Aluminum alloy dyeing common problems and solutions
China Aluminum Industry Network: When facing issues in the dyeing process of anodized aluminum, it's essential to identify and resolve the root causes systematically. First, if the surface appears uncolored, check whether the anodizing film thickness is sufficient. Ensure that the anodizing process follows standard procedures, and verify that temperature, voltage, and conductivity are stable. If everything seems normal, consider increasing the oxidation time to meet the required film thickness. Another common issue is a high pH in the dye solution. To correct this, use glacial acetic acid to adjust the pH to the recommended level. If the workpiece remains in the dye bath for too long, it may lead to uneven color absorption. It’s best to dye promptly. In such cases, re-activate the workpiece in an anodic oxidation tank or a nitric acid neutralization tank before dyeing again for better results. Choosing the wrong dye can also cause problems, so always use the appropriate type. If the dye has decomposed or become moldy, replace it immediately. An insufficient oxidation temperature can result in a dense oxide layer, so increase the temperature slightly. Poor conductivity, often due to dirty anode copper rods or cathode lead sheets, should be addressed by cleaning them thoroughly to ensure good electrical contact. Second, white spots or dew-like marks often occur due to inadequate washing. Improve the rinsing process to remove residues effectively. If the rinse water is contaminated, replace it regularly to maintain quality. Airborne pollutants like soot, acid fumes, or alkali mist can also damage the oxide film. Enhance washing and speed up the dyeing and transfer process to reduce contamination. Oil and sweat from handling the workpieces can cause discoloration, so avoid touching the surface directly. Insoluble impurities or oil in the dye solution may lead to uneven coloring, so filter or replace the solution as needed. For parts with deep holes, ensure thorough rinsing to prevent residual acid from causing issues. Chloride ions (Cl-) in the dye solution can cause point corrosion, so replace the dye and take care to avoid introducing impurities during operation. Third, color inconsistency or uneven film thickness may stem from non-uniform temperature or concentration in the anodizing bath. Use compressed air to stir the solution for even distribution. Similarly, if the dye solution is not well mixed, introduce a stirring process. Dyeing too quickly can lead to uneven coloration, especially on the bottom part of the workpiece. Dilute the dye and extend the dyeing time for better results. Poor conductivity can cause loose rack connections, so ensure all contacts are tight. If the dye is too diluted, add more dye to increase the concentration. A low dye temperature can also affect the outcome, so warm the solution to below 60°C. Improper dissolution of dyes or floating insoluble particles can cause color variation, so improve the dissolving method. Fourth, issues like dyeing hair or color fading may occur due to low pH in the dye solution. Adjust the pH using dilute ammonia. Inadequate cleaning can lead to residue buildup, so intensify the washing process. Incomplete dye dissolution can cause uneven color, so ensure full dissolution. High dye temperature can also cause fading, so lower the temperature accordingly. Small pores in the oxide film, often due to low oxidation temperature, can lead to poor dye absorption. Adjust the oxidation temperature properly to avoid this. If the dyeing is too fast and the time is too short, dilute the solution, lower the temperature, and extend the time. Low sealing solution temperature can also affect the finish, so heat the solution. If the sealing solution pH is too low, adjust it with dilute ammonia. Lastly, if the surface is easily wiped off, it may indicate a rough film caused by excessive oxidation temperature. Always control the temperature within the specified range to prevent this.
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