US2571709A - Apparatus for electroplating articles - Google Patents

Description

Oct. 16, 1951 A. N. GRAY APPARATUS FOR ELECTROPLATING ARTICLES 2 SHEETS--SHEET 1 Filed Aug. 26, 1947 INl ENTOR AN. GRA Y BY A 7'7'ORNEV Oct. 16, 1951 A. N.H GRAY I APPARATUS FOR ELECTROPLATING ARTICLES Filed Aug. 26 1947.

ot g My 7 TA W r Lfu l l NN a H v, 8 N 6? ob x Mn L A TTORNE V Patented Oct. 16, 1951 APPARATUS FOR ELECTROPLATING ARTICLES Alvin N. Gray, Joppa, Md., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application August 26, 1947, Serial No. 770,645

1 Claim.- 1

This invention relates to apparatus for electroplating articles, and more particularly to apparatus for electroplatin filamentary articles.

In the manufacture of metal-covered articles, such as conductors having steel cores surrounded by coatings of copper, it is desirable to deposit the metal coatings on the cores electrolytically. The rate of electrodeposition of metal upon a core varies directly with the current density on the surface of such a core. The total current passing into such a core is proportional to the voltage applied between the core and the material forming the other electrode. Hence, the apparent average current density on the core would.seem to be directly proportional to this voltage, and the higher the current density, the higher the rate of electrodeposition upon the cores.

However, in the past it has been found that hydrogen barriers have been formed partially around the cores when high current densities have been used, and these barriers prevent current from passin therethrough. Consequently, instead of having a uniform current density on the entire periphery of such a core, the current density would be very high in some portions of the cores and quite low in other portions of the cores where hydrogen bubbles are adhering. Hence, while the apparent average current density of the core might not appear to be high, the phenomenon known as burning would occur, and the metal deposited on at least some portions of the core would be coarserained and flaky, and would not adhere firmly to the core. Hence, lower current densities had to be used to plate cores satisfactorily. As a result, relatively low rates of plating were all that could be effected.

It is desirable to develop satisfactory methods by which high current densities may be em-' ployed to plate metals rapidly and uniformly on conducting cores, such as wires and the like. Also it is desirable to provide suitable apparatus which the several variables present in electroplatingprocesses may be controlled and adjusted in order that full scale operations may be simulated, and optimum conditions for electroplatin processes may be determined without the necessity of building and testing large installations.

An object of the invention is to provide new and improved apparatus for electroplating articles.

A further object of the invention is to provide new and useful apparatus by means of which full scale electroplating operations may be sim ulated without the use of full scale apparatus.

An apparatus illustrative of certain features of the invention includes a container for holding an electrolyte, means for immersing an article to be electroplated in an electrolyte held in the container, means for applying a difference of potential between the article and the container, means for effecting relative movement between the article and the electrolyte, and means for varying the operating conditions of the resulting electroplating cell to control the plating of the article.

A complete understanding of the invention may be obtained from the following detailed description of an apparatus illustrative of certain features thereof, when read in conjunction with the appended drawings, in which:

Fig. 1 is a top, plan view of an apparatus illustrative of certain features of the invention;

Fig. 2 is an enlarged, vertical section taken along line 2-2 of Fig. 1, and

Fig. 3 is an enlarged, vertical section taken along line 3-3 of Fig. 1.

Referring now in detail to the drawings, there is disclosed therein an apparatus for simulating actual conditions to be encountered in a fullsize electroplating apparatus for depositing metal on continuous articles, such as steel or copper wires, which are advanced through the apparatus continuously. This apparatus includes a mixing tank In for mixing and storing a supply of a cyanide copper plating electrolyte, which is one of several metal-bearing electrolytes. which may be used in the apparatus. A suitable pump unit serves to pump the electrolyte from the tank l0 through pipes l2, I3 and M to a filter unit I5 of a well-known type of construction, and from the filter unit l5 through a pipe IE to a tank H. A pipe l8 having a valve [9 therein connects the tank ll to the pipe I3 so that the electrolyte may be pumped from the tank to the filter unit through the pipe [4 or back to the mixing tank It through a pipe 26.

A steel wire 36, upon which copper is to be plated, is secured at one end to an eye bolt 3| of conductive material. The eye bolt 3| is fastened to a wall 32 (Fig. 2) of a container 33 and is insulated therefrom by a fitting 34 made of a suitable insulating material, such as hard rubber, a polymerized chloroprene (neoprene) compound, or the like. The wire 30 is strun through a close-fitting bore 35 ina T-coupling 3G composed of a suitable insulating material, such as a polymerized chloroprene compound, through a tapped bore 40 formed in the elbow 36, and through a copper pipe 4| having'one end threaded into the tapped bore 40 and the other end threaded into a tapped bore 42 formed in a T-coupling 43 composed of an insulating material, for example, a polymerized chloroprene compound. The wire 3i! passes through the T- coupling 43, a short nipple 44 and a bore 45 formed in. a cap..45.,composedofinsulating material, such as apelymerized Ichloroprene com pound.

The wire 36 is connected electrically and mechanically to a negative conductor 59 of a direct current power line by an eye 130113551, a turnbuckle 52 and a rod 53, which is mounted in an insulating fitting 54. The fitting 54 is positioned in a bore 55 formed in a wall Bfi-ofthe container 33, and the rod 53 is fastened mechanically'to the fitting 54- and electrically to the conductor 50. A conductor 60 connected-*inparallel with the conductor 50 is connected electrically to the.

eye bolt 3! so that both ends of the wire 30 are maintained at the same potential.

A supply pipe 10 connects an inlet port II of theTecoupling 1 33 too. variable output pump I2 (Fig. 1) of standard design. The supply pipe iii supports the elementsfifi, 4|, 43, M and" it in positions completely out of contact with the container 33. The pump 72 is or" the vertical centrifugal type, and may be manually adjusted to deliver any desired rateof flow. The pump 72 serves to pump the electrolyte from the tank I! through a pipe 23, a rubber hose id; afioattype of flow meter 15 of a conventional design, a rubber hose 88, a pipe 8!, the pipe it, the"?- coupling #3, the copper pipe 4|, the 'T-coupling 36 and hoses B5 85 to a .sump 83 of the tank ill. The copper pipe M is maintained at a positive potential by a positive conductor 82 of the direct current power-line, which includes the negative conductors 55 and 66. A rheostat 3 8 is provided for varying the voltagebetween the conductor 82 and the conductors iiiand 5e, and an ammeter 84 serves tomeasure the current flowing through the conductor 82.

In the operation of the apparatus described hereinabove, tocarry out one method illustrating certain features of the invention, the steel wire 3a is secured in place, and the electrolyte :is pumped through the copper pipe bythe pump 12 'at a high rate of speed to simulate the speed at which a conductor, such as a steel wire, would be advanced through an elongatedfull-size electroplating tank. The relative velocity between the stationary wire 38 and the electrolyte may be computed by dividing the reading of the meter 75, which measures the volume of flow of the electrolyte per unit of time, by the difference between the cross-sectional area of the interior oi. the pipe 4i and the cross-sectional area of-the conductor 30, both of which are known. The pump (2 may be adjusted to pump the electrolyte through the pipe 4! at any velocity within the range of. the pump unit. The copper pipe 5] acts as a soluble anode, and when it has been weakened as it is eaten away, it may be-replaced by a new copper pipe.

It has been found that by forcing the electrolyte through the copper pipe M at a high velocity, hydrogen plating of the wire 38 is pre vented and, as a result, the rate and quality of electrodeposition of copper upon the wire '36 are high. Also, when there is high'r'elative velocity between the electrolyte and the wire 3ll,.so that any hydrogen --tending-to cling to the wire 39 is washed loose therefrom-the current density onthe wire 3ii-is uniform. Hence, the-computed or apparent average current density on-the Wire 30 when there is a highcurrentfiowing between theelectrolyte and the wire 36) closely approximatestheactual current density on any por electrolyte and cathode may be determined without the necessity of experimenting with an electroplating apparatus of the large size required for commercial production. For example, the

velocity of relative movement between the electrolyte and the wire 30 may be varied over a wide range. Also, the potential difference between the wire 30, which is the cathode, and the copper pipe 4|, which is the anode, may be varied as desired by means of the rheostat 18 to vary the current density on the wire 3i] so that the highest current density to give a satisfactory plating on the wire 38 for a predetermined velocity of relative movement between the wire and the electrolyte may be determined.

The temperature of the electrolyte may be controlled by immersing one or more tubular coils in the electrolyte at appropriate points and by passing either a refrigerant or a heating medium therethrough. By this means the temperature of the electrolyte may be maintained constant, while the other variables, such as the cathode current density and the velocity of movement, are varied or the other variables may be maintained constant while the temperature is changed. The use of temperature controlling coils of this type is common in the electroplating art, and persons skilled in that art will be able to employ such coils where needed without a specific illustration of such coils in the drawmg.

In order to describe the invention fully, the following specific examples are given of tests made by the use of apparatus of the type described hereinabove:

Example I A length of high strength steel wire having a diameter of 0.032" was affixed in an apparatus such as has been described previously in the position occupied by the wire 30 in the drawings. A three-quarter inch copper pipe was used as the anode through which the steel Wire extended.

he electrolyte was a known copper-potassium cyanide plating solution similar to that described on pages 174 and 1'75 of Modern Electroplating, published in 1942 by The Electrochemical Society, 1110., except that it did not contain any brightener or anti-pit agent, but did contain a quantity of potassium carbonatesuch as iscommon in cyanide copper plating baths.

This electrolyte was pumped through the copper pipe at the rate of 2.24'feet per second, and the voltage applied was varied to determine the optinmm cathode current densities for plating copper rapidly and uniformly on the steel wire. The temperature 'of the electrolyte was kept substantially constant at about 175 Fxwhile this test was being made. It was found that under these conditions, the optimum cathode current density'iell within the range of from about 46 to about 50 amperes per square foot.

Example II In this exam'ple the same electrolyte was employed'as lwas'use'cl-in' Example I, the same kind and size Oman wire-'was-used as the cath'ode,

the same size copper tube was used as the anode, and the same bath temperature was employed. The electrolyte was pumped through the copper tube at a velocity of 3.35 feet per second, and the cathode current density was varied by varying the applied voltage until the optimum current densities were ascertained. It was found that when the apparatus was operated under these conditions, the optimum cathode current density was from about 65 to about 75 amperes per square foot.

Example III The electrolyte, anode, cathode and bath temperatures employed in this example were the same as were employed in the previous examples. However, in this particular case, the solution was pumped through the copper tube forming the anode at a rate of 4.5 feet per second, and it was found that under these conditions the optimum current density was increased to from about 90 to about 100 amperes per square foot.

These examples emphasize the fact that as the velocity of relative movement between the cathode and the electrolyte increases, the optimum cathode current density increases. This means that a much higher rate of deposition would be possible with a rapidly moving wire than would be the case with a wire moving slowly through the electrolyte.

Obviously, the procedure employed to determine optimum operating conditions could be changed so that the applied voltage is maintained constant, and the velocity of flow of the electrolyte through the anode tube is varied until the optimum velocity of relative movement between the cathode and the electrolyte could be determined for a given applied voltage, or, in other words, for a given cathode current density.

Other electrolytes may be used with the abovementioned apparatus to copper plate a wire connected as a cathode in the apparatus described. For example, a solution containing copper fiuosilicate, copper pyrophosphate, copper fluoborate, copper sulphate, copper sulphamate, copper aryl sulphonate, or other suitable copper salt could be used in place of the copper cyanide solution referred to hereinabove.

Furthermore, if desired, other types of wires may be plated by suitable metals. If so, the copper pipe 4| may be replaced by a pipe of the plating metal to be used and a suitable electrolyte is used. Also, an insoluble anode ipe, such as a carbon pipe, could be used in place of the pipe M and the electrolyte replenished by known methods. For example, a copper wire might be plated with brass, lead, nickel, chromium or tin, employing known plating baths and a soluble or an insoluble anode as required by the plating bath used.

What is claimed is:

An apparatus for copper plating steel wires, which comprises a container, 2. copper pipe extending along the container, a drain fitting composed of electrical insulating material secured to one end of the pipe and having an opening in alignment with the pipe through which a steel wire to be plated may extend in closefitting relationship, said fitting having a channel for directing liquid from the pipe, a supply fitting composed of electrical insulating material secured to the other end of the pipe and having an opening in alignment with the pipe through which the steel wire may extend, said supply fitting also having a channel for directing liquid to the pipe, a supply pipe connected to the supply fitting and supporting the supply fitting, the copper pipe and the drain fitting in positions out of contact with the container for supplying electrolyte to the copper pipe, electroconductive wire-streaching elements connected to and electrically insulated from the walls of the container for supporting the steel wire in a position centered for creating a difference of potential between the copper pipe and the wire-stretching elements.

ALVIN N. GRAY.

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

UNITED STATES PATENTS Number Name Date 28,590 Mathews, Jr. June 5, 1860 1,068,411 Chubb July 29, 1913 1,322,494 Merritt Nov. 18, 1919 1,476,284 Clark Dec. 4, 1923 1,731,269 Rich Oct. 15, 1929 1,886,218 Olin et a1. Nov. 1, 1932 1,927,162 Fiedler et a1 Sept. 19, 1933 2,392,687 Nachtman Jan. 8, 1946 FOREIGN PATENTS Number Country Date 667,252 France June 10, 1929

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