In recent years, galvanized trivalent black passivation process has been widely used because of its advantages of low cost and good performance.In the process of using zinc plating trivalent black passivation, in order to make the passivation solution have better stability and lower failure rate, we need to understand the influence of various process conditions on the coating.So how do they affect the coating?
Bigolly Technology made an analysis based on the field experience and the characteristics of the product zinc plating trivalent black passivator BZ-216. There are four main points:
1. The concentration of passivation solution. When the concentration of trivalent black passivator BZ-216 is 80~150ml/L, a uniform black passivation film can be obtained.When the concentration is lower than 80 ml/L, the film forming speed is slow, the color of the passivation film is not black enough, and the corrosion effect is not good;When the concentration is higher than 150 ml/L, the film formation speed is faster, and the color of the coating is black and bright, but there will be a phenomenon of color.
2. The pH value of the passivation solution. When the pH value of trivalent black passivator BZ-216 is 1.8~2.2, the coating can get a black film with better appearance quality.When the pH value is lower than 1.8, the appearance of the coating turns blue, the zinc coating dissolves quickly, and the corrosion resistance is poor;When the pH value is higher than 2.2, the coating will be black and brighter, but there will be a color phenomenon, the coating will dissolve slowly, and the corrosion resistance will be better. Considering the appearance and film thickness, pH should be controlled at 1.8~2.2.
3. The temperature of the passivation solution. Generally, the film thickness of the passivation film will increase with the increase of temperature, but will decrease when it reaches a extreme point.Trivalent black passivation BZ-216 can obtain a black passivation film with better appearance quality at 25~35℃;When the temperature is lower than 25 ℃, the film formation is slow, and the corrosion resistance of the coating is poor;When the temperature is higher than 35°C, the zinc coating dissolves too fast, and a thicker passivation film cannot be obtained.
4. The passivation time of the workpiece. The thickness of the passivation film of the coating will increase with the passivation time, and the passivation time of BZ-216 is 40~80 seconds to obtain a uniform black passivation film.When the passivation time is less than 40 seconds, the color of the coating is not black enough or has streaks;When the passivation time is more than 80 seconds, the coating will be black and bright, and there will be a phenomenon of color, which will affect the appearance of the product.
Therefore, we need to strictly control these four process conditions in the process of using zinc plating trivalent black passivator to ensure that the workpiece coating has good appearance, color and performance.