Since the reform and opening up, hardware production has developed very rapidly. In addition to the use of pure gold plating for specific high-grade products, it is more common to plate 24K imitation gold plating. In the decorative plating process, imitation gold plating is the most widely used electroplating process. Lighting, locks, ceiling fans, luggage, lighters, eyeglass frames, tie clips and other products have a variety of appearances, but most of them are still gold-plated, there are many ways to get a golden look, with gold plating, Copper-plated zinc, copper-tin or copper-tin imitation gold, gold electrophoretic paint, gold-on-gel process. Among them, imitation gold plating is a commonly used process.
Imitation gold plating technology
First, imitation gold plating solution formula
1. The most commonly used and most stable copper-zinc, copper-tin or copper-zinc-tin gold plating solution is cyanide plating solution. Domestic factories generally use their own alloy plating solutions.
Cuprous copper 28-30 grams
Sodium cyanide 60-65 g
Zinc cyanide 7-8 g
Potassium sodium tartrate 6-8 g
Potassium hydroxide 10-12 g
Sodium stannate 1.5-2.5 g
Cobalt sulfate
2. Foreign-funded factories and some domestic factories also use the bronze salt provided by foreign electroplating raw materials to make imitation gold. Its process recipe and operating conditions are:
Bronze salt 80～100g/L
Ammonia water 1~2ml/L
Temperature 35 to 50 degrees
Plating composition:
Cu 15～18g/L
Zn 6～8g/L
Free NaCN 8～10g/L
Second, imitation gold plating is not only the composition of the complex and copper, zinc, tin ternary content and temperature, but more important is the choice of current and time, the current is divided into three different amperage, the third gear current is controlled by time, Pulling high, medium and low cathode currents, first high and then low, the hanging device keeps shaking gently. Under the action of current, the coating is from white to yellow → near yellow 24K
Imitation gold plating
Third, the role of various ingredients and control skills
Sodium cyanide
The increase of the content is beneficial to the formation of Zn(CN)j, and reduces the amount of zinc precipitated in the plating solution; on the other hand, it enhances the degree of complexation of copper cyanide ions with cyanide and reduces the precipitation of copper. From the experience of our team's long-term control: the right amount of sodium cyanide can turn the reddish color to yellow, and it may turn too white and white. This process of color change depending on the amount of sodium cyanide must be remembered!
In the new formulation of the adjustable solution, the complexation transition between the various ions is not completed immediately, in order to achieve a steady state chemical equilibrium of the various complex ions, when sodium cyanide or sodium hydroxide is added Evenly mixing and mixing for a period of time can make the coloring effect obvious
2. Sodium hydroxide
1) It is the second complexing agent of zinc and the only complexing agent of tin. The ratio of zinc and tin in the alloy plating layer directly affects the color. When the content is increased, the ratio of zinc precipitation is also increased. If the coating is reddish, the addition of sodium hydroxide may turn the color into yellow, but with the premise that there is sufficient zinc in the solution and a not too high amount of sodium cyanide. On the contrary, the sodium hydroxide content is too low, which is not conducive to the precipitation of zinc. In order to obtain the ideal imitation gold color, it is necessary to increase the zinc content of the super ratio to make up for the deficiency of zinc precipitation.
2) In addition, I want to inform everyone that: sodium hydroxide is too low, but it is also not conducive to the stability of sodium stannate, and even gradually hydrolyzed into meta-thin acid impurities deposited in the bottom of the tank. This reaction is irreversible in the tank, but once it is not complexed, even if the sodium hydroxide is increased later, the metastannic acid will no longer dissolve and return to sodium stannate.
3) There is another case: when the ratio of copper to zinc in the solution is appropriate, sometimes the sodium hydroxide is too high, which makes the imitation gold appear reddish khaki (like yellow earth color) or zinc red. If this zinc red is considered to be a copper red with too much copper in the coating, it will be a mistake to continue to replenish the amount of sodium hydroxide or zinc. At this time, an acidic substance should be used to reduce the amount of sodium hydroxide to convert zinc red into gold.
3. Sodium potassium tartrate
It is a third complexing agent with weaker complexation of both copper and zinc. The addition of sodium potassium tartrate can improve the brightness of the gold-plated coating, especially in the electroplating process for a long time, which can maintain the brightness of the coating, function as a semi-brightener and activate the anode.
4. The amount of cobalt sulfate is very small, about 0.05~0.10g/L, which promotes the imitation gold, making the golden light soft.
Fourth, the process conditions
In addition to the effects of these main salts, the process conditions are also very important for imitation gold plating, such as:
(1) Temperature As an auxiliary means of toning, the increase in temperature is beneficial to the electrical resolution of copper, so that the color of the imitation gold increases the red hue. Generally, it should be 40 ~ 50 ° C, if necessary, up to 60 ° C, according to the needs of the color and the composition of the solution is properly adjusted. temperature
The increase can increase the conductivity of the solution, making the color uniform and bright. However, too high a temperature will accelerate the decomposition and consumption of sodium cyanide, which is not conducive to the stability of the solution.
(2) Current density. In order to obtain the imitation gold of the color-forming foot, the ratio between the metals and the ratio between the complexing agent and the complexing agent are required to satisfy the ratio of the precipitation of the metal to the optimum imitation gold in a certain potential current, and the repeating accuracy is achieved for the current control. To ensure color reproducibility, a dedicated three-speed current timing controller is used. The current controller includes three adjustable time relays, which automatically turn on and off the three voltage regulators according to the predetermined time. Each time, the predetermined voltage of the third gear is gradually input and input into a transformer, and the output current is rectified. The currents of the three different sizes are sequentially input into the imitation gold tank according to the predetermined voltage. The power supply device of this imitation gold tank is different from the power supply device of other slots, and the three-speed current is divided into inrush current, transient current and imitation gold current. It is important to control and select the timing and magnitude of each current, with the last gear being the most important.
(3) Imitation gold time. The sum of the time of each gear is 20~30s, and the length of the inrush current is not caused by local scorching or the decrease of the brightness. The time of the imitation gold current is to obtain the uniform imitation gold with sufficient chromaticity. The time of the 3rd current should be allocated reasonably. The inrush current time should not be too long, about 20%~30% (25% is appropriate); the transition current time is slightly longer, about 40%~45% ( 43% is appropriate); imitation gold current time should be just right, about 30% to 35% (32% is appropriate).
In this time, the appropriate thickness of the imitation gold layer should be obtained. If the time is too short, the imitation gold layer may be too thin to cause partial fading and discoloration; if the time is too long, the imitation gold layer is too thick to damage the vivid color of the imitation gold. If the best imitation gold color cannot be displayed or fully displayed within the appropriate time, fine-tune or necessary adjustments should be made to the gold-plated bath when the corresponding current is not effective. The magnitude of the inrush current is uniformly plated on the outer surface of the entire part without scorching, and the magnitude of the imitation gold current is obtained to obtain the ideal imitation gold.
Imitation gold plating technology
First, imitation gold plating solution formula
1. The most commonly used and most stable copper-zinc, copper-tin or copper-zinc-tin gold plating solution is cyanide plating solution. Domestic factories generally use their own alloy plating solutions.
Cuprous copper 28-30 grams
Sodium cyanide 60-65 g
Zinc cyanide 7-8 g
Potassium sodium tartrate 6-8 g
Potassium hydroxide 10-12 g
Sodium stannate 1.5-2.5 g
Cobalt sulfate
2. Foreign-funded factories and some domestic factories also use the bronze salt provided by foreign electroplating raw materials to make imitation gold. Its process recipe and operating conditions are:
Bronze salt 80～100g/L
Ammonia water 1~2ml/L
Temperature 35 to 50 degrees
Plating composition:
Cu 15～18g/L
Zn 6～8g/L
Free NaCN 8～10g/L
Second, imitation gold plating is not only the composition of the complex and copper, zinc, tin ternary content and temperature, but more important is the choice of current and time, the current is divided into three different amperage, the third gear current is controlled by time, Pulling high, medium and low cathode currents, first high and then low, the hanging device keeps shaking gently. Under the action of current, the coating is from white to yellow → near yellow 24K
Imitation gold plating
Third, the role of various ingredients and control skills
Sodium cyanide
The increase of the content is beneficial to the formation of Zn(CN)j, and reduces the amount of zinc precipitated in the plating solution; on the other hand, it enhances the degree of complexation of copper cyanide ions with cyanide and reduces the precipitation of copper. From the experience of our team's long-term control: the right amount of sodium cyanide can turn the reddish color to yellow, and it may turn too white and white. This process of color change depending on the amount of sodium cyanide must be remembered!
In the new formulation of the adjustable solution, the complexation transition between the various ions is not completed immediately, in order to achieve a steady state chemical equilibrium of the various complex ions, when sodium cyanide or sodium hydroxide is added Evenly mixing and mixing for a period of time can make the coloring effect obvious
2. Sodium hydroxide
1) It is the second complexing agent of zinc and the only complexing agent of tin. The ratio of zinc and tin in the alloy plating layer directly affects the color. When the content is increased, the ratio of zinc precipitation is also increased. If the coating is reddish, the addition of sodium hydroxide may turn the color into yellow, but with the premise that there is sufficient zinc in the solution and a not too high amount of sodium cyanide. On the contrary, the sodium hydroxide content is too low, which is not conducive to the precipitation of zinc. In order to obtain the ideal imitation gold color, it is necessary to increase the zinc content of the super ratio to make up for the deficiency of zinc precipitation.
2) In addition, I want to inform everyone that: sodium hydroxide is too low, but it is also not conducive to the stability of sodium stannate, and even gradually hydrolyzed into meta-thin acid impurities deposited in the bottom of the tank. This reaction is irreversible in the tank, but once it is not complexed, even if the sodium hydroxide is increased later, the metastannic acid will no longer dissolve and return to sodium stannate.
3) There is another case: when the ratio of copper to zinc in the solution is appropriate, sometimes the sodium hydroxide is too high, which makes the imitation gold appear reddish khaki (like yellow earth color) or zinc red. If this zinc red is considered to be a copper red with too much copper in the coating, it will be a mistake to continue to replenish the amount of sodium hydroxide or zinc. At this time, an acidic substance should be used to reduce the amount of sodium hydroxide to convert zinc red into gold.
3. Sodium potassium tartrate
It is a third complexing agent with weaker complexation of both copper and zinc. The addition of sodium potassium tartrate can improve the brightness of the gold-plated coating, especially in the electroplating process for a long time, which can maintain the brightness of the coating, function as a semi-brightener and activate the anode.
4. The amount of cobalt sulfate is very small, about 0.05~0.10g/L, which promotes the imitation gold, making the golden light soft.
Fourth, the process conditions
In addition to the effects of these main salts, the process conditions are also very important for imitation gold plating, such as:
(1) Temperature As an auxiliary means of toning, the increase in temperature is beneficial to the electrical resolution of copper, so that the color of the imitation gold increases the red hue. Generally, it should be 40 ~ 50 ° C, if necessary, up to 60 ° C, according to the needs of the color and the composition of the solution is properly adjusted. temperature
The increase can increase the conductivity of the solution, making the color uniform and bright. However, too high a temperature will accelerate the decomposition and consumption of sodium cyanide, which is not conducive to the stability of the solution.
(2) Current density. In order to obtain the imitation gold of the color-forming foot, the ratio between the metals and the ratio between the complexing agent and the complexing agent are required to satisfy the ratio of the precipitation of the metal to the optimum imitation gold in a certain potential current, and the repeating accuracy is achieved for the current control. To ensure color reproducibility, a dedicated three-speed current timing controller is used. The current controller includes three adjustable time relays, which automatically turn on and off the three voltage regulators according to the predetermined time. Each time, the predetermined voltage of the third gear is gradually input and input into a transformer, and the output current is rectified. The currents of the three different sizes are sequentially input into the imitation gold tank according to the predetermined voltage. The power supply device of this imitation gold tank is different from the power supply device of other slots, and the three-speed current is divided into inrush current, transient current and imitation gold current. It is important to control and select the timing and magnitude of each current, with the last gear being the most important.
(3) Imitation gold time. The sum of the time of each gear is 20~30s, and the length of the inrush current is not caused by local scorching or the decrease of the brightness. The time of the imitation gold current is to obtain the uniform imitation gold with sufficient chromaticity. The time of the 3rd current should be allocated reasonably. The inrush current time should not be too long, about 20%~30% (25% is appropriate); the transition current time is slightly longer, about 40%~45% ( 43% is appropriate); imitation gold current time should be just right, about 30% to 35% (32% is appropriate).
In this time, the appropriate thickness of the imitation gold layer should be obtained. If the time is too short, the imitation gold layer may be too thin to cause partial fading and discoloration; if the time is too long, the imitation gold layer is too thick to damage the vivid color of the imitation gold. If the best imitation gold color cannot be displayed or fully displayed within the appropriate time, fine-tune or necessary adjustments should be made to the gold-plated bath when the corresponding current is not effective. The magnitude of the inrush current is uniformly plated on the outer surface of the entire part without scorching, and the magnitude of the imitation gold current is obtained to obtain the ideal imitation gold.
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