Step 1: Quickly identify the category based on the appearance of the unevenness
1. Localized spots or irregular dark patches: Likely caused by incomplete dye dissolution, dye particle splashing/staining, or precipitation on the fabric surface due to anionic-cationic reactions.
2. Large-area color unevenness: Likely caused by insufficient liquor level, excessively rapid heating, adding exhaustion agents all at once, or uneven pH across the fabric surface during pretreatment.
3. Edge-to-center or localized shade variation: Likely caused by temperature or pH differences between the fabric edges and the center, uneven fabric width, or excessive curvature of the spreader frame.
4. Striped or regular patterns: Likely caused by excessive steam impact, blockages in the equipment circulation system, or excessive yarn waste wrapped around the rollers.
Step 2: Quickly troubleshoot based on process operations
1. Check dyeing liquor level: Confirm if the bath level is too low and if any parts of the fabric are not fully submerged.
2. Check dosing records: Confirm if exhaustion agents were added in batches at low temperatures and if the steam was turned off to lower the temperature before mid-process additions.
3. Check heating curve: Confirm if the heating rate above 80°C was too fast and if the high-temperature holding time was sufficient.
4. Check pretreatment records: Confirm if scouring and washing were thorough and if the fabric surface pH remained uniform.
5. Check sulfur dyeing conditions: Confirm that the sodium sulfide content is at least 4 g/L to prevent unstable dyeing caused by a deficiency of sodium sulfide.
Step 3: Quickly troubleshoot based on equipment and materials
1. Check dye condition: Confirm that the dye was filtered through a sieve and that disperse dyes were dissolved in cold water before entering the vat, ensuring no undissolved particles remain.
2. Check equipment cleanliness: Confirm there is no excessive yarn waste wrapped around the bottom rollers and no residual dye aggregates inside the machine.
3. Check auxiliary compatibility: Confirm that anionic and cationic dyes or auxiliaries were not mixed directly in the same bath, preventing precipitation reactions.
4. Check water quality: Ensure there are no excessive metal ions that could cause dye aggregation and adsorption onto the fabric surface.
5. Check equipment circulation: Confirm that the dye liquor circulation system is free of blockages, pump pressure is normal, and the dye liquor flows evenly throughout the system without any stagnant zones.
Step 4: Rapid verification and troubleshooting
1. Take a sample of undyed greige fabric from the same batch and conduct a small-scale test dyeing; if uneven dyeing (patchiness) still occurs, the issue can be directly attributed to the dyes, auxiliaries, or the greige fabric itself.
2. If the small-scale test yields uniform results without anomalies, the issue lies with large-scale machine operation, equipment circulation, or the production environment; the problem can be quickly resolved by making targeted adjustments to the relevant parameters.
