アルミニウムDI缶の黒すじ発生機構

抄録

It is revealed that the bleed-through defect occurrs in drawing and redrawing operation and not in ironing operation. The ironed and drawn sidewall surfaces of many can samples are examined by scanning electron microscopy. The dull and fissured surface with a lot of micro aluminum flakes is observed on the bleed-through defect. Lubrication conditions in drawing operation on the degree of the defects are investigated to give the results that the bleed-through defect is affected by viscosity and concentration of lubricant, and pressure between tools and the surface of materials used. The bleed-through defect on aluminum D&I cans is caused primarily by lack of lubrication on the deforming metal in drawing and redrawing process. On the basis of the above results and micrographs of sidewall of cups and redrawn samples by SEM, a model of a formation mechanism of the bleed-through defect is suggested as follows. Numerous small debris from ledges of material surface are created in the deficiency state of lubricant, and then those debris embeded into the surface of the material produce a dull and fissured surface observed optically as dark stripes. According to the model, it is assumed that the asperities of the surface of materials, in conjunction with other variables such as applied cupping lubricants, tooling and forming speed should influence the occurrence of bleed-through defects.