US2375613A - Method for producing designs on stainless steel - Google Patents

Description

i May 8, 1945. c. BATCHELLER METHOD FOR PRODUCING DESIGNS ON STANLESS `STEEL Filed Oct. 28, 1959 /4 lf/////6 ,l //4 //f /////////%A VE To v 7eme/W3 a/che//ef ,47- TOR/vir Patented May 8, 1945 METHOD FOR PRODUOIN G A STAINLESS STEEL DESIGNS N 'Clements Batcheller, Glens Falls, N. Y. Application October 28, 1939, Serial No. 301,805 6 Claims. (Cl. 204-143) In my Letters Patent Nos. 2,172,353, 2,219,554, and 2,243,787, I have disclosed methods of treating stainless steels whereby a color film containing oxides of the metals in the steel itself s formed in and substantially integral lwith the surface of the steel.

'Ihe processes are applicable to all alloy steels belonging to what is commonly termed the stainless group and all of which contain chromium in quantities of 6% or more, by weight, either alone or with 'other alloying elements, such as nickel, silicon, molybdenum and the like. Steels colored by any of these methods are rendered extremely resistant Ato corrosion and the color lm, under ordinary conditions, is only removable with such difllculty, as by abrasives, that it may be said to .be substantially permanent. Such color films offer unusual possibilities for producing permanent decorative orv utilitarian designs, such as signs and the like, on stainless steel surfaces. vWhile it Iwould seem possible to mask certain portions of the steel surface and thus color only the unmasked portions to produce the desired design, the.coloring. process is preferably performed at comparatively high temperatures, and no masking substance which will satisfactorily withstand the treatment has been discovered.

In my copending applications, Serial No. 216,719 led June 30, 1938 now Patent No. 2,243,787 and Ser. No. 380,241 iiled February 24, 1941, now Patent No. 2,233,171, I have disclosed a method of producing color designs on stainless steel by rst 4forming.a color film of metallic 'oxide over the entire surface of the steel, then cutting a stencil of the desired design which is used as a mask to permit the color film to be rubbed oli through the openings in the stencil by means of a suitable abrasive. This method produces very beautiful designs but is quite expensive, and it is impossible to produce in. this Way a design involving ne details. Eurthermore, due to the facts that the color lm is in and integral with the surface of the steel, rather than merely on the surface thereof, and is extremely thin, it is impossible to rub it off or out with an abrasive without materially changing the original physical texture and finish of the steel. Thus, ifthe surface of the steel before coloring has a highly polished, mirror-like finish, this nish is not affeet-ed by the coloring treatment but, in rubbing oil the color, this nish is destroyed and the surface is dulled where the color is removed.

The present invention concerns the production f of colored designs either for decorative or utilitarian purposes on stainless steels by a method which can not only be cheaply and quickly per- -forrned but :by means of which it is possible to produce on the steel a design having details substantially as line as those of an etching or engraving.

In the preparation of such a design the surface of the stainless steel is rst given the desired nnish such as that produced by any of the various types of pickling, cold rolling, belt sanding, or

'polishing by any of themethods well known in the art. The entire surface of the steel is then colored by forming a film of metallic oxides therein. Such a film may be formed .by treating the steel in a solution containing sulphuric acid and water together with an etching-inhibiting, oxidizing agent at any temperature from ordinary room temperature up to somewhat below the .boiling point of the solution; the preferred temperature being between Aabout F1. and about 220 F.

The solution should preferably contain from 23 to 54 parts, by weight, of sulphuric acid (1.84 sp. g.) and from 35 to 64 parts, by weight, of `wa ter, or in other Words, have an acid concentration of from about 25% to about 60%; the best results Ibeing obtained withvacid concentrations above about 40%. Sulphuric acid solutions of this strength will immediately attack and quickly dissolve a specimen of stainless steel immersed therein, and an etching inhibitor and oxidizing agent, such for example as chromic acid,` the chromates and dichromates of aluminum,I ammonium, barium, bismuth,I cadmium, calcium, cobalt, copper, iron, lead, lithium, magnesium, mercllry, nickel, potassium, sodium, strontium or' zinc; the vanadates or metavanadates of ammonium, potassium or sodium, vanadic acid or metavanadic acid; the manganates or permanganates o1' the alkali metals of Group 1, the manganates or permanganates of the alkaline earth metals oi' Group 2 or manganese dioxide; is therefore 1 added to the acid solution in a quantity at least suflicient to prevent etching of the steel at the temperature employed inthe treatment. Anywhere from 4 to z5 parts, by Weight, may .be used, but I prefer to use a quantity not greatly in excess of that necessary to prevent etching of the steel at the temperature selected for the treatment. 'lhis quantity can be easily determined by adding the etching-inhibiting oxidizing agent to the sulphuric acid solution in small quantities and testing the mixture after each addition with a specimen of the steel to ybe colored. i

The addition of any of the above mentioned chromates or dichromates to the sulphuric acid solution forms chromic acid and asulphate or bisulphate of the chromate or dichromate-forming element; the addition of` any of the above mentioned vanadates or metavanadates forms vanadic or metavanadic acid together with a sulphate or bisulphate; and the addition of a manganate or permanganate forms manganic or permanganic acid and a sulphate or bisulphate.

The treating solution made up as above described is maintained at the temperature selected for the treatment and the steel is simply immersed therein until it acquires the desired color, whereupon it is removed, washed and dried.- For any given acid concentration, the time required depends upon the temperature. Usually ,15 to 30 minutes with the preferred solutions and preferred temperatures will be found sufficient.

'I'he design to be imparted to the steel is then printed or painted'thereon with a resist such as common paint, lacquer, varnish, or a printing or lithographing ink. The comparatively new art of screen painting through silk is admirably adapted for imparting the desired design to the colored surface of the steel. The paint, ink, or other resist employed, when dry, need merely forma waterproof, non-,porous film capable of withstanding the solution hereinafter described, and be readily removable by suitable solvents after treatment vln'thout damage to the color lm. After the resist has dried the steel is subjected to an.l electrolytic treatment whereby the color in the unpainted or unprinted zones is removed.

In the electrolytic treatment any controlled source of direct current may be used and; in the accompanying drawing, I have illustrated in a diagrammatic way an apparatus suitable for removing the color,

In the drawing- Fig. 1 is a perspective view showing an arrangement for removing the color from one side only of the steel;

Fig. 2 is a section of Fig. 1 in the plane 2-2;

Fig. 3 is a section of Fig. 1 in the plane 3 3;

Fig. 4 is a section similar to Fig. 2 showing a modified type of vat which may be used for removing the color from both sides of the steel;

Fig. 5 is a fragmentary elevation view of a thermometer scale; l

Fig, 6 is a section of Fig. 5 inthe plane 6-6 drawn to a somewhat enlarged scale; and

Fig. 7 is alsection similar to Fig.6 showing the finished product.

Referring to the drawing, I represents a tank or vat which may be a pickling tank such as is commonly used in the metal industry except that the lining thereof must be formed of some substance which will resist destruction by the action of the electrolyte used therein. For my purpose a lining 2 of 18-8 (18 chromium-8 nickel) stain.

less steel has been found satisfactory. In my process such a lining may serve as either the anode or cathode. However, the lining of the tank may be so constructed as to limit the electrical removal of the color film to one side of the steel thus leaving intact the color on the opposite side. Such a construction is shown in Figs. 1 and 2. Here one side or end 3 only is provided with a lining 4 of 18-8; the other portions of the tank being lined with an insulating material 5 such asr rubber, gutta percha, asphalt or the like.

' It may be said generally'that the electrolyte in which the electrodes are immersed and which carries the current from electrode to electrode may contain any substance which will impart' good electrical conductivity to the solution, and

' will not detrimentally affect either the surface of ver-like color may be imparted to the steel.

the steel or the functioning of the resist. In other words, 'a solution to which the surface of the steel itself is substantially immune from destructive attack, such as by etching or pitting, when i-mmersed therein. Substances which result in the evolution of chlorine, for example, are generally not satisfactory. Since the surface condition of the stainless steel after the removal of the color film is' of extreme importance, it may be preferable to use only those solutions that are adapted for or commonly used in the electrolytic pickling of stainless steel. It must Ibe understood that the removal of my color film is not at all dependent upon a pickling of the surface of the steel because, by selecting a proper electrolyte the color may tbe removed without in any way altering the physical texture and finish of the surface of the steel from its condition prior to coloring, however, the surface of the steel may be given a. desired pickle finish as an incident to the removal of the color iilm by using a pickling solution as the electrolyte. In any event, a solution is chosen which will leave the desired iinish on the surface of the steel; for example, a water solution containing l0% nitric acid and 5% hydrofluoric acid imparts a slight whitlsh tinge to the stee1 due to a very fine etching thereof, and thus, :by means of such a solutlona sil- On the other hand, a solution of household lye containing approxi-mately '75 grams `per liter of water leaves the stainless steel surface in its original condition before coloring with no evidence of pickling. A solution containing approximately 75 grams of sodium nitrate per liter of water also leaves the stainless steel surface unmarred by pickling. Where an extremely bright surface is desired on the stainless steel after the removal of the color lm of metallic oxides, any bright pickling solution may be employed. For example, a solution containing 70% of phosphoric acid and 30% of sulphuric acid with citric acid dissolved therein may be employed, as well as 85% `phosphoric acid solutions. While I prefer to maintain the electrolyte at a temperature of from 50 to 100 C. during the treatment, electrolytes at room temperature work very .well.

The character of the surface of the stainless steel from which the color is removed may also depend to a considerable extent upon the amperage of the current used and the duration of vthe treatment. In general, better control is attained if either the voltage or amperage is so regulated that no gas is visibly given oi from the surface of the anode. For` instance, when using a solution containing 10% nitric acid and 5% hydroluoric acid good results are obtained by using a current of from 1.0 to 1.1 amperes and treating the steel for approximately 20 seconds for each square inch of film to be removed. Violent evolution of gas from the surface of the colored stee1 winch forms one electrode may remove or injure the resist, particularly in the marginal zones thereof, and, if permitted to continue after the removal of the color film may etch or pit the surface of the steel.

In any particular solution the proper current and duration of the treatment may be easily determined as follows: Immerse in the solution a known slu'fiace area. Such a sample may be suspended in the solution .by means of stainless steel hookslasshowninFig. 1. lisasourceof direct current, here indicated as a storage battery, the proper terminal of which is electrically connected' to the specimen 6 through the bar 9 Y :lill does not last long in immersion thermometers.

and hooks l to make the specimen 6 the anode in the electrolyterwThe other terminal of the battery is connected through the adjustable rheo- -stat I6 to the lining I at one end of the tank which here forms the cathode. It will be noted that the anode and cathode are opposed to each other and that the cathode is entirely on one side of the anode, or, in other words. every straight line that can be' drawn from. the cathode toused in the printing is then removed with a suitwards the anode will intersect the plane of the face of the anode before passing through the specimen v6 and intersecting the back thereof.` With this arrangement the color will be removedonly from that side of the specimen 6 which faces the cathode. By adjusting the rheostat the current may be gradually increased until the surface of the specimen 6 begins to lighten in color. Current is permitted to flow at this amperage until the color film'is removed or becomes easily removable by light rubbing. Since with this set-up the `color is removed from only one side of the anode the area of this side only should be considered, By dividing the ltime required to remove the lm, or to render it easily removable, by the area in square inches of one side of specimen 6, the time required per square inch may be-ascertained. For any piece thereafter the proper total time required for the treatment will'be the total area of the surface .from

which the color is to be removed, multiplied by the required time per square inch. If the color is tobe removed from allsides of the specimen, the specimen should :be entirely surrounded by the other electrode which serves as a cathode. After the removal of the color the paint-ink or lacquer used asa resist may be removed with a suitable solvent.

The voltage employed does not seem to be ma- `terial except that it may affect the amperage which is preferably kept low enough to prevent the visible evolution of gas from the anode where the surface of the steel from which the color is removed is to be maintained free of visible pickling or etching.

One of the recent applications of my process is in the making of stainless Steel thermometer scales. Such scales, which must stand the action of certain chemicals, have usually been produced of 18-8 stainless steel. Heretofore, in the preparation of these scales, the polished steel face of the scale has been rst printed with a, special resist, xsuch as a mixture of asphalt and dragons blood or the like, over all areas of the face not intended to be etched'. That is to say, the numerals and graduations are not covered with the resist so that they may be exposedto the action of an 'etching solution, such as an aqueous solution of iron perchloride. After the etching of the numerals and graduations has progressed to a desired depth, usually three or four thousandths of an inch. the resist is removed with a suitable a solvent to produce the thermometer scale in its l first stage. 'I'he etched numerals and graduations are then filled in, by a tedious and exacting hand operation, with a special black paste. Thereafter the scale is subjectedto a baking treatment -to harden the inlaid color. Even under the most favorable conditions this color able solvent and the scale is finished.`

Obviously, if it is desired to have the numerals and graduations appear in the color of the stainless steel on a dark ileld, the fieldv is printed instead of the numerals and graduations and the color is removed only from the numerals and graduations. a

By the term stainless steel" as used herein,

I mean a corrosion o f resisting ferrous alloy containing 6% or more of chromium.

What I claim is: l 1. Those steps in the method of producing a design in color on a polished surface of a corrosion-resisting, alloy steel containing a substantial quantity, by weight, of chromium and having therein and substantially integral therewith a film containing oxides of iron and chro- -mium imparting a distinctive dark coloration to said surface which comprise, coating those portions of said surface'which it is desired to preserve in color with a resist. and thereafter removing V the color film from the uncoated portions of said surface by subjecting said uncoated portions to electrolytic action as anode in an aqueous electrolyte having good electrical conductivity.

2. 'Those steps in the method of producing a design in color on a polished surface of a. chromium-containing, corrosion-resisting alloy steel as set `forth in claim 1 in which the electrolyte employed is an aqueous alkaline electrolyte.

3. Those steps in the Amethod of producing a design in lcolor on a polished surface of a chromium-containing, corrosion-resisting alloy steel as set forth in claim 1 in which the electrolyte employed is an aqueous` acid electrolyte.

4. Those steps in the method of producing a design in color on a polished surface of a corrosion resisting., chromium containing steel which comprise irst forming in and substantially integral with lthe surface of said steel, but without changing the physical texture and finish thereof, athin film containing oxides of chromium and iron to impart a distinctive coloration to said surface by treating said steel in a solution of sulphuric acid, water and an etchinginhibiting-oxidizing agent; the sulphuric acidwater solution being of such acid concentration, in the absence of the inhibitor, as quickly to attack and dissolve a specimen of said steel when immersed therein, and the inhibitor being present in a quantity at least sufficient to prevent said solution from etching said steel by chemical attack; coating those portions of said colored surface which it is desired to preserve in the finished design with a resist, and removing said film from the uncoated portions of said surface Without substantially affecting the surface ilnish and texture of the steel itself by subjecting said steel to electrolytic action as anode in an. aqueous electrolyte of good electrical conductivity and under conditions which do not cause the surface of the steel to be attacked during the removal of said 111m by said anodic treatment.

' 5. Those steps in the method of producing a.

6. Those steps in the method of producing a design in color on a polished surface of a chrommm-containing, corrosion-resisting alloy steel as set forth in claim 4 -in which the\electrolyte 5 employed is an aqueous acid electrolyte.

CLEMIN TS BATCHELLER.

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