Anti-Rust Measures for Sheet Metal Fabrication

After the sheet metal processing welds are pickled and then phosphated and powder coated, some rust water may seep out after a period of time. How should this issue be addressed during the pre-treatment process?

During pickling, the acid in the gaps is not neutralized or not fully neutralized, resulting in incomplete phosphatization which is prone to rust. After a period of painting, the rust spreads and oozes out from the gaps.

2. The acid washing and alkaline degreasing process left residues in the crevices, which were not fully cleaned after neutralizing with each other. After drying, a white substance formed in the crevices. After a period of painting, this white substance reacted with corrosive agents in the air, causing it to overflow from the crevices.

Solutions to Prevent Rusting in Sheet Metal Processing:

1. The defatting process requires a weakly alkaline method, free of sodium hydroxide. The TAL level should be maintained around 15 points, and the pH should not exceed 13.

2. Pickling can also be done with sulfuric acid. Avoid extended pickling time. Use phosphoric acid.

3. Neutralized with 1-2 moles of sodium carbonate after pickling.

4. Surface adjustment with oxalic acid, using a concentration of 1~2.

5. Zinc phosphating treatment requires an acidity at the upper limit. Immersion treatment concentration: TA: above 35, FA: 1.2, AC: 8 (20CC fermentation tube).

6. All washing operations must be thoroughly cleaned, and the washing process should maintain overflow.