US2422902A - Method of electrolytically cleaning and plating conductors consisting principally of copper - Google Patents

Description

June 1947' K. M. HUSTON 2,422,902

METHOD OF ELECTROLYTICALLY CLEANING AND PLATING CONDUCTORS CONSISTING PRINCIPALLY OF COPPER Filed Feb. .24, 1942 FIG. I

IN VEN TOR K. MHU TON ,4 rromvn Patented June 24, 1947 METHOD OF ELECTROLYTICALLY CLEAN- ING AND PLATING CONDUCTORS GON- SISTING PRINCIPALLY OF COPPER Kenneth M. Huston, Baltimore, Md., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application February 24, 1942, Serial No. 432,149

3 Claims. 1

This invention relates to methods of treating metal articles and more particularly to continuous methods of electrolytically cleaning and plating wires.

Considerable difficulty has been experienced in commercially producing lead covered conductors having a. strongly adherent coating of lead and in brass plating such a coating of lead. In one method of production, a conductor is passed through a cleaning bath consisting of fused alkali metal compounds, washed and quenched in a cold water bath and then carried into a lead electroplating bath.

It was found that when a lead coated conductor produced by this method was passed through the core tube of a rubber extruding machine in. order to apply a rubber covering, the lead coating occasionally was sheared free from the conductor and piled up in front, of the core tube. Thus, the core tube opening became so restricted that the conductor could no longer pass through and would break. The time lost while the machine was being put intooperating condition after such an occurrence, as well as the loss of material, added materially to the cost of production.

The prevailing practice of lead plating and brass plating conductors at widely separated times necessitates cleaning the conductors before the brass plating operation to remove the lead oxide coating found thereon. This cleaning operation is both time consuming and costly.

An object of this invention is to provide new and improved processes for continuously electrolytically cleaning and plating articles.

These and other objects are accomplished by the improved methods comprising the present invention, as shown in the annexed drawing and hereafter described.

In general, an improved process of treating metallic articles embodying the present invention includes immersing the article in a molten cleaning bath, and making the article an electrode in an electrolytic cell in which the electrolyte consists of a solution of fluosilicic acid. The article is then made a cathode and sequentially passed through a lead electroplating cell and a brass electroplating cell. 7

The accompanying drawing illustrates diagrammatically one form of apparatus in which a process embodying the present invention may be practiced. In the drawing,

Fig. 1 is a vertical, longitudinal, sectional view oi a portion of an apparatus for cleaning and plating wire. and

Fig. 2 is a continuation of Fig 1 and is a view like Fig. 1 of the remaining portion of the apparatus.

Referring now to the drawing, the numeral Ill designates a conductor which may be made of any of several kinds of metal. For example, the conductor may consist of or be surfaced with copper, tin, lead or stainless steel, or one of the alloys copper-tin, lead-tin, lead-antimony and lead-tinantimony. The invention is particularly useful in the treatment of a bronze conductor which may have some tin left on the surface thereof from a previous drawing operation,

The conductor I0 is first passed through a cleaning bath l I which, in this particular embodiment of the invention, consists of a mixture composed of equal amounts of fused sodium hydroxide and sodium nitrite. Sodium nitrate maybe substituted for either of the above ingredients, or a mixture of all three components may be used. The corresponding potassium compounds may likewise be used, if desired. The fused bath serves to remove grease and other impurities from the wire.

The bath I I may be kept at temperatures varying from 500 F. to 1000" FL, so that the conductor may be annealed as well as cleaned during its passage through the bath. This is especially important when the conductor being treated is a hard copper wire, for such a conductor may be annealed to lower the hardness thereof to the desired degree by controlling the temperature of the bath ll. The level of the molten bath is kept above the conductor in order to thoroughly cover it and in actual practice, the overflow is caught in a tank (not shown), from which the molten material is recirculated to the bath II by any suitable pumping device. A wiper l2 removes the excess material-still clinging to the conductor as it is withdrawn. from the cleaning bath II.

From the bath l l the conductor passes through a water bath M, which acts both as a quench and a wash. Positioned at the outlet of the bath I4 is a wiper I 5 for removing the excess water before the conductor passes between contact rollers l6 and I8 which transmit an electrical charge to the conductor. In the particular embodiment of the invention wherein a bronze conductor containing some tin upon its surface is treated, the conductor receives a negative charge, but the conductor may be made either the anode or the cathode depending upon the type of conductor being treated.

From th contact rollers l6 and I8, the conductor passes into a cleaning tank I! provided e wvwmsmm with a lining 20 made of a suitable insulating and corrosion resistant material, such as rubber, and containing an electrolyte 2i consisting of an aqueous solution of fluosilicic acid of from about 10% to about 60% concentration. The temperature of the electrolyte 2| is kept below 85 F. to prevent excess volatilization of the fluosilicic acid. A graphite anode 22 is used to complete the electric circuit, although any other suitable anode not interfering with the operation of the bath would be equally effective. The electrolytic action which takes place in the cleaning tank l9 removes the other deleterious impurities not removed from the conductor by the fused bath 1 I.

The conductor leaves the cleaning tank l9 through a wiper 24, then passes between contact rollers 25 and 26 which impart a negative potential to the wire, and enters a lead plating tank 21. Like the tank IS, the lead plating tank 21 is provided with a corrosion resistant, insulating lining 29. The tank 21 holds an electroplating solution 30 which consists of a solution of lead fiuosilicate and free fiuosilicic acid, the concentrations of the ingredients being such as to obtain the desired lead plate upon the conductor. Lead anodes 3l-3I are suspended in the plating bath.

30 to keep the lead concentration of the electroplating solution substantially constant, since the lead plated out on the conductor I is replaced by lead going into solution from the lead anodes. The conductor is drawn out of the lead plating tank 21 through a wiper 33.

The conductor ll passes through washing means wherein the electrolyte carried out of the tank 21 by the conductor is removed from the conductor. This washing means is shown schematically in Fig. 2 of the drawings as a wash tank 34 containing a wash fluid 35, such as water. From the tank 34 the conductor advances between negatively charged contact rollers 36 and 38 into a bras-s plating tank 39. The tank 39 is lined with a suitable corrosion resistant insulating lining 40 and is provided with a wiper 42 positioned at the outlet end thereof. A lbrass plating solution 43 held in the tank 39 contains zinc and copper ions in solution in such a ratio that a brass plate of the desired composition is deposited upon the conductor I0. Brass anodes 46--46 supply zinc and copper ions to the brass plating solution 43 in order to maintain a constant concentration of these ions therein.

A suitablewashing means is provided to remove the electrolyte carried upon the surface of the conductor after it leaves the tank 39. In the drawings the washing means is represented schematically as a wash tank 44 containing a wash liquid 45, such as water. Suitable means, not shown, are provided for advancing the conductor through the apparatus described hereinabove.

Not only does the presence of fluosilicic acid in both the electrolytic cleaning bath 2| and the lead plating bath 30 obviate the necessity of a wash ibath between the cleaning and plating operations, but, in addition, the fluosiliclc acid dragged out by the conductor from the cleaning bath 2| aids in maintaining the requisite free acid concentration in the plating bath 30.

It has also been found that when the conductor enters the electrolytic cleaning bath, it is largely free from contaminating inorganic matter.

However, in the processes of the prior art some alkaline matter from the molten cleaning bath frequently is retained in crevices in the surface of the conductor and tends to inhibit the depositionof lead upon the conductor in the subsequent plating operation which is carried out in an acid bath. This alkaline material cannot be removed readily by mechanical means. Because of the inhibiting action of the contaminating alkaline matter, a conductor cleaned by the prior art processes may pass some distance through the lead plating bath before any coating is formed upon the conductor. In accordance with the process of this invention, the fiuosilicic acid cleaning bath not only removes other deleterious matter from the conductor, but also chemically removes all of this alkaline matter from the conductor, thus permitting a thicker as well as a more adherent lead coating to be deposited upon the conductor.

It was the prior practice to wind the lead plated wire onto reels and allow it to stand until it was to be brass plated. While so standing the lead coating oxidized and the oxide coating had to be removed by special cleaning methods before a brass plate could be applied.

When the lead covered conductor is brass plated immediately after becoming coated with lead, the lead coating has no opportunity to become corroded and the conductor may be set aside for a considerable period of time and subsequently coated with rubber without any additional cleaning of the conductor being necessary. Thus the electroplating of lead and brass on the conductor in tandem as described reduces materially the time and cost of producing the resultant product. By means of this process conductors may be treated at a rate as high as 500 feet per minute.

It is obvious that in actual commercial use, the invention will include the treatment of several conductors at once and not merely one conductor as shown in the diagrammatic sketch presented in the drawing.

The detailed description has had particular reference to the cleaning and plating of electrical conductors, but it is to be understood that the invention is equally applicable to the treatment of metallic strip'or sheet material and of separate metallic articles.

The accompanying drawing is merely a schematic presentation of an apparatus by means of which the invention may be practiced and does not purport to show a complete apparatus. For example, any suitable type of means for supplying electrolytes to the various cleaning and plating tanks may be used. In addition, any means suitable for collecting the overflow from the various tanks is contemplated.

What is claimed is:

1. The process for treating conductors consisting principally of copper, which comprises making such a conductor an electrode in an electrolytic cell in which the electrolyte consists solely of an aqueous solution of fluosilicic acid containing at least 10% but not more than about 60% of said acid, and immediately introducing said conductor into a lead plating bath con Jisting essentially of a solution of lead fiuosilicate and free fluosilicic acid.

2. The process for continuously treating bronze conductors, which comprises rapidly passing such a conductor as a cathode through an electrolytic cell in which the electrolyte consists solely of an aqueous solution of fluosilicic acid of from about 10% to about 60% concentration, and immediately and simultaneously passing said conductor through a lead plating bath consisting essentially of a solution of lead fluosilicate and free fiuosilicic acid.

3. The process for continuously cleaning and plating bronze conductors partially coated with tin, which comprises continuously and simultaneously advancing such a conductor as a cathode through an electrolytic cleaning cell in which the electrolyte consists solely of a fluosilicic acid solution of from about 10% to about 60% concentration, advancing the conductor directly from the electrolytic cleaning cell through a lead electroplating cell including an electrolyte consisting essentially of a solution of lead fiuosiiicate and free fluosilicic acid, and making the moving conductor a cathode in the lead electroplating cell to cause lead to be deposited thereon.

KENNETH M. HUSTON.

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

Number OTHER REFERENCES 1 Trans. Eiectrochem. $00., v01. 80 (1941), pp.

(Copy in Div. 56.)

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