Five methods for eliminating phosphating defects of fasteners

1. Phosphating film does not form

There is a hardened layer on the surface of the part, the content of sulfate in the solution increases, the phosphating solution is mixed with impurities, the content of phosphorus pentoxide is too low, the surface is corroded with strong acid to expose the metal grains, and the sulfuric acid is treated with barium carbonate For roots, the phosphating solution should be replaced and phosphate should be added.

2. There is a blank piece of phosphating film

Insufficient nitrate, low phosphorus pentoxide content, too low temperature, more ferrous sulfate in the pickling tank, add zinc nitrate, add phosphate, increase the temperature of the solution, and replace the sulfuric acid solution.

3. Phosphating parts are yellow and white

Sediment, rust at the riveting joint of the assembly, sediment in the solution, insufficient nitrate, and the phosphating solution has not been rinsed, fish out the sediment in the tank, replenish zinc nitrate, and remove the phosphate film in the acid solution Phosphate again.

4. The anti-corrosion ability of phosphating film is reduced (Guide: Knowledge of fasteners: Requirements for hot-dip galvanizing of nuts)

The crystals of the yellow rust phosphating film are coarse or too fine, there are residual salts on the surface of the phosphating parts, the metal is over corroded, the free acidity is too high, the phosphate is lacking, adjust the ratio of free acidity to total acidity, and strengthen the Neutralization and washing, control the number of repetitions of phosphating, supplement zinc nitrate, supplement nitrate.

5. The phosphating film is too thin and the crystal is too fine

Insufficient phosphating time, too low ferrous content, too high total acidity, hardened layer on the surface of parts, too low temperature, prolonging the phosphating time, supplementing ferric dihydrogen phosphate, adding water to dilute the solution or adding phosphate to adjust the acid Use strong acid to corrode the surface, increase the temperature, the redness of the phosphating film, and reduce the corrosion resistance. The iron slag in the pickling solution is attached to the surface, and the copper ions infiltrate the phosphating solution. Replace the pickling solution. Be careful not to use copper hangers. , The phosphating film has coarse crystals, excessive ferrous ion content, residual salt on the surface of the part, insufficient nitrate content in the solution, increased nitrate content in the solution, and excessive corrosion of the surface of the part. Use hydrogen peroxide to reduce iron, increase the temperature, and strengthen Neutralize or wash with water, add zinc nitrate, treat nitrate with barium carbonate, control the concentration and time of acid, uneven phosphating film, staining and degreasing, phosphating temperature is too low, the surface is passivated, and the parts are caused by The heat treatment processing method is different, strengthen the degreasing, adjust the temperature, strengthen the pickling, adjust the acid concentration to expose the metal crystal grains on the surface.

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