Oxide scale removal is a critical step in the acid pickling and passivation process, directly impacting the final quality of metal products. However, many companies encounter issues where oxide scale is not completely removed, leading to surface defects. These defects not only affect the appearance of the product but can also weaken its corrosion resistance and reduce its lifespan.

Problem Analysis:

1. Insufficient Acid Concentration: The concentration of the pickling solution is a key factor in the effectiveness of oxide scale removal. If the acid concentration is too low, it may not effectively dissolve the oxide scale on the metal surface, especially when dealing with thicker or more stubborn oxide layers.

2. Inadequate Treatment Time: If the pickling time is too short, the acid may not have enough time to fully interact with and dissolve the oxide scale. This issue is exacerbated in low-temperature conditions, where the reaction speed of the acid is slower, further hindering the thorough removal of oxide scale.

3. Insufficient Surface Preparation: If the metal surface is not adequately pre-treated before pickling, such as through degreasing or mechanical cleaning, residual contaminants can interfere with the acid’s ability to contact the metal surface, resulting in incomplete oxide scale removal.

Solution:

1. Optimize Acid Formula and Concentration: Adjust the acid formula and concentration based on the specific material and thickness of the oxide scale to ensure it has sufficient corrosive power. Regularly monitor and adjust the acid concentration to maintain it within an optimal range. Additionally, consider using more aggressive or higher penetration pickling solutions to enhance the removal efficiency of the oxide scale.

2. Extend Treatment Time and Optimize Temperature Control: Within safe limits to prevent over-etching, extend the pickling time to ensure the acid has ample opportunity to act on the oxide scale. Additionally, optimize the pickling temperature; if working in lower temperatures, consider raising the temperature slightly to accelerate the pickling reaction, thereby ensuring more complete oxide scale removal.

3. Enhance Surface Preparation: Conduct thorough pre-treatment of the metal surfaces before pickling, including degreasing and removing any surface contaminants. Combining mechanical cleaning with chemical cleaning ensures a clean surface, allowing the acid to evenly interact with the metal and improve oxide scale removal effectiveness.

These improvements can significantly enhance the removal of oxide scale during acid pickling and passivation processes, ensuring better product quality and extending the product’s lifespan.