Process Characteristics Of Plastic Plating-Electroless Nickel Plating

Process characteristics of plastic plating-Electroless Nickel plating.
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Electroless nickel plating is a method to obtain the coating by self-catalytic reaction on the surface of the material by using metal salt and reducing agent. So far, electroless nickel plating is one of the fastest growing surface treatment processes abroad, and it has the widest range of applications. The rapid development of electroless nickel plating is determined by its superior process characteristics.
I. technological characteristics of electroless nickel plating.
1. Thickness uniformity.
Uniform thickness and good uniform plating ability is one of the major characteristics of electroless nickel plating, and it is also one of the reasons for wide application. Electroless nickel plating avoids the uneven thickness of electroless coating caused by uneven current distribution, and the thickness of electroplated coating varies greatly in the whole part, especially on the parts with complex shape. in the corner of the part and near the anode, the coating is thicker, while the coating on the inner surface or far away from the anode is very thin. Can not even plating, the use of electroless plating can avoid this deficiency of electroplating. During electroless plating, as long as the surface of the part is in contact with the plating bath, the components consumed in the bath can be replenished in time, and the coating thickness of any part is basically the same, even if grooves, gaps and blind holes are the same.
two。. There is no problem of hydrogen embrittlement.
Electroplating can convert nickel cations into metal nickel and deposit them on the anode by means of chemical reduction. the experimental results show that the entrainment of hydrogen in the coating has nothing to do with the chemical reduction reaction, but has a lot to do with the electroplating conditions. the hydrogen content in the coating usually increases with the increase of current density.
In nickel plating bath, except a small part of hydrogen is produced by NiSO4 and H2PO3 reaction, most hydrogen is produced by hydrolysis caused by electrode reaction when the two poles are electrified. In the anodic reaction, hydrogen on the cathode precipitates with metal Ni-P alloy at the same time to form (Ni-P) H, which is attached to the deposition layer. Due to the formation of excess atomic hydrogen on the surface of the cathode, part of it is desorbed to form H2. If there is no time for desorption, it remains in the coating, and part of the hydrogen left in the coating diffuses into the matrix metal, while the other part accumulates to form a hydrogen mass at the defects of the matrix metal and the coating, which has a very high pressure. Under the action of pressure, the defects lead to cracks, and under the action of stress, a fracture source is formed, which leads to hydrogen embrittlement fracture. Hydrogen permeates not only into the matrix metal, but also into the coating. it is reported that electroplated nickel can basically remove hydrogen from the coating after heat treatment at 400 ℃ × 18h or 230 ℃ × 48h, so it is very difficult for electroplating nickel to remove hydrogen. however, electroless nickel plating does not need hydrogen removal.
3. The functions of many materials and parts, such as corrosion resistance and high temperature oxidation resistance, are reflected by the surface layer of materials and parts. in general, some electroless nickel plating layers with special functions can be used to replace the whole solid materials prepared by other methods, and cheap matrix materials can also be used to replace parts made of valuable raw materials. Therefore, the economic benefit of electroless nickel plating is very great.
4. It can be deposited on the surfaces of various materials, such as steel-nickel-based alloys, zinc-based alloys, glass, ceramics, plastics, semiconductors and so on, thus creating conditions for improving the properties of these materials.
5. It does not need the DC motor or control equipment needed for electroplating, and the heat treatment temperature is low, as long as different corrosion resistance and wear resistance can be obtained after different holding time below 400 ℃. Therefore, it does not have the problem of heat treatment deformation. it is especially suitable for processing parts with complex shape and wear resistance and corrosion resistance.
6. The thickness of the chemical deposition layer can be controlled, the process is simple, the operation is convenient, the temperature is low, and the cost is lower than other surface treatment protection, so it is suitable for small and medium-sized factories or small batch production.