Causes of Black spots And Mechanical Lines In Aluminium Profile

Sometimes we notice some black spots on aluminium profiles. These spots will not be shown before anodizing; you can see it only after anodizing process. The hardness is very low in these spots.

What causes it?

• The concentration and temperature of the pretreatment alkaline etching tank are too high; the alkaline etching tank is polluted; the alkali etching time is too long; the cleaning after alkali etching is not timely or the cleaning is not clean enough, these may cause black spots and mechanical lines.
• Chemical polishing scale imbalance, temperature, time, moisture, aluminium ions, impurities, workman operation, after cleaning.

Strictly control operating processes such as alkali etching and polishing time, temperature and concentration. Strict requirements on operators when operating must be careful, careful observation, even if the problem can be found.

• The temperature and concentration of the oxidation tank are high, and the high voltage will lead to the loose quality of the oxide film, and the binding force of the oxide film may lead to the loss of the oxide film.
• White or black spots may also appear when aluminium ions in the oxidation tank exceed 15g/L.

Strengthen the maintenance and maintenance of the oxidation tank liquid, often analyze the concentration of the oxidation tank liquid and the content of other impurities.

• After oxidation, the oxide film was not stained in time, causing the oxide film to be polluted by the external environment, or it was damaged by contact with other things before dyeing.
• The cleaning before dyeing is not clean enough, and the acid solution is not thoroughly cleaned.
• The quality of water in the cleaning tank is also affected.

After oxidation, the product should be dyed in time, and the liquid water should be cleaned. Before dyeing, the product should be neutralized with 10% ammonia water and washed with multiple channels of deionized water.