1.How does dust trigger this process?
Providing low surface tension points: The surface energy of the dust itself (especially organic dust and oily particles) or the contaminants adsorbed by the dust is typically much lower than that of the liquid coating.
Disrupting coating continuity: When the coating flows and covers dust particles, the coating at that point cannot wet the dust and will quickly shrink, attempting to "escape" this low surface energy point.
Forming permanent defects: Because the coating is fluid before baking and curing, the surrounding coating will try to fill in, but this cannot be done successfully due to the low surface tension at that point, ultimately leaving an unclosed hole after the coating has cured.
2.What are the sources of dust/particulate matter pollutants?
Air dust, equipment wear powder, powder coating particles
Tiny particles may be visible at the center of the pores; their distribution is random.
3.What are the sources of oil/grease contaminants?
Rolling mill lubricating oil, hydraulic oil, fingerprints, and oil droplets in compressed air
Shrinkage cavities are typically larger and rounder; they may be accompanied by fisheyes.
4.What are the impacts and consequences?
Appearance Quality: Severely affects the product's aesthetics and is an unacceptable defect on high-quality building exterior panels or appliance panels.
Protective Performance: Pinholes completely disrupt the coating's continuity, exposing the substrate directly to the environment and becoming the starting point for corrosion, significantly reducing the coating's corrosion resistance and weather resistance.
Subsequent Processing: During subsequent bending and stamping processes, pinholes easily become stress concentration points, potentially causing the coating to peel off from the edge of the pinhole.
5.What are the solutions and preventative measures?
Substrate Inlet Cleaning:
Utilize a highly efficient degreasing cleaning section to thoroughly remove rolling oil, rust-preventive oil, and dust from the galvanized substrate surface through alkaline washing, brushing, rinsing, and drying.
Regularly maintain cleaning brushes and nozzles to ensure effective cleaning.
Coating Environment Control (Critical Priority):
Cleanroom Standards: The coating room and curing oven entrance areas should be kept sealed and maintain positive pressure to prevent the entry of dusty external air.
Air Filtration: The air supply system must be equipped with a three-stage filtration system (pre-filter + medium-efficiency + high-efficiency filter), and filter bags/cartridges should be replaced regularly.
Temperature and Humidity Control: Maintain stable temperatures and reduce electrostatic dust adsorption.
Equipment and Process Management:
Coating Machine Cleaning: Regularly and thoroughly clean the coating rollers, feed rollers, and paint trays to prevent dry paint debris from entering.
Chain and Ductwork: Ensure proper lubrication of the conveyor chain (using silicone-free lubricant) to prevent dripping; regularly clean accumulated dust from the curing oven and ductwork.
Paint filtration: The paint should be thoroughly filtered before being loaded onto the machine (e.g., using a filter screen of 100 mesh or higher).