Patent GB-466662-A (GB)
Title: A process of cleansing and coating metal articles
IPC: C23C22/70
Filed: 1935-10-26
Abstract: Metal articles, particularly ferrous or cuprous articles, are cleaned by subjecting them to the action of a molten bath containing not less than about 30 per cent by weight of one or more alkali metal phosphates, with or without one or more of the alkali metal nitrates, carbonates, and hydroxides, and with or without one or more fluxing agents such as manganese dioxide or copper sulphate.  For cleaning copper brass, or bronze, the bath preferably contains an alkali metal phosphate and hydroxide in about equal proportions, while for cleaning ferrous metals there is preferably at least 66 per cent of phosphate in the bath. Manganese dioxide or copper sulphate is preferably added in an amount between 0,5 and 10 per cent to increase the fluidity of the bath.  An example gives a bath comprising 4 parts of trisodium phosphate, 1 part of sodium hydroxide, and 1 part of potassium nitrate.  By adjusting the temperature and composition of the bath and the duration of treatment, grease, oil, sand, scale, paint, lacquer, vitreous or non-vitreous enamel, and metallic coatings such as tin, zinc, and cadmium platings may be removed from the articles.  In removing metal coatings, the removed metal is usually precipitated in combined form as a sludge.ALSO:Metal articles, particularly ferrous or cuprous articles, are cleaned and given a corrosion-resistant surface coating by subjecting them to the action of a molten bath containing not less than about 30 per cent by weight of one or more alkali metal phosphates, with or without one or more of the alkali metal nitrates, carbonates, and hydroxides, and with or without one or more fluxing agents such as manganese dioxide or copper sulphate. For treating copper, brass, or bronze the bath preferably contains an alkali metal phosphate and hydroxide in about equal proportions, while for treating ferrous metals there is preferably at least 66 per cent of phosphate in the bath.  Manganese dioxide or copper sulphate is preferably added in an amount between 0,5 and 10 per cent to increase the fluidity of the bath.  An example gives a bath comprising 4 parts of trisodium phosphate, 1 part of sodium hydroxide, and 1 part of potassium nitrate.  By adjusting the temperature and composition of the bath and the duration of treatment, grease, oil, sand, scale, paint, lacquer, vitreous or non-vitreous enamel, and metallic coatings such as tin, zinc, and cadmium platings may be removed from the articles.  In removing metal coatings, the removed metal is usually precipitated in combined form as a sludge but in some cases it appears in the molten state.  In addition to cleaning the articles, a very thin corrosion-resistant surface coating is formed which is a good base for coatings of paint, lacquer, enamel, metal, &c.  The molten bath may, particularly when used at temperatures of 600-900 DEG  F., be employed to anneal the articles and in certain cases it may be heated above 900 DEG  F., for example to 1200 or 1500 DEG  F., to heat treat the articles to remove internal stresses.  After treatment in the molten bath the metal is washed either with water or with a neutralizing solution containing hydrochloric, sulphuric, or oxalic acid or iron sulphate, or first with water and then with the neutralizing solution.  To colour and reinforce the coating obtained in the molten bath, it may then be dipped in an aqueous solution containing one or more colouring agents such as hemotoxylin, iron sulphate, nigrosine, or tannic acid.  The treatment of plates, castings, screws, bolts, nuts, washers, &c. is referred to.