How to make supplemental plating on poor nickel plating
For various reasons, the quality of the nickel coating will be more or less unqualified. If appropriate remedial measures can be taken, unnecessary rework of plating can be reduced. In addition to polishing and repairing on non-glossy, burr-plated coatings, supplementary plating is also commonly used on parts that are not easily polished or the substrate is exposed after polishing.
Nickel coatings are easily passivated, especially in air and alkaline solutions. Therefore, the key to performing supplemental plating on nickel layers is to activate the surface of the nickel layer. Only when the surface of the nickel layer is in a good activation state, can it be successful to perform supplemental plating. .
Different methods should be used for supplementary plating according to the nature, shape, and requirements of the part. For example, if acid copper is suitable for plating, the substrate can be directly plated with copper and nickel after the surface is activated without iron. In the case of acid copper plating or exposed iron on the substrate, after the surface is activated, nickel plating should be performed directly for supplementary plating.
The specific method is as follows: the chromium-plated parts are subjected to chrome removal treatment, and the foamed and peeled parts of the plating layer are removed. According to the specific conditions of the parts, the selection methods are as follows.
(1) Suitable for copper and nickel plating: degreasing (preferably by chemical method)-cleaning-water-polishing (large parts)-concentrated hydrochloric acid activation-cleaning-dilute sulfuric acid etching-acid copper plating-cleaning-dilute Sulfuric acid etching-nickel plating-cleaning-chrome plating-cleaning (recycling)-drying-sending for inspection.
(2) Suitable for supplemental nickel plating: degreasing (preferably by chemical method)-cleaning-water polishing, car brushing (large parts)-concentrated hydrochloric acid activation-cleaning-nickel plating-cleaning-chrome plating-cleaning (recycling)-drying- Submit for inspection.
(3) The electropolishing activation method can also achieve better results. Electropolishing activation formula and process parameters:
For industrial sulfuric acid (density 1.849 / mL), please refer to the “formulation” of chromic anhydride 509 / L and glycerol 509 / L
Solution density l. 58 ～ 1.629 / mL temperature
Anode current density l ～ 10A / dm2 time 3 ～ 5s
Preparation of the solution: firstly inject 2/3 volume of concentrated sulfuric acid (density 1.849 / mL) into a lead tank (or ceramic tank, plastic tank), and add 509 glycerol per liter of concentrated sulfuric acid, in another lead tank (Or ceramic tank, plastic tank) use a little water to dissolve the chromic acid (Cr0.). The amount of chromic acid is 509 sulfuric acid per liter, and then add the concentrated sulfuric acid solution with glycerin to the chromic acid solution. Be very careful, add several times. As the solution is added, the electrolyte starts to generate heat and violently emit gas. The addition of each part of the sulfuric acid mixed solution with glycerin must be vigorously stirred, and it should be performed after the last stop of gas evolution. After the solution is prepared, the density should be 1.58 to 1.629 / mL. The solution is cooled to 30 ° C, and a lead plate is used as a cathode and a nickel plate is used as an anode.
2. Inferior copper, nickel, chromium supplemental plating process: upper hanger-cleaning-electropolishing activation-cleaning-dipping in dilute hydrochloric acid-cleaning-pre-plating-dipping sulfuric acid-cleaning-nickel plating-cleaning-hot water-hanger-drying One for inspection, one for cleaning, one for chrome, one for cleaning, one for hot water, one for drying, one for inspection.