THE EFFECT OF A SURFACE OXIDE LAYER OF ELECTROLYTIC TIN PLATE ON THE FRICTIONAL-PROPERTIES DURING THE IRONING OPERATION OF A 2-PIECE CAN-MAKING PROCESS

Nonpassivated electrolytic tin plates without conventional chemical tr eatment self-oxidize in ambient atmosphere and form a yellow stain on the outermost surface during long-term storage. The degree of yellowne ss of the stain increased linearly with the oxide thickness due to the interference color of SnO2. Even though the thickness of the oxide la yers was very thin, less than 100 Angstrom, it exerted an undesirable influence on the can-making processes, particularly the stripping beha vior after ironing. Investigations were carried out on the morphologie s of the coating layers, the changes in oxide thickness during success ive can-making processes and the average friction coefficients with th e different oxide thickness. These oxide layers were broken up and dis tributed within the bulk tin coating during the ironing process. This redistribution of the oxide layer prevented smooth pressing-aside of t he tin coating layers, resulting in an increase in the ironing frictio n coefficient. As the friction coefficient was increased, the residual stress along the can wall thickness (i.e. the hoop stress) was also i ncreased, Due to both the oxide layer accumulation, which increased th e friction coefficient and the hoop stress, can stripping efficiency w ithout roll-back was reduced. (C) 1998 Elsevier Science S.A.