MANUFACTURE OF STAINLESS STEEL STRIP GALVANIZED WITH ZN OR ZN-NI ALLOY

摘要

PURPOSE:To improve the adhesive strength of plating, by applying activating treatment to a plating surface and regulating the acid condition of a bath to a specific pH value or below at the time of electroplating Zn or Zn-Ni alloy on a stainless steel strip. CONSTITUTION:The surface of a stainless steel strip is subjected, after degreasing stage, to activating treatment, to which electroplating is applied in a galvanizing bath or Zn-Ni alloy galvanizing bath in which pH values are regulated to =3.5, respectively. As the above activating treatment, immersion treatment in a 0.5-40wt.% aqueous solution of sulfuric acid of 25-90 deg.C or in a 1-100wt.% aqueous solution of sulfuric acid of 50-90 deg.C or cathodic electrolytic treatment is preferred. This activating treatment is important, and, no matter how properly the degreasing and plating stages before and after the above activating treatment are performed, adhesive strength of plating cannot be improved unless the surface of the steel strip is activated. Moreover, when pH exceeds 3.5, the adhesive strength of plating is deteriorated regardless of whether the bath is of chloride or of sulfate, even though proper activating treatment is applied.