In addition to the common features shared with other plating processes, chrome plating has many unique aspects, mainly reflected in the following:
A. The main component of the chrome plating electrolyte is not a chromium salt, but highly oxidizing chromic acid.
B. The current efficiency is very low, generally ranging from 13% to 16%, and can reach a maximum of only about 23%. As a result, a large amount of hydrogen gas is released during the chrome plating process, carrying toxic chromic acid mist. Therefore, effective ventilation systems and chromic acid mist suppressants are required.
C. A small amount of specific anions, such as SO₄²⁻, F⁻, and SiF₆²⁻, must be added to the solution. Additionally, a certain concentration of trivalent chromium (Cr³⁺) must be maintained in the electrolyte.
D. The throwing power is low. For parts with complex shapes, conforming anodes and auxiliary cathodes must be used to achieve a good plating layer.
E. A very high current density is used, sometimes tens of times higher than that used in other plating processes. The cell voltage during chrome plating is also relatively high, often requiring a power supply of over 12 volts, whereas other plating processes can usually be satisfied with a 6-volt supply.
F. Strict control of temperature and current density is required, and the two must be closely coordinated. If the current density is fixed, the temperature can only vary within 1–2°C; if the temperature is fixed, the current density can only vary within 2–3 A/dm².
G. The anode used in chrome plating is not metallic chromium, but insoluble anodes made of lead, lead-tin alloy, or lead-antimony alloy.
H. Due to the tendency of chromium layers to passivate, interruption of the electrical current during plating is generally not allowed.
The above points reflect some of the unique characteristics of chrome plating production. These special features distinguish the chrome plating process from other electroplating processes. However, chrome plating is still a type of electroplating and therefore follows the general principles of electroplating. We should proceed from practical production experience, gradually study and understand the entire chrome plating process, and grasp both its unique and universal laws, in order to better serve production.
Ningbo Qianhao has over 30 years of experience in casting and machining. The company operates in-house production lines for lost wax casting, lost foam casting, silica sol casting, composite casting, and shell mold casting, with a combined annual capacity of 60,000 tons. Qianhao also provides precision machining and a variety of surface treatments to fully meet customer requirements.
Head of Engineering Department: Wang Bo