1.What are the main process flows?
Unwinding and sewing---Entry looper---Pretreatment/chemical treatment---Coating---Baking and curing---Post-treatment/finishing---Cooling---Exit looper---Coiling---Inspection and packaging
2.What is the purpose and process of coating?
Purpose: To accurately and evenly apply liquid coating on both sides (front and back) of the pretreated strip.
Main technology: Roller coating is the absolute mainstream technology.
Roller coater: The core equipment, usually composed of multiple precisely controlled rollers (pick-up roller, metering roller, coating roller).
Coating method: Forward coating: The coating roller rotates in the same direction as the strip. The coating is thicker and fuller in appearance, but "roller marks" may be produced.
Reverse coating: The coating roller rotates in the opposite direction to the strip. The coating is thinner, more uniform, the surface is smoother and more delicate, and the control accuracy is high. It is the preferred method for high-quality coatings (especially topcoats).
3.What is the purpose and process of baking and curing?
Purpose: To volatilize the solvent in the coating and initiate the cross-linking reaction of the resin to form a tough, durable solid paint film.
Equipment: Multi-section, forced hot air circulation curing oven.
Process: Preheating zone: Gently increase the temperature to allow most of the solvent to evaporate (avoid explosion holes and pinholes). Reaction/curing zone: Reach the peak metal temperature (PMT) required by the resin and maintain it for a sufficient time (usually tens of seconds to several minutes). PMT is the highest temperature of the strip itself and is a key parameter for curing quality (different resins require different PMTs, such as polyester about 224-232°C, PVDF about 241-249°C).
Cooling zone: Rapidly cool the strip to the reeling temperature, stop the curing reaction, and stabilize the coating performance.
4.What are the characteristics and advantages of the process?
Continuous and efficient: The production line speed can usually reach 80-200 meters/minute, and the production efficiency is extremely high.
High degree of automation and controllability: The process parameters (temperature, speed, coating amount, tension, etc.) are precisely controlled by computers to ensure stable and consistent product quality.
Excellent coating quality: Coating and curing in a clean and controllable environment avoids problems such as sagging, orange peel, dust pollution, etc. that may be caused by spraying and other processes. The coating is uniform, dense and smooth. Environmental protection (relative): Volatile organic compounds and waste gases generated during coating and curing are collected and treated centrally, and VOC emission control is better than traditional spraying. Chromium-free pretreatment technology is becoming increasingly popular.
Economic efficiency: High-speed continuous production, high material utilization rate (close to 100%), and low labor costs. Diversity: Products that meet various performance and appearance requirements can be produced by selecting coatings (primers, topcoats), colors, gloss, textures (embossing, printing), lamination, etc. with different resin systems.
5.What are the key influencing factors?
Substrate quality: The uniformity and surface cleanliness of the galvanized layer directly affect the pretreatment and coating adhesion.
Pretreatment effect: The quality of the conversion film is the cornerstone of the long-term adhesion and corrosion resistance of the coating.
Coating performance and ratio: The selection and stability of resin type, pigment, additive, solvent.
Roller coating accuracy: The uniformity and precise control of the coating amount.
Curing process: The accurate achievement and retention time of PMT directly affect the crosslinking degree, weather resistance and mechanical properties of the coating.
Environmental control: Cleanliness, temperature and humidity control of the coating and curing area.