The effect of a surface oxide layer of electrolytic tin plate on the frictional properties during the ironing operation of a two-piece can-making process

Abstract

Nonpassivated electrolytic tin plates without conventional chemical treatment self-oxidize in ambient atmosphere and form a yellow stain on the outermost surface during long-term storage. The degree of yellowness of the stain increased linearly with the oxide thickness due to the interference color of SnO 2. Even though the thickness of the oxide layers was very thin, less than 100 Å, it exerted an undesirable influence on the can-making processes, particularly the stripping behavior after ironing. Investigations were carried out on the morphologies of the coating layers, the changes in oxide thickness during successive can-making processes and the average friction coefficients with the different oxide thickness. These oxide layers were broken up and distributed within the bulk tin coating during the ironing process. This redistribution of the oxide layer prevented smooth pressing-aside of the tin coating layers, resulting in an increase in the ironing friction coefficient. As the friction coefficient was increased, the residual stress along the can wall thickness (i.e. the hoop stress) was also increased. Due to both the oxide layer accumulation, which increased the friction coefficient and the hoop stress, can stripping efficiency without roll-back was reduced.