1.How do the basic properties of the substrate (galvanized layer) affect the "base layer anti-rust ability"?
Zinc Coating Weight and Uniformity
The zinc coating weight must meet the corresponding standards (e.g., the common Z100-Z275, which means a zinc coating weight of 100-275g per square meter). Insufficient weight increases the risk of substrate exposure.
The zinc coating uniformity must meet the standards (e.g., as determined by metallographic examination or spot testing). If the zinc coating is partially thin, even if the coating is intact, premature zinc consumption may cause substrate corrosion, leading to blistering and delamination of the coating.
Zinc Coating Adhesion
The zinc coating must adhere tightly to the steel substrate (this can be verified by a bend test to ensure no large areas of zinc fall off after bending). Poor zinc coating adhesion can cause "interlayering" during coating processing or use, leading to complete delamination of the coating.
Galvanized Sheet Surface Cleanliness
The substrate surface must be free of defects such as oil stains, oxidation spots, and zinc slag. Oil stains can prevent uniform coating adhesion, oxidation spots can become the starting point for rust, and zinc slag can cause localized protrusions and pinholes in the coating, compromising coating integrity.
2.What impact does the core performance of the coating have on "protection and decorative life"?
Coating adhesion (with the substrate/between coatings) is the most fundamental performance characteristic: the coating must adhere tightly to the galvanized layer. Poor adhesion can lead to paint peeling during transportation, processing, or use, and the exposed galvanized layer will rapidly rust and spread.
For multi-layer coatings (primer + topcoat), interlayer adhesion must also meet standards to prevent the topcoat from peeling off.
Weather resistance-a core characteristic for outdoor applications-must resist natural environmental degradation, including resistance to UV aging, humidity and heat, and acid and alkali resistance.
3.How is the appearance and application adaptation performance reflected?
Appearance Quality
The surface must be smooth and free of defects: pinholes, cavities, bubbles, color variations (color variation within the same batch: ΔE ≤ 2), or scratches (depth ≤ 1/2 coating thickness). Appearance directly impacts product value, especially in decorative applications such as building exteriors and appliance housings.
Coating Gloss Consistency: Depending on the desired finish (e.g., matte, semi-gloss, or high-gloss), the gloss variation within the same batch must be ≤ 5 units (e.g., gloss at a 60° angle must be controlled within ±5 GU).
Processing Compatibility
Compatible with subsequent processing techniques: For example, the coating must not generate harmful fumes during welding (low-VOC coating) and must not exhibit large-scale cracking at the coating edge during cutting.
Heat Resistance: For applications in high-temperature environments (e.g., oven housings), the coating must meet short-term temperature resistance requirements of ≥ 150°C (without discoloration or wrinkling).
4.What are the differences in "performance emphasis" in different scenarios?
Outdoor construction (such as factory siding and fencing): Prioritize weather resistance (UV and salt spray resistance) and coating adhesion.
Home appliance interiors (such as refrigerator side panels): Emphasize appearance (color difference and gloss) and flexibility (no cracking during processing).
Industrial piping/ducting: Emphasize zinc coating weight (to prevent rust on the base material) and coating wear and corrosion resistance.
5.Mechanical protection performance: How to deal with damage during processing and use?
Hardness and Abrasion Resistance: The coating must have a certain hardness (e.g., pencil hardness ≥ H) to prevent exposure to the underside due to friction during transportation and scratches during installation.
Flexibility and Bending Resistance: Color-coated coils often undergo bending and stamping processes (e.g., to make air ducts and wall panels). They must pass the "T-bend test" (e.g., T=2, meaning the inner radius of the bend is twice the thickness of the board, with no cracking in the coating) and the impact test (e.g., a 50cm drop, with no peeling of the coating).