US2377321A - Enamel coated article - Google Patents

Description

June 1945- 'M. BROWN ETAL 2,377,321-

ENAMEL COATED ARTICLE Filed May 20, 1939 3 F76. Z I

M/Vf/VTORS M. BRaw/v R. E. HARE lav Z7 [H I A TTOR/VEY Patented June 5, 1 945 ENAMEL COATED ARTICLE Morris Brown, LaGrange, and Russel E. Harr, Chicago, Ill., assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application May 20, 1939, Serial No. 274,750

6 Claims.

This invention'relates to enamel coated articles and to methods of making enamel coated articles. Objects of the invention are the production of articles having a highly ornamental and serviceable enamel coating, and the provision of efllcient and economical methods for making such ary ticles.

The invention is particularly adapted to the production of enameled articles such as the number plates which are incorporated in; telephone dials. These plates comprise ametal base with ill a coatingwfhvitreous enamel on the portions of the base that are exposed in the dial assembly. A highly adherentenamel-coating is requiredto withstand rough 'usagefand it is especially desir able' to provide a particularly smooth, even and pose and the material is selected primarily on the basis of cost and formability;

After the ring-shaped base is formed, it is cleaned by the usual methods and then completely coated with a layer of copper H. The copper can be applied conveniently in a conventional copper cyanide electroplating process and a coating weight around 20 milligrams per squareinch is generall satisfactory.

In the next operation, an alloy I2 is applied over the copper. in a uniform layer. Three types of alloy are suitable and good results are obtained by alloying .nickel'with iron, or cobalt,

unbroken surface on the enamel; The plates are often exposed to dirt-laden atmospheres in service and under these conditions even minute imperfections in' the enamel surface may-accumulate dust, dirt, lint and the like. These foreign materials are dimcult to remove from surface cracks and pits, and the plate very soon becomes unsightly if any of these defects are present. Certain types of number plates receive a multi-color finish in which variously colored enamels are applied successively and fired after the application of each color. Under this practice, the repetitive firing tends to develop surface defects or to aggravate defects lnprevi'ously matured enamel.

In one embodiment of the'invention, an improved number plate having an adherent and unpitted enamel coating is produced by forming a base from inexpensive sheet iron, copper plating the base, electrodepositing on the copper a uniform layer of nickel alloyed with a metal selected from the group consisting of iron, cobalt and manganese, applying a vitreous enamel on the alloy layer, firing the base to fuse the enamel, applying a second enamel or contrastin color on portions of the fused enamel, and refiring the base to mature the second enamel.

A more complete understanding of the invention may be had by reference to the following or manganese. i

... j:If a nickel-ironalloy is used, the iron content should be between .50% and 10.0% with the balance nickel and the best results are secured with an alloy having an iron content around 1.50%.

This optimum composition can be obtained from,

an aqueous electroplating bath containing the following ingredients and operated under the following conditions:

Composition of bath Ounces per allon of solution Nickel sulphate 24.0 Sodium chloride 3.0 Boric acid 1.0

Ferroussulphate .L ".0666

Sufficient sulphuric acid is added to keep the solution in a slightly acid condition, a pH of 5 being satisfactory. The process is operated cold at a current density around 10 amperes per square foot of cathode surface. Since a variation of this current density will affect the proportions of iron in the deposited alloy for the to consider this" interrelation of current density jand alloy composition for different solution concentrations and operating" temperatures.

The

' ferrous sulphate can be added as such to initiate the process and then maintained by placing pure iron anodes in parallel with pure nickel anodes in the bath.

If the nickel is alloyed with cobalt, a cobalt content between 1.0% and 15.0% is operabl and a cobalt content of 5.0% is preferred. If a nickelmanganese alloy is employed, the manganese percentage is held between .20% .and 5.0%, and

, 1.0% manganese is optimum. The nickel-cobalt and nickel-manganese alloys can be electrodeposited on the copper in a plating bath contaming appropriate salts and anodes of the respective metals, corresponding to the elements employed for electrodepositing the nickel-iron alloy, as above described.

After the copper and the alloy coatings have been deposited, the base is ready to receive the enamel which is applied only on the face of the ring. The enamel is restricted to the face of the ring, which is the portion exposed in service, in order to minimize the cost of the article and also to facilitate the maintenance of over-all dimensional tolerances.

A coating of white enamel 13, such as a lead bore-silicate enamel opacified with arsenic oxide, is applied first. The enamel is distributed on the alloy surface either in the form of dry powder or by a wet process in which the enamel particles are mixed with water and a flotation agent, such as clay. The base is then fired at 1600 F. for four and one-half minutes to fuse the enamel.

Identifying characters in contrasting colors are usually required to complete the plate. ,One type of plate, shown in the drawing, has a background 14, letters i5 and numerals it. These characters are produced with an inky suspension of colored metallic oxides or frits in a vehicle such as linseed oil and are applied on the surface of the white enamel by a printing operation. The background, which may be blue or black, is applied first and the plate is then baked at about 300 F. to harden the ink so that it will not be marred in subsequent printing operations. The letters, which are usually black, are then applied and the plate is then again baked at a temperature of about 300 F. The numerals are usually colored red and are applied in the same manner, after which the entire plate is again fired to fully mature the ceramic ink which requires a temperature around 1300 F. for approximately 4.5 minutes.

The resultant enamel coating is highly adherent and all portions thereof have a smooth, continuous surface that does not tend to accumulate foreign materials. In this type of product, pitting of the enamel is a serious source of trouble. The occurrence of very small pits is not easily detected when the plates are new, but after a period of service dirt and other foreign particles tend to accumulate and become imbedded in the pits to form smudges. Thesesmudges are very dimcult to remove, particularly because the number plates are not readily accessible for cleaning after they are assembled in a dial. Use of the described combinations of cop-- per and alloy undercoatings prevents the formation of pits in the enamel. The initially applied enamel is smooth, glossy and free of pits and these desirable surface characteristics are preserved during any refiring operations and are reflected in all portions of the completed enamel coating. For most applications, a coating weight of milligrams per square inch for both the copper and the alloy is satisfactory. It may be desirable to vary these values somewhat for different enamel compositions and in general, the copper and alloy layers should be of about equal weight.

The combination of copper and alloy layers also adequately protects the portions of the base that are not covered with enamel against atmosphere corrosions.

Although the invention has been described in connection with the manufacture of number plates for telephone dials, it will be apparent that it is equally applicable to other ornamented enameled articles and it is to be understood that the invention is limited only by the scope of the appended claims.

What is claimed is:

1. An enameled article comprising a ferrous metal base, a layer of copper over the base, a

layer ofnickel-iron alloy containing from .50% to 10.0% iron and the balance nickel over the copper and a fused enamel coating over the alloy layer.

2. An enamel coated article comprising a ferrous metal base, a copper coating thereon, a layer of nickel-iron alloy containing substantially 1.5% iron and the balance nickel over the copper, and a vitreous enamel coating over the alloy layer.

3. An enamel coated article comprising an iron base, a copper plated coating of around 20 milligrams per square inch thereover, a layer of nickel-iron alloy over the copper plate, said alloy comprising from .5% to 10.0% iron and the balance nickel and being substantially the same thickness as the copper plate, and a fused enamel coating over the nickel-iron alloy.

4. A method of forming an enamel coated article which comprises copper plating a ferrous metal base. electrodepositing an alloy of from 0.50% to 10.0% iron and the balance nickel on the copper plate, and applying a vitreous enamel coating over the alloy plate.

5. In a method of forming an article, the steps of electrodepositing a copper coating on a ferrous metal base, electrodepositing a nickel-iron alloy comprising 1.50% iron and the balance nickel on the copper, applying a vitreous enamel to the coated base, and firing the article to fuse the enamel and form an enameled coating.

6. A method of forming an enamel coated article which comprises plating a copper coating on a ferrous metal base, electrodepositing a nickel-iron alloy on the copper in a plating solution comprising substantially 24 ounces of nickel sulphate and .0666 ounce of ferrous sulphate per gallon of solution at a current density around 10 amperes per square foot, applying a vitrifiable material on the coated base, and firing the article to fuse the material and form smooth and durable coating.

MORRIS BROWN. RUSSEL E. HARR.

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