Defects in Rolling

ย Defects in Rolling

Defects may be present on the surfaces of rolled plates and sheets, or there may be internal structural defects. Defects are undesirable not only because they compromise surface appearance, but also because they may adversely affect strength, formability, and other manufacturing characteristics. Several surface defects (such as scale, rust, scratches, gouges, pits, and cracks) have been identified in sheet metals. These defects may be caused by inclusions and impurities in the original cast material or by various other conditions related to material preparation and to the rolling operation. Wavy edges on sheets are the result of roll bending. The strip is thinner along its edges than at its center); thus, the edges elongate more than the center. Consequently, the edges buckle because they are constrained by the central region from expanding freely in the longitudinal (rolling) direction. The cracks are usually the result of poor material ductility at the rolling temperature. Because the quality of the edges of the sheet may affect sheet-metal-forming operations, edge defects in rolled sheets often are removed by shearing and slitting operations. Alligatoring is the phenomenon and typically is caused by non uniform bulk deformation of the billet during rolling or by the presence of defects in the original cast material.

Defects in Rolling: (a) wavy edges; (b) zipper cracks in the center of the strip; (c) edge cracks; and (d) alligatoring
(a) wavy edges; (b) zipper cracks in the center of the strip; (c) edge cracks; and (d) alligatoring

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