The Basic Process Of Plastic Plating-electroplating And The Function Of Each Process

The basic process of plastic plating-electroplating and the function of each process.
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1 basic working procedure of electroplating in electroplating processing plant.
(material polishing "electroplating polishing)" hanging "degreasing and oil removal" water washing "(electrolytic polishing or chemical polishing)" pickling activation "(pre-plating)" electroplating "water washing" (post-treatment) "water washing" dry "hanging" inspection packaging.
2 the function of each process.
2.1 Pretreatment: all processes before plating are called pre-treatment, the purpose of which is to trim the workpiece surface, remove grease, rust skin, oxide film, etc., and provide the electroplating surface for the subsequent deposition of the coating. Pretreatment mainly affects the appearance and adhesion. According to statistics, 60% of the defective electroplating products are caused by poor pretreatment, so pretreatment plays an important role in the electroplating process. In the countries with developed electroplating technology, great attention is paid to the pretreatment process, which accounts for half or more of the whole electroplating process, so that the coating with good surface condition can be obtained and the defect rate can be greatly reduced. Sandblasting: remove rust, welding slag, carbon deposits, old paint layer, and other dry grease on the part surface; remove sand and oxide on the part surface after casting, forging or heat treatment; remove burrs and directional wear marks on the part surface; reduce the roughness indicated by the part to improve the adhesion of paint and other coatings; make the part in a diffuse extinction state.
Polishing: remove burrs, rust, scratches, welds, welds, sand holes, oxide and other macro defects, so as to improve the flatness and electroplating quality of the parts.
Polishing: the purpose of polishing is to further reduce the surface roughness of the parts and obtain a bright appearance. There are mechanical polishing, chemical polishing, electrochemical polishing and other methods.
Degreasing and degreasing: remove grease from the surface of the workpiece. There are organic solvent deoiling, chemical deoiling, electrochemical deoiling, wiping deoiling, drum deoiling and other means.
Pickling: remove rust and oxide film on the surface of the workpiece. There are chemical pickling and electrochemical pickling.
2.2 Electroplating.
Getting the required coating on the surface of the workpiece is the core process of electroplating, which directly affects the properties of the coating. The main factors that have important influence on the coating in this process are as follows: 2.2.2.1 main salt system.
Each kind of plating will develop a variety of main salt systems and corresponding additive systems. For example, there are cyanide zinc plating, zincate zinc plating, chloride zinc plating (or potash zinc plating), ammonia zinc plating, sulfate zinc plating and so on. Each system has its own advantages and disadvantages, such as good dispersibility and depth of cyanide zinc plating bath, fine crystallization, good adhesion to substrate, good corrosion resistance, wide process range, stable bath, easy operation and insensitive to impurities. But it is extremely toxic and seriously pollutes the environment. Chloride zinc plating bath is a single salt plating bath without complexing agent, the waste water is easy to be treated, the brightness and flatness of the coating are better than other systems, the current efficiency is high, the deposition rate is fast, and the steel with low hydrogen overpotential is easy to be plated, such as high carbon steel, castings, forgings, etc. However, because the weak acidity of chloride ion has a certain corrosiveness to the equipment, on the one hand, it will cause some corrosion to the equipment, on the other hand, this kind of plating solution is not suitable for deep holes or tubular parts that need auxiliary anodes.
2.2.2 Additives.
Additives include gloss agent, stabilizer, softener, wetting agent, low zone walking agent and so on. Gloss agent is divided into main gloss agent, carrier brightener and auxiliary gloss agent and so on. For the same main salt system, there is a great difference in the quality of the coating by using additives made by different manufacturers. Generally speaking, developed countries such as Europe, the United States and Japan have the best additives, followed by Taiwan, and the mainland is relatively inferior to the first two. The combination of the main salt and the additives of a specific manufacturer determines the overall performance of the bath used. Excellent additives can make up for the shortcomings of some properties of the main salt. For example, the deep plating ability of the bath obtained by the combination of excellent chloride zinc plating additive and chloride main salt is better than that of many cyanide zinc plating baths.
2.2.3 Electroplating equipment.
Hanger: square hanger is used with square plating bath, circular hanger is used with circular plating bath. The circular plating bath and the hanger are more conducive to ensuring the uniform current distribution, while the square hanger needs to install scattered current devices such as barbed wire around the hanger or shorten the length of the anode plates on both sides, using the oval anode arrangement shown in the picture. Stirring device: promote solution flow, uniformly distribute solution state and eliminate bubble retention on the workpiece surface. Power supply: DC, good stability, low ripple coefficient.
2.3 Post-processing.
After plating, various treatments are carried out to enhance the properties of the coating, such as corrosion resistance, discoloration resistance, solderability, etc.
Dehydration treatment: add a dehydrating agent to the water, such as bright nickel plating.
Passivation treatment: improve the corrosion resistance of coatings, such as galvanizing.
Anti-discoloration treatment: add anti-discoloration agents to the water, such as silver plating, tin plating, imitation gold plating, etc.
Improve solderability treatment: such as tin plating, so the post-treatment process directly affects these functions of the coating.