The chrome plating ability is poor, and the deep recesses of the parts cannot be plated with chrome There are many reasons for this type of failure, such as the roughness of the blank or the rough bottom plating; the temperature of the bright nickel is too high or the pH value is too high, There are sulfur-containing substances such as fuse powder in the nickel plating solution; the nickel layer has been left in the air for too long; the anode of the chrome plating has poor conductivity or poor contact with the hanger; the chrome plating solution The content of chromic acid is too low or the content of sulfuric acid is too high; too much trivalent chromium or too much foreign metal impurities and the presence of nitrate in the chromium plating bath. If the fault originated before chrome plating, carefully check the roughness of the blank and whether the bottom plating is rough. If you use pyrophosphate copper plating or cyanide copper plating to make the parts as the base before nickel plating, it is often because the undercoat is relatively rough. On the one hand, hydrogen is on the rough surface. The overpotential is small, and it is easy to evolve hydrogen and repel the deposition of chromium. On the other hand, the rough surface has a large specific surface area, which results in the current density at low current density during chromium plating is too small to deposit chromium. This can be corrected by reducing the roughness of the blank and skipping the pyrophosphate copper plating or cyanide copper plating and then testing to find the origin of the failure. If the fault originated in the chrome plating process, first check the contact of the hanger and the surface condition of the anode. If the anode surface is yellow, it means that poorly conductive lead chromate has formed on the anode. At this time, the anode should be removed. After removing the yellow lead chromate with a wire brush, re-hang the plating tank when the power is on to prevent the re-generation of lead chromate. If the anode surface is brown, the anode conducts well. If the anode conduction is very good, then adjust the ratio of Cr03 to H2s04 according to analysis or angular cathode test. If the fault still exists after adjusting the ratio, it may be NO; or the influence of excessive trivalent chromium and foreign metal impurities. Due to the influence of NO, not only the deep plating ability is poor, the chromium layer will also lose its luster and present a grayish white or dark gray appearance, and too much trivalent chromium and foreign metal impurities generally do not affect the appearance of the chromium layer, so from Phenomenon can also be distinguished. In addition, large anode area and small cathode area can be used to observe the phenomenon after a period of electrolysis. Through experiment and observation, correct the fault after finding out the cause of the fault. The brightness of the chrome layer is poor and it is prone to scorching. Most of these failures are caused by internal factors in the chrome plating process. For example, the content of chromic acid or sulfuric acid in the chromium plating bath is too low; the content of trivalent chromium is too low or too high; there are too many foreign metal impurities; the temperature is too low or the cathode current density is too large, the anode conductivity is poor, or there is a small amount in the plating bath NO exists and so on. According to the reasons mentioned above, it is easy to check the temperature, cathode current density, and anode conductivity. If there is no problem in the above three aspects, then check the composition of the bath and the content of trivalent chromium and foreign metal impurities. If the content of sulfuric acid and trivalent chromium is low, the chromium layer will have a bluish-blue appearance, and the plating layer is also relatively soft, and sometimes marks can be drawn by scratching with a fingernail. Excessive trivalent chromium and foreign metal impurities often increase the resistance of the plating solution. During electroplating, the tank voltage is high, and the current is sometimes unstable, and the color of the chromium plating solution becomes darker. These phenomena can be used as a reference when analyzing faults. If through observation and chemical analysis, it is determined that the trivalent chromium content in the chromium plating bath is too low, you can add 0.5mL/L of alcohol to the chromium plating bath, and see if the malfunction disappears after 20 minutes to 30 minutes of electrolysis. If the failure phenomenon disappears, the cause of the decrease in trivalent chromium content may be that the anode area is too large, and the anode area should be appropriately reduced. If it is not the above reason, it may be the influence of a small amount of NO3. At this time, electrolytic treatment can be used to correct it. |
