US2283171A - Colored steel - Google Patents

Description

May 19, 1942. c. BATCHELLER COLORED STEEL U Z N w R Egg/ O V V T w Z w 6 w, M r. m 2 v M F m A 7 0 T Patented May 19, 1942 COLORED STEEL Clements Batcheller, Glens Falls, N. Y., assignor to Allegheny Ludlum Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Original application June 30, 1938, Serial No.

216,719. Divided and this application February 24, 1941, Serial No. 380,241

, Claims.

My invention relates to the surface coloration of stainless steels and particularly to the production of patterns thereon of distinctive color which may be purely decorative or of a utilitarian nature such as signs, badges, name plates, license plates, picture or the like.

Panels or trim of stainless steel having a uniform surface color throughout, either of the natural metal or as uniformly colored by my processes, may be very monotonous to the eye particularly when of large area, and one of the objects of my invention therefore is to provide a simple method whereby such stainless steel surfaces may be treated to form thereon or therein decorative patterns in which the pattern and the background have distinctive colorations. The same method used in producing a purely decorative effect in which the utility of the finished article lies largely in its aesthetic characteristics may also be used in the production of signs, name plates, license plates, badges and the like having, in addition to aesthetic properties, great practical utility because of the permanence of the article. It is therefore to be understood that the objects of my invention include the production of such articles.

I accomplish the foregoing and other objects by the method described below and illustrated in the accompanying drawing in which- Fig. 1 is a plan view of a mask or stencil of a simple design;

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

Fig. 3 is a plan view of a surface of stainless steel decorated in accordance with my process and in which the mask or stencil shown in Fig. l is used;

Fig. 4 is a plan view of the stainless steel article shown in Fig. 3 which has been treated by a modification of the process used in producing the article of Fig. 3;

Fig. 5 is a highly magnified section of Fig. 3 in the plane 5-5;

Fig. 6 is a highly magnified section of Fig. 4 in the plane 6-6; and

Fig. 7 is a front view of a stainless steel sign or name plate produced by my process.

In carrying out my invention, I first color the surface of the steel throughout by subjecting it to the action of an oxidizing agent for a sufficient length of time to produce thereon or therein a coherent and tenaciously adherent color film. The agent employed should be of such character as to produce this film without etching or in any way otherwise affecting the surface finish of the steel. That is to say, if the steel is highly polished, the oxidizing agent employed should be so adjusted that this surface is not affected in any way other than to produce a color thereon or therein.

It i to be understood that the pattern produced on the steel may be in color on the natural steel background or of a natural steel color on a colored background, or the pattern and the background may be both colored by my process but to different color or tone values.

In my copending application Serial No. 206,043 I have described a method of coloring the surface of stainless steel by immersing the same in a solution of the following composition:

Formula. 1

Parts by weight Etching inhibitor 4-25 Sulphuric acid (1.84 sp. gr.) 23-54 Water 35-64 In the above formula it will be noted that the acid concentration in the sulphuric acid-water solution varies from 23 parts in a total of 87 parts (23+64), to 54 parts in a total of 89 parts (54-1-35), or from about 26% to about 61%.

By heating the above solution and maintaining it within a temperature range of about 185 F. to 200 F. a specimen of polished stainless steel of the 18-8 type (18 Cr., 8 Ni.) or a straight 17-18 chromium type when immersed therein for a period of about one hour will acquire a color running from a light yellow gold through the bronzes and darker browns up to a deep, jet black, depending principally upon the duration of the treatment, the acid concentration in the solution, its temperature, and the presence or absence of alloying elements in the steel other than chromium.

Where a jet black color is desired, I prefer to use the ingredients in the above formula within the following limits:

Formula 2 Parts by weight Etching inhibitor 10-14 Sulphuric acid (1.84 sp. gr.) 36-50 Water 30-50 In the above formula it will be noted that the acid concentration in the sulphuric acid-water solution varies from 36 parts in a total of 86 parts (36+50) to 50 parts in a total of parts (50+30), or from about'42% to about 63%.

The color build up is very gradual during the earlier stages of the processing but progresses very rapidly during the last few minutes up to what is apparently its maximum color and film depth.

When the temperature of the solution is permitted to approach the boiling point, which is around 250 F. to 260 F., the rate of color deposition is so extremely rapid that the film formed is neither coherent nor adherent. Furthermore, the surface of the steel may be destructively etched by the high acid concentration and the aesthetic qualities of the product thus impaired or destroyed. Y

Where the acid concentration of the solution is materially reduced below that stated in Formula 2, it is difiicult, if not impossible, to produce a deep black film. In this case, the color film instead of being black may range all the way from a dark bronze to a brass-gold color. Moreover, a much longer time is necessary in this case to produce the color.

While I have indicated that the temperature of the treating solution is preferablymaintained between about 185 F. and 200 F., because this is the best temperature to produce rapidly and economically a permanent deep black color with my preferred formula above, a comparable result can be obtained by treating the steel in a solution at normal room temperature. In this case, however, the time necessary to produce a black color film of equivalent thickness to that produced by my preferred treatment requires many hours. Solutions at a temperature of say 70 F. are therefore workable 'but their commercial practicability may be open to question because of the long time factor.

As an etching inhibitor in the above formula, I prefer to use sodium dichromate, although other chromium salts such as ammonium dichromate, potassium dichromate or even chromium trioxide, either alone or in combination with each other or with sodium dichromate form satisfactory inhibitors.

Where it is desired to produce a color film of less intensity, such as a light yellow gold, a bronze, or a brown film, I may use the following solution:

' Formula 3 I Parts by weight Etching inhibitor 4- 6 Sulphuric acid (1.84 sp. gr.) 7-11 Water 19-23 In the above formula it will be noted that the acid concentration in the sulphuric acid-water solution varies from 7 parts in a total of 30 parts (7+23), to 11 parts in a total of 30 parts (11+19), or from about 23% to about 37%.

The time required to form these lighter color films at the preferred treating temperature of from 185 F. to 200 F., however, is somewhat longer than that required to produce the black films with a higher acid concentration. Moreover, these films are considerably less in thickness than the black films.

Where it is desired to produce a color more closely resembling the color of true'gold than can be produced by theabove formulae, I use, as an inhibitor in my acid solution, a salt of the metal vanadium in place of the chromium. In such -a case, I prefer to use a solution of the following order:

Formula 4 Parts by weight Ammonium metavanadate 4-30 Sulphuric acid (1.84 sp. gr.) 20-60 Water 35-70 (Water should be preferably free of iron and lime.)

' monium metavanadate is employed.

solutions in about to hours where time is not an important factor.

Where the pattern to be imparted to the steel is to appear in the natural color of the steel surface, I prepare a mask or stencil having cut-out portions corresponding to the desired pattern.

Any suitable sheet material may be used for forming the mask or stencil, as, for example, any of the well known masking papers now on the market in which the pattern may be cut out. One proprietary article which I have found very satisfactory for my purpose is sold under the trade name Scotch Tape," and is provided with an adhesive on one side whereby it may be temporarily adhered to the surface of the steel.

In Fig. 1' of the drawing, I have shown a mask or stencil I having cut-out portions 2 and a layer of adhesive 3 on the back thereof. The stencil shown is adapted for use in forming a rectangular border on a panel of stainless steel colored as above described.

The stencil or mask is superimposed on the colored surface of the steel to which the pattern is to be imparted and must be held or otherwise secured in fixed relation thereto during the buffing operation hereinafter described. Preferably, but not necessarily, it is adhesively secured to the colored surface of the steel. The color in those portions of the steel which are exposed through the cut-outs in the mask is then removed by applying thereto a simple buifing wheel or roll carrying upon its surface a grit or rouge of such abrasive properties as will fairly quickly and completely grind or bufi out the color and produce the desired finish on these portions of the steel. After such bufllng operation is completed, it is simply necessary to remove the mask to find that the exposed portion of the colored metal is now in its original color, as shown at 4, while the colored areas which have been protected by the mask are completely intact, as indicated at 5 and 6. The small zones of color which remain because they were covered by the connectors III in the mask can be buffed off after the removal of the mask.

It seems obvious that the above process may be slightly modified by adhering, or otherwise holding in fixed relation, to the surface of the colored steel, a rectangular frame-like mask such as might be represented by the cut-outs 2 and bufling the color from the surface of the steel around the mask. In this case, when the mask is removed, the color pattern thereunder will be found intact and the background will be the original stainless steel.

By the additional step, hereinafter described, it is possible to produce a two color effect.

After removing the mask and thoroughly cleaning the surface of the steel, it may again be immersed in any of the above solutions, for a sufiicient period of time, to produce upon those portions of the surface where the original color has been buffed out a color of lighter tone value.

For example. a bright gold tone may be imparted resulting effect is so slight as not materially to affect its original appearance.

My invention will be found extremely valuable in its adaptability to produce very rapidly and inexpensively extremely attractive signs, tablets and the like by simply using a piece of highly polished stainless steel colored by my process and using "stock cut-out letters, patterns and the like to produce thereon an unlimited variety of designs.

The surface finish or texture of the colored portions conforms to the surface texture or finish of the steel to which the color is applied. Hence, if it is desired to produce, for example, a dull colored background or dull colored letters or patterns, the surface of the stainless steel may, before coloring, be given a slight acid pickle or even an electro-etch to reduce its surface from the characteristic cold rolled planish to a uniformly dull surface. When a specimen so treated is colored and the portions exposed through the mask are polished as above described, it is possible to produce highly polished buffed letters or patterns on a dull background or dull letters or patterns on a highly polished background.

The color films produced by my process are substantially integral with the steel and therefore do not peel, crack or craze. Microchemical tests and spectrographic analyses show the presence in the films of oxides of the metals in the steel, and their thickness, determined by calculations from their interference colors, does not exceed about 1500 Angstrom units.

Due to the extreme thinness of the film of color, those zones where it is buffed off are not perceptibly lower than the colored zones and it is quite impossible, either by eye or by touch, to detect any diflerence in elevation of these zones. The surface of the steel seems perfectly smooth throughout.

While I have described my invention in its preferred embodiments, it is to be understood that the words which I have used are words of description rather than of limitation. Hence, changes within the purview of the appended claims may be made without departing from the true scope and spirit of my invention in its broader aspects.

This application is a division of my copending application Serial No. 216,719, filed June 30, P38.

What I claim is:

1. A new article of manufacture formed of stainless steel having substantially integral with the surface thereof in certain zones only, an extremely thin, but coherent and tenaciously adherent film of color containing oxides of iron and chromium; said colored zones being so correlated and disposed with respect to the other zones of said surface as to form a predetermined design.

2. A new article of manufacture formed of stainless steel alloy having substantially integral with the surface thereof in certain zones only an extremely thin film of dark color containing oxides of the metals in said steel; said colored zones being so correlated and disposed with respect to the other zones of said surface as to form a predetermined design.

3. Anew article of manufacture formed of alloy steel containing chromium and having substantially integral with the surface thereof in certain zones only a thin lustrous film of dark color formed principally of oxides of iron and chromium; said zones being so correlated and disposed with respect to the other zones of said surface as to form a predetermined design.

4. A new article of manufacture formed of alloy steel containing chromium and nickel and having substantially integral with the surface thereof in certain zones only a thin lustrous film of dark color formed principally of oxides of iron, nickel and chromium; said zones being so correlated and disposed with respect to the other zones of said surface as to form a predetermined design.

5. A new article of manufacture formed of stainless steel alloy having substantially integral with the surface thereof in certain zones only an extremely thin film of color containing. oxides of the alloying metals in said steel; the intensity of the color in some zones differing from that in other zones, and said colored zones of different intensity being so correlated and disposed with respect to each other and to the uncolored zones of said surface as to form a predetermined design.

CLEMENTS BATCHELLER;

Images