US2560534A - Method of operating a continuous electroplating system - Google Patents

Description

July 17, 1951 ADLER 2,56%534 METHOD OF OPERATING CONTINUOUS, ELECTROPLATING SYSTEMS Filed July 12', 1946 Patented July 17, 1951 METHOD OF OPERATING A CONTINUOUS ELECTROPLATING SYSTEM Orville E. Adler, Niles, Mich., assignor to National- Standard Company, a corporation of Michigan Application July 12, 1946, Serial No. 683,096

1 Claim. (01.. 204-28) 1 This invention relates to a continuous electroplating system and a method of operating the same, and more particularly to a system in which .electric current is introduced continuously to a conductive body, such as a wire, through a deplating liquid contact.

In continuously plating wires, for example with copper, it has heretofore been customary to feed the wire over metal wheels and utilize one or .more of these wheels as one of the electrodes in the plating system. The wheel electrode has always had a considerable number of disadvantages. It was impossible to eliminate sparking. The resistance of the contact was not constant over short periods of time, and over long periods of time would vary enormously due to accumulations of dirt, grease, and electrolyte on the bearings through which the current was supplied.

Furthermore, the wires had to be brought into considerable tension upon the rotating contacts in order to assure a good contact, and this tension led to frequent breakages of the wire. A break in the wire was a very serious matter because re-establishment of the system required a considerable time and a considerable amount of labor, and in many cases meant the stopping not only of the single broken wire but of the other wires undergoing treatment. Normally sixteen or more wires are plated in a single bath.

In the present system these difiiculties are all overcome by the provision of at least one, and preferably two contact cells or electrolytic contacts, through which the current is introduced to the wire. The current is then removed from the wire through the plating electrolyte. It is obvious that the contact electrolytes through which the current is introduced will act as deplaters and theoretically will remove the same electrochemical equivalent of metal that is plated in the plating bath. [have found, however, that the electrolyte in the deplating baths may be readily selected so that the deplating efiiciency thereof is markedly less than the plating efliciency of the plating bath, with the result that only a small deplating action occurs. Furthermore, in a system in which two electrolytic contacts are employed, one before the plating bath and one after it, the deplating effect in part is used up upon the underlying metal, and in many cases the loss of this metal will do no appreciable harm and may even be an advantage. If desired, the deplating may all be carried out upon the underlying metal, but I have found that this is not necessary if the deplating bath is properly selected for low efficiency. The deplating baths 2 may of course be interspersed between a plurality of plating baths.

The invention is illustrated diagrammatically in the drawing, in which [0 represents a wire being fed continuously through the system. The wire passes first through the contact cell l I, then through the plating cell l2, and finally through the second contact cell I3. The contact cell II and the contact cell [3 are both connected to the negative pole of a generator I4 The positive pole of the generator is connected through the .usual electrodes to the electrolyte I5 in the plating cell 2. The contact cell ll contains an electrolyte l6, and the contact cell l3 contains an electrolyte IT. The usual electrical means for adjusting the current density are not indicated in the drawing, but are of courseutilized in the usual manner.

In some cases it is possible to use the same electrolyte in the contact cell as that used in the plating cell by adjusting the current density in the contact cell to provide less efiiciency therein. In almost all cases this may be done by raising the current density in the contact cell. Contact cells are, therefore, preferably made small, or the electrodes therein made small in order to provide a higher current density than .that in the plating cell.

vfrom the anode necessarily does so because it establishes substantial anode polarization.

The process has been found particularly desirable in plating copper upon hot galvanized ,steel wire of the type described in Domm Paten 2,002,261.

' In this process steel wire having approximately the following composition:

Per cent Carbon .65 Manganese .80 Phosphorus .015 Sulphur .025 Silicon .095

is coated with zinc by a hot galvanizing process and thereafter is provided with a thin coating of electrolytic copper.

In carrying out the present process on such wire, it is preferred to use a solution of trisodium phosphate in the preplating contact cell. A solution of 4. oz. per gallon is quite satisfactory. In the postplating cell a copper plating solution having the same composition as the plating bath itself may be employed. The plating solution itself consists preferably of approximately 35 grams per liter of copper, and 25 grams per liter of free cyanide, with or without carbonate in the desired proportions.

The material in the postplating cell may be varied considerably. For example, a solution consisting of 85 grams per liter of copper, 7 grams per liter of free cyanide, and 30 grams per liter of lye is satisfactory.

Using these baths in the postplating cell, and an anode current density of 1100 amperes per square foot, a deplating efliciency of only 7% is produced.

In the preplating contact cell, the trisodium phosphate may be replaced by any material having a low deplating effect, or in those cases where the deplating effect in this cell is of no importance, may be replaced by any electrolyte, but preferably one which will not adversely affect the composition of the plating bath.

I have used trisodium phosphate at temperatures of 80, 100 and 150 F. I have likewise used sodium carbonate, sodium silicate, and sodium tetraphosphate. In the case of sodium silicate, 4 oz. of Na2SiO3, plus /2 oz. of NaOH was employed.

In a preferred example, 4 oz. of NaOI-I and 4 oz. of NaCN were used per gallon andthe operation was conducted at a temperature of 180 F.

The solution in the preplating bath should of course be one which does not chemically affect, in any disadvantageous manner, the underlying surface.

It is preferred in the postplating cell to use a solution similar to that in the plating bath because in this way any dissolved metal will not interfere with the bath, which may be circulated with the solution of the main plating bath and kept at constant concentration.

However, other solutions may be employed in the postplating cell so long as they do not chemically affect the plated metal and provided they may be caused to give a low deplating efiiciency. For example, in connection with the copper plating already described, oxalates, tartrates, and chlorides have been employed with satifactory deplating efiiciencies.

The process of the present invention may be employed with any metal plating or other plating bath. Zinc, cadmium, tin, arsenic, antimony and nickel will most commonly be used. With each such metal for plating, the selection of the pre and postplating contact baths may easily be accomplished. In most cases the plating bath itself may be employed by adjustment of current den- 'sity, and generally it is desirable to increase the current density to a point many times that at which customary plating is carried out. For example, in connection with copper, the customary current density is around 30 amperes per square foot in a cyanide bath. I prefer to have the deplating bath at densities at least ten times, and preferably 35 to 40 times, the preferred operating densities. The system is particularly valuable for plating alloys such as brass or bronze. In such cases the composition of the plated alloy depends upon the current density. By using the present system it is possible for the first time to procure complete regularity of the deposit.

The word deplating is used in the specification to describe the metal-removing action on the wire as an anode, regardles of whether the metal being electrolytically removed is actually a plate, or is merely base metal.

The trisodium phosphate preplating bath is also valuable as a cleaning agent and gives a combined cleaning and current feeding action.

This application is a continuation-in-part of my co-pending application Serial N 0. 355,838, filed September 7, 1940, now abandoned.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessar limitations should be understood therefrom.

I claim:

A method of electroplating a continuous zinc coated steel base which comprises passing said base through a plating bath of cyanide and copper in which the base is a cathode of an electric circuit, and thereafter passing said base through a second bath of cyanide and copper in which the metal base is an anode of said circuit, maintaining the base free from any solid electric contact during its passage through said baths, regulating the current density in the plating bath to give an efiicient plating operation, and establishing a very high current density in the second bath whereby only very slight electrolytic removal of plated metal occurs in said bath.

ORVILLE E. ADLER.

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

UNITED STATES PATENTS Number Name Date 1,068,410 Chubb July 29. 1913 1,509,101 Dana Sept. 23, 1924 1,517,910 Kirs'chner Dec. 2, 1924 1,745,912 Richardson Feb. 4, 1930 2,078,869 Oplinger Apr. 27, 1937 2,293,810 Domm Aug. 25, 1942 FOREIGN PATENTS Number Country Date 434,116 Great Britain Aug. 23, 1935

Images