Inspection of appearance defects of cold-rolled packaging steel strip pressed into oxide scale

(1) Defect characteristics: the hot-rolled iron oxide scale is pressed into the surface of the steel plate, showing black spots in the shape of fish scales, strips or spots. The distribution area varies in size, and the depth of pressing is also inconsistent.
　　(2) Cause: The hot-rolled steel replaces the iron oxide scale, which remains on the surface of the steel plate after rolling.
　　(3) Prevention and elimination methods: The supply plant takes measures to prevent the surface of the hot-rolled packaging steel strip from being pressed into the oxide scale.
　　 (4) Inspection judgment: Check with naked eyes. The national standard of ordinary board and high-quality board does not allow press-in oxide scale. The general board standard stipulates that a slight oxide scale is allowed to be pressed in.