Phosphating treatment is to immerse the metal in a phosphating solution composed of phosphoric acid, phosphate and other components to form an insoluble phosphate layer on the metal surface through chemical action. In recent years, the fastener industry has developed rapidly. More and more attention to the surface of fasteners
Phosphating treatment is to immerse the metal in a phosphating solution composed of phosphoric acid, phosphate and other components to form an insoluble phosphate layer on the metal surface through chemical action. In recent years, the fastener industry has developed rapidly. More and more attention is paid to the surface treatment technology of fasteners. Let us introduce the phosphating treatment of fasteners.
The main problem is that the corrosion resistance of the phosphating film is tested in accordance with GB11376-1989 for neutral salt spray, and no rust is produced for 90 minutes. The fasteners have a neutral salt spray test failure rate of 45%. The appearance and color of the phosphate film are inconsistent, the crystal is coarse, and the ash is much.
Factors that will be caused
1, the solution into the distribution ratio is not good
The composition and ratio of the solution have a great influence on the quality of phosphating. When the self-adjusting calcium salt phosphating solution is used for production, the phosphating film formed on the surface of the workpiece has coarse crystals, high ash, and poor appearance quality. The prepared black phosphating solution produces relatively more precipitates during production, and basically needs to smash the sediment every day. PF-MIAM and PF-MIAR phosphating solutions were used for comparison with various phosphating solutions. The phosphating solution is simple to adjust, and the phosphating film is finely crystallized, so that the corrosion resistance of the automobile fastener is greatly improved, and the workpiece has less ash and less solution precipitation. Its phosphating effect can basically meet the black phosphating requirements of automotive steel fasteners.
2, the acid ratio is not correct
The acid ratio refers to the relationship between free acidity and total acidity. The free acidity is too high, and the effect of steel parts is fast, and a large amount of hydrogen is precipitated, so that the interface layer phosphate is not easily saturated, resulting in difficulty in crystal nucleation formation, coarse and loose pores, loose pores, reduced corrosion performance, and phosphating time. Prolonged; the free acidity is too low, the phosphate film is thin, and even no phosphate film is formed. If the total acidity is too high, the film layer will be too thin, and the total acidity will be too low to make the film layer loose and rough. Therefore, the total acidity is generally controlled at 85~140 points.
3. Influence of pre-phosphorization treatment
The small fasteners are packed in baskets, the workpieces are easy to contact, and they cannot be fully phosphatized during the phosphating process. It is difficult to form a complete phosphating film at the contact parts, so the resistance to neutral salt spray is poor; if it is mounted or let the workpiece If it does not touch, so that it can fully react, it will have a multiplier effect on improving the resistance to neutral salt spray.
4, the effect of solution temperature
When the temperature of the phosphating solution is increased, the bonding strength, hardness and corrosion resistance of the phosphating can be improved. However, the temperature should not be too high, otherwise Fe2+ will be oxidized to Fe3+, and the precipitate will be increased, and the solution will evaporate quickly, resulting in unstable solution.
Reasons for the poor corrosion resistance of phosphating fasteners and countermeasures
(1) Poor distribution ratio of solution: Improved phosphating solution formulation, using PL-VM phosphating solution.
(2) The acid ratio is not correct: the free acidity is too high, and it can be adjusted by adding manganese carbonate: the total acid is too low, and the main agent can be adjusted, and the total acid is controlled at 85 points or more.
(3) The main component of the solution is low: the main liquid is added.
(4) The main component of the solution is incorrect: after the solution is cleared, the bath temperature is controlled at about 95 °C.
(5) The phosphating time is too short: the phosphating time is controlled at 10~15min.
(6) High Fe2+ content in the solution: adjust the Fe2+ content by adding an oxidizing agent such as hydrogen peroxide or replace the bath.
(7) Oxide in the solution: replace the bath, or strengthen the cleaning of the workpiece before pickling.
(8) Pre-treatment is not clean: sandblasting or fasteners are used to maintain good surface condition before phosphating.
(9) Excessive load: Use the hanging or reduce the load to keep the fasteners in a certain gap so that they can fully react.
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