process for stellenweisen coating of ferrous materials

摘要

1,220,772. Galvanizing ferrous metal strips; cathodic pickling; electrolytic coating with chromium and chromiumoxide. STEEL CO. OF CANADA Ltd. March 14, 1969 [March 14, 1968], No. 13678/69. Headings C7B and C7F. Ferrous strip is coated with zinc by hot-dipping on one side only by first electro-depositing a chromium and hydrated chromium oxide coating containing at least 3À0 mgm per sq. foot of chromium and at least 2.0 mgm per sq. foot of chromium oxide on the side not to be coated. The coating is applied on one side by forming the strip into a U and using a tin-lead anode on the outer side of each arm of the U. The bath may be 50 to 60 g/1 chromic acid, 0À20 to 0.40 g/1 sulphuric acid, and 0.5 to 1.0 g/1 fluoboric acid. The strip is made cathodic at current densities of 200 to 300 amps. / sq. ft. The side of the strip to be galvanized may be sprayed with flux while the other side is sprayed with water to prevent flux creepage. The strip may be cathodically cleansed at a current density of 60 amps. per sq. ft. at 190‹ F. in a solution containing 70 g/1 NaOH and 20 g/1 alkali cleaner, and subsequently cathodically derusted.