There is the polishing process of the mill finish aluminum coil,including manual degreasing, chemical degreasing, pickling neutralization and chemical polishing. Let’s have a look of its specific process.
1. Manual degreasing
Detergent: 20-25 ml/L
Na3PO4·12H2O: 5-10 g/L
Temperature: >70℃
2. Chemical degreasing
Degreasing is the second key of the entire process. If the grease is not removed completely, it will not only affect the polishing and anodizing quality, but also pollute the polishing liquid and anodizing liquid.
NaOH: 2~3g/L
Na₂CO₃: 15~25g/L
NaHCO₃: 15~25g/L
Emulsifier: l~29/L
Temperature: >90℃
Time: 2~3 min
3. Pickling neutralization
HNO3: 30%
4. Chemical polishing
The commonly used chemical polishing liquids for aluminum and aluminum alloys are phosphoric acid, sulfuric acid and nitric acid.
Nitric acid: 60~65 ml/I
Hydrofluoric acid: 15-20 ml/L
Glycerin: lml/L
Temperature: room temperature
Time: 1-2 min
On the one hand, the Nitric acid reacts with Al on the surface to form an aluminum oxide film. On the other hand, the alumina film is dissolved in time to generate aluminum nitrate, which plays a major role in improving the quality of chemical polishing.
Hydrofluoric acid is used to increase the brightness. As the general strong acid-containing polishing liquid is prone to over-corrosion, glycerin can act as a corrosion inhibitor to prevent parts from over-corrosion and ensure smooth surface.
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