US2271374A - Process of coating metal surfaces - Google Patents

Description

-Patented Jan. 21, 11942 UNITED STATES PATENT :OFFICE PROCESS OF COATING METAL SURFACES Cecil J. MacKay, Montreal, Quebec, Canada, as-

. signor to Rust Proofing,

Company of Canada,

Limited, Montreal, Quebec, Canada, a corpora tion of Canada No Drawing.' ippuaaonm, 14, 1939, Serial No. 284,557. In Canada August 13, 1935 16 Claims. (CI. 148-6) This invention relates broadly to the treatment of metal articles for the preparation of the metal surfaces to resist rusting or corrosion and to recel've surface coatings of various sorts and in some cases for Sthe improvement of characteristics tion is a continuation in part ofmy prior application Ser. No. 36,217, filed August 14,.1935, re- "sulting in Patent 2,244,526, June 3, 1941.

The primary object of the invention is to pro,- vide a process of treating surfaces of iron, steel, ferrousalloys, copper and cuprous alloys to render themresistant to rusting; oxidation and cor rosion and'better adapted to receive and-retain surface coatings such as paint, lacquer and nonimmersing the articles to be treated in baths of .-of the metal articles, and the present applicavitreous enamels (either natural or synthetic resin or celluloslc): vitreous enamels and all manner of metal coatings whether deposited electrolytically or by hot dipping, rolling, tumbling or spraying processes.

Another object is to provide a process of imparting to metal articles a flnish'which does not interfere with electric or acetylene welding or 1 brazing and which serves to diminish or inhibit electrolytic action between different metals.

' Various other objects and the advantages of the invention may be ascertained from the following description.

In its broadest aspect, the invention comprises,

firstly, subjecting the articles to be treated to. the action of a molten coating agent comprising an alkali metal phosphate or mixture of alkali metal phosphates with the addition of one or more of the alkali metal nitrates, and, if desired, with the further addition of alkali metal carbonate. To any of these mixtures therevmay be added an oxygen carrying agent, a fluxing agent or a stabilizing agent; secondly, treating the articles with a neutralizing solution and thirdly and optionally treating the articles with a-colouring, sealing andfinishing solution. The articles may bewashedwith water as may be desired or necessaryw between the several treatments.

More particularly, the invention comprises the features and combinations of featuresherein (118- closed together with all such modifications thereof and substitutions of equivalents therefor as are within the scope of the appended claims.

The treatment is effected fnost conveniently by stripping and coat- The molten bath is'composed essentially of an alkali metal phosphate or mixture of alkali metal phosphates in admixture with one or more of the.alkali metal nitrates, and hydroxides, and if desired, alkali metal carbonate, with or without b'ath fluxing, or stabilizing agents, or both. For treating iron, steel and ferrous alloys, it is preferred that the predominant constituent of the bath be a mixture of alkali-metal phosphate,

with one or more of the alkali metal nitrates and possibly alkali metal carbonate, and that the alkali metal hydroxides, if used at all, be present 'in minor proportion; but for treating copper,

brass and bronze, it is preferred that alkali metal phosphate or mixtures thereof with alkali metal nitrate or nitrate and carbonate, and an alkali metal hydroxide or mixture of alkali metal hydroxides be present'in about equal proportions.

Thus, for treating iron, steel and ferrous alloys,

66% or more of the molten bath is preferably,

composed of mixtures of alkali metal phosphate with one or more of the alkali metal nitrates and carbonates and the remainder, being 34% or less,

' is composed of one or more of the alkali metal The invention is primarily intended to provide a durable and attractive surface finish on ferrous and cuprous and aluminous metallic articles, in-

dependently of any other. surface coating and which-flnish is resistant to rusting, oxidation and corrosion oi the metal'and forms an improved foundationfcr other surface coatings.

hydroxides. .For treating copper and its alloys, the bath is composed preferably of about of a mixtureof alkali metal phosphate with one or more of the alkali metal nitrates and carbonates and about 50% of alkali metal hydroxide. The addition of a small proportion of manganese dioxide .or crystalline copper sulphate asa fliix improves the fluidityof the bath and thus reduces the loss-through dragout on the articles treated.

The manganese dioxide has oxidizing andalso catalytic or accelerating action. The amount of either manganese dioxide or copper sulphate should be between 0.5% and 10% of the bath and preferably is about.1% or 2%. Copper sulphate appears also to have a stabilizing effect on the bath, especially at higher temperatures.

n it is desired'to impartthe most eflective rust and corrosion retarding finish to the surface of" the metal, the bath temperature should'be between 500, and 900 preferably between The actual temperature used- 700" and 900 F. depends upon the composition of the bath, the metal treated and the duration of the treatment,

which last .dependsup'on the: necessity, or otherof first removing rid-existing coating. As

the duration of treatment depends to someextent on the temperature; the nature of the articles immersed .will have some. influence. Thus, comparing a compactcasti'ng. and a thin plate of equal it is preferred that they be transferred to a finishing bath, preferably after washing to remove any free acid from the surface thereof. This finishing bath is composed of iron sulphate,crystalline haematoxylin, water soluble nigrosine, tannic acid or other suitable sealing or colouring agent in solution in water. The bath is made up with "any of the .above' ingredients present in proportion of: approximately 4 ounces to 1 imperial surface areas',-the casting will'require somewhat longer immersioni on account of heat loss from the bath to the'casting- The molten bethegreaets,

integral with the metahwhich is an excellent retardant of rust and corrosion. This coating is so thin it does notcause any significant increase in the dimensions of the articles treated. Screws or bolts with very fine threads are not appreciably tighter .in cooperating tapped holes after treatmentthan before treatment. Thin steel sheets treated as described may be bent back and r forth at: small radius curvature with no apparent detriment to the surface finish until about the time fracture of the metal occurs.

quer, non-vitreous and vitreous enamels and w n I withthemetaltopro-- duce a very strongly-adherent coating practically The coating .is', moreover, a better foundation for paint, lacis'maintained preferably at a temperature of approximately 180 F., but the temperature may be lower or higher, for example between 100 and 200' F'.; and the articles are immersed therein for .two to ten minutes and then removed and washed with' water. The resulting finish is more resistant .to rust and corrosion than that proued-mthe first bath and is a better base for paint, enamel and metal plating. The finish is 'ofuvery good appearance, ranging from gun meta to dark blue or black. If given a coat of oil"or"fclear lacquer, the appearance is similar to good blackf'e namel. In addition to colouring the metal plating such as zinc, tin, cadmium, copper, i

nickel, and the like (electrolytic, hot dip, tumbled or rolled) than the metal of the article itself and such surface coatings applied to articles treated according to this invention are more adherent than when applied to bare metal.

Articles to be treated in the molten bath are merelyimmersed therein and no agitation of the articles or of the bath is necessary. The material of the bath is very penetrating and goes into the most -min'ute crevices. Metal plates closely packed together'receive as good a finish on the contact surfaces as on exposed surfaces and do not show-any traces of the contact such as would occur in electroplating or after dipping in paint or enamel. Small articles such as bolts, nuts, washers and the like may be treated in bulk in baskets.

After immersion in'the molten bath, the are finish im orted in the first bath,'the materials used enter the pores or intermolecular spaces of the finishandseal the same against entrance of rust or corrosionproducing agents;

The neutralizing bath is very important if a paint, lacqur- 1or enamel is to be, applied subsequentlyasfevery trace of alkali must be removed to avoid'jthe: appearance of blemishes in the final coating.

'. .The condition;iof the second and third baths "shouldbe tested; from time to time as to acidity 'andalkalinity and adjusted as necessary by addition of acid or other ingredient to correct the condltiom. r Steel-articles which have been tempered or case hardened may be treated according to this invention withoutfafiecting the temper or hardness. Also, the finish imparted does not interfere with electric .or acetylene welding or brazing.

Specific examples of various molten bath formulae are given below but it will be understood ticles are lifted out, drained for a :few'seconds and then washed with water either by immersion therein or by spraying. The washing should be more thorough if the molten bath contains a large percentage of sodium or potassium hydroxide than if it contains only a little or none at all.

The'washed articles are next immersed in a neutralizing bath being a weak aqueous solution of hydrochloric, sulphuric, oxalic or other suitable acid or an'aqueous solution of iron sulphate, maintained preferably at a temperature of-about 160" F., but the temperature may be lower or higher, for example, from 100 to 200 F. 'A 1% boring to the metal but darkens and improves the appearance ofthe finish impartedin the molten After treatment in the neutralizing bath, the articles may be discharged and used as they are or may be painted, enamelled or metal plated, but

materials or proportions of the examples.

' Fmsr Bun Example I Trlsodium phosphate i. 3 Potassium nitrate 2 s amp 1e11 Trisodiu m phosphate 3 .Sodium hydroxide v 2 n '1 Example III Trlso'dium phosphate r' 4 Potassium nitrate 1 Sodium hydroxide. 1

Example'IV Trisodium phosphate-""4"; 4 Sodium carbonate 1 Sodium hydroxide 2 Example V' Triaodium phosphate 2 Potassium phosphate 2 the invention is not in any way limited to the Sodium hydroxide 4 In preparing amr of the molten baths it is essential to first melt the nitrate or hydroxide or mixturethereof and then add thephosphate gradually holding the bath temperature as low as possible until all the phosphate has been added and meltedinto the bath. To any of the foregoing mixtures'there may be added, 11 desired, from 0.5% to 10% of manganese dioxide v airman v 3 Example?! I mfinish and more resistanarflt to rust and cor- Trisodium h t v on 18 0d 18 0188 1n m u g g f g the third bath also. It is usually preferable to sodium 3 use iron sulphate in one only of the baths, that sodiumhbdmnde 2 is, if it is used in the second bath one of the v other agents is used in the third bath, but if Example Vlf the sulphate is to be used in the third bath, the modlum h t 2 second 9 3 7 d with y Potassium nitrate 3 chloflc other 10 .Having thus described my invention, what I ExampleV III laim is: an: 4 A process 0 coa articles of iron, copper, g gfi fi g g g "f 'f""" g and alloys of each of -them, which process come prises fusing together a-mixture, of alkali metal Example IX colgfiounds infiludlng alkali metal phosphate and v a metal trate, the resulting mixture being fgg fi 5 g in the molten state reactive with the metal treatfi g 1 ed to produce a coating thereon, and subjecting um hy r9 5 the articles to theaction of the molten mass. 1

Example X ,20 2. A process of coating articles of ironfcop per, and alloys of each of them, which process ggg g gl g grgg t f comprises fusing together a mixture' alkali sodium by dr on 3 metal compounds including alkali me 'phosphate and alkali metal hydroxide, the resulting Example XI g5 mixture being in the molten state reactive with the metal treatedrto produce a coating thereon, 3.333% $31 22? *"f f 2 and subjecting the articles to the action of the molten mass.

Potassium hydroxide "-""':"-"'-'""T 3. A process of coating articles of iron, copper, x mp e XII and alloys of each of them, which process commodmm phosbhatg 50 prises fusing together a mixture of alkali me al Sodium hydroxide 50 compounds including alkali metal phosphate, al-

kali metal nitrate and alkali metal hydroxide, the

, resulting mixture being in the molten state reacor crystalline copper sulphate as afiuxing and stabilizing agent, the preferred amount being l to 2%.

In any of the foregoing examples, the alkali metal compounds named may be replaced by the 1 similar compound of the other alkali metal.

Instead of trisodium phosphate, there may be substituted any of the other sodium phosphates,

but trisodium phosphate is preferred on account of its melting point and ready miscibility in the invention, and especially that resulting from imtive with the metal treated to-prbduceja coating thereon, and subjecting the articles to the action of the molten mass. 3

. 4. A process ef coating articles of iron, copper, and alloys of each ofthem', which process comprises fusing together a mixture of alkali metal compounds including alkali metal phosphate, al

kali metal carbonate and alkali metal hydroxide, the resulting mixture being in the molten state reactive with the metal treated to produce a coating thereon, and subjecting the articlesto the action of the molten mass.

r 5. A process of coating articles of iron, copper, and alloys of each of them, which process comprises fusing together a mixture of alkali metal compounds including alkali metal phosphate, al-

i kali metal nitrate and alkali metal carbonate, the

mer sion in all three baths, is very durable and tenacious, so that metal sheets thus treated may be formed in dies without injuring the finish.

The finishing treatment, especially when temperatures between 600 and 900 E. are used, has an annealing effect which improves the strength of the metal. In certain cases where annealing isrequired between forming operations, the parts may be treated according to this invention between the forming operations and annealing thus effected simultaneously with surface finishing. It is possible also .to heat the bath above 900 F., say to l200 or even' bath may be omitted, but a better appearing I nitrate.-

resulting mixture being in the molten state reactive with the metal treated to produce a coating thereon, and subjecting-the articles to th'e action of the molten mass.

6. A process accor ing to claim 1 in which the mixture has added to it nganese dioxide.

7. A composition of matter for use as a molten bath in surfacecoating ferrous and cuprous articles comprising the product resultingfromfusing together a mixture of alkali metal compounds including alkali metal phosphate and alkali metal 8. Acomposition of matter for use as a molten bath in surface coating ferrous and cuprous articles comprising the product resulting from fusing together a mixture of alkali metal compounds including alkali metal phosphate and alkali metal hydroxide.

9. Ferrous and cuprous articles having on the surface and' in the pores thereof axtenaciously adhering rust and corrosion resisting coating produced by subjectingthe articles to the action of a molten mass resulting from fusing together alkali metal phosphate and alkali metal nitrate.

10. lferrous and cuprous articles having on the surface and in the pores thereof a tenaciously adhering rust and corrosion resisting coating pro- .duced.by subjecting the articles to the action of a molten mass resulting from fusing together a mixture of alkali metal compounds including'alkali metal phosphate and alkali metal hydroxide 11. The process for producing a protective coating on ferrous, rust susceptible metallic surfaces which consists in subjecting such surfaces to a molten bath consisting of hydroxide and a phosphate.

12. The process for producing a protective coating on ferrous, rust susceptible metallic surfaces that consists in subjecting such surfaces to a molten bath consisting of sodium nitrate, sodium hydroxide, and a phosphate.

13. The process for producing a protective coating on ferrous, rust. susceptible metallic surfaces which consists in subjecting such surfaces to a molten bath composed of chemicals including hydroxide and a phosphate.

a mixture of alkali metal compounds including 14 The process for producing a protective coating on ferrous, rust susceptible metallic surfaceswhlch consists in subjecting such surfaces to a molten bath consisting of'hydroxide, an oxi-v dizer' and a phosphate.

15. A-process of coating articles of iron, copper, and alloys of each of them, which process. comprises fusing together a mixture of alkali metal compounds including alkali metal phosphate as the essential ingredient and manganese dioxide, the resultingmixture being in the molten state reactive with the metal treated to produce a strongly adherent coating thereon, and subjecting the articles to the action of the molten mass.

16.-A process of coating articles of iron, copper, and alloys of each of them, which process comprises fusing together a mixture of alkali metal compounds including trisodium phosphate as the essential ingredient, the resulting mixture being in the'molten state reactive with the metal treatedto produce a srongly adherent coating thereon, and subjecting the articles to the action of the molten mass.

QECIL J. MACKAY.