Causes and solutions for pitting of cold-rolled packaging steel strip
by：Hongmei
2021-03-15
(1) Defect characteristics: There are rough surfaces or black dot-like spots on the surface of the packaging steel strip. It is in the form of stripes, dots, blocks, with partial or continuous pits of different sizes distributed in pieces, and individual black spots.
(2) Cause
①The strip steel raw material slightly presses on the iron oxide scale, and it falls off into a rough surface or unremoved residue during rolling or pickling.
②The cold-rolled emulsion is too dirty. Impurities press on the surface of the board and become black pits after annealing.
(3) Prevention and elimination methods
①The supply plant takes measures to prevent the surface of the strip steel material from pressing on the iron oxide scale.
② Frequently clean the rolling mill and replace the emulsion. Ensure that the rolling emulsion is clean.
(4) Inspection and judgment
① Check with the naked eye.
②The reverse side of the high-quality board I cyan board allows the slight pitting within one-fourth of the thickness tolerance of the board to be no greater than the minimum thickness. The two sides of the U plate are allowed to have less than one-half of the thickness Slight pitting in the smallest thickness range. Three groups of boards are allowed to have slight pits and local pits that are not greater than the minimum thickness range within one-half of the thickness tolerance. On the reverse side, slight pits that are not greater than the minimum thickness range within the tolerance range are allowed. According to the national standard of ordinary boards, local pits with a depth not greater than half of the thickness tolerance are allowed. The general board standard stipulates that local pits with a depth of not greater than 0.7 times the tolerance of the gnawing degree are allowed.
③ Local pits can be removed by grinding.
(2) Cause
①The strip steel raw material slightly presses on the iron oxide scale, and it falls off into a rough surface or unremoved residue during rolling or pickling.
②The cold-rolled emulsion is too dirty. Impurities press on the surface of the board and become black pits after annealing.
(3) Prevention and elimination methods
①The supply plant takes measures to prevent the surface of the strip steel material from pressing on the iron oxide scale.
② Frequently clean the rolling mill and replace the emulsion. Ensure that the rolling emulsion is clean.
(4) Inspection and judgment
① Check with the naked eye.
②The reverse side of the high-quality board I cyan board allows the slight pitting within one-fourth of the thickness tolerance of the board to be no greater than the minimum thickness. The two sides of the U plate are allowed to have less than one-half of the thickness Slight pitting in the smallest thickness range. Three groups of boards are allowed to have slight pits and local pits that are not greater than the minimum thickness range within one-half of the thickness tolerance. On the reverse side, slight pits that are not greater than the minimum thickness range within the tolerance range are allowed. According to the national standard of ordinary boards, local pits with a depth not greater than half of the thickness tolerance are allowed. The general board standard stipulates that local pits with a depth of not greater than 0.7 times the tolerance of the gnawing degree are allowed.
③ Local pits can be removed by grinding.
