Abstract
In the commercial production of striped, partially Sn pre-coated TFS-CT (Tin Free Steel-Chromium Type), it is very important to control the amount of metallic Cr deposited on the tin and bare Fe. On the basis of the fundamentally electrochemical behavior of Sn and Fe in a Cr plating bath, a technique for controlling the amount of metallic Cr on a continuous plating line is disclosed.
The following results were obtained;
1) It was possible to achieve control of the coating amount of metallic Cr on Sn and Fe on an industrial scale using a method involving low current density at the front plating cells and high current density at the rear cells.
2) If the reductive removal of Sn-oxide film grown by aging after Sn preplating is incomplete, Cr coverage becomes insufficient and a brownish discoloration of Sn occurs. This may be avoided by applying a cathodic dichromate treatment after Sn plating, and by adjusting the Cr plating current density.
