What are the technological characteristics of chromium plating?

(1) Chromium is very stable in many media, which is caused by its easy passivation. In essence, chromium is a very active metal, and its atomic structure has some characteristics different from other metals. Therefore, when chromium plating is carried out in chromic acid solution, a continuous coating can only be obtained at a very negative potential. Compared with other metal electroplating processes, the cathodic reaction of chromium plating is more complicated, including the deposition of metallic chromium and the formation of trivalent chromium, but a large amount of hydrogen gas is precipitated, which leads to particularly low cathodic current efficiency. The electrode reaction from chromate ion reduction to chromium metal is very complicated, and the intermediate process is still a controversial issue. In addition, some anions, such as so42+, must be added to the chromium plating electrolyte to maintain a certain amount of Cr3X in the electrolyte, thus realizing the chromium plating process. (2) The current density used in chromium plating is very high, which is several times higher than that of ordinary electroplating; The bath voltage of chromium plating process is also very high, so it is often necessary to use a power supply with DC output voltage of 15V. (3) The anode used for chromium plating is not metal chromium, but lead antimony or lead-tin alloy as insoluble anode. This is because chromium is brittle and easy to break, so it is difficult to do chromium plating. In addition, when chromium metal is dissolved, it will enter the solution in different valence states, which will cause great changes in the solution and bring difficulties to the maintenance of the plating solution. (4) In the process of chromium plating, the range of obtaining bright chromium layer is very narrow. This requires strict control of process specifications and correct control of the relationship between plating solution and current density in production operation, so as to obtain a wide and satisfactory bright chromium layer. (5) The dispersion ability of chromium plating electrolyte is extremely low. For parts with complex shapes, it is difficult to plate all uniform chromium layers or thicken chromium layers. In production, protective cathode and auxiliary anode are often used to obtain high quality coatings. (6) At present, many people have studied the process of chromium plating with chromium salt instead of chromic acid, trying to overcome many shortcomings of chromic acid plating. If trivalent chromium plating process is adopted, a coating similar to polished stainless steel can be obtained. Trivalent chromium electroplating is a transitional technical measure in the case of stricter control of chromic acid pollution.