Failure of electroplated brass production line and its treatment method: Plating is red or dark red
Cause analysis and processing methods:
(1) The bath temperature is too high
The temperature has a great influence on the composition and appearance color of the copper-zinc alloy coating. When the temperature is high, the content of copper in the alloy coating increases, the color becomes reddish, the cathode allows the current density to increase, and the current efficiency increases. In general, for every 10° C. increase in bath temperature, the content of copper in the coating will increase by 5%. 6%, but it will also accelerate the decomposition of sodium cyanide, with the decrease of NaCN content, the coating is susceptible to graying or burr. The temperature is too low, the zinc content in the coating is high, and the coating is grayish white
Treatment method: Control bath temperature to process specification
(2) The copper content in the bath is too high
As the copper content in the bath increases, the copper content in the coating increases accordingly. When the copper content is high, the bath can work at a higher current density. The content is too high, the coating color reddish. The key of copper-zinc alloy electroplating solution is to control the ratio of copper and zinc in the plating solution. In general, the ratio of copper to zinc in the plating solution is 2 to 2.5. When the ratio is high, the content of copper is high, and the color of the coating is reddish; when the ratio is low, the content of zinc is high, and the coating becomes yellow with a white sense (ie, white or gray).
Treatment method: supplement zinc salt, adjust bath composition
(3) Low cathode current density
In the electroplating solution, the degree of polarization of copper is smaller than that of zinc, so the copper content in the brass layer increases as the cathode current density decreases, and the zinc content decreases as the cathode current density decreases. Therefore, the cathode current density is too low, the copper content in the coating increases, the color of the coating is reddish, the cathode current density is too high, the content of copper in the coating is reduced, and the coating is yellowish (or off-white) with a white feeling.
Treatment method: According to process requirements, reasonable setting current value
(4) Insufficient free sodium cyanide
The free sodium cyanide can stabilize the bath, ensure that the copper and zinc are precipitated in proportion, and the anode is dissolved normally. When the content of free sodium cyanide in the bath is too low, the content of copper in the coating increases, the color changes to dark red, the color is uneven, and when the coating is rough, the anode is blunted, the anode is passivated, and the plating solution is turbid; when it is too high, the plating layer Reduction of copper content in loose dark gray color, reduced cathodic current efficiency, and even severe hydrogen evolution
Treatment method: Analyze the addition of sodium cyanide to the process specification
(5) The pH is too low
The pH of the bath is generally controlled between 10-11. If the pH is too high, the amount of zinc in the coating increases, and the coating appears bluish-white; if the pH is too low, the amount of copper in the coating increases, and the color of the coating becomes reddish. In copper-zinc alloy baths, the bath is most stable at pH = 10.3 and cannot be adjusted with ammonia when it exceeds 11.5. Reduce the pH value with dilute sodium bicarbonate or tartaric acid solution to prevent hydrogen from escaping; adjust the pH to adjust with dilute sodium hydroxide solution
Treatment method: Use dilute sodium hydroxide solution to adjust pH to process specification
(6) The ammonia content in the bath is too low
Ammonia is an auxiliary complexing agent and stabilizer in baths. It forms complex salts with zinc and copper. It is mainly involved in the complexation of zinc and increases the zinc content in the bath. It can also expand the cathode current density range and stabilize the pH. Therefore, the color of the coating is not easily reddish and the dispersibility and brightness are improved. Ammonia also inhibits the decomposition of sodium cyanide and stabilizes the bath. However, excess ammonia will cause the coating to contain more zinc, which is yellowish white. The ammonia is too low, the amount of copper contained in the coating is too large, and the color of the coating is reddish. In order to stabilize the electroplating of brass liquid, it is recommended to add it to the plating solution every day. 0.4mL/L? 25% ammonia solution.
The role of ammonia is summarized as follows:
a. When the current density changes from the minimum to the maximum range, the appearance of the coating is obviously improved due to the addition of ammonia.
b. Due to the addition of ammonia water, the total current efficiency can be slightly increased;
C. In the case of different copper-zinc ratios and different current densities in the plating solution, the chemical composition of the coating is relatively stable, which is the largest contribution of ammonia
This is due to the fact that the [CuNH3(CN)3]2 complex ion formed after the addition of ammonia is more stable than the [Cu(CN)3]2 complex ion, resulting in a difference in the precipitation potential of copper and zinc compared to the cyanide containing no ammonia. Closer in plating bath
However, when the content of ammonia in the plating solution is 0.5 to lg/L, the effect is not significant. Only when the content of ammonia is 2 g/L, the cathode potential of copper and zinc moves to a negative value. In the plating solution, ammonia (NaCN+2H20-HCOONa+NH3) is also produced due to the hydrolysis of cyanide, but it cannot meet the requirements of the process and is also a waste.
Treatment method: Add ammonia to process specification