The frame serves as a critical structural component in commercial vehicles, including trucks, passenger cars, and combined passenger-cargo vehicles. These frames are typically manufactured using hot-rolled steel plates that are stamped into shape and then assembled through riveting, welding, or bolting. In China, the coating process varies significantly depending on the scale of production and the available equipment. It is generally divided into two main categories: mass production and small-batch production.
In mass production, the process begins with cutting and blanking the steel plates, followed by descaling, rust prevention, stamping, welding, and riveting. Afterward, the parts undergo degreasing, phosphating, electrophoretic coating (electro-coating), or dipping, drying, and finally, applying a top coat as needed. Most major truck manufacturers in China rely on this method due to its efficiency and consistency.
On the other hand, small-batch production involves similar initial steps—cutting and blanking, stamping (or purchasing pre-stamped vertical and horizontal beams), and drilling. The process continues with welding or riveting, assembly, derusting, cleaning, dipping or painting, and then drying, either artificially or naturally. However, due to differences in material quality and process control, the final coating quality can vary greatly from one batch to another.
The coating quality of vehicle frames in China shows significant variation. Mass production tends to yield better results compared to small-batch manufacturing. A common issue is incomplete coverage on sharp edges, welds, and joints. Even with cathodic electrophoresis, these defects can persist due to structural limitations and inadequate pre-treatment, especially when rust occurs between processing stages.
Compared to international standards, China’s best frame coating levels are comparable to those of Japan and South Korea. However, they still lag behind the advanced techniques used in Europe and the United States, where stricter quality controls and more sophisticated processes ensure superior durability and corrosion resistance. As the industry continues to evolve, improving coating technology and process standardization will be key to closing this gap.
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