Chrome electroplating is a traditional surface electroplating technology that has been used for more than 70 years. The chrome-plated layer has high hardness, wear resistance, corrosion resistance and can keep the surface bright for a long time, and the process is relatively simple and the cost is low. For a long time, in addition to being a decorative coating, chromium plating has also been widely used as a wear-resistant and corrosion-resistant coating for mechanical parts. Electroplating hard chrome plating technology is often used to repair damaged parts.
However, the hard chromium electroplating process can cause serious environmental problems. It's not chromium itself that causes environmental problems.
It's the chrome plating process. Chromium is an inactive element and can be safely used in daily necessities and even artificial joints.
The main problem is that the chromic acid solution used in the chromium plating process produces Cr(VI) acid mist and wastewater. Therefore, countries are
The chrome plating process will become more and more restrictive. For example, the United States changed the current air emission standards for hexavalent chromium from
0.1Mg/M 3 is reduced to 0.0050~0.0005Mg/M 3. According to estimates by the U.S. Navy Department, the U.S. Navy alone will need a one-time investment of $22 million to update equipment after the implementation of this standard, and will spend $46 million each year for collection, processing, and other expenses.
In addition, there are other disadvantages of electroplating hard chrome plating:
(1) The hardness of electroplated hard chromium coating is generally HV 0.3 800~900, which is far less than that of some ceramics and cermet materials, which have high hardness and good wear resistance. Moreover, the hardness of hard chromium coating will be due to its internal stress when the temperature rises. Its working temperature can only be lower than 427ºC, so it is difficult to adapt to the working requirements of modern machinery at high temperature and high speed.
(2) There are microcracks in the chromium plating layer, which will inevitably produce penetrating cracks (see Figure 1), causing corrosive media to penetrate from the surface to the interface to corrode the substrate, causing rust spots or even peeling on the surface of the plating layer.
(3) The deposition speed of the electroplating process is slow (about 25μm/h), and it usually takes 2 to 3 shifts to plate 0.2-0.3mm thick coatings, which is not conducive to the application of thick coatings.
Therefore, people have been trying to find a coating process to replace hard chromium electroplating. With the recent development of coating technology
With continuous development, some coatings have proved to be cleaner and more effective than hard chrome plating, and even
The cost is lower. These coating technologies include physical vapor deposition (PVD), chemical vapor deposition (CVD), laser coating
Layer technology and thermal spraying technology, among which the cost of the HVOF coating is similar to that of the electroplating hard
The chromium plating layer is equivalent, some powder materials are already lower than the cost of electroplating, and are still decreasing, while the hard chromium electroplating
The cost of coating is on the rise, and more importantly, thermal spray coating technology is used in textile machinery, papermaking, and aviation.
The surface has been successfully applied.
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