Q:Why should the substrate be pretreated before color coating?
A:Purpose: Remove oil and oxide layer from the surface of steel coils and enhance coating adhesion.
Key steps: Degreasing and cleaning: Alkaline solution to remove grease (temperature: 60~80℃, concentration: 3%~5%).
Water washing: High-pressure spray to remove residual chemical agents.
Chemical conversion treatment: Phosphating or chromating treatment to form a dense conversion film (thickness: 0.5~3 μm).
Drying: Hot air drying (temperature: 80~120℃) to ensure that the substrate is dry and free of moisture.
Q:Compared with ordinary galvanized sheets, why is the production process of color-coated coils more complicated?
A:1. Multi-coating system: primer, topcoat and backcoat need to be applied in layers, and the process parameters of each layer are independently controlled.
2. Dependence on precision equipment: high-precision roller coaters, long curing furnaces and online detection systems require large investments.
3. Strict quality control: color consistency, weather resistance, adhesion and other indicators need to be monitored throughout the process.
Q:What is the difference between the process of color coated coil and galvanized coil?
A:The core difference between the process of color-coated coils and galvanized coils is that galvanized coils are based on the galvanizing process (hot-dip or electro-galvanizing), focusing on the corrosion protection of the steel surface; color-coated coils add complex processes such as pretreatment, painting, and baking on the basis of galvanized coils to achieve decorativeness and higher performance.
Q:What are the precautions for the pretreatment process of color coated coils?
A:Pretreatment needs to ensure that the substrate surface is "clean, rough, and activated", that is, free of oil and impurities, with a microscopic roughness suitable for coating adhesion, and sufficient surface chemically active groups (such as hydroxyl groups). Negligence in any link (such as incomplete degreasing, too thin phosphating film) will cause the coating to blister, fall off, or reduce corrosion resistance. Therefore, the quality of pretreatment needs to be guaranteed through precise process parameter control, equipment maintenance, and real-time quality inspection.
Q:What impact does the pretreatment of color coated coils have on the environment?
A:The environmental impact of pretreatment of color-coated coils is characterized by complex pollution types, many toxic substances, and high treatment costs. The key is to control the compliance of heavy metals, phosphorus, and VOCs emissions, as well as the recycling rate of water resources and standardized management of hazardous waste. Enterprises need to balance production benefits and ecological protection through dual means of process upgrades (such as low-toxic agents, clean production) and end-of-pipe treatment (such as waste gas purification and wastewater reuse).