US3806356A

US3806356A - Flux and method of coating ferrous article

Info

Publication number: US3806356A
Application number: US00275610A
Authority: US
Inventors: C Shoemaker
Original assignee: Bethlehem Steel Corp
Current assignee: BIEC INTERNATIONAL Inc A CORP OF DE
Priority date: 1972-08-09
Filing date: 1972-08-09
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23

Abstract

THIS INVENTION RELATES TO THE PROCESS OF COATING FERROUS ARTICLES BY THE MOLTEN METAL IMMERSION METHOD, MORE PARTICULARLY TO THE PROVISION OF AN AQUEOUS FLUX APPLIED TO SAID ARTICLE PRIOR TO THE METAL COATING THEREOF. SPECIFICALLY, THE PROCESS INCLUDES CLEANING THE FERROUS ARTICLES, WETTING THE SURFACES WITH AN AQUEOUS FLUX OF FLUOSILICIC ACID, WITH UP TO FOUR COMPOUNDS FROM THE GROUP CONSISTING OF HYDROCHLORIC ACID, HYDROFLUORIC ACID, POTASSIUM FLUORIDE AND ZINC CHLORIDE, DRYING SAID FLUX ON THE SURFACE, IMMERSING SAID ARTICLE IN A MOLTEN METAL BATH CONSISTING ESSENTIALLY OF AT LEAST 25% BY WEIGHT ALUMINUM, BALANCE ESSENTIALLY ZINC, AND AFTER REMOVAL FROM THE BATH, SHAKING OFF EXCESS METAL AND COOLING TO YIELD A FERROUS ARTICLE HAVING A CONTINUOUS AND ADHERENT LAYER OF SAID ALUMINUM ALLOY.

Description

United States Patent O 3,806,356 FLUX AND METHOD OF COATING FERROUS ARTICLE Carlyle E. Shoemaker, Bethlehem, Pa., assignor to Bethlehem, Steel Corporation, Bethlehem, Pa. Filed Aug. 9, 1972, Ser. No. 275,610 Int. Cl. C23c 1/08; C23f 17/00 US. Cl. 117-50 11 Claims ABSTRACT OF THE DISCLOSURE essentially of at least 25% by weight aluminum, balance essentially Zinc, and after removal from the bath, shaking off excess metal and cooling to yield a ferrous article having a continuous and adherent layer of said aluminum alloy.

BACKGROUND OF THE INVENTION This invention is directed to the concept of coating ferrous metal articles, by the hot metal immersion method, to enhance the articles appearance and resistance to corrosion attack. To effect such results, an adherent and continuous layer of a corrosion resistant material on the ferrous article is essential. The prior art using various combinations of salts and acid has met with limited success in galvanizing and aluminizing processes due to production costs, processing controls and product performance.

Typically, the ferrous article to be coated had to be cleaned of' grease and scale (oxides of iron) prior to the application of the metallic coating. In a continuous strand operation, i.e. strip or wire, the material preferably is cleaned and then bathed in an oxide reducing atmosphere, and without exposing it to the atmosphere is immediately immersed in a molten metal bath containing the coating metal. For batch operations, particularly for large structural members, atmospheric exclusion is virtually impossible. Accordingly, alternatives for protecting the cleaned surfaces were found. Generally, the procedure was to apply athin flux coating following the cleaning, and then immersing the flux coated ferrous article into the molten metal bath. Naturally, the nature of the fluxing composition is important to its effect on the ferrous base, for its ability to provide a proper surface for the reception of a metal coating, which is both continuous and adherent. Thus there is a relationship between the flux and coating metal.

While the prior art has made some significant contributions in the area of galvanizing and aluminizing, such efforts have not been totally satisfactory forpreparing ferrous surfaces for the reception of an aluminum-zinc coating. However, with the discovery of a fluosilicic acid containing flux, an effective means was found to prepare the surface of a ferrous article for subsequent coating by an aluminum-zinc alloy.

3,806,356 Patented Apr. 23, 1974 "ice SUMMARY OF THE INVENTION This invention relates to the process of coating ferrous articles by the molten metal immersion method, more particularly to the provision of a suitable aqueous flux containing fluosilicic acid for applying to the surfaces of the ferrous article prior to the metal coating thereon. In its preferred embodiment, said process includes cleaning the ferrous surfaces to remove grease, etc., pickling to remove scale, dipping directly into a flux bath containing from about 2 to about 15% by weight, H SiF with up to about a total of 25%, by weight of the flux bath, of the compounds from the group consisting of HCl, HF, KF, and Zn C1 where the quantity of said compounds depends on the alloy content of the ferrous article, drying the flux in situ, and immersing the flux coated ferrous article in a molten metal bath of at least 25% by weight aluminum, balance essentially zinc. Upon withdrawal from the molten bath, and removal of excess metal, such as by bumping, the metallic coating solidifies to produce a ferrous article having a continuous, adherent coating of an aluminumzinc alloy.

BRIEF DESCRIPTION OF THE DRAWING The figure is a flow sheet illustrating the preferred sequence of steps followed in carrying out the process of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to a more detailed review of the invention, as set forth in the illustrated flow sheet of the figure, it will be seen that the present invention provides an improved hot metal immersion coating procedure yielding a ferrous article having a continuous, adherent coating of an aluminum-zinc alloy thereon.

The coating method generally comprising wetting the cleaned scale free ferrous article with an aqueous solution containing from about 2 to 15 by weight, H SiF with up to a total of about 25 by weight, of the compounds selected from the group consisting of HCl, HF, KF, and ZnCl Following the wetting thereof, the ferrous article is dried such as by heating to a low temperature of up to about 400 F. to remove all signs of dampness. This is important, especially from a safety standpoint, to avoid splashing of the subsequently applied molten coating metal.

The dry flux coated ferrous article is then immersed for from 2 to about 5 minutes, depending on the depth of metallic coating desired, in a molten metal bath containing at least 25 by weight, aluminum, preferably up to about balance essentially zinc. After removal, excess coating metal is removed, such as bumping or agitating the coated ferrous article, where it may be cooled by air or water quenching. The resulting product exhibits a continuou's, adherent alloy coating on the processed ferrous article.

At this juncture, it should be made clear that as used herein, the term article is intended to include strip and wire (treated in a continuous manner), and shapes, such as structural members treated in a batch process. Actually, the greatest benefits from this invention are realized in the batch treatment of ferrous shapes, such as large structural steel members used in the construction industry. Though not limiting, the further description and exemplary showings shall be directed to batch operations.

Optimum results, particularly in the treatment of alloy structural steels, were observed with fluxing compositions containing from about 4.0 to 8.0%, by weight, H SiF 3 .7 r :4 and about 5.0 to 20.0%, by weight, of a plurality of the consisting essentially of fluosilicic acid, and up to four remaining compounds listed above. For example, from compounds from the group consisting of hydrochloric acid the standpoint of coating coverage, adherence and appearhydrofluoric acid, potassium fluoride and zinc chloride, ance, a preferred fiuxing composition is as follows: removing said article from the aqueous acidic figx, drying q said article by heating to a low temperature, an immersg g Percent by g 5 ing the article in a molten bath containing said aluminumi 6 zinc coating alloy. KF The method claimed in claim 1 wherein the fluozncl d L8 silicicacrd is present in amount between about 2 to V Balance 10 by weight, of said aqueous flux.

- n V 3. The method claimed in claim 2 wherein at least one To further illustrate the effectiveness of the fluxing comof said four compounds is present up to a total amount of position on surface coverage, evaluations were made on by weight, of said aqueous flux. two common grades of structural steel, with variations in 4. The method claimed in claim 2 wherein said fluofiux composition. The said variations are listed in Table I, 15 silicic acid is present in an amount between about 4 to 8%. with the results in Table II. 5. The method claimed in claim 4 wherein at least one TABLE I Flux baths, weight percent A B C D E F G H J K L M N P Q Components:

TABLE II Percent surface covered, 5 minutes dip A B C D E F G H .T K L M N P Q While it may be gleaned from the foregoing tabulaof said four compounds is present in an amount between tion, as it pertains to alloyed steels, optimum results or about 5 to 20%, by weight, of said aqueous flux. surface coverage were noted with the richer fluxes, i.e. 6. The method claimed in claim 5 wherein a plurality those containing a plurality of said compounds. However, of said four compounds are present in said aqueous flux. with leaner ferrous articles, such as mild or low carbon 7. The method claimed in claim 5 wherein at least steels, simpler flux combinations, with the components 40 three of said four compounds are present in said aqueous named, may be formulated. flux.

For instance, aqueous fluosilicic acid may be used alone 8. A flux for the treatment of a ferrous article prior to or in combination with only one or two of the remaining its immersion in a molten bath containing an aluminumcomponents. Some combinations which have been found zinc alloy, comprising an aqueous acidic solution consuitable for mild carbon steel sheet and strip are listed sisting essentially of from 2 to 15%, by weight, of fluobelow. silicic acid, and a total of from 5 to 20%, by weight, of

' at least one compound selected from the group consisting TABLE In of hydrochloric acid, hydrofluoric acid, potassium fluoride, and zinc chloride. f if g gg 9. The flux claimed in claim 8 wherein said fluosilicic N P Q acid is present in an amount between about 4 to 8%.

10. The flux claimed in claim 9.wherein a plurality of said four compounds are present in the aqueous fluxQ i jjj"jjj 11. The flux claimed in claim 10 wherein at least three g 10 of said four compounds are present in the aqueous flux. I

References Cited Since the foregoing represents the preferred embodi- U ITE STATES PATENTS merits of this invention, it is contemplated that variations 2 571,737 3 1954 jominy et 1 1172.51 may be effected herein by those skilled in the art, par- 2 907 104 1 959 Brown et 1 9 ticularly after reading these specificatiions. accordingly, 2 174 551 10 1939 Cinamon et 1 117 5.2 no limitation is intended to be impose on t 's invention except as set forth in the appended claims. FOREIGN PATENTS 1 l i 1,025,603 4/1966 Great Britain 117-52 1. A method of forming a continuous alloy coating consisting of from 25% to about by weight alumi- RALPH KENDALL, Pflmafy Exflmlller num, balance essentially zinc, on a ferrous article, com- W. BALL, Assistant Examiner prising the steps of cleaning said ferrous article to re- U S C1 XR move grease and oxides from the surfaces thereof to be 70 coated, immersing said article in an aqueous acidic flux 117 -50, 114 C, 114 A; 14823