First, when the oxide film starts to have powdery gray spots, we should first try to see if it can be wiped off. We need to remove the sealing gray caused by the closing process and the powdery residue caused by electric shock.
Next, let's analyze the root causes of powder formation during oxidation one by one. Generally, powder formation on the coating is caused by the following factors: 1. The temperature of the oxidation tank is too high; 2. The concentration of sulfuric acid is too low; 3. The aluminum ion content exceeds 18g/L. (The rapid increase in aluminum ions is often due to the oxidation tank being too hot, or because debris in the tank wasn't removed in time)
Next, we analyze the origins of the oxidized powder ash one by one.
Generally, powdering of the coating is caused by the following points:
1. The oxidation tank temperature is too high;
2. The sulfuric acid concentration is too low;
3. The aluminum ion content exceeds 18g/L. (The rapid increase in aluminum ion content is often caused by the oxidation tank temperature being too high, or by dropped items in the tank not being retrieved in time)
If the oxidation tank temperature is too high, does that mean the refrigeration equipment isn't big enough? If the normal cooling capacity is still okay, then you need to consider the size of the chilled water circulation. Check if the circulation pump is blocked, causing the high temperature, and troubleshoot one by one.
The sulfuric acid content should be based on the daily sulfuric acid loss and intake in the oxidation tank. Regularly check and replenish the acid. Keep the concentration within the process range (180-220g/L is best).
The temperature of the electrolyte has a huge impact on the wear resistance of the oxide film. Generally speaking, if the temperature drops, the wear resistance of the anodic oxide film on aluminum and aluminum alloys increases. This is because the electrolyte dissolves the film more slowly. To get an oxide film with higher hardness, it's best to control the temperature within ±2℃ when doing hard anodizing.
