SURFACE BLACKENING METHOD OF STEEL PLATE OR STEEL STRIP

摘要

PURPOSE:To achieve the reduction in annealing time by dipping an ungreased steel plate as one pole into a tannin-contained electrolytic bath and supplying current under the specific conditions thereby forming a black film on the steel plate surfaces. CONSTITUTION:At the time of subjecting a cold rolled steel plate to continuous annealing treatment, it is dipped with its rolling oil being held unremoved into the aqueous solution containing tannin or tannic acid. Next, if DC voltage and AC voltage are applied simultaneously and in the direction where a positive DC bias is applied to the steel plate, between the steel plate and counter electrode, then the oil contents are removed when the steel plate surfaces are polarized to negative and tannin or tannic acid deposits thereon when they are polarized to positive, whereby the black film of a uniform thickness is formed. Thereby, the thermal efficiency in the next annealing process is enhanced considerably and the annealing time may be reduced.