US2415361A - Method of forming engraved markings in a ferrous article - Google Patents

Description

Patented Feb. 4, 1947 METHOD OF FORMING ENGRAVED MARK- INGS IN A FERROUS ARTICLE.

Clifford W. Mell, Moorestown, N. .l., assignor to Radio Corporation of America, a corporation of Delaware No Drawing. Application August 25, 1944, Serial No. 551,271

4 Claims. 1

This invention relates to a method of engraving, and more particularly to a method of forming engraved markings in ferrous articles having an organic finishing coat thereon.

There are many types of equipments employing panels provided with various types of markings, such as lettering, numerals, or the like. In many of these equipments it has been found desirable to apply a suitable organic finishing coat over the panels for the sake of protecting the panels from the elements, for ornamental purposes, etc. In many instances, as in the case of electrical test equipment, panels of the type under consideration have been made of aluminum or other light metal. Due to the scarcity of aluminum and other light metals necessitated by present conditions, panels of steel have been resorted to. The steel panels, like those of aluminum, are also desirably finished with an organic wrinkle finish on the front, and frequently also with an enamel finish on the back, some panels having portionscovered only by electroplated metal for the purpose of making electrical connection thereto.

Whatever the type of panel employed, it is desirable to apply lettering on the front thereof which must be en raved through the wrinkle finish into the metal for the sake of permanence. Aluminum does not require any protective plating on the lettering, but steel panels must have the lettering protected against rust. It has been proposed, heretofore, to finish the lettering engraved in steel by filling with white wax or the like, but this has not been found satisfactory. Silver plating produces a finish which is more durable and also more satisfactory in appearance. However, due to the character of the organic finish, the silver cannot be deposited by electroplating for more than a few minutes, since more prolonged electroplating loosens the organic finishing coat and causes it to come oif. For this reason, it has been proposed to apply the silver by immersion deposit in a humid atmosphere, but such deposits of silver, while not being detrimental to the organic finish, will prevent rusting of the steel for only a few hours.

The primary object of my present invention is to provide an improved method of engraving markings in steel panels or other ferrous articles provided with an organic finish, which method will not be subject to the defects and limitations of prior art methods proposed for this purpose.

More particularly, it is an object of my present invention to provide an improved method of providing markings in ferrous articles having an organic finishing coat thereon, together with a method of protecting both the organic finish and the ferrous article so that neither will be injured.

Another object of my present invention is to provide an improved method of engraving markings in ferrous articles as aforesaid which Will result in markings which stand out prominently and which are of lasting character.

Still another object of my present invention is to provide an improved method of engraving markings in steel panels. or the like covered with a suitable organic finish, together with a protective coat therefor, which method will result in markings and a protective coat which will successfully withstand a salt spray test at least hours, this being a prerequisite in many equipments employed in naval vessels.

It is also an object of my present invention to provide an improved method of forming engraved markings and a protective coat therefor as aforesaid which are relatively inexpensive and highly efiicient.

In accordance with my present invention, the steel panel or the like in which the markings are to be formed is cleaned and treated with a phosphate to obtain a frosty, uniform, black coating of iron phosphate. A wrinkle or other suitable finish of organic material capable of becoming cured in the course of time is then carefully applied to the iron phosphate coating. The wrinkle or similar finish is then cured until a firm, hard finishing coat is obtained, but care should be taken that this coat will not have been cured to the point of becoming brittle. With most organic finishes, a curing time of from about 3 to 30 days is sufiicient. The lettering or other marking is then engraved in the finishing coat and the steel panel by cutting with an appropriate, sharp cutting tool, the tool preferably being one which forms the bottom of the letters fiat. After smoothing the engraved markings, they are cleaned by brushing gently with a soft brush and by treating With a solution of sodium cyanide. The engraved markings are then plated with a suitable adherent metal, such a cadmium or the like, after which the panel is washed and plated with silver. When dry, the panel is then given a transparent, protective coating of clear lacquer. The engravings formed and finished as above described Will be very durable, the organic finish will not come loose during plating, and the finished panel can be subjected to a salt spray test of at least 100 hours at 35 C. Without failure of either the wrinkle finish or the electroplating.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, together with additional objects and advantages thereof, will best be understood from the following more detailed description of one way of carrying it into practice:

Let it be assumed that the article to be treated is a steel panel which is to be engraved with certain lettering or other desired markings. The panel is first thoroughly degreased in a suitable solvent or in vapor, or both, in known manner, after which it is alkaline cleaned as thoroughly as for electroplating, so that no water breaks appear after dipping in 30 percent muriatic acid. The panel is then washed in clean, cold tap water, after which it is dipped in 30 to 50 percent muriatic acid and again thoroughly washed in clean, cold tap water. The panel is then treated with phosphoric acid in a phosphate treating bath to provide a thin, uniform, greyish-black, frosty, crystalline, surface coating of iron phosphate. This procedure is well known in the art and need not be described in further detail, it being pointed out merely that the iron phosphate provides a strong bond between the organic finishing coat and the steel base so that the finishing coat will stand up against the subsequent plating operations. The treated panel is then again washed thoroughly and dljed, after which masking tape may be placed on all areas or portions thereof which are to receive plating of appropriate metals to provide suitable electrical contacts for external connection where this is necessary.

The panel is then sprayed with a suitable grade of organic material in a manner to provide the type of finish desired, that is, smooth, wrinkled, orange peel, or the like. This finish may be applied either to both sides of the panel, or only to the front thereof, and in the latter case, the back of the panel may be coated with an appropriate grade of enamel or the like. It is important that the organic finish be applied carefully and thoroughly, and care must be taken to completely cover alledges. The organic finish on the coated panel may then be baked in the heat cycle to which'it is best adapted. With certain, conventional, organic materials used for wrinkle finishes, a baking time of the order of 23 minutes at about 250 F. is satisfactory, but other baking cycles 'may be found more desirable, depending upon the type of material used and the thickness of coating desired; In any case, the baked finish should be hard and firm but not brittle. 'It will usually be found that this condition is obtained with most conventional organic finishes in a period from about 3 days to about 30 days.- The particular material which may be employed for the organic finish is not a part of the present invention, and any suitable material may be used.

After the finish has cured properly, the lettering orother markings are engraved with a sharp, preferably flat-bottomed, tool, since dull cutting tools tend to tear and loosen the organic finish. The cutting or engraving is performed in three distinct steps. The first cut should he just through the organic finish; the second out should penetrate the metal of the steel panel to the proper depth; and the third cut is made to smooth the surfaces of the markings in the organic finish and. in the panel and to remove projections and burs in the engravings. The heavy electroplate required to withstand severe corrotrical contact points for hooks or the like.

sion conditions will build up and emphasize every irregularity in the engraved letters; hence, it is imperative that the engraved surfaces be as smooth as possible in order to obtain plated letters which have a good appearance.

The engraved panel should thenbe protected from air until it is plated. This may be done by carefully wrapping in paper or other suitable wrapping. Electroplating should be performed within about 8 hours after engraving or sufficient oxide will very likely form on the steel to interfere with proper electroplating. At this point, the masking tape is removed from the areas of the panels where electroplating is desired, and the engraved surfaces are cleaned and prepared for plating by gently brushing with a soft brush and a solution of cold sodium cyanide containing about 6 ounces of sodium cyanide per gallon. Conventional methods of preparing metal or plating are not suitable in this case because of the chances of injuring'the organic finish. Dummy racks or plates are then placed in a cadmium plating bath as cathodes and the current density is adjusted so that the cathodes will plate at a rate just below the gassing point. Enough of the organic finish on the top or on the back edge of the panel is carefully removed, as by cutting away with a knife, to provide elec- The panel is then placed in the cadmium plating bath as a cathode and the current density is adjusted to allow for any exposed areas, usually on the back of the panel, which are to be plated. The area of the engraved letters is usually too small to be determined and to be taken into account in the adjustment of the current density, and therefore the, proper current density is adjusted to the dummy cathodes. Care must be taken that the engraved letters will not gas during plating, sin e gassing tends to lift and loosen the plating. Any other plating which does not gas during the plating operation and which, like the cadmium, will form an adherent metal coating, may be deposited in place of the cadmium. When a flash of copper, for example, is deposited from a cyanide bath at a very low current density, it'may be followed by acid copper or nickel.

Where the metal being plated is cadmium, the

plating should continue for about 15 minutes to obtain a deposit of from about 0.00025 inch to 0.0003 inch in thickness. Equivalent thicknesses of other metals would be satisfactory. When the plating operation has been completed, the coated and plated panel is washed thoroughly in cold, clean tap water. A silver strike is then applied for about 30 seconds, and the panel is then placed in a silver plating bath for about 10 minutes with a current density adjusted to about 5 amperes per square foot as measured .on cathodes having a square foot or more which may be plated along with the panel. This forms an electro-deposited coating of silver over the silver strike. The panel is then washed in a silver reclaim rinse, after which it is washed in clean, cold tap water. The panel should not be washed with hot water, as this may be detrimental. Excess liquid'is carefully blown off with an air jet which is not permitted to come closer than 12 inches from the plated areas or injury may result to the edges of the organic finish.

The panel is then dried for about 10 to 15 minutes, preferably in an air circulating .oven operating at about F. to 200 F., and it'is then permitted to cool to room temperature.

Within a period of time sufiicient to prevent the plated silver from becoming tarnished (this is usually within about 2 hours after electroplating), a transparent protective coating is applied to the plated markings. This coating may consist of a single coat of water clear organic baking lacquer or two coats of water clear air drying lacquer. The baking lacquer is to be preferred. The lacquer is applied only to the front face of the panel, care being taken especially to completely cover the plated letters. The backs of the panels should not, of course, receive the lacquer since the plating on th exposed surfaces thereof is for electrical contact purposes.

Engraved markings formed as above described are quite smooth and silvery white. The organic finish will not be lifted or broken at any spot, and panels prepared in the manner set forth above will be found to withstand salt spray tests of 100 hours or more with very satisfactory results.

Although I have described my invention in considerable detail, it will undoubtedly be apparent to thoseskilled in the art that many v variations thereof are possible. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of forming engraved markings in a ferrous article which comprises first treating the surface of said article with a phosphate to form thereon a frosty, crystalline, even, greyblack deposit of iron phosphate, then applying thereto a finishing coating of organic material capable of becoming cured to a hard, firm condition in the course of time and which, in aid condition, is insoluble in sodium cyanide solution, then causing said finishing coat to become cured to said condition, then cutting said markings through said finishing coat and into said article, then cleaning said markings with the aid of a solution of sodium cyanide, then applying a coating of cadmium thereto, subsequently electroplating a coating of silver on said cadmium coating, and finally covering aid silver coated markings with a protective coating of clear lacquer.

2. The invention set forth in claim 1 characterized in that said markings are rendered smooth prior to cleaning thereof.

3. The invention set forth in claim 1 characterized in that said markings are made in steps by first cutting through substantially only said finishing coat, then cutting into said article below the surface thereof, and finally rendering the cuts in said finishing coat and in said article smooth prior to the cleaning thereof.

4. The method of forming engraved markings in a ferrous article which comprises first treating the surface of said article with a phosphate to form a coating of adherent iron phosphate thereon, then applying thereto a finishing coat of organic material capable of becoming cured to a hard, firm condition in the course of time and which, in said condition, is insoluble in sodium cyanide solution, then causing said finishing coat to become cured to said condition, then cutting said markings through said finishing coat and into said article, then cleaning said markings with the aid of a solution of sodium cyanide, then applying thereto a coating of an adherent, stable metal capable of being electroplated with another metal, subsequently electroplating a coating of silver over said adherent metal coating, and finally covering said silver coated markings with a transparent protective coating.

CLIFFORD W. MELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS France May 30, 1938