The corrosion resistance of the black passivation film on the galvanized layer is similar to that of the military green passivation film, and the process has developed rapidly in recent years.
The black passivation process is divided into two categories: copper salt and silver salt. The materials are available on the market and the preparation is very convenient.
The disadvantage of the galvanized black passivation process is that it takes some time to maintain the solution. A slight change in the solution ratio and process conditions has a greater impact on the quality of the film and requires strict control.
The following takes CK-836(A)(B) produced by Kaifeng Andi Electroplating Chemical Co., Ltd. as an example to illustrate the problems that need attention in the operation of the black passivation process of the galvanized layer.
Pay attention to solution purity
The accumulation of harmful impurities in the solution has a greater impact on the passivation film. Deionized water is required when preparing the solution. It is better to use deionized water before the passivation part enters the passivation tank to reduce harmful impurities. Extend the service life of passivation liquid.
Follow the passivation solution preparation procedure
The preparation method of this process is simple, add the calculated amount of agent A into a tank containing deionized water and stir evenly, then dilute the calculated amount of agent B with a small amount of deionized water, and slowly add it to agent A under vigorous stirring , There will be brown precipitates when it is first added, and the brown will disappear quickly over time. After adding water to the specified volume, measure the pH value of about one liter, and try it after the temperature reaches the appropriate process conditions.
There are instructions for reference in the commercially available ready-made materials for other process formulas, so I won’t repeat them here.
Passivation process arrangement
(1) Galvanized. The thickness of the galvanized layer should be higher than 8mm.
(5) Passivation: time in solution 120～180s, residence time in air 20～30s
(6) Cleaning: time <20s.
Chromic anhydride lg/L
(8) Blow dry.
Ten points to pay attention to in passivation process
(1) The thickness of the coating should be over 8btm.
(2) The plated parts of the passivation parts should be immersed and brightened, and there is no dirt on the surface.
(3) During passivation, the plated parts should move slowly in the solution, and should not swing violently, otherwise it may cause the film to bloom due to excessive impact. Static passivation is also not suitable, otherwise it may loosen the film and affect the bonding strength between the film and the zinc layer.
(4) Master the passivation time. If the time is too short, the film will appear rainbow colors, and the passivation film will be dissolved if the time is too long.
Also consider the solution temperature. When the solution temperature is slightly higher, the passivation time should be appropriately reduced, and when the solution temperature is slightly lower, the passivation time should be appropriately increased.
(5) The temperature of the solution should not exceed 30℃, and the passivation film will become black when the temperature is too high, opaque and foggy.
(6) Maintain the normal concentration of passivation solution. When the concentration of the passivation solution decreases, the obtained film will appear gray and not bright, or even have interference colors. At this time, if 20% of the process formula concentration can be added, the effect will often be immediate.
(7) The cleaning time after passivation should not be too long to avoid dissolution and shedding of the passivation layer, but it must be cleaned.
(8) After passivation, it must be sealed with 1g/L chromic anhydride solution, otherwise it will fade easily.
(9) Strictly observe the drying time and temperature. Too high temperature or too long time may make the passivation film yellow and bloom.
(10) In order to maintain the natural color of the passivation film for a long time and prevent the surface from being damaged, soak, spray a thin layer of varnish or apply protective grease.