Compared with other plating types such as copper plating, nickel plating and zinc plating, hard chromium plating is a special plating type in electroplating , which is embodied in the following points:
1. The composition of plating bath is relatively simple
2. The anode adopts insoluble anode
3. obtained by reduction reaction of chromium layer with high valence ions;
4. High requirement of power waveform
5. The dispersion ability and coverage ability are poor, which belongs to negative leveling
6. The edge effect and tip effect are large, and the tooling is complicated
7. The process current is high, and the limit current density decreases with the increase of chromic acid concentration; 8. The current efficiency is low and decreases with the increase of chromic acid concentration and temperature
9. The process temperature is high, and the heat in the chromium plating process is large, so it is necessary to configure heating and cooling
10. There are two valence states of chromium in the solution at the same time;
11. DC lines have high heat generation and high requirements for conductivity
12. The bath solution is oxidized greatly, and the metal is easy to be passivated. For the easily passivated metal, it is necessary to choose reasonable pretreatment mode, bath entry mode and electricity application mode. Moreover, it is necessary to ensure the stability and continuity of current in the chromium plating process, and it is impossible to cut off power
13. The bath solution is highly corrosive, and metals easily dissolved by chromic acid need to be charged into the bath
14. The amount of hydrogen evolution is large, and hydrogen atoms are mixed in the chromium layer and hydride is formed. For some thin-walled parts, elastic parts or parts with special requirements, hydrogen removal treatment is needed
15. The coating has high hardness and brittleness
16. Hard chromium layer not only has stable body-centered cubic lattice, but also has unstable close-packed face-centered hexagonal lattice
17. Generally, there are a large number of microscopic reticulations in the chromium layer formed during hard chromium electroplating
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In short, hard chromium plating needs to strictly control the process parameters, ensure the stability of power supply and small ripple coefficient, design reasonable tooling and fixture, and select appropriate pretreatment and groove entry methods according to different materials. We have more than 30 years of chrome plating field experience and chrome plating equipment, tooling design experience, welcome to consult!