I. Fabric Blockage: The most common and serious operational fault.
Fabric blockage refers to the fabric becoming entangled and stuck in the dyeing bath or circulating pipes, preventing the equipment from operating normally.
The main causes are:
Feeding is rushed before the fabric has been running stably for 3-5 minutes after entering the machine; mechanical devices (such as return valves and nozzles) are not adjusted in time, causing mechanical blockage.
Lightweight, high-density fabrics (such as spring spun and polyester taffeta) float on the surface of the liquid; without full overflow or the addition of deoxygenating agents, they are prone to knotting and blocking.
Excessive foam in the dye bath creates an "air blast" phenomenon, hindering fabric flow.
Operators fail to detect initial blockage in time, missing the optimal time to activate the backflushing deblocking device, causing the blockage to deepen.
Solutions: Strictly follow operating procedures; adjust equipment parameters before processing; use a full overflow process for easily floating fabrics; add an appropriate amount of defoamer to control foam; continuously monitor during operation, and immediately activate the backflushing function if any abnormality is detected.
II. Color Spots and Stains: The Core Problem of Uneven Dyeing
Color spots manifest as inconsistent color depth on the fabric surface, affecting the finished product grade.
Main causes include:
Excessively rapid heating, especially above 80℃, causes the dye to fix before sufficient penetration, resulting in uneven migration.
Inappropriate selection or insufficient dosage of leveling agent leads to poor dye dispersion.
Incomplete chemical treatment results in incomplete dissolution of dye particles, which agglomerate into color spots at high temperatures.
An excessively small or large liquor ratio affects the uniformity of dye liquor circulation.
Solutions: Control the heating rate (recommended ≤1.5℃/min), use a high-efficiency leveling agent, add the dye after thorough pulping and dilution, and set a reasonable liquor ratio (usually 1:6～1:8).
III. Wrinkles (Chicken Claw Marks): Physical Damage Difficult to Repair at High Temperatures
Wrinkles mostly occur on polyester and its blended fabrics, appearing as chicken claw or eyebrow-like marks, and are permanent creases.
Cause Analysis:
When the fabric cools at high temperatures, it passes through the second glass transition temperature, causing permanent wrinkles to form at the folds.
Rapid temperature rises and falls, especially rapid cooling, exacerbate differences in fiber shrinkage.
Incomplete desizing during pretreatment prevents the release of internal fiber stress, hindering the free movement of interlacing points during dyeing.
Excessive fabric capacity or slow fabric speed leads to prolonged stacking time in the J-shaped dyeing box, increasing the risk of over-stacking.
Prevention Strategies: Thorough desizing and relaxation treatment before dyeing; avoid direct cooling with cold water; use softeners to reduce friction; control fabric capacity and increase fabric speed to shorten stacking time.
IV. Excessive Foam: A Hidden Danger Causing a Chain Reaction
Foam is one of the most common problems in jet overflow dyeing, and in severe cases, it can lead to nozzle suction, pressure drop, and even shutdown.
Causes:
High-speed fabric movement (200-450 m/min) and vigorous agitation of the dye liquor generate high-energy turbulence.
The dyes or auxiliaries have strong foaming properties, the water hardness is high, and the foam suppression effect is poor.
Solution: Use defoamer throughout the process, preferably in stages-add a portion of the defoamer first, then the dye, and replenish the remaining amount during operation to reduce the total dosage and maintain the effect. Prefer organosilicon or octanol-based defoamers with good compatibility that do not affect dyeing reproducibility.
V. Slow Heating/Cooling: Thermal Control Issues Affecting Production Rhythm
Slow heating may be due to: insufficient steam pressure, blocked steam traps, malfunctioning temperature controllers, or air leakage in the tank.
Slow cooling is often due to: insufficient cooling water pressure, excessively high water temperature (>25℃), damaged control valves, or high return water back pressure.
Solution Recommendation: Regularly check the steam and cooling water systems, clean the steam traps, calibrate the temperature controllers, and ensure that the cooling water temperature is controlled below 25℃.
VI. Dye Agglomeration and Dye Spots: Chemical Problems Affecting Fabric Cleanliness
Dye spots and discoloration after dyeing are common in polyester fabrics.
Analysis shows that approximately 50% are due to the precipitation of polyester oligomers, 30% are due to dispersant issues, and 20% are due to impurities such as fiber debris.
Solutions: Strengthen pretreatment; the alkali reduction and impurity removal rate should reach over 10%; select high-quality disperse dyes and auxiliaries; if necessary, perform reduction cleaning to remove floating dye and impurities.
