SURFACE BLACKENING METHOD OF STEEL PLATE OR STEEL STRIP

摘要

PURPOSE:To enhance the heat radiation efficiency at the annealing by dipping a steel plate into an aqueous tannic (acid) solution containing cationic surface active agent and applying the specific voltage to form a black film on the surface. CONSTITUTION:In continuously annealing a cold rolled steel plated, it is beforehand dipped in a treating bath composed of an aqueous tannic (acid) solution added with cationic surface active agent to let it be coated electrolytically with a black film of tannin iron. If at this time the steel plate surface has been degreased and cleaned, applying of DC voltage to the steel plate as cathode suffices. In the case of treating the same held deposited with rolling oil, it is necessary to apply the controlled asymmetrical AC voltages by using a counter electrode having such rectifying action by which the steel plate is biased to negative or to apply the AC voltages seperposed with DC voltage in the direction where the steel plate biases to negative, as a result of which the oil components disappear when the steel plate is polarized to negative and tannin iron forms and deposits when it is polarized to positive.