Generally the hard chromium plating process is applied to machines, which are usually used under high temperature, such as moulds, etc. However, what factors will affect the hardness of chromium layer during the chromium plating process? We would like to share some information with you as follows.
1. The relationship between the concentration of chromium trioxide and hardness.
When other process conditions remain unchanged, the hardness will be high if the concentration of chromium trioxide is low. But if the concentration is low, the plating solution will change fast and be unstable.
2. The relationship between sulfuric acid content and hardness
According to normal standard of chromium plating process, the ratio of chromium trioxide and sulfuric acid should be kept at 100:1. When other concentration remain unchanged, increase the sulfuric acid content and the hardness of chromium layer will be higher correspondingly. However, when the ratio is 100:1.4, the hardness of chromium layer will decrease if keep increasing the sulfuric acid content.
3. The relationship between current density and hardness
At normal temperature, the hardness of chromium layer will increase as the increasing current density. When the current density reaches a limit, the hardness will tend to be stable.
4. The relationship between stability of chromium-plating solution and hardness
At higher temperature (about 65-75℃), the chromium layer plated by dilute solution is 15-20% harder than those plated by concentrated solution; at lower temperature (about 35-45 ℃), the hardness of the chromium layer plated by dilute solution is not much different from those plated by concentrated solution.
5. The relationship between thickness and hardness of chromium layer
Generally, the hardness of the chromium layer will get harder as the thickness increases, the hardness will be the highest when the thickness reaches about 0.2mm. After that, the hardness won’t improve any longer even the thickness keep on increasing.
6. As the temperature getting higher, the hardness of the chromium layer decreases observably
In order to improve the current efficiency, hardness, gloss, covering power and throwing power, our company has developed additives which are specially designed for hard chromium plating: HN-25 hard chromium plating process and HN-25R hard chromium plating process.
They have common characters: the formula won’t contain fluoride and won’t corrode the LCD area of workpiece; won’t corrode tin-lead alloy anode and don’t need to use special anode material; cathode current efficiency is high and can reach 22-26%; the thickness is even and deposit is bright; the layer has high microhardness and good anti-corrosion.
In addition, to eliminate environmental pollution of chromium fog and save maintenance cost of exhaust equipment, our company also has developed a chromium fog inhibitor, HN-701 Chromium fog inhibitor. It not only can save the use of chromic acid, but also improve the microcrack degree of chromium layer, enhance hardness of layer and increase adhesion.