method for pretreatment of steel surface prior to the application of ribbons of galvanic coatings

摘要

1423064 Electrolytic pickling HENKEL & CIE GmbH 22 June 1973 [26 June 1972] 29721/73 Heading C7B Steel sheet, prior to electro-plating is, after an optional preliminary cleaning, electrolytically cleaned in a 1-10 wt per cent solution at pH 13.5 of a cleansing agent which contains free caustic alkali and from 2-40 wt per cent of an alkanolamine having at least 3 free OH groups, at a temperature of 50-90‹C and a current density of 3-15A/dmSP2/SP, followed by acid pickling in HCl, H 2 SO 4 and/or HNO 3 . Solutions of NaOH and triethanolamine are specified which may contain e.g. Na 3 PO 4 , Na silicate, Na gluconate and a polyalkylenether wetting agent. The pickling bath is preferably 5-10% H 2 SO 4 optionally containing 1-5% HNO 3 together with an additive e.g. urea or amidosulphonic acid, to inhibit nitrogen oxide formation. Alternating current may be used.