US2114151A - Art of finishing ferrous metal - Google Patents

Description

Ill

This invention relates tothe m of finishing Fntenten "rimericanchemlcal Paint Company, Ambler,

Yo a corporation of Delaware No Drawing. Continuation of application Serial No. 743,839, September 13, 1934. This application July 9. 1935, Serial No. A69

acclaim. (c1, mic-0.5)

resulting color will depend on the temperature re s PATENT- oFF cE ierrous metal and its principal object is to provide a final finish the life of which is materially lengthened due to greatly increased resistance to the destructive effects of corrosion or mechanical etrmn,

A further object of the invention is to provide a ferrous metal surface with a coating of paint, varnish, lacquer, japan or the like, the life of which coating is greatly increased and its adhesion promoted, especially, as stated, where it may be subjected to atmospheric corrosion or mechemical strain.

An eddiuonal object is to produce finishes of very high luster with very thin coatings of paint or the like.

Still another object is the provision of e. proc ess for the g oi metallic surfaces which will avoid the formation of hard, adherent incrustetions on the vet, hosting coils or other equipment used in treating the metal especially where this equipment is made of steel or other corrodible metal. Y

Another object is to increase the longevity of the protection eifordeol by temporary finishes such as oil, grease, was, water-point, white-wash, etc. i r In connection with all oi the foregoing objects it is a further important object oi. my invention 39 to remove oil end grease from the surface of the metal while simultaneously providing it with 9.

- peint presewetive coating. 5

Attention is called to the fact that this application is e, continuation of my earlier application Serial No. l lSfiSQ, filed September 13, 1934.

K have discovered that chromic acid in solution may he activated so as to produce the desirable efiect of increasing the longevity of finishes ap plied to ferrous metal surfaces.

Broadly speaking, the invention consists in treating the metallic sin-feces to co finished with a solution containing chromite sold and one or more of o number of activating substances to be and time of treatment as well as upon the composition and concentration 01 the solution.

Generally stated the activating substance is an anion which acts catalyticelly to increase the 5 action of the chromic acid solution on the. metal.

In my .search for activator anions I have found that chloride, bromide, iodide, fluoride and ferricyanide anions are highly efiective. .Ferroline earth metals, iron, zinc, cadmium, copper,

mercury, etc, is not detrimental, although none of these ions is essential to the operation of the process, nor do any of them act as activator ions. The essential ingredients of my improved treeting process are chromic acid and anions of the activator type above described by which are meant helogenions, ierricyanides, end others which produce my desired result.

' I have found, in general that the desired effect can be obtained from solutions which contain at least .(l3 gram equivalents of activator onions per liter. Furthermore, the-most generally applicable solution also contains free chromic acid, although in certain instances the presence of dichromotes of certain metelssuch as zinc, iron, etc, furnishes sumcient acidity to operate the process and in such cases only the minimum quantity of activator onions need be present. However, solutions in which no free chromic acid is present are primarily useful only in instances where the surface to be treated is thoroughly degreased.

In the more generally applicable solutions, which contain free chromic acid, the concentration of activator onions should he at least twotenths the concentration of the free chromic acid by weight. Four times as much activator anion as of free chromic acid or more may be used, but excessive amounts oi activator anions lead to a decrease in the effectiveness of the treatment and I prefer to use activator anions at a concentration of from two-tenths to four times those of .the free chromic acid, provided that a minimum of .03 gram equivalents of activator anion per liter is present.

Chromic acid behaves as a monobasic acid to ward Bromfiresol Greenindicator, the dichromates oi the alkalies being barely alkaline and zinc dichromateibarely acid toward this indicator. For the purpose ofthe present disclosure, therefore, I consider the "free chromic acidv in the solution to be that quantity of the chromic acid present which is capable of being titrated with caustic soda solution before the development of a green color when using Brom Cresol Green as the indicator. Combined" chromic acid is considered to constitute all of the chromic acid presout "not free as defined above.

As a specific example, I will describe my improved process as it may be applied to the coating of a steel stamping, such as an automobile tender.

The stamping as it comes from the press is generally contaminated with: mill oil, grease, and/or drawing compound, and these impurities may be removed by any of the well known conventional cleaning processes if so desired, but the-process of my invention makes it possible to eliminate such a precleaning step. If precleaning is resorted to, scale and rust may be removed with an acid pickle followed by washing with water, and oil and grease maybe removed by However, if the stamping does not bear objectionably heavy rust or scale, it is unnecessary to resort to such a precleaning step as stated above, provided that the treatment hereinafter described is thoroughly eilected. My treatment will remove oil and grease and even though scale or rust are not removed, I have discovered that it will produce very satisfactory paint life without the necessity of any precleaning step. In the case oi scale or rust the treatment apparently removes or renders harmless the corrosion stimulative materials and while tightly adherent scale or rust may interfere somewhat with the smoothness of the final finish, it will not stimulate further corrosion.

Furthermore, it should he noted that my improved process is quite insensitive to any precleaning method which may be. used because the @103, since chromic acid, HzCIOc, is not a stable,

weighable compound:

. Formula N0. 1

Chromic acid (010:) lb 0.033, Common salt lb 0.167 Water, to make "gal..- 1.000

sumcient of the solution'of the foregoing formula is prepared to fill the tank of one section of a conventional metal-washing machine, and preferably heated to a temperature between about and 200 F. and preferably in the neighborhood of 180 F., although the solution may be employed at any temperature up to its boiling point, to which end the tank is provided with some suitable means of heating, such, for example, as steam coils.

I prefer to wash the treated surface before applying the final finish because I find that to do so improves the character of the To this end, therefore, a second section of the wash= ing machine is filled with water which may be cold or may be heated to accelerate the drying of the washed stampings. The stampinzs are then passed through the washing machine by a conveyor orother suitable means, the pumps of the washing machine being operated to keep jets of the solution and the water impinging strongly on the stamplngs in the respective sections.

The stampings should be subjected to the impinging action of the solution in the first stage of the washing machine for approximately- 1 'minute or thereabouts although the time re- I, is without eifect when the treatment has been properly performed in accordance with this disclosure.

The treatment is of distinct advantage over prior practices familiar tothe art especially where equipment or a corrodible nature is employed,

such as a steel vat with heating coils, because with my improved process no serious incrustation of the vat, heating coils or other equipment occurs. This is a distinct advantage over processes employing solutions of phosphates in which aheavy stone-like incrustation soon covers the vat and the heating coils or other equipment, which incrustation, of course, interferes greatly with the transmission of heat through the solution and necessitates frequent draining and has a tendency to cause a certain degree of corrosion although this is not so serious as to preclude its use in metallic apparatus oi this mud. However, such corrosion entails a useless consumption oi chemicals and where metallic vats cleaning of the vat. It should be noted. however, thatin the-case of steel equipment, the solution and/coils are employed, it is preferable to construct them of some non-corrodible material such as stainless steel.

After the treatment in the washing machine the stampings are dried. This may be accomplished by any convenient means, but it is prelerable to dry the stampings at an elevated temperature, as for instance, in an oven which may which will cause oxidation or the steel with the be maintained at any temperature below that consequentiormation of a scale. When dry the just described is quite vigorous in its action and in order to reduce the violence of this action as well as to bullet the solution and to furnish an auxiliary supply of potentially "free" chromic acid I prefer to add to the solution, in addition to the free chromic acid and activator anion,

aiiaici chromic acid combined with a metal or metals capable of forming water insoluble normal or basic chromates.

Such solutions will then contain chromate ions, activator anions, sufiicient hydrogen ion to be capable of titration as free chromic acid, in accordance with the above definition, and ions of a metal or metals which are capable of forming insoluble basic or normal chromates.

Among the metals whose dichromates have been used to successfully buffer these solutions are zinc, cadmium, calcium, aluminum, iron, chromium, manganese and, copper. Solutions prepared in this way have the further advantage that they produce the desired effect on the longevity and adhesion of applied finishes with less attack on the metal undergoing treatment and this results in economy of chemicals consumed and reduces the frequency oitesting and of additions of reagents.

A solution, buffered as described, is given below:

Formula No. 2

Chromic acid (CrOs) lb.. 0.042 Zinc dichromate lb 0.202 Sodium chloride lb' 0.083 Water, to make gal 1.000

This solution is ready for use, although for economy in shipping and storage it may be prepared in concentrated form by mixing the chromic acid with about .15 gallon of water and stirring in zinc oxide and sodium chloride gradually, in the proper proportions, until dissolved, after which the concentrated solution may be diluted to conform to the above formula before it is used.

Another useful formula is given below:

- Formula N0. 3

Chromic acid; "1b-; 0.0500

Ferric chloride "lb-.. 0.0700 Common salt lb 0.0750 Water, to make gal 1.0000

As mentioned above, certain types of metal surface may be processed in solutions containing no free chromic acid. In these solutions the chromic'acid can be considered to be present as the dichromates of one or more metals.

of at least 0.03 gram equivalents per liter, although concentrations as high as 0.10 gram. equivalents or more are permissible. However, the results obtainedare less satisfactory when the concentration of activator anion exceeds 0.07

gram equivalents per liter. These solutions produce practically effective results only when the metals are entirely free of grease or other contaminants when treated. A solution containing no free chromic acid which is suitable for treating grease-free steel, may be made as follows:

Formula; No. 4

Chromic acid ..lb 0.2500 Zinc oxide lb 0.1067 Sodium chloride 1b 0.0333 Water, to make gal- 1.0000

Activator anions must be present in a concentration of water. For instance, the solution of Formula No. 1 may be prepared as follows:

Eormula No. 5 I Chromic acid (CrO3) 1b 0.333 Common-salt lb 0.667

The above dry admixture may be conveniently and economically shipped in sealed containers. When it is to be used it is dissolved in enough water to yield four gallons of a solution identical with that of Formula No. 1.

Another method of preparing a dry admixture is to evaporate to dryness a concentrated solu-- tion such as that given under Formula No. 2. The resulting residue, reduced to particles of convenient size, serves, on solution in the appropriate amount of water, to reproduce the solution of Formula No. 2.

The solutions of any of the above formulas may be applied by any method which will cause them properly to wet the surfaces to be treated. However, where no precleaning step is employed more or less vigorous mechanical treatment may be found necessary to achieve thorough wetting of the surface of the metal, and this, of course,

. will depend somewhat upon the nature and ouchtity of the contaminating materials which are present. For instance, the treating solution may be applied by flowing, brushing, mopping, or wiping oi the surface with or submergingit in the solution as well as by impingement of jets of the solution in a washing machine as described above.

In case such procedures are adopted, certain ob vious precautions may become necessary. its the speed of any chemical process is largely affected by the temperature, it will be necessary to increase the time of treatment as the eflective temperature of the surface is lowered. This is exemplified by the directions under Formula No. 2. It is sometimes useful when the treatment of the surfaces is carried out in the cold to use solutions more concentrated than those given in the examples. Such changes, however, will be obvious to one skilled in the art.

In addition to its value in producing longlived finishes generally, my process has the advantage of malringpossihle the production of finishes of very high luster with very thin coatings of paint, varnish, lacquer, japan or the like. Moreover. incidental scratches or other injuries to the finished surfaces are prevented from spreading under the organic coating material. l' iuthermore, as stated above, the treating process of this invention is useful in increasing the longevity of the protection afforded by temporary finishes such as oil, grease, wax, water, paint,

whitewash, etc. which are often applied during fabrication or while awaiting the application of like.

' the class which consists of zinc, cadmium, cal-" 2. The method of finishing the surface of fer- 'rous metal which compflses forming a chromate a finish of paint, varnish, lacquer, japan, or the 3. The method of finishing the surface of ferrous metal which comprises forming a chromate coating thereto. by treating it with a solution containing free chromic acid and activator anionsfrom the class which consists of halogens and ferricyanides, the concentration of the activator anions in the solution being from about twotenths to four times the concentration of the free chromic acid, by weight, but not less than .03 gram equivalents per liter, and applying to the coated swim a finish of paint, varnish, lacquer, japan, or the like.

4i. 'lhe method of claim 2 wherein the solution also contains dichromte of at least one metal of the class which consists of zinc, cadmium, calcium, aluminum, iron, chromium, manganese, and copper. 5. The method of claim 3 wherein-the solution also contains dichromate of at least one metal of cium, aluminum, iron, chromium, manganese, and copper;

7 ii. The method of finishing the surface of fer rous metal which comprises forming a chro'mate coatingthereon' by treating it with a solution containing free chromic acid and sodium chloride, the concentration of the chloride ion from the sodium chloride, being from about two-tenths to four times' the. concentration of the free chromic acid, by weight, but not less than 0.03 gram-equivalents per liter, washingand drying the coated surface, and then applying a finish of paint, varnish, lacquer, japan, or the like.

7. The method of finishing the surface of ferrous metal which comprises forming a chromate coating thereon by treating it with a solution containing free chromic acid, zinc dichromate and sodium chloride, the concentration of the chloride ion from the sodium chloride, being from about ttvo-tenths to four times the concentration of the tree chromic acid, by weight, but not less than @103 grem=eouivalents per liter, washing and drying the coated surface. and then applying a finish of point, we s-a t lacquer, japan, or the like.

8. The method lei-finishing the surface of iron or steel comprises forming a chromate coating thereon hy treating it with a solution of approximately the following composition:

Chromic acid (@rOal lb. 0.083 Common salt lb 0.167 Water, to make gal 1.900

washing and drying the coated surface and then in applying a finish of paint, varnish, lacquer, japan, or the like.

9. The method of finishing the surface of iron consist or steel which comprises forming a chromate coating thereon by treating-it with a solution of. approximately the following composition:

Chromic acid (CrOa) 1e o.es2 Zinc dichromate ..s lb c202 Sodium chloride lh 0.083 Water, to make "gal" 1.0M

washing and drying the coated surface, and then applying a finish of pmnt, varnish, lacquer, japan, or the like.

10. The method of finishing the surface of iron or steel which comprises forming a chromate coating thereon by treating it with a solution of approximately the following composition:

Chromic acid (@r03) lb 0.2500 Zinc oxide lb 0.1067 Sodium chloride lb 6.0333 Water, to make "gal" 1.0000

- thereof a finish of paint or the like applied to an integral chromate coating having the composition resultingfrom treating the article with a solution containing free chromic acid and activator anions from the class which consists of halogens and ferricyanides wherein the concentration of activator anions in the solution is between about two-tenths and four times the concentration of the free chromic acid, by weight, but not less than .03 gram-eqmyalents per liter of the treating solution.

14. A ferrous metal article having on the surface thereof a finish of paint or the like applied to an integral coating of the composition resulting from the treatment of claim 6.

15. A ferrous metal article having on the sur face thereof a finish of paint or the like applied to an integral coating of the composition resulting from the treatment of claim 7.

16. A ferrous metal article having on a surface thereof a finish of paint or the like applied to an integral coating of the composition resulting from the treatment of claim 8.

17. A ferrous metal article having on a surface thereof a finish of paint or the like applied to an integral coating of the composition resulting from the treatment of claim 9.

18. A ferrous metal article having on a surface thereof a finish of paint or the like applied to an integral coating of the composition resulting from the treatment of claim 10.

GER-AID C. ROMIG.