Electrolytic descaling of cold rolled stainless steel strip - which alternately forms the anode and cathode in both neutral sulphate bath and nitric acid bath

摘要

The strip is subjected to alternative anodic and cathodic treatment in an aq. soln. (I) of neutral alkali salts, e.g. Na2SO4 and K2SO4; followed by alternative anodic and cathodic treatment in an aq. soln. (II) of nitric acid. A central busbar system is pref. used to supply current for both solns. (I, II). The polarity of the strip is pref. the same at the inlet and exit of both baths. Soln. (I) pref. contains 100-250 g/l Na2SO4 at 50-80 degrees C., and is used for 0.5-2 minutes with an anode- and cathode- current density (ACCD) of 4-14 A/dm2. Soln. (II) is pref. at 50-75 degrees C and contains 5-20% HNO3, and ACCD being 3-15 A/dm2 used for 0.5-2 minutes. Used for stainless steels contg. min. 11% CR and possibly other alloying metals such as Ni and Mo, and avoids the use of HF in soln. (II). The process ensures complete removal of the residual scale.