GB236242A - Improvements in method of treating and coating low grade sheet steel stock, and the resulting products - Google Patents

Abstract

236,242. Madsenell Corporation, (Assignees of Knauss, F. V.). June 27, 1924, [Convention date]. Void [Published under Sect. 91 of the Act]. Pickling.-Ferrous metal objects such as steel sheets, after treatment by an electrolytic pickling process to remove surface carbon and occluded hydrogen or other gas, are treated with sodium carbonate or other alkaline solution. The alkali is allowed to dry on and is then dissolved off with distilled water, rain water, or water slightly acidulated with hydrochloric or sulphuric acid. It is stated that the alkali treatment causes black or dark blue matter to ooze out from the metal object which is removed in the subsequent rinsing. The treated object may be coated with metal by dipping, spraying, or flowing, or may be coated with paint, vitreous enamel or baking enamel. The preliminary pickling comprises degreasing in hot caustic soda or other alkali, rinsing, and pickling in dilute sulphuric or hydrochloric acid. This is followed by washing, if acid other than sulphuric has been used, and anodic treatment in a bath of strong sulphuric acid, preferably above 84.5 per cent strength. The cathode may be of lead or of iron or steel covered with lead, or of iron or steel. A series resistance about five times that of the cell may be used. The current density is preferably 20 amps per sq. ft. of anode surface, but 5 amps. per sq. ft. or less may be used. The treatment is continued until the current falls to a constant value about one-fifth or less of the initial current. The temperature should be about 100‹ F. Hollow bodies are treated by filling with acid and inserting the cathode therein. The acid need not completely fill the body, provided the body be rotated so that the whole of the interior surface receives treatment. The body should be rinsed after treatment.