US3436322A - Plating apparatus and process - Google Patents

Description

April 1, 1969 L. GOOD E 3,436,322

PLATING APPARATUS AND PROCESS Filed Aug. 19. 1965 INVENTORS'.

' LOUISE L. GOOD RAYMOND B. GOOD ROBERT LWHlTNEY AMigROSE L. PIETROWICZ United States Patent Office 3,436,322 Patented Apr. 1, 1969 U.S. Cl. 20428 6 Claims ABSTRACT OF THE DISCLOSURE Gold is electrodeposited on an article having an electrically conducting surface by continuously passing said article such as a wire through an electroplating bath of electrolyte containing the metal to be deposited, applying a cathodic charge to said article externally of said electrolyte, and continuously circulating said electrolyte from said bath through a zone remote from the article being plated located externally of said bath and containing an anode remote from the article being plated.

This invention relates to a plating apparatus and process, and more particularly to an apparatus and process which is suitable for plating fine wire, both round and ribbon, and which is especially suitable for gold plating.

In the electroplating of gold on fine wire, it is quite important to carry out the plating operation in such a way that a uniform deposit of the gold on the wire is obtained. In the conventional system in which the article to be plated, such as wire, forms the cathode in an electroplating bath to which the anode current is applied in a conventional manner, a substantial amount of time is required to obtain a uniform density of gold on the article to be plated. Relatively low voltages and current densities are used in plating gold from conventional plating solutions by conventional plating methods.

One of the objects of the present invention is to provide a new and improved apparatus and process for electroplating wire with gold continuously.

Another object of the invention is to provide an apparatus and process for plating gold on wire which makes it possible to obtain a uniform deposit of the gold on the wire in a shorter period of time than with conventional methods and apparatus.

Other objects and advantages of the invention will appear from the following description in conjunction with the accompanying drawing in which the single figure is a view in perspective and partly in section of an apparatus which represents the best mode contemplated for the practice of the invention.

In brief, the invention consists of an apparatus and process especially adapted for the plating of gold on wire or other articles of limited surface area wherein the electrolyte or plating solution is disposed in a suitable tank or container, the wire or similar material to be plated is cathodically charged and passed through the electrolyte, the anode to which a positive electrical charge is applied is disposed outside of the electrolyte in a separate container and the electrolyte is pumped or circulated by any suit-able means in contact with the remotely disposed anode. Optionally, a filter is employed to filter the electrolyte while it is being circulated.

In this system higher current densities can be employed than in the conventional system. Much finer current distribution is obtained and a more uniform deposit is achieved in a shorter period of time. Thus, in a conventional gold potassium cyanide electrolyte, a typical composition would be one ounce per gallon of gold as metal and ten ounces per gallon of free potassium cyanide. The normal current density used would be three amperes per square foot. By using the system of the present invention five to ten times this amount of current can be passed through the electrolyte and consequently equally thicker deposits are obtained. Furthermore, the wire to be plated can be passed through the electrolyte at speeds from 35 to 100 feet per minute. Voltages on the order of 16 to 50 volts, direct current, are employed to achieve the high current densities. Such high voltages cannot be employed ordinarily in a conventional plating arrangement where the cathode and anode are in the same tank. Furthermore, by using the system of the present invention, the distribution of the deposit is even, the grain refinement better, the porosity less, and the corrosion resistance greater.

The rate of circulation of the electrolyte through the remote anode chamber should be sufiiciently high to maintain substantial agitation.

The composition of the electrolyte does not constitute a part of the invention. Various electrolytes can be employed containing, for example, 0.5 to 2 ounces per gallon of gold and 7 to 13 ounces per gallon of potassium cyanide dissolved in water, preferably with the addition of conventional brighteners which may include such substances as nickel, copper, silver and organic brighteners.

The wire to be plated can be any electrically conductive wire normally employed for this type of plating. This is usually a fine wire and can either have a round or flat cross section.

In the practice of the invention it is desirable that the anode area be greater than the surface area of the cathode in order to avoid current requirements that are too high. Since wire affords a relatively limited cathode area, the invention is especially useful in the plating of wire. In any case, however, it is preferable to use a remote anode in the form of a mesh or screen which provides greater surface area than a conventional solid anode.

In the embodiment of the invention illustrated in the drawing, the electrolyte 1 is held in a tank or container 2 and the wire to be plated 3 is passed through the electrolyte 1 first over a pulley 4 mounted for rotation on a shaft 5, secondly over a pulley 6 mounted for rotation on a shaft 7, then over apulley 8 mounted for rotation on a shaft 9, and finally over a pulley 10 mounted for rotation on a shaft 11. The arrangement of pulleys can be varied in any suitable manner in such a way as to immerse the wire in the electrolyte for the desired period of time to obtain a uniform plate or coating of predetermined thickness. The wire is normally pulled through the electrolyte by a motorized machine (not shown) at the takeup end.

The plating tank or chamber 2 contains at opposite ends an exit tube 12 and an entry tube 13. The elecrolyte is circulated through the tubes 12 and 13 by means of a pump 14 operated by a suitable motor 15, a connecting tube 16 which affords a passageway to a filter 17 and a connecting tube 18 which affords a passageway to the anode chamber 19. In the anode chamber 19, the circulated electrolyte is brought into contact with a stainless steel wire mesh anode 20 which is electrically connected to a suitable source of positive potential through a wire 21. An ammeter 22 is provided in order to indicate the electrical potential. The wire 3 is cathodically charged from a suitable source of negative potential introduced through wire 23. The charge on wire 3 is actually applied through pulley 4 outside of the electrolyte.

The wire to be plated is prepared for plating by cleaning and pickling in the usual manner and after it has been plated it is given conventional treatments, such as rinsing,

neutralizing, final rinsing and drying. These preliminary and after treatments do not constitute a part of the invention and therefore they have not been described in detail.

The invention is especially useful in plating copper wire, and wires made from various types of alloys (e.g., Kovar and Invar). It can be used in plating any type of metal wire. While the invention can also be employed in plating other types of articles, it is especially useful in continuous wire plating.

The invention is hereby claimed as follows:

1. A process for electrodepositing gold continuously on an elongated article having an electrically conducting surface which comprises passing said elongated article in a continuous path through an electroplating bath of electrolyte containing the gold to be deposited, applying a cathodic charge to said article externally of said electrolyte, and continuously circulating said electrolyte through conduits from said bath through a zone remote from the article being plated located externally of said bath and containing an anode remote from the article being plated, thereby applying an anodic charge to said electrolyte externally of said bath and remote from the article being plated, and a continuous bridge of electrolyte being maintained between said bath and said zone.

2. A process as claimed in claim 1 in which said circulated electrolyte is filtered before being returned to said bath.

3. A process as claimed in claim 1 in which said remote anode has a greater surface area than the surface area of the portion of the article to be plated which is immersed in said bath.

4. A process as claimed in claim 1 in which the article to be plated is a wire which is moved continuously through said bath.

5. In an electroplating apparatus, the combination of:

(a) a tank adapted to hold an electrolyte;

(b) means to move an article to be plated continuously through the electrolyte in said tank;

(c) a chamber externally arranged with respect to said tank;

(d) an anode in said external chamber remote from the article to be plated;

(e) means for circulating electrolyte from said tank into said chamber and in contact with said anode and for returning said circulated electrolyte to said tank;

(f) means for imparting a positive potential to said circulated electrolyte through said anode; and

(g) means for imparting a negative potential to said article to be plated externally of the electrolyte in said tank.

6. An apparatus as claimed in claim 5 comprising means for filtering the circulated electrolyte after it is removed from said tank and before it is brought into contact with said anode in said external chamber.

References Cited UNITED STATES PATENTS 883,756 4/1908 Steiner 204-26 2,828,255 3/1958 Gempe 204l99 1,515,092 11/1924 Cowper-Coles 204-23 8 2,695,269 11/1954 De Witz et a1 204-234 3,123,543 3/1964 Chapman et a1 20428 FOREIGN PATENTS 215,409 9/ 1941 Switzerland.

JOHN H. MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner.

US. Cl. X.R. 204238. 211

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