①  Influence of Chromic Anhydride Concentration

Chromic anhydride is the main source of hexavalent chromium, and its concentration significantly impacts the plating layer. A high chromic anhydride concentration improves the conductivity of the plating solution and enhances the brightness of the coating, but it reduces the hardness of the chromium layer and decreases the wear resistance of the printing plate. A moderate chromic anhydride concentration results in higher current efficiency, better dispersion capability, and a harder, more wear-resistant chromium layer, though with reduced brightness. Therefore, medium-concentration chromic anhydride solutions are typically used for gravure cylinder chrome plating.

②  Influence of Sulfuric Acid Concentration

The sulfuric acid concentration has a considerable impact on plating quality. If the sulfuric acid content is too low, chromium deposition on the cathode becomes difficult, leading to a rough, less glossy coating with reduced hardness. Conversely, if the sulfuric acid content is too high, chromium deposition is also hindered. Only when the sulfuric acid content is in the correct proportion to hexavalent chromium does the cathode reaction proceed normally, producing a glossy, high-hardness coating.

③  Influence of Trivalent Chromium Content

A certain concentration of trivalent chromium is essential in the chrome plating solution. Without trivalent chromium, metallic chromium cannot deposit on the cathode effectively. The solution must first undergo electrolytic treatment to generate an appropriate amount of trivalent chromium. During production, maintaining an anode-to-cathode area ratio of 2:1 or 3:2 helps stabilize trivalent chromium levels. If trivalent chromium is insufficient, large cathodes and small anodes can be used for electrolysis; if excessive, the opposite approach is taken. In practice, insufficient trivalent chromium reduces dispersion capability, lowers current efficiency, diminishes coating brightness, decreases hardness, and weakens coverage. Excess trivalent chromium results in black, rough coatings with poor brightness and a narrower bright current density range.

④  Influence of Iron Ions

During electroplating, if the steel cylinder is not properly sealed, iron ions and other harmful impurities may enter the plating solution. When iron ions reach a certain level, they reduce the current density, degrade coating brightness, and darken the color. Therefore, strict measures must be taken to prevent iron ions from contaminating the plating solution.

⑤  Relationship Between Hardness, Temperature, and Current

Under normal plating conditions, chromium layer hardness is closely related to temperature and current. Only by applying the appropriate current and temperature can a high-hardness chromium layer be achieved. Generally:

· Low temperature and high current density: The coating appears dark gray, with high hardness but significant brittleness.

· High temperature and low current density: The coating appears milky white, with low hardness but good plasticity.

· Moderate temperature and current density: The coating exhibits excellent brightness and high hardness.

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