Q: What are the common surface defects and causes of SPCC coils?
A: Scratches: Roll damage / guide scratches → Inspect equipment, optimize packaging
Oxidation color: Poor annealing atmosphere → Adjust H₂/N₂ ratio
Edge waviness / Center waviness: Uneven rolling force → Fine-tune leveling mill roll gap
Inclusions: Insufficient steelmaking cleanliness → Improve LF refining and continuous casting protective slag quality
Q: How to determine the surface quality of SPCC?
A: According to JIS G3141: Grade A: No visible defects; Grade B: Minor scratches / indentations are allowed, not affecting forming.
Q: What are the causes and handling of thickness tolerance deviations?
A: Causes: Roll wear / AGC fluctuations; Handling: Replace rolls, calibrate AGC, downgrade coils with deviations or deliver according to agreement.
Q: How to solve sheet shape defects (such as camber)?
A: Adjust coiling tension, fine-tune leveling mill work roll bending/shifting, and in severe cases, trim edges or slit.
Q: What causes rust spots on SPCC coils?
A: Insufficient oiling/ineffective rust-preventive oil, storage humidity >60%, damaged packaging leading to water ingress; Prevention: Use VCI rust-preventive film, moisture-proof plugs for the coil, and control humidity between 40-60%.