Metal coating technology
Metal coating technology lies at the intersection of materials science and engineering. By continuously incorporating advances in automation control, new materials, and environmental science, it has developed a diverse technical framework. Based on the underlying principles, it can be categorized into four main types: solvent-based coating, water-based coating, powder coating, and electrophoretic coating. Each technology offers unique application scenarios and performance advantages. Driven by the wave of intelligent manufacturing, metal coating technology is transitioning from traditional, empirical operations to digital and intelligent ones. The application of technologies such as robotic spraying and online quality monitoring has enabled coating uniformity tolerances to be controlled within ±2μm, far exceeding the ±10μm achieved with manual operation.
Solvent-based coating technology once dominated due to its ease of application and excellent film properties, but its high VOC emissions (reaching over 500g/L) have gradually become a drawback. This technology forms the coating film through solvent evaporation. Commonly used diluents include aromatic hydrocarbons such as toluene and xylene. During the spraying process, approximately 30% of the solvent evaporates directly into the air. To comply with environmental regulations, high-solids coating technology has emerged. By increasing the resin content and reducing the solvent ratio, VOC emissions can be controlled to below 300g/L. A steel structure plant replaced traditional solvent-based coatings with high-solids epoxy coatings. While maintaining the same film thickness, this not only reduced VOC emissions by 40%, but also lowered material costs by 15% due to the increased coverage rate. However, solvent-based technology remains irreplaceable in some applications where gloss and leveling are crucial, such as high-end instrument housings.
Waterborne coating technology uses water as a dispersion medium, reducing VOC emissions to below 50g/L and making it the most mature environmentally friendly coating technology. Its film-forming mechanism involves the gradual fusion of polymer particles through water evaporation, requiring precise control of the temperature (20-25°C) and humidity ( 60-70%) of the application environment. The automotive industry is a major application area for waterborne coating technology, with major global automakers already implementing waterborne body topcoats. A joint venture automaker’s waterborne basecoat line successfully addressed paint cratering by implementing a flash-drying zone humidity gradient control technique, achieving a first-pass pass rate of 98.5%. A bottleneck for waterborne technology lies in its higher substrate pretreatment requirements and approximately 20% higher drying energy consumption compared to solvent-based coatings. However, with the application of infrared radiation drying and heat pump technology, this gap is gradually narrowing.
Powder coating technology, a representative solvent-free coating method, adheres powder coating to metal surfaces through electrostatic attraction, then cures at high temperatures to form a coating with virtually zero VOC emissions. Its core technology relies on controlling the powder’s charge and fluidization state. Commonly used powder types include epoxy, polyester, and epoxy-polyester blends. Polyester powder is widely used in outdoor installations due to its excellent weather resistance. Powder coating typically has a film thickness of 50-150μm, meeting corrosion protection requirements in a single application. It is particularly suitable for large components such as pipelines and guardrails. A wind power company employed ultra-thick powder coating technology (300μm), extending the corrosion life of wind turbine towers from 15 to 25 years while reducing the number of coating passes. However, this technology suffers from insufficient coverage of edges and corners on complex workpieces, and the high cost of color change and cleaning limits its application in high-variety, small-batch production.
Intelligent coating technology is a concrete manifestation of Industry 4.0 in the surface treatment field. It leverages digital twins and the Internet of Things (IoT) to achieve precise control of the entire process. Automated coating production lines typically consist of pre-treatment robots, spray robots, intelligent drying ovens, and online inspection systems, using PLC and MES systems for data interoperability. A smart coating line at a home appliance company uses robotic vision to automatically adjust spray parameters based on workpiece shape, and uses infrared temperature measurement to correct the curing curve in real time, reducing the standard deviation of coating performance by 60%. More advanced systems also incorporate machine learning algorithms to analyze historical data to predict coating defects and optimize process parameters in advance. For example, when the system detects rising ambient humidity, it automatically increases paint viscosity and extends flash-off time to prevent pinholes in the paint film. Intelligent technology not only improves product consistency but also reduces energy consumption by 30% and labor costs by 50%, representing the future development direction of metal coating technology.
