Patent GB-466661-A (GB)
Title: Process of cleaning metal surfaces
IPC: C23F1/44
Filed: 1935-10-26
Abstract: Scale, sand, grease, oil, and surface coatings such as paint, lacquer, vitreous and non-vitreous enamels, tin, zinc, and cadmium platings are removed from metal articles, e.g. ferrous, cuprous, or aluminous articles, by immersion in a molten bath comprising one or more of the alkali metal nitrates, one or more of the alkali metal carbonates and hydroxides, and a fluxing agent such as manganese dioxide or copper sulphate, the nitrate or nitrates being the preponderating constituent of the mixture.  The treated articles may be washed with water or an aqueous solution containing one or more of the substances hydrochloric acid, sulphuric acid, oxalic acid, and iron sulphate.  The molten bath forms a surface coating on the articles which forms a good base for paint, lacquer, non-vitreous and vitreous enamels and coatings of metal such as zinc, tin, cadmium, copper, or nickel.  Baths may be formed, for example, of (a) 5 parts of sodium nitrate, 5 parts of potassium nitrate, and 1 per cent of sodium hydroxide, or (b) 65 parts of potassium nitrate and 34 parts of sodium hydroxide, 0,2--10 per cent of manganese dioxide or copper sulphate being added in each case.  Directions are given showing the temperature and the duration of treatment required for removing various surface coatings.  It is stated that metal coatings removed are usually precipitated, mostly in combined form, as a sludge which can be removed, but may appear in molten metallic form.  When removing vitreous enamel the removed material may be precipitated by introducing steam.  Reference is made to the treatment of sheets, castings, and small articles such as screws, bolts, nuts, and washers.  Specifications 14462/89, [Class 82], and 464,982 are referred to.ALSO:Scale, sand, grease, oil, and surface coatings such as paint, lacquer, vitreous and non-vitreous enamels, tin, zinc, and cadmium platings are removed from metal articles, e.g. ferrous, cuprous, or aluminous articles, by immersion in a molten bath comprising one or more of the alkali metal nitrates, one or more of the alkali metal carbonates and hydroxides, and a fluxing agent such as manganese dioxide or copper sulphate, the nitrate or nitrates being the preponderating constituent of the mixture.  The treated articles may be washed with water or an aqueous solution containing one or more of the substances hydrochloric acid, sulphuric acid, oxalic acid, and iron sulphate.  The molten bath forms a surface coating on the articles which forms a good base for paint, lacquer, non-vitreous and vitreous enamels, and coatings of metal such as zinc, tin, cadmium, copper, or nickel. Baths may be formed, for example, of (a) 5 parts of sodium nitrate, 5 parts of potassium nitrate, and 1 per cent of sodium hydroxide, or (b) 65 parts of potassium nitrate and 34 parts of sodium hydroxide, 0,2-10 per cent of manganese dioxide or copper sulphate being added in each case. Directions are given showing the temperature and the duration of treatment required for removing various surface coatings.  It is stated that metal coatings removed are usually precipitated, mostly in combined form, as a sludge which can be removed, but may appear in molten metallic form.  When removing vitreous enamel the removed material may be precipitated by introducing steam.  Reference is made to the treatment of sheets, castings, and small articles such as screws, bolts, nuts, and washers.  Specifications 14462/89, [Class 82], and 464,982 are referred to.