Production techniques for electroplating nickel-free white and white copper-tin
Electroplated nickel-free white is one of the most widely used alloy coatings for all types of hardware products and plating plants. It has the advantages of good brightness of the plating, lower cost, environmentally friendly nickel-free, good decorative effect, corrosion resistance and suitable hardness; it can prevent the diffusion of the underlying metal to the surface layer and prevent discolouration of the metal plating layer, etc. High tin nickel-free white is also known as silver mirror alloy or white copper-tin, which can be used as a substitute for silver and chromium layer. The plating is 31% copper, 65% tin and the rest zinc. The appearance of this nickel-free white is similar to that of stainless steel, which is whiter than the nickel plating and can be maintained for a longer period of time without discolouration.
The following formulations are currently available on the market.
Copper metal (g/L) 10-15
Tin metal (g/L) 17-25
Zinc metal (g/L) 1 to 2
Free potassium cyanide(g/L)30～50
A little brightening agent
pH 12.4～12.9
Specific gravity 15～21
Free cyanide to copper metal 3.0～4.2:1
Copper metal to tin metal 0.5 to 0.7:1
Many colleagues in this plating will find, just open the tank when the plating product colour stable white, production sometime after the appearance, yellowing, black, poor alignment, dark, fog and other undesirable phenomena, according to our Le will team's field experience summed up each plating factory failure, to be controlled from the systemic: 1.
1. If it is only used for decorative surface colour, the tank is not big and the colour effect is high, it is better to use potassium cyanide than sodium cyanide, the cost increases a little but it can bring the stability of the plating solution and colour.
2. Most of my colleagues in the maintenance of this tank are not standardized, see the plating out of the product has a problem, it rushed to the tank to pour sodium stannate, copper, etc. to adjust the tank "surgery"! This will result in insufficient hydrolysis of the drug complex, the composition is easy to disorder. The colour is naturally unstable. Here we will suggest: using potassium cyanide (imported grade) 280g/L, copper cyanide 143g/L, zinc oxide 8g this ratio into copper water spare, then use 300g sodium stannate with 1L of LJ-29 complexing agent spare. Both drugs must be dissolved clear and treated with activated charcoal powder and topped up 1:1 to ensure the composition of the main salt is not out of balance. The standard operation of replenishment is the key to good control of this type of plating.
3. Hang the plating at a temperature of 55-60 degrees. For barrel plating, the temperature is not very high and the anode can be added with a small amount of pure tin plate anode, which reduces the addition of commercial sodium stannate and reduces the cost.
4. Then the next is to control the pH of the plating solution, normal replenishment of copper water, replenishment of potassium hydroxide by 10 grams. If the pH is high, add 30% phosphoric acid solution; if the pH of the plating solution is low, add 25% potassium hydroxide solution.
