precision plating|Points to be paid attention to in electroplating
01 Jan

precision plating|Points to be paid attention to in electroplating

Generally speaking, electroplating is carried out on individual parts, and as the final process of manufacturing parts, the electroplating process will not be carried out after the individual parts are connected into assemblies. Most manuals often mention the electroplating of assemblies. In some standards, electroplating of assemblies is even prohibited. When it is necessary to electroplating assemblies, it is necessary to negotiate with the process department to formulate mutually agreed technical specifications.
 1. There are still many assemblies that need to be electroplated in factory production. The reason is very simple. Changing the electroplating of individual parts to the one-time electroplating of assemblies will greatly shorten the production cycle and save expenses. In addition, in certain processes of product processing The assembly does need to be electroplated during the link.
When the assembly is electroplated, in order to adapt the various parts to chemical and electrochemical reactions, it is necessary to use a suitable solution, and the operation method is also very particular. In addition, the pretreatment of electroplating is particularly critical. If the materials of each part of the assembly are the same, the electroplating process can be processed according to this material, but the combination method and the processing state of the parts still need to be considered. If the materials of each part of the assembly are different, the solution is difficult to adapt to each part due to the different electrochemical characteristics of the material during electroplating, causing the parts to be over-corroded, or the metal ions are replaced and precipitated on the parts, so the suitability of the solution needs to be fully considered. The process method should take into account all parts.
 2. The following is an example of a combination of steel parts and parts of other materials.
1. There are copper parts in the assembly
Degreasing and etching can be carried out according to the process of copper parts. In order to remove the copper ions that are replaced and precipitated on the steel parts, passivation is required, and then weakly corroded and electroplated in a human bath. In order to improve the surface brightness, chemical polishing of the assembly can be carried out, but a special solution must be used to adapt to the different activities of steel and copper. The following polishing liquid and passivation liquid can be used.
(1) The polishing liquid is:
    Phosphoric acid 70.5%-93.6%
    Nitric acid 29.5%-6.4%
    Room temperature, l 1-2 minutes
    
(2) Passivation after polishing, the passivation solution is:
    Chromic acid 25-30 g
    Sulfuric acid 5-8 ml
    Room temperature, 2 to 4 minutes.
    Then carry out weak corrosion (10% hydrochloric acid) water washing and electroplating in the human tank.
   
2. There are nickel-plated stainless steel parts in the assembly
    Stainless steel has a strong tendency to passivation. Without special treatment, it is difficult to obtain a firm coating. When there are stainless steel parts in the assembly, it needs to be electro-galvanized, that is, after immersing in concentrated hydrochloric acid for 1 to 3 minutes, immediately galvanizing for 1-2 minutes and de-zincing. This operation is repeated twice, and then electroplated in a bath. When the assembly needs to be plated with nickel, it can be pre-plated with nickel for 2 to 4 minutes after immersing in concentrated HCI. Normal nickel plating is performed immediately without cleaning. When there are nickel-plated parts in the assembly, conventional chemical degreasing can be used, and the process of stainless steel parts can be referenced for activation and pre-nickel plating.
3. There are lead-tin parts in the assembly
The lead-tin parts in the assembly include tin-plated parts, lead-plated parts, lead parts, soldering parts (using lead-tin alloy solder), etc., all of which are amphoteric metals, and the electrode potential is relatively negative. Dissolving. Assemblies containing such parts should not be pretreated with strong alkalis and strong acids, and should be degreased with organic solvents (gasoline, trichloroethylene, etc.) first. The chemical degreasing and electrolytic degreasing oil used should be weak alkaline solution, the temperature should not exceed 65℃, and the time should be as short as possible. If necessary, use a normal temperature metal cleaner or a multifunctional alkaline degreasing agent to help brush the light. The LJ-7 and LJ-9 degreasers produced by Xiamen Lejiang Science and Technology Co., Ltd. can be applied to the assembly of brass, zinc-based alloy and lead alloy welding at the same time, which increases the qualified rate of plating parts from 70% to 95%.
Lead parts use fluorine-containing boric acid (42%) 120-250nIlL/ solution, room temperature, 10 to 155 tin parts can use ordinary dilute acid solution, room temperature, 5-10S. Lead-tin soldering parts should be cleaned first, followed by degreasing and acid leaching. The degreasing and acid leaching time should not be too long, otherwise the solder flow phenomenon will occur. After the above assembly parts are pretreated, they can be directly plated with copper and then plated Other metals. Polishing should be carried out at low speed and low pressure after plating to prevent deformation or peeling of the plating layer.
4. There are castings in the assembly
Commonly used such composite parts are iron castings and zinc alloy die castings. Powder metallurgy parts can also be classified into this category due to their similar organization. Its characteristic is that the material has many pores, and the solution will penetrate into the pores during pretreatment and electroplating, which is not easy to clean, which affects the quality of electroplating. Such assemblies should be mechanically leveled and baked before assembly. After assembling, the sealing process is carried out, that is, immersing 20mjll in molten zinc stearate (135-180℃), then sandblasting and mechanical polishing.
5. There are plastic parts in the assembly
This type of assembly is a combination of metal and plastic by casting. Plastic parts should not be broken or scratched, and there should be no burrs, inclusions or un-glued gaps at the junction of metal and plastic. There should be no plastic residues on the surface of the metal parts. Stress should be eliminated before electroplating. High temperature and strong oxidizing solutions should be avoided during pretreatment. Coating conductive coatings with plastic parts, and then electroplating according to the corresponding second art. Use sandpaper sanding or sawdust rolling to remove the excess zinc stearate layer on the surface, and then perform degreasing and erosion according to conventional methods, but strong corrosion should be avoided and inter-process cleaning should be strengthened. Then pre-plating in the cyanide copper plating solution for 5-10 minutes, then other metal coatings can be electroplated.