It has to be admitted that rust water often seeps out after the phosphating treatment of automobile sheet metal parts, which is a difficult problem for many sheet metal fabrication plants. So how to avoid rust and deal with this problem? First, people need to find the reasons for this situation to carry out analysis.
- 1. During pickling and passivation, the acid in the gap is not neutralized or not completely neutralized, and the acid pickling and phosphating is not complete and easy to rust. After spraying, the rust will spread and overflow into the gap after a period of time.
- 2. Passivation by strong alkali pickling and degreasing by strong partial alkali. After the drugs remaining in the crevices are neutralized by oxidation, many manufacturers have not cleaned them with tap water, which results in milky white formation on the crevices after drying. After spraying for a period of time, this milky white product and the corrosive substances in the gas cause some kind of exothermic reaction in the overflow gap. This problem mostly occurs between March and December.
The solution to people’s sheet metal fabrication to avoid corrosion problems is the following:
- 1. Deoiling must use weak partial alkali deoiling, must not contain flake alkali, TAL should be controlled at around 15POINT, and PH should not exceed 12.
- 2. For the process of pickling and passivation, hydrochloric acid can be used for pickling and passivation. The time of pickling and passivation is good and it does not need to be too long. It is just right to use ammonium sulfate.
- 3. After pickling and passivation, please use 1~2 sodium carbonate to neutralize.
- 4 Surface adjustment is best to use organic chemicals such as hydrochloric acid, and the concentration value of 1~2 degrees can be used.
- 5. The phosphating acid value of zinc-based pickling should be limited, and the pre-dipping solution should be tried: TA: about 45, FA: 1.3AC: 8 (20cc hair alcohol tube).
- 6. All hand-washing projects must not be cleaned and tidy, and hand-washing should maintain overflow.
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