Electrochemical Approach to the Conductor-Roll Dent Problem in a Reel-to-Reel Strip Electroplating Line

In a continuous reel-to-reel strip electroplating apparatus, electrical current is fed to a moving cathode strip through a conductor-roll in contact with the strip. Dent defects are occasionally induced on the strip surface from a irregular surface texture on the conductor-roll generated by non-uniform metal deposition onto the conductor-roll in the vicinity of the up-stream contact line area. We attempted numerical simulation of metal electrodeposition onto a conductor-roll in a thin drag-out electrolyte close to the contact line. The overall approach of the model was to treat the system as a problem of secondary current distribution, using measured electrochemical kinetics as the boundary conditions in binary alloy electrodeposition, under the assumption that the mass-transport effect is of minor importance. The potential posed on the domain thus obeys Laplace's equation, and the boundary conditions apply as non-linear functions determined by the anodic and/or cathodic polarization curves. An electrogalvanized steel sheet was used as the anode and a hastelloy sheet as the cathode. Using contact resistance between strip and couductor-roll, electrolyte resistance, strip ohmic resistance, difference in equilibrium potential, and activation overpotential, as the process variables pertaining to metal deposition on the conductor-roll, the electrodeposition rate onto a couductor-roll surface was numerically simulated for a zinc-nickel alloy electrodeposition system.