Automotive Structural Components Gantry Stepped Electrophoresis Line

　　(1) For electrophoretic coating of general metal surfaces, the process flow is as follows: Pre-cleaning → Loading onto the line → Degreasing → Water rinsing → Rust removal → Water rinsing → Neutralization → Water rinsing → Phosphatizing → Water rinsing → Passivation → Electrophoretic Coating → Off-line Cleaning → Ultrafiltration Water Rinsing → Drying → Unloading from the line.

　　(2) The substrate material and pre-treatment of the object being coated significantly influence the electrophoretic coating film. Cast parts typically undergo sandblasting or shot blasting to remove rust, followed by wiping the workpiece surface with cotton yarn to eliminate loose dust. Any residual steel shots or other debris on the surface are then removed using 80- to 120-grit sandpaper. For steel surfaces, degreasing and derusting treatments are applied; if higher surface quality is required, additional phosphating and passivation processes are carried out. Before anodic electrophoresis, black metal components must undergo phosphating treatment—otherwise, the resulting paint film will exhibit poor corrosion resistance. During phosphating, zinc-based phosphate coatings are commonly used, achieving a film thickness of approximately 1–2 μm, with a requirement for fine and uniform crystal formation in the phosphate layer.

　　(3) In the filtration system, a single-stage filter is typically used, featuring a mesh-bag design with pore sizes ranging from 25 to 75 μm. The electrophoretic coating is pumped vertically through the filter for purification. Considering factors such as the overall replacement cycle and coating film quality, a 50-μm pore-size filter bag is optimal—it not only meets the required coating film quality standards but also effectively addresses the issue of filter bag clogging.

　　(4) The volume of the circulation system in electrophoretic coating directly affects the stability of the bath solution and the quality of the paint film. Increasing the circulation rate reduces sedimentation and bubble formation in the bath, but it also accelerates bath aging, boosts energy consumption, and compromises the overall stability of the bath. Therefore, maintaining a circulation frequency of 6 to 8 cycles per hour is ideal—it not only ensures high-quality paint films but also guarantees stable operation of the bath solution.

　　(5) As production time extends, the impedance of the anode membrane increases, leading to a drop in the effective operating voltage. Therefore, during production, the power supply's operating voltage should be gradually increased—based on the observed voltage loss—to compensate for the voltage drop across the anode membrane.

　　(6) The ultrafiltration system controls the concentration of impurity ions carried in by the workpieces, ensuring high-quality coating performance. During operation, it’s crucial to note that once the system is started, it should run continuously—intermittent operation is strictly prohibited—to prevent the ultrafiltration membrane from drying out. If the membrane dries, resin and pigment particles can adhere to it, making thorough cleaning impossible and severely compromising both the membrane’s water permeability and its overall service life. Additionally, the system’s water output rate tends to decline over time; therefore, to maintain optimal performance and ensure adequate supply of ultrafiltration water for soaking and rinsing processes, the membrane should be cleaned every 30–40 days of continuous operation.

　　(7) Electrophoretic coating is well-suited for large-scale, assembly-line production processes. The renewal cycle for the electrophoresis bath solution should be kept within 3 months. For instance, in an electrophoretic production line capable of manufacturing 300,000 steel rims annually, scientific management of the bath solution is crucial. This involves regularly monitoring various parameters of the bath solution and making timely adjustments or replacements based on the test results. Typically, bath solution parameters such as pH, solid content, and conductivity are measured daily for electrophoresis fluid, ultrafiltration fluid, ultrafiltration cleaning fluid, cathode (anode) fluid, circulating rinse fluid, and deionized cleaning fluid. Additionally, the pigment-to-binder ratio, organic solvent content, and results from small-scale lab tests are assessed twice a week.

　　(8) For managing the quality of the paint film, regularly inspect the uniformity and thickness of the coating. The appearance should show no pinholes, sagging, orange peel, or wrinkles. Additionally, periodically check the coating’s adhesion and its resistance to corrosion—key physical and chemical properties. Inspection intervals should follow the manufacturer’s testing standards, with each batch typically requiring evaluation. 
　　The adoption of electrophoretic coating and waterborne paints marks a significant advancement in the coatings industry. 
　　Electrophoretic coating boasts fast application speeds, enabling mechanized and automated continuous operations while significantly reducing labor intensity. It produces uniform coatings with exceptional adhesion, ensuring even coverage—even in hard-to-reach areas like rib plate welds, which are often challenging to coat effectively using conventional methods. As a result, the finished film is consistently smooth, flat, and visually appealing. Moreover, this process achieves a remarkable paint utilization rate of 90% to 95%. Since electrophoretic coatings use water as their primary solvent, they offer key advantages such as non-flammability, non-toxicity, and ease of handling. After baking, the resulting coating exhibits outstanding adhesion properties, along with superior performance in terms of rust resistance, corrosion protection, and weather durability—qualities that far surpass those of traditional paints and conventional application techniques.