US2424173A - Electrolytic production of alloy coatings - Google Patents

Description

'July 15, 1947.

K. M. HUSTON ETAL.

' ELECTROLYTIC PRODUCTION OF ALLOY COATINGS Filed April 29, 1942 l N VE N TOPS K. ALHUSTON KARAYBURN A 7' TORNEV Patented July 15, 1947 ELECTROLYTIC PRODUCTION OF'ALLOY COATINGS Kenneth M. Huston and Vincent A. Rayburn, Baltimore, Md assignors to- Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application Apr-i129, 1942,. Serial No. 440,948

9 Claims. (01. 20428) This invention relates to electrolytic production of alloy coatings and more particularly to methods of electrolytically coating continuous lengths of metallic material with a non-ferrous alloy coating.

In the manufacture of electric conductors, it

has been found to be highly desirable to brass plate conductors in order to-cause outer covering-s of vulcanized rubber to adhere firmly thereto. Heret'ofore, such brass. coatings have been applied by making the conductors cathodes while passing them through an electrolyte in which solid rods, bars or plates made of a brass alloy were employed as anodes. Since these solid anodes had to be made up especially for this purpose, the cost Of the brass coating was relatively high. Not only the cost, but the scarcity of the metal due to the great present day demand for it, has led to increased effortsv to. conserve metals and to employ reclaimed metals, Wherever possible. Further, as dissolution of the solid anodes progressed; the anode area decreased. thereby increasing the anode current density proportionately and contributing to the non-uniformity of plating conditions. In addition, the corroded anodes required considerable time for removal and necessitated a shutdown of the apparatus while they were being replaced.

An object of this invention is to provide new and improved methods for the electrolytic production of alloy coatings.

One method of coating metallic articles,.which embodies the invention comprises providing. an electrolytic cell including a metallic container which retains an electrolyte in which the metal of which the container is made is insoluble. Divided metallic material of a predetermined composition is placed in thebottom of the container in direct contact therewith and a positive potential is applied to the container which, in turn, is transmitted to the divided metallic material and makes this material the anode of the electrolytic cell. An. article to be coated is immersed in the electrolyte and made the cathode of the cell to plate it with metal anodically dissolved from the divided anode material. The composition of the metal deposit is regulatedwithin' predetermined limits. by adding to the divided anode material from time to time as the electrolysis progresses, divided metallic material containing, the metal or metal whose amounts it is desired to increase. Inorder to obtai-nthe optimum results, it is also desirable to washt-he dividedanode material with the. electrolyte to remove therefrom the sludge, formed by the impurities in the anode material which tends to cover the divided anode material and to. interfere with the anodic corrosionv thereof.

Other features and advantages of the. invention willbecome apparent .from the following. detaileddescri'ption of 'a specific embodiment thereof,.when read in conjunction with the accompanying. drawings, in which Fig. 1 is a fragmentary side elevation of an electroplating apparatus embodying the invention, a part of which is shown in section; and

Fig. 2 is a top pla'nview'of the apparatus shown in Fig. 1.

The invention may be practiced in connection with the apparatus. disclosed in the accompanying drawings in which a plurality of' conductors l0-'-|.0' are first advanced from the. right toward the left, as seen in Figs. 1 and 2; through contact rolls (not shown) which carry a negative electrical potential and which may beidentical with rolls H--l l. Through contact with these rolls, the conductors Iii-i0 are also given a negative potential; The conductors enter a container l-2 through weirs (not shown) formed in the righthand end of the container, which are similar to weirs 14-44 formed in the end [6 of the container, and leave the container through the weirs M-M'; The conductors then pass between the contact rolls I l--H which likewise have a negative potential.

A suitable electrolyte isi'ssupplied to the container [2 at a rate sufi'icient' to maintain the level of the electrolyte considerably above the bottom of the weirs in the ends-of the container. In this mannenthe conductors lilifl-are completely immersed in the electrolyte l8- during their entire passage through the container 12. The. electrolyte which overflows from the container I2- through the weirs falls into a collecting tank |9- and: is conveyed toa reservoir (not shown) from which it is later pumped back intothecontainer It;

In actual practice. the conductors may be advanc'edthrough the apparatus ata'rategas high as 500- feet per minute. so. that a pluralityofcontainers-similar to the container t2 shown in the accompanying drawings, is required to obtain a coating of the desired thickness.

The container I2 is given a positive electrical potential, so that a divided metallic material 20 lying on the bottom of the container l2 becomes the anode in an electrolytic cell in which the conductors lB-Hl form the cathodes. The divided anode material 2e may be of any composition suitable for plating the desired coating on the conductor Iii-I and may be of any suitable size, shape or configuration. The initial composite composition of the anode material is such as to supply copper and zinc ions to the electrolyte in substantiall the same proportions in which these ions are present in the electrolyte initially. In the particular embodiment of the invention now being described, the anode material is finely divided metal scrap consisting-principally of brass punchings, clippings, turnings,

bolts, nuts, washers and the like, with suficient copper and/or zinc scrap of similar origin added thereto to obtain a composite anode having a.

composition of about 65% to 90% copper and about 35% to 10% zinc.

The electrolyte i8 is pumped from a reservoir (not shown) through a pipe 2| to distributing heads 2222 connected thereto by branch pipes 23-23. The distributing heads 22-22 are insulated from the container 12 in any suitable manner; a very desirable arrangement being described in the copending application Serial No. 441,002, filed April 29, 1942, by V. A. Rayburn. Feed pipes 2424 are connected to the distributing heads 2222 and carry the electrolyte to distributing pipes 25-45, which are closed at their ends by screw caps 2626. A plurality of apertures 2l21 are formed in the distributing pipes 25-25 so as to project rapidly moving streams of electrolyte diagonally upwardly and downwardly on alternate distributing pipes 2525 and to create considerable turbulence in the electrolyte. Preferably all of the apertures 21-21 are on the left side of the distributing pipes 25-25, as seen in Figs. 1 and 2, and cause the rapidly moving electrolyte to carry the sludge washed oif of the divided metal scrap toward the left-hand of the container I2 and out through the Weirs l4l4 at that end of the tank, along with the electrolyte overflowing therethrough. The downwardly projected streams of electrolyte stir up the sludge which is on the divided anode material, while the upwardly projected streams tend to keep the sludge in suspension so that it will pass out of the container l2 throughthe Weirs l4l4 along with electrolyte in which it is suspended. The electrolyte flowing over the weirs l4-M is collected and purified by suitable means (not shown) before it is returned to the container 12. As the plating proceeds, the composition of the brass coatings plated upon the conductors is kept substantially constant by adding divided brass or copper or Zinc, or a mixture of any two or all three of these metals, to the original divided anode material in such quantities and proportions as to maintain the concentrations of the copper and zinc ions in the electrolyte substantially constant and at substantially their initial values. a

In order to more particularly describe the invention, the following specific example is given:

A plurality of lead plated bronze conductors 1 5-10 are advanced at the rate of 350 feet per minute through the contact rolls which impart to the conductors a negative electrical potential.

trolyte to be substantially 11.2.

4 The conductors are then advanced as cathodes through an electrolyte l8 retained in three containers similar to the container I2 whose combined length is 54 feet. The containers bear a positive electrical potential which is imparted to the divided metallic material held therein making this divided material the anode. A cathode current density of approximately 40 amperes per square foot is maintained in the electrolytic cell during the plating operation. employed in the container comprises 9.8 ounces of copper cyanide per gallon of electrolyte, 1.8 ounces of zinc cyanide per gallon of electrolyte, and 4 ounces of free sodium cyanide per gallon of electrolyte, together with a sufficient quantity of sodium hydroxide or sodium bicarbonate to cause the pH value of the elec- The temperature of the electrolyte is maintained at about 90 F. and the anode scrap consists of approximately copper and 20% zinc. Under these conditions, a brass plate having a composition of approximately 78% copper and 22% zinc is deposited upon the conductors.

The use of divided metallic anodes in electroplating conductors represents a material improvement over the prior art. In the present invention, metallic material containing noticeable percentages of impurities frequently found in brass, such as lead, may be used as the anode material and as a result, scrap metal may be employed. The composition of the brass alloy deposited upon the conductors l0|0 may be controlled within predetermined limits by adding metal scrap consisting principally of copper and/or zinc to that already in the container I 2 as the electrolysis proceeds. For example, should the percentage of zinc ions in the electrolyte fall below a certain minimum, sufficient metal consisting principally of zinc is added to the container to raise the amount of zinc in the electrolyte to within the range required for plating brass of the desired composition. Should the percentage of copper ions in the electrolyte drop below the minimum amount required. to plate the desired composition of brass, metal consisting principally of copper is added. Brass and combinations of brass with copper and/or zinc may be added to the anode material to regulate within predetermined limits the amounts of copper and zinc therein.

Previously the composition of a cyanide brass plating bath was usually controlled by adding the very expensive cyanide salts of copper and/or Zinc to the bath, since it was impossible to alter the composition of the solid metal anodes. The regulation of the composition of the electrolyte within predetermined limits by merely adding in divided form the metal in which the electrolyte is deficient is'simple, flexible, rapid and very much cheaper than adding the more costly cyanide salts. In addition, this procedure eliminates the loss of time which formerly was consumed in replacing anodes. Thus, the present process decreases the cost of controlling the composition of the bath, as Well as'the cost of the original anode material, while at the same time, it conserves metal which, at the present time, is extremely scarce.

A process using divided anode material is not only much cheaper than the electroplating processes disclosed in the prior art, but is better adapted to plating rapidly moving lengths of metallicstrands. Due to the speed of the movement 7 The electrolyte of the conductors lfl-Hl through the container l2, the surfaces of the conductor are exposed to the plating of the electrolyte in each container l2 for approximately three seconds. When three containers similar to container I2 are used, the conductors are immersed in the electrolyte for a total of approximately nine seconds.

In order to obtain a coating of the desired thickness upon the conductors in this short period of time, it is necessary to maintain a high cathode current density, which results in a rapid removal of copper and zinc ions from the electrolyte. Because of the relatively small surface area of the solid anodes formerly used, the copper and zinc could not go into solution at a rate equal to that at which they were plated out of solution onto the conductors. Then too, the dissolution of the anodes decreased the anode surface area which increased the anode current density. As a, result, the brass coating was non-uniform and streaky. The brass coating deposited when divided brass anodes are used is uniform, since the divided nature of the anode metal greatly increases its surface area, whereby the rate at which the anode metal will go into solution is proportionately increased. Furthermore, it is relatively easy to maintain the desired anode composition Without stopping the process by adding divided anode material from time to time as the operation progresses.

It is preferable to provide means for washing the sludge from the divided anode material, be-

cause the sludge deposited upon the anode material tends to suppress the anodic corrosion thereof. By using the electrolyte to wash the sludge from the anode material, no dilution of the electrolyte occurs and, consequently, no loss in the plating efficiency of the electrolytic bath results.

What is claimed is:

l. The method of continuously electroplating a uniform brass coating upon a metallic strand, which comprises advancing such a strand as a cathode through an electrolytic cell employing an aqueous copper-zinc cyanide electrolyte of such composition as to plate a brass coating of predetermined composition upon the strand, making a mass of divided bodies composed of metal of the group consisting of brass, copper, and zinc the anode in the cell, the initial composite composition of the anode being such as to supply copper and zinc ions to the electrolyte in substantially the proportions in which these ions were present in the electrolyte initially, passing an electric current through the cell to continuously plate a brass coating upon successive increments of the moving strand, and maintaining the composition of the brass coating plated upon the strand substantially constant by adding divided bodies composed of metal of the group consisting of brass, copper, and zinc to the divided anode bodies as the plating progresses in such quantities and proportions as to maintain the concentrations of the copper and zinc ions in the electrolyte substantially constant and at substantially their initial values.

2. The method of continuously electroplating a uniform brass coating upon a metallic strand, which comprises advancing such a strand as a cathode through an electroyltic cell employing an aqueous copper-zinc cyanide electrolyte of such composition as to plate a brass coating of I predetermined composition upon the strand, making a mass of divided bodies composed of metal of the group consisting of brass, copper, and zinc the anode in the cell, the initial composite composition of the anode being such as to supply, copper and zinc ions to the electrolyte in substantially the proportions in which these ions were present in the electrolyte initially, passing an electric current through the cell to continuously plate a brass coating upon successive increments of the moving strand, maintaining the composition of the brass coating plated upon the strand substantially constant by adding divided bodies composed of metal of the group consisting of brass, copper, and zinc to the divided anode bodies as the plating progresses in such quantities and proportions as to maintaian the concentrations of the copper and zinc ions in the electrolyte substantially constant and at substantially their initial values, and continuously washing the divided anode bodies with electrolyte to remove sludge therefrom by projectin a plurality of small, spaced, rapidly moving jets of the electrolyte into the mass of divided anode bodies so as to impinge directly upon the divided anode bodies.

3. The method of continuously electroplating a uniform brass coating upon a metallic strand, which comprises advancing such a strand as a cathode through an electrolytic cell employing an aqueous electrolyte having the composition of approximately 9.8 ounces of copper cyanide per gallon of electrolyte, 1.8 ounces of Zinc cyanide per gallon of electrolyte, and 4 ounces of free sodium cyanide per gallon of electrolyte; making a mass of divided bodies of scrap material composed of brass and metal of the group consisting of copper and zinc the anode in the cell, the initial composite composition of the anode ioeing approximately copper and 20% zinc; passing an electric current through the cell to continuously plate a brass coating having a composition of approximately 78% copper and 22% zinc upon successive increments of the moving strand; maintaining the composition of the brass coating plated upon the strand substantially constant by adding divided bodies of scrap material composed of brass and metal of the group consisting of copper and zinc to the divided anode bodies as the plating progresses in such quantities and proportions as to maintain the concentrations or the copper and zinc ions in the electrolyte substantially constant and at substantially their initial values; and continuously washing the divided anode bodies with the electrolyte to remove sludge therefrom by causing a plurality of small, rapidly moving jets of the electrolyte to impinge directly upon the divided anode bodies, said jets being directed in one general direction but alternately upwardly and downwardly whereby a turbulent stream of the electrolyte is produced.

4. The method of continuously electroplating a uniform brass coating upon a metallic strand, which comprises advancing such a strand as :a cathode through an electrolytic cell employing an aqueous electrolyte having the composition of approximately 9.8 ounces of copper cyanide per gallon of electrolyte, 1.8 ounces of zinc cyanide per gallon of electrolyte, and 4 ounces of free sodium cyanide per gallon of electrolyte; making a mass of divided bodies of scrap material composed of brass and metal of the group consisting of copper and zinc the anode in the cell, the initial composite composition of the anode being approximately 80% copper and 20% zinc; passing an electric current through the cell to continuously plate a brass coating having a composition of approximately 78% copper and 22% zinc upon successive increments of the moving strand; and maintaining the composition of the brass coating plated upon the strand substantially constant by adding divided bodies of scrap material composed of brass and metal of the group consisting of copper and zinc to the divided anode bodies as the plating progresses in such quantities and proportions as to maintain the concentrations of the copper and zinc ions in the electrolyte substantially constant and at substantially their initial values.

5. The method of continuously coating metallic strands, which comprises advancing a metallic strand as a cathode through an electrolytic cell including an aqueous brass plating electrolyte, mixing divided scrap composed of brass and metal of the group consisting of zinc and copper in such proportions as to provide a composite composition of from about 65% to about 90% copper and from about 35% to about zinc, making the divided scrap material the anode in the cell, passing an electric current through the cell to plate a brass coating of a predetermined composition upon the metallic strand, adding sufiicient finely divided scrap of the group consisting of brass, copper and zinc to the anode mixture at intervals as the plating progresses to maintain substantially constant the composition of the brass plating electrolyte thereby producing a brass plating of substantially uniform composition upon the strand, and continuously supplying the brass plating electrolyte to the electrolytic cell in a plurality of small, rapidly moving jets which enter the cell at spaced points in direct contact with the divided anode material, whereby sludge is washed from the anode material.

6. lhe method of coating metallic strands, which comprises making such a strand a cathode in an electrolytic cell including an aqueous alkaline cyanide brass plating electrolyte, making a thin layer of divided scrap material of the group consisting of brass, zinc and copper the anode in the cell, the initial composite composition of the anode being such as to supply copper and zinc ions to the electrolyte in substantially the proportions in which these ions were present in the electrolyte initially, passing an electric current through the cell to plate a brass coating upon the strand, adding sufficient finely divided scrap material of the group consisting of brass, zinc and copper to the layer of divided anode material at intervals as the plating progresses to maintain substantially constant the composition of the brass plating electrolyte thereby producing a brass coating of substantially uniform composition upon the strand, and continuously supplying electrolyte to the cell in the form of a plurality of small, rapidly moving jets introduced at spaced points adjacent to the divided anode material so as to impinge directly upon the anode material, whereby sludge is washed from the divided anode material.

'7. The method of coating metallic strands, which comprises rapidly advancing such a strand as a cathode through an electrolytic cell, causing an elongated stream of an aqueous alkaline cy anide brass plating electrolyte to pass longitudinally along the strand, making an elongated, thin layer of divided scrap material consisting of metals of the group consisting of brass, zinc and copper the anode in the cell, said metals being present in said layer in such proportions as to provide a composite brass anode of a predetermined composition, which will supply copper and zinc ions to the electrolyte in substantially the proportions in which these ions were present in the electrolyte initiall passing an electric current through the cell to plate a brass coating upon the strand, adding sufficient finely divided scrap material of the group consisting of brass, Zinc and copper to the layer of divided anode material at intervals as the plating progresses to maintain substantially constant the composition of the brass plating electrolyte thereby producing a brass coating of substantially uniform composition upon the strand, and continuously supplying the electrolyte to the cell solely in the form of a plurality of small, rapidly moving jets introduced at spaced points adjacent to the divided anode material so as to impinge directly upon the anode material, said jets being directed in one general direction but alternately diagonally upwardly and downwardly, whereb a turbulent stream of electrolyte is produced which washes sludge from the divided anode material.

8. The method of continuously brass plating metallic strands, which comprises imparting a positive electrical potential to an elongated, insoluble metal container, placing a thin layer of divided scrap material consisting of brass and copper on the bottom of the container, whereby a positive potential is imparted to the divided material, causing a stream of an aqueous alkaline cyanide brass plating electrolyte of sufiicient depth to cover the divided scrap material to flow over the scrap material, the initial composite composition of the anode being such as to supply copper and zinc ions to'the electrolyte in substantially the proportions in which these ions were present in the electrolyte initially, continuously passing a metallic strand as a cathode through the electrolyte in the container to cause a brass plate to be deposited thereon, adding (11-- vided scrap material consisting of brass and copper to the layer of divided anode material as the plating progresses in such quantities and in such proportions as to maintain the plating conditions substantiall constant, and continuously supplying the electrolyte to the container solely in the form of a plurality of small jets of high velocity introduced at spaced points near the bottom of the container so as to impinge upon the divided anode material, whereby sludge is washed from the divided anode material.

9. The method of continuously brass plating metallic strands, which comprises imparting a positive electrical potential to an elongated, insoluble metal container, placing a thin layer of divided scrap material consisting of brass and metal of the group consisting of zinc and copper on the bottom of the container, whereby a positive potential is imparted to the divided material, causing a stream of an aqueous alkaline cyanide brass plating electrolyte of sufiicient depth to cover the divided scrap material to flow over the scrap material, the initial composite composition of the anode being such as to supply copper and zinc ions to the electrolyte in substantially the proportions in which these ions were present in the electrolyte initially, continuously passing a metallic strand as a-cathode through the electrolyte in the container to cause a brass plate to be deposited thereon, adding divided scrap material consisting of brass and metal of said'group to the layer of divided anode material as the plating progresses in such quantities and in such proportions as to maintain the plating 7 conditions substantially constant, and continuhigh velocity introduced at spaced points near the bottom of the container so as to impinge upon the divided anode material, said jets being directed in one general direction but alternately diagonally upwardly and downwardly, whereby a turbulent stream of electrolyte is produced which washes sludge from the divided anode material KENNETH M. HUSTON.

VINCENT A. RAYBURN.

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

UNITED STATES PATENTS Number Name Date 1,363,186 Merritt Dec. 21, 1920 1,768,358

Number Name Date Re. 17,141 Rosenquist Nov. 20, 1928 898,189 Cowper-Coles Sept. 8, 1908 FOREIGN PATENTS Number Country Date 19,411 Great Britain 1906 312,600 Great Britain May 27, 1929 OTHER REFERENCES Principles of Electroplating and Electroforming, by Blum and Hogaboom, second edition (1930), pages 380 and 381.

Applied Electrochemistry, by Allmand and Ellingham, second edition (1924), page 358.

Modern Electroplating, special volume by The Electrochemical Society (1942), pages 87 to 99, inclusive.

Electrochemistry, by Creighton and Koehler,

arriso J1me 1930 20 first edition, volume II (1935), page 149.

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