US2791525A

US2791525A - Composition for and method of forming oxalate coatings on ferrous metal surfaces

Info

Publication number: US2791525A
Application number: US390734A
Authority: US
Inventors: Rausch Werner; Mayr Arthur
Original assignee: Parker Rust Proof Co
Current assignee: Parker Rust Proof Co
Priority date: 1952-11-11
Filing date: 1953-11-06
Publication date: 1957-05-07
Anticipated expiration: 1974-05-07

Description

United States Patent 2,791,525 COIVIPOSITION FOR AND METHOD OF FORMING OXALATE COATINGS 0N FERROUS METAL SURFACES Werner Rausch, Frankfurt am Main, and Arthur Mayr, Frankfurt am Main Sossenheim, Germany, assignors to Parker Rust Proof Company, Detroit, Mich, a corporation of Michigan No Drawing. Application November 6, 1953, Serial No. 390,734

Claims priority, application Germany November 11, 1952 12 Claims. (Cl. 148-6.14)

The present invention relates to compositions for and a method of producing firm, adherent oxalate coatings on ferrous metals which serve as an excellent surface protector during metal deformation operations and which are also suitable as a base for paint.

Various processes for the formation of ferrous oxalate coatings on iron and steel surfaces have been known and used for many years. Boiling oxalic acid was early proposed for this purpose and improved upon somewhat later by the employment of oxidizing agents, such as sulfites and peroxides. A number of other special additives have been proposed to increase the rate of reactivity of aqueous oxalic acid solutions on metals which are difficult to coat, such as stainless steel, including the ferric ion, and the halides. It has also been proposed to form oxalate coatings on iron, steel and stainless steel by the use of aqueous solutions containing oxalic acid, alkali metal phosphate and a chromate.

Most of the heretofore known ferrous oxalate coatings have been relatively soft and contain a large proportion of dust as an outer layer. Soft dusty coatings are useful and serve as an effective parting layer between the die and the metal in metal deformation operations. However, such soft, dusty oxalate coatings are insufficiently adherent to be effective in all types of metal deformation, being of least value where the deformation is extreme. While the inclusion in aqueous oxalic acid solutions of alkali metal phosphates and chromates improves the ad herence of the resultant coating, the most adherent coatings are formed only as the pH value of the operating solution is allowed to increase toward about 3.0. At such pH values the operating solutions have a tendency to produce undesirable quantities of sludge.

It is the primary object of the present invention to provide a composition which will produce on a metallic sur' face contacted therewith a firmly adherent oxalate coating while producing practically no sludge in the operating solution.

Another important object is to provide a method for forming firm adherent oxalate coatings on ferrous surfaces which are relatively free of dust and especially suitable for use in deformation operations, or as a base for paint, Varnish, lacquer, enamel or other conventional finish coating.

A further objective of this invention is to provide a method for forming oxalate coatings on ferrous surfaces which is easily controlled, inexpensive to operate and which produces a minimum of undesirable sludge.

A still further object is to provide a replenishing material suitable for maintaining such compositions at proper strength during continuous processing.

Other objects and advantageous features of this inven tion will become apparent upon considering the present disclosure in its entirety.

In accordance with the present invention, the above and related objects are achieved by the use in aqueous oxalic acid solutions of the fluoborate ion in conjunction with a suitable oxidizing agent. Optionally the compositions ice of this invention may include the aluminum ion. The presence of the aluminum ion has been found to produce coatings on ferrous surfaces having higher adherence than is obtainable in its absence, and the preferred compositions of this invention include the aluminum ion.

The fluoborate ion may be introduced into an aqueous oxalic acid solution in various forms such as fiuoboric acid or the alkali metal salts thereof, for example, the sodium or potassium fluoborates, the salt form being preferred.

Oxidizing agents which are capable of oxidizing the ferrous ion to the ferric ion in an aqueous oxalic acid solution Without concurrently oxidizing the oxalic acid may be satisfactorily used for the purposes of this invention. Suitable oxidizing agents include the chlorates, bromates, iodates, nitrites and hydrogen peroxide. Unusually strong oxidizing agents such as permanganate and nitrate are not recommended for use because of their tendency to rapidly oxidize the oxalic acid. Similarly, the relatively Weak oxidizing agents such as the organic nitro compounds including sodium meta nitro benzene sulfonate, picric acid, etc. are not nearly as desirable as chlorates, 'brornates, nitrites and peroxide'although some limited benefit may be obtained from their use.

The presence of both the fluoborate ion and a suitable oxidizing agent in the aqueous oxalic acid solutions of this invention enables the operation of the solutions at pH values well below that usually employed when phosphoric acid is present as an ingredient in such solutions, and for best results it is advisable to maintain the pH of the operating solution in the range of 0.7 to 2.0 and preferably in the range of 1.0 to 1.3. Under such conditions the resultant coating is firm, adherent and relatively free of dust, and even after extended continuous operation there is only an extremely minor amount of sludge formed in the operating solution. 1

Broadly, the proportion of the ingredients which are suitable for use in the aqueous compositions of this invention are set forth in Table I.

TABLE I Concentration grams/liter Fluoborate ion (BFr) 1.6-12.0 Chlorate ion (C10?) ODS-2.0 Oxalic acid 5-15 The other oxidizing agents indicated above to be suitable for use may be employed in suitable quantities to produce equivalent oxidizing of the ferrous to ferric ion in the solution. For the bromates and iodates approximately the same quantity is required as that indicated for chlorates, while somewhat smaller numerical quantities of nitrites and peroxide are satisfactory.

For the production of oxalate coatings on ferrous surfaces with the solutions of the type set forth in Table I having the highest order of adherence it is desirable to incorporate in such solutions a proportion of the aluminum ion between about 0.3 gram/liter and about 1.6 grams/liter. The aluminum ion may be introduced in the form of an aluminum salt such as aluminum sulfate or aluminum oxalate. Care should be taken however, in introducing aluminum not to concurrently introduce an undesirable anion such as nitrates or chlorides. The presence of chloride has been found to be undesirable, and nitrates are incompatible with the oxalic acid.

In general the method of this invention comprises the steps of contacting a preliminarily cleaned metallic surface with the compositions of this invention at a suitable temperature and for a suitable time, separating the part from the solution, rinsing and drying the coating. Thereafter, and if desired, the coating may be either oiled in a conventional manner to further enhance the corrosion resistance or it may be painted, varnished, lacquered, enameled or coated with other siccative finishcoating. Additionally, the coating may be treated with lime or other lubricants conventionally employed for such purpose, such as soaps, and the coated part thereafter subjectcd to deformation. Even without subsequent treatment after rinsing, the coatings of this invention have proved to be very effective in the deep extrusion of sheet iron, pipes, tubes and wires. The temperature of the solution and time of contact are not critical, and a wide variety of conditions may be satisfactorily used. Temperatures between about 90 F. and 160 F. and times between about 3 and 15 minutes may be employed. One of the advantageous features of this invention is that relatively low temperatures such as 105 F. to 120 F. produce more adherent coatings than higher temperatures. Preferred operating conditions are at temperatures of 105 F.-l20 F. for to minutes.

The compositions and method of this invention are illustrated in greater detail in the following examples.

Example 1 A 1 liter solution was prepared containing 5 grams sodium fluoborate, 5 grams aluminum sulfate -18H2O, 10 grams oxalic acid -H2O, 2 grams sodium chlorate. Low carbon steel panels having a surface area of 128 square inches, preliminarily degreased and pickled in cold hydrochloric acid were inserted in the solution at 113 F. for 5 minutes and withdrawn. The pH of the solution was between 1.0 and 1.2. 50 such panels were inserted in this solution and all of the panels upon withdrawal were found to be coated with a firm, adherent, greenishgray colored coating. A check on the surface weight of the coatings showed an average of 418 mg./sq. ft. Periodic checking during the processing to maintain the concentration of the ingredients at the initial levels required the addition of 16.6 grams of oxalic acid -2Hz0 and 6 grams of sodium chlorate.

A more complete check on the depletion of the ingredients showed that the ingredients were depleted at the following rates:

Oxalic acid -2Hz0 1 lb./1000 sq. ft. Sodium chlorate .4 lb./ 1000 sq. ft. Aluminum sulfate -18H2O .15 lb./1000 sq. ft. Sodium fluoborate .16 lb./ 1000 sq. ft.

A concentrated replenishing material which was found to be suitable for maintaining the ingredients within the above prescribed ranges of proportions was prepared having the following composition by weight: 6667% oxalic acid -2H2O, 17% sodium fluoborate, 15-17% aluminum sulfate -18H2O. This concentrate may be added periodically as necessary.

Example 2 A 200 liter bath was compounded and analyzed to contain the following: 5 grams/liter sodium fluoborate, 10 grams/liter oxalic acid -2H2O, 5 grams/liter aluminum sulfate 181-120, and 2 grams/liter sodium chlorate. The bath was maintained at about 110 F. and was used for immersing steel wires having a Mohs scale hardness of about 5 and a diameter of about .08 inch. The wires were preliminarily pickled in cold hydrochloric acid and water rinsed before immersion in the heated oxalate solution for about 10 minutes. The wire was withdrawn, cold water rinsed, dipped in a dilute lime suspension and dried at 110 C. The coated wire was then drawn on multiple extrusion machines in a series of 8 drawings to reduce the diameter to .031 inch, a total decrease of 84%, at a velocity of 315 feet per minute. The surface of the wire was inspected after drawing and found to be uniformly smooth. After drawing 1100 pounds of wire, very little wear could be detected on the Surface of the extrusion dies.

1 Example 3 An oxalate solution was prepared having the composition of that set forth in Example 2 and 10 steel tubes 2.6 feet long were immersed in the solution at 113 F. for 10 minutes and withdrawn. The surface of the tubes was covered with a firmly adherent, dark oxalate coating. After drying, the tubes were treated with dry soap and two of the tubes were drawn dry and two of the tubes were drawn wet in 4 passes to obtain a decrease in crosssection of 72%. The surfaces of all tubes after drawing were uniformly smooth and free from slivers or breaks.

What is claimed is:

l. A composition for forming oxalate coatings on metallic surfaces which comprises an aqueous solution consisting essentially of about 1.6 to about 12 grams per liter of the fluoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion and about 5 to'about 15 grams/liter of oxalic acid, said composition having a pH in the range of 0.7 to 2.0.

2. A composition of matter which comprises an aqueous solution consisting essentially of about 1.6 to about 12 grams/liter of the fluoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion, about 0.3 to about 1.6 grams/ liter of the aluminum ion and about 5 to about 15 grams/liter of oxalic acid, said composition having a pH. in the range of 0.7 to 2.0.

3. A replenishing material for replenishing an aqueous solution comprising oxalic acid, the fluoborate ion and the aluminum ion which material consists of in percentage by weight: 66%-67% oxalic acid dihydrate, 15% 17% sodium fluoborate, 15 %17% aluminum sulfate 131-120.

4. A method for forming an oxalate coating on metallic surfaces which comprises the steps of contacting the metal surface to be coated with an aqueous composition consisting essentially of about 1.6 to about 12 grams/liter of the fluoborate ion, about 0.08-about 2.0 grams/liter of the chlorate ion and about 5 to about 15 grams/liter of oxalic acid, said composition having a pH in the range of 0.7 to 2.0.

5. A method for forming an oxalate coating on metallic surfaces which comprises the steps of contacting the metal surface to be coated with an aqueous composition consisting essentially of about 1.6 to about 12 grams/liter of the fluoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion, about 0.3 to about 1.6 grams/liter of aluminum ion and about 5 to about 15 grams/liter of oxalic acid, said composition having a pH in the range of 0.7 to 2.0.

6. A method for deforming metal which comprises the steps of contacting the metal surface to be drawn with an aqueous composition consisting essentially of about 1.6 to about 12 grams/liter of the fluoborate ion, about 0.08 to about 2.0 grams/ liter of the chlorate ion and about 5 to about 15 grams/liter of oxalic acid, said composition having a pH in the range of 0.7 to 2.0, drying the coating grams/liter to about 12 grams/liter of the fluoborate ion,

about 0.08 to about 2.0 grams/ liter of the chlorate ion and about 5 to about 15 grams/liter of oxalic acid, said composition having a pH in the range of0.7 to 2.0, treating the coating with a lubricant, drying the coating on the metal surface and thereafter deforming the coated metal.

8. A method for deforming metal which comprises the steps of contacting the metal surface to be drawn with an aqueous composition consisting essentially of about 1.6 to about 12 grams/liter of the fluoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion, about 5 to about 15 grams/liter of oxalic acid and about 0.6 to about 1,6 grams/liter of the aluminum ion, said composition having a pH in the range of 0.7 to 2.0, drying the coating on the metal surface and thereafter subjecting the coated metal to deformation.

9. A method for finishing metallic surfaces which comprises the steps of contacting the metal surface to be finished with an aqueous solution consisting essentially of about 1.6 to about 12 grams/liter of fiuoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion, and about grams/liter to about 15 grams/liter of oxalic acid, said composition having a pH in the range of 0.7 to 2.0, and thereafter covering the coated metal with a siccative coating.

10. A method for finishing metallic surfaces which comprises the steps of contacting the metal surface to be finished with an aqueous solution consisting essentially of about 1.6 to about 12 grams/liter of fiuoborate ion, about 0.08 to about 2.0 grams/liter of the chlorate ion, and about 5 grams/liter to about 15 grams/liter of oxalic acid and about 0.3 to about 1.6 grams/liter of the aluminum ion, said composition having a pH in the range of 0.7 to 2.0, and thereafter covering the coated metal with a siccative coating.

11. A composition of matter which comprises an aqueous solution consisting essentially of about 1.6 to about 12 grams/liter of the fluoborate ion, about 5 to about 15 grams/ liter of oxalic acid and at least one oxidizing agent selected from the group consisting of chlorates,

bromates, iodates, nitrites and hydrogen peroxide in an amount suflicient to produce an equivalent oxidizing efiect as that produced by about 0.08 to about 2.0 grams/liter of the chlorate ion, said composition having a pH in the range of 0.7 to 2.0.

12. A method for forming an oxalate coating on metallic surfaces which comprises the steps of contacting the metal surface to be coated with an aqueous composition consisting essentially of about 1.6 to about 12 grams/ liter of the fluoborate ion, about 5 to about 15 grams/ liter of oxalic acid and at least one oxidizing agent selected from the group consisting of chlorates, bromates, iodates, nitrites and hydrogen peroxide in an amount sufi'icient to produce an equivalent oxidizing effect as that produced by about 0.08 to about 2.0 grams/liter of the chlorate ion, said composition having a pH in the range of 0.7 to 2.0.

References Cited in the file of this patent UNITED STATES PATENTS 2,066,842 Lodeesen Jan. 5, 1937 2,081,449 Cook May 25, 1937 2,273,234 Tanner Feb. 17, 1942 2,500,673 Gibson et al. Mar. 14, 1950 2,669,532 Gibson Feb. 16, 1954 2,672,976 Overath et al. Mar. 23, 1954

Claims

1. A COMPOSITION FOR FORMING OXALATE COATINGS ON METALLIC SURFACES WHICH COMPRISES AN AQUEOUS SOLUTION CONSISTING ESSETIALLY OF ABOUT 1.6 TO ABOUT 12 GRAMS PER LITER OF THE FLUOBORATE ION, ABOUT 0.08 TO ABOUT 2.0 GRAMS/LITER OF THE CHLORATE ION AND ABOUT 5 TO ABOUT 15 GRAMS/LITER OF OXALIC ACID, SAID COMPOSITION HAVING A PH IN THE RANGE OF 0.7 TO 2.0.