Coated aluminum coil process

Coated aluminum coil, a key material in architectural decoration and industrial protection, is produced through a process that integrates the essence of metallurgy, surface engineering, and coating techniques. This article systematically analyzes the entire production chain, from raw material processing to finished product packaging, revealing the crucial role each link plays in the final product's performance.

Substrate Preparation Stage

The choice of aluminum coil substrate directly impacts the quality of the finished product. Aluminum alloys such as 3003 and 5052 are commonly used. Before receiving raw materials into storage, three-dimensional coordinate measurement (CMM) is required to ensure that the thickness tolerance is within ±0.02mm. For use in building curtain wall applications, particular attention must be paid to the aluminum's ductility to ensure that the substrate does not deform during the subsequent roller coating process.

Surface Pretreatment Process

1. Degreasing is performed using a five-tank, serially mounted cleaning line. The alkaline cleaning agent temperature is maintained at 55±2°C, and the solution activity is monitored in real time using a conductivity meter. The treated aluminum surface must meet the hydrophilic standard of a water drop angle ≤5°.
2. The chromization treatment utilizes chromium-free conversion technology, performed in a zirconium phosphate system with a pH of 3.8-4.2. The film thickness is strictly controlled within the range of 0.8-1.2μm. The crystallinity of the conversion film is measured by X-ray diffractometer to ensure a uniform network structure.
3. The water washing process utilizes a countercurrent rinse design, with the final rinse water conductivity ≤20μS/cm to prevent the presence of impurity ions.

Precision Coating System

A double-coating, double-baking process is currently the mainstream technology. The primer coating weight is controlled at 8-12g/㎡, and epoxy-modified resin is used to enhance adhesion. The topcoat is applied using electrostatic rotary cup spraying, achieving a paint utilization rate of over 85% at an atomization pressure of 0.4MPa. The curing oven is precisely controlled in three temperature zones: preheating at 120°C in the entrance, main curing at 230±5°C in the middle, and a slow cooling zone at the exit to prevent sudden cooling and embrittlement of the paint film. Quality Control System
The online inspection system includes four core modules: ① A laser thickness gauge monitors coating thickness fluctuations in real time; ② An infrared spectrometer scans the coating cure degree every 30 seconds; ③ A colorimeter maintains a ΔE value within 0.8; and ④ A crosshatch knife adhesion test with three samples per roll. The offline laboratory is equipped with a salt spray chamber, which conducts a 1000-hour neutral salt spray test in accordance with GB/T1771 to ensure compliance with corrosion resistance standards.

Warehouse and Logistics Specifications
Finished coils are vacuum-sealed with a vapor phase anti-rust film, and the steel strapping pressure is set between 200-250 N·m. The storage area implements temperature and humidity control, maintaining a temperature of 15-25°C and a relative humidity of 45% ± 5%. Coils must not be stacked more than five layers. Transport vehicles are equipped with air suspension systems, and acceleration on bumpy roads is controlled to less than 0.3g to prevent microcracks in the coating.