layer; excess velocity damages yarns, mandating precise pressure-flow balancing.
Running Marks
Fabric Defect
Linear distortions and uneven colour stripes can develop along the length of woven or knitted materials during wet processing. The appearance of running marks arises when a fabric remains creased in the same position while running through a rope dyeing machine. This structural fault shows up as long, dark bands that cannot be removed by simple washing.
Dyeing Mechanism
Jet and beck dyeing systems subject the fabric rope to constant movement and folding. If the fabric does not change its folding pattern as it passes through the venturi nozzle, dye liquor accumulates along the crease lines. This uneven liquid distribution results in localized dye exhaustion differences that become permanently fixed during the fixation cycle.
Knitted fabrics made from synthetic fibres are particularly susceptible to this defect due to their thermoplastic nature.
Prevention Strategy
Dye houses use chemical lubricants in the bath to reduce friction between fabric layers and facilitate shifting. Lowering the cooling rate after high-temperature cycles also prevents the setting of creases before the fabric is straightened.
Finishing Impact
Severe marking reduces the yield of usable fabric and leads to garment panel rejection during cutting. Corrective stripping and redyeing can salvage the lot but weaken the fibre strength and increase processing costs.