US3474011A - Electroplating method and apparatus - Google Patents

Description

Get. 21, 1969 c. D. GUERTIN ET AL 3,474,011

ELECTROPLATING METHOD AND APPARATUS Filed Aug. 5, 1967 2 Sheets-Sheet l I I I I 1 I I I f I l a I k' MC Me M;

M4 ma 2 I I a j I *4 A x Me M4 INVENTORS E a MFG/9D a GII/ERT/N 1 51- BY SAAVATOKE 04mm Get. 21, 1969 c, uam- ET AL 3,474,011

ELECTROPLATING METHOD AND APPARATUS Filed Aug. 5. 1967 2 Sheets-Sheet 2 CURR NT (1' INVENTORS CZ/FFOAD D. GUXT/N SAZ /ATO/PAF E 027/4470 T 12] E f wrap/v19? Unite States ELECTROPLA'HNG METHOD AND APPARATUS Clifford D. Guertin, River Vale, N..l., and Salvatore F.

DAmato, Floral Park, N.Y., assignors to American Bank Note Company, New York, N.Y., a corporation of New York Filed Aug. 3, 1967, Ser. No. 658,075 lnt. Cl. B011; 3/00 lU.S. Cl. 204-49 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an electroplating system, and more particularly, to a method and apparatus for electrodeposition of metals which enable the deposition of extremely large amounts of metal. The system provides for regenerating metal ions by a most eflicient arrangement for introducing metals into solution.

The present invention is especially adapted to high quantity production of nickel plating and provides for the introduction of a continuous supply of nickel into an electrolytic solution.

In the production of certain items by electroplating, it is quite often highly desirable that the anode which is to be utilized in the process be insoluble or substantially insoluble in the electrolyte. In other words, it is sometimes preferred that the anode be a passive element in the process and be substantially inert to the electrolytic action. Such an arrangement is particularly important in the case of electroforming articles such as intaglio printing plates, where it is necessary to keep the distance between anode and cathode substantially constant. In the manufacture of these intaglio printing plates for continuous web printing, it becomes a paramount objective that the plates be formed as continuous cylindrical shells of quite large dimensions. For example, it might be required to produce a cylindrical shell having an inside surface area of 12 square feet. To fabricate such a shell a non-consumable or inert electrode serving as anode is concentrically placed with respect to the inside surfrace of the shell which is to be electroformed. A master plate which has been suitably treated acts as the cathode in the electroplating operation and the transported nickel ions build up on this suitably treated surface to form the cylindrical shell.

However, in fabricating such large size printing-plate shells, it is necessary not only to keep the distance between the central anode and the cathode substantially constant but it is also necessary in this particular context that the metal ions which are to be supplied almost entirely from the plating bath, i.e. from the electrolytic solution, be furnished in very large amounts.

In order to fulfill the requirement of supplying sufficient metal ions to such a large cathode, constant replenishment or regeneration of the plating solution is called for. Otherwise as the process is carried on, the metal ions will be very quickly depleted and the desired goal of obtaining a massive printing-plate shell will be frustrated.

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Because of the fact that amelioration of the problem of metal ion depletion is most demanded in the case of the electroplating of nickel, the present invention will be particularly described and referred to in that context. However, it should be borne in mind that the techniques and apparatus provided in accordance with the present invention are quite generally applicable.

A technique for regenerating nickel in an electrolytic solution has been described before in US. Patent 2,541,721 to Roehl et al. In that patent a nickel replenishing arrangement has been described in which an electrolytic solution is constantly circulated between a plating tank and a replenishing tank. In the latter tank, consumable nickel electrodes are immersed in the solution and a direct current source is connected to these electrodes. It was found, in accordance with the disclosure in the Roehl et a1. patent, that the direct current supplied to the electrodes had to be reversed at intervals of from about one to about fifty seconds. By suitable control over the essential parameters of the electroplating process, such process was found by Roehl et al. to be satisfactory for the purposes contemplated.

However advantageous the technique of the above-noted patent may prove for its intended objectives, such technique can not meet the demand of supplying the great amount of metal ions for the electroforming of massive electroformed printing plates as well as for other similar purposes. One of the reasons for the inability to utilize the Roehl et al. technique in such an environment is the fact that it is simply not feasible to have direct current reversal, that is, switching of the current, with the attendant high inductive effects, where current magnitudes of 1000 amperes are involved.

What has been discovered is that, contrary to previous expectations, alternating current such as of cycles or otherwise, can be employed in a replenishing or regenerating operation for supplying vast amounts of metal ions to a plating electrolyte, and that by provision of suitable means operative therewith, current magnitudes on the order of 1000 amperes can be readily handled to furnish the metal ions in solution. Such current magnitudes result, for example, in the efficient fabrication of nickel plating in amounts of the order of 2.0 to 2.4 pounds which can be electrodeposited in a matter of 1 hour.

Accordingly, it is a primary object of the present invention to facilitate the regeneration of metal ions in large amounts in an electrolytic solution.

Another object is to eliminate the requirement for reversing a direct current supply to a nickel plating regenerating apparatus.

Briefly stated, the present invention provides regenerating apparatus for the electrodeposition of metals having as one of its important features the cyclical exposure of the electrodes of the regenerating apparatus and the synchronization therewith of the current supply to these electrodes. The synchronization is such that the maximum area of one electrode is exposed in a direct or straight line current path to an opposite electrode while the area of that other electrode is a minimum; and at this very time, maximum current is being supplied to the electrodes. It is by virtue of this arrangement, therefore, that metal ions are most efficiently placed in solution without being plated on to the cathode. Maximum dissolution of the metal occurs because at the time of maximum current flow there is maximum unbalance between the exposed electrode areas, that is, the anode area greatly exceeds the cathode area. Also, by this arrangement, there is enabled the use of alternating currents for the dissolution of the metal, and thereby the need for special power supplies as would be required for direct current is obviated.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawmgs.

FIG. 1 is a diagram of an electroplating system particularly illustrating the novel regenerating apparatus of the present invention.

FIG. 2 is a fragmentary view showing parts of the drive means.

FIG. 3 is a schematic diagram of the relationship between the exposure of the surface area of the electrodes of the regenerating apparatus and the current supplied to those electrodes as a function of time.

Referring now to FIG. 1 there is shown the environment in which the regenerating apparatus of the present invention is operative. The system or environment comprises a conventional plating tank 1 in which a plurality of typical electrodes such as an anode 2 and cathode 3 are utilized. These electrodes are shown immersed in an electrolytic solution within the tank 1, and a direct current power supply 4 is shown connected to these electrodes. For circulation of the electrolytic solution between the plating tank 1 and the regenerating apparatus there is provided a plurality of pipes or conduits 5 and 6, in which there are connected pumps 7a and 7b.

The regenerating apparatus of the present invention is generally designated by the number 8 and, as aforenoted, is shown connected to the plating tank 1 for circulation of the electrolyte. The regenerating apparatus 8 comprises a tank 9 and a plurality of electrodes 10 and 11 which are shown immersed in the electrolytic solution in the regenerating tank 9.

The electrodes 10 and 11 are constituted by a plurality of nickel balls which are shown disposed in their respective guides 12 and 13 and in their respective cages 14 and 15, the latter being situated within the tank 9 for purposes to be explained. The nickel balls which form the electrodes 10 and 11 are consumable, that is, they are dissolved in the solution present in the tank 9. By force of gravity the balls move down the guides 12 and 13 as the balls present in the cages 14 and 15 are constantly being eroded. The supply of electrolytic nickel in the form of these balls can thus be easily replenished. The balls in the cages 14 and 15 are, of course, suitably restrained by a mesh screen or the like provided as part of the cages. Preferably the cases 14 and 15 are constituted of a non-reactive material such as titanium or the like.

Effectively, in the operation of the circuit in which the electrodes are connected, the current flow between electrodes 10 and 11 is in a direct path between the juxtaposed surfaces of the nickel balls, that is, the surfaces of these balls which are disposed in the cases 14 and 15, so as to face each other in the solution. As noted above, these nickel balls form consumable electrodes and the action of the current flow is to cause nickel continuously to go into solution. The dissolution of the nickel is maximized by the means which will now be described.

In order to cylically expose the opposed surfaces of the electrodes 10 and 11, that is, to expose the surfaces presented by nickel balls in the cases 14 and 15 to the electrolytic solution, a synchronized drive means is provided. This drive means assures that the proper exposure of the surface areas will occur when the desired amount of current is flowing. The drive means, generally designated by the numeral 16 is connected to the rotor of the synchronous motor 17. Afiixed to one set of gears 1641 are pairs of shafts 16b and 160. The shaft 16b fits within the shaft 16c and is used to drive the plate a, whereas the shaft 16c drives the plate 20b. Because of the gear arrangement, of course, the shafts 16b and 160 are rotated in opposite directions and hence the plates 20a and 20b are rotated oppositely. A gear box 16 is disposed between the rotor shaft of the motor 17 and the drive shaft 16c. This gear box is simply used to change speeds, for a purpose to be noted hereinafter.

It will be appreciated that the other pair of rotating plates 21a and 21b, i.e. the plates for electrode 11, is similarly driven. A chain drive 16g extends from shaft 162 to shaft 16h, for this purpose. Gear set 16k, shaft 161 and 16m correspond to previously noted parts 16a, 16b and 160 respectively.

It will be understood that since all of the rotating plates are driven in common from the rotor shaft of motor 17 they have the same speed-typically in the case of the use of 60 cycle alternating current, a speed of 1800 rpm. or 30' revolutions per second.

It should be noted here that, although the plates 20a, 20b, 21a, 21b have been illustrated in the form of disc segments, other shapes are, of course, possible. For example, the plates could be rectangular in shape. Their shape in the illustrative embodiment has been chosen to correspond best to the shape of the exposed area of the nickel balls in the cages 14 and 15.

The various parts that make up the drive means 16 for properly rotating the plates in the solution can be made of conventional materials. However, it is preferable that the plates themselves as well as their driving shafts be constituted of non-reactive material such as reinforced plastic or hard rubber. The bearings and/or shaft seals are made of graphite and/ or ceramics.

As best seen in FIG. 3, the pair of plates 20a, 20b have a physical displacement of from the position at any given instant of time of the corresponding pair of plates 21a and 21b respectively. This is for the aforenoted purpose of exposing a maximum surface area of one electrode while exposing a minimum area of the other electrode. Thus, looking at a typical position of the plates such as position 1 (at the very top of FIG. 3), it will be seen that plates 20a and 2% are in such position as to shade the surface area of the nickel balls of their adjacent electrode 10. Effectively, then, although a direct path for current is provided, there is minimization of any plating on the electrode 10 (considered now to be acting as the cathode). In other Words, with the plates 20a and 20b opposed at this point in time there is an absolute maximum of dissolution into solution, because at the same instant, the plates 21a and 21b are in a conjunctive state, that is, they are overlapped such that a maximum surface area of their electrode 11 is exposed.

The converse situation exists at the illustrated point 3, that is, converse in the sense that the pair of plates 20a and 20b and the opposite pair of plates 21a and 21b have interchanged their positions. At this instant of time, plates 20a and 20b are conjunctive, thereby exposing maximum electrode area, whereas plates 21a and 21b are opposed, th'ereby exposing a minimum of surface area. But again, maximum dissolution of metal ions is occurring at this point in time. Recurring points of interchanged maximum and minimum exposure of surface area are also found, for example, at the points of time designated 5, 7 and 9. The proper functioning of the several pairs of plates are realized by the synchronization of the above-described movement of the plates so that maximum and minimum exposure of the surface area of opposite electrodes coincide with the occurrence of maximum values of current. This, of course, requires that there be aninitial setting of the plates on their respective shafts so that the desired spatial relationship between the pairs of plates is fixed and maintained for their continuous operation during the regenerative process.

The rotation of the plates is precisely synchronized with the flow of current between electrodes 10 and 11 in the following manner. A 60 cycle alternating current wave is supplied to the electrodes 10 and 11 by way of branch circuit 22 from one of the secondaries of transformer 30. The primary of transformer 30 is shown connected to an AC. power supply 32. The other secondary is connected to form branch circuit 24 in which is disposed synchronous motor 17. The rotor shaft of motor 17 is synchronously related to the current flow and flux of its stator. Thus, by synchronizing the current wave that is supplied to electrodes and 11 with the current wave supplied to the stator of the motor 17, the rotor shaft of the motor 17 will have an established relationship with the current Wave of the current passing between the electrodes 10 and 11. Synchronization of the aforesaid two current waves is achieved by any suitable means, such as by connecting test lines, as illustrated, to the respective branch circuits 22 and 24 for the motor and the electrodes. Although the current waves may initially be out of phase because of the diflering power factors of the respective branch circuits, adjustment is made, such as by means of capacitor 40, while observing the current wave forms on a double beam oscilloscope 42 which is connected by the test lines to the branch circuits. Once these current waves are brought in phase, a given point on the rotor shaft now has a fixed relationship to a point on the illustrated current wave of FIG. 2, i.e. the current flowing between electrodes 10 and 11. It now remains only to make the initial setting for the plates a and 20b, 21a and 21b, on their respective shafts. It is a simple matter to calibrate or adjust the initial positions, such that conjunction or overlapping of one pair of these plates occurs exactly at a point of maximum amplitude for the current flowing between the electrodes 10 and 11. This is accomplished by Selecting a suitable time base for the oscilloscope 42 so that the current wave is traced out and the occurrence of the maximum point on the current wave can thus be easily observed. Then, in simultaneity with this maximum, the rotating plates are fixed into position on their shafts respectively by suitable means so that a maximum area of the electrode surface is exposed. Thus, for example, the positioning of the plates 20a and 20b on their shafts 16b and 160 would be adjusted so that the plate 20a would overlap plate 20!), thereby exposing a maximum surface area of electrode 10 at the point of mwimum positive current. To facilitate such synchronization, the rotational speed of the plates would be reduced, at this time, from their normal rate of 30 revolutions per second to approximately 1 revolution per second. The gear box 16 would be used for this purpose of effecting speed reduction, in a well-known manner. As noted before, the other pair of plates, that is, plates 21a and 2112 are then adjusted for their 90 displacement from plates 20a and 2011 respectively.

It should also be noted that the rotational speed of the plates 20a, 20b and 21a, 21b is, of course, related to the rotational speed of the rotor shaft of motor 18 by the gear ratio between them. For the illustrated embodiment, the overall gear ratio would be 1:1 so that the speeds would be the same.

It will be understood that in the example given of a power supply frequency of 60 cycles, the current wave will traverse two complete cycles in the time it takes for a pair of discs to go from their initial positions, as for example, from their positions at point 1 through a complete cycle to arrive again at the same position, as shown at point 9. It will be appreciated that with the timing being such that a pair of discs, such as plates 20a and 2%, go through a complete revolution of 360 in the time that the current wave goes through two cycles, that the electrodes 10 and 11 interchange roles as cathode and anode during this period.

Recapitulating the operation of the regenerating apparatus, the two plates, for example 20a and 20!), are providing a minimum exposed surface area of electrode 10, while the two plates 21a and 21b are providing a maximum area of exposure of their electrode 11; and this is happening at a time (point 1 in FIG. 3) when the current Wave has attained its maximum amplitude in the negative half of the cycle.

At the next point in time, that is point 2, the plates 20a and 20b and the plates 21a and 21b have moved such that the exposed areas of electrodes 10 and 11 are equal. It will be noted that this occurs when the current is a minimum, that is, the zero point or no current flow. At point 3 an opposite situation to point 1 obtains, that is, a maximum area of electrode 10 is exposed because the plates 20a and 20b are in conjunction, whereas plates 21a and 21b are opposed. Now, of course, the plating is opposite in effect, that is current flow is opposite to the direction which obtained at point 1. At point 4 a condition of balanced electrode exposure occurs, i.e. the same situation as at point 2, exists and, again, at such point the current flow is zero.

Repeated states of maximum-minimum and intermediate exposure then occur successively at points 5, 6, 7, 8 and 9 as will be apparent. At point 7 when the current flow again is in the same direction as it was at point 3, with plating going from left to right. However, the exposed area of electrode 10 is now to the right or opposite to that shown at point 3. This tends to give an even wear to the nickel balls that form the electrodes.

In order that the man skilled in the art may fully appreciate the prevent invention and be able to practice its technique most easily, the following sets of specifications, in the form of illustrative examples, are provided. However, it will be understood that the principles of the present invention are not restricted to this detailed description.

The plating solutions and conditions to be employed in the process in accordance with the present invention are as follows:

Nickel sulfamate 9 to 11 oz. of Ni./ gallon. Nickel chloride .5 to 1.5 oz./ gallon. Boric acid 4 to 8 oz./gallon. pH 4.0 to 4.5. Temp, to F. +Addition Agents. Current 50 to 100 amperes/sq. foot of plating surface.

Nickel sulfate 4 to 8 oz./gal1on. Nickel chloride 40 to 50 oz./ gallon. Boric acid. pH 4.3 to 4.8. Temp. 110 to F. +Addition Agents. Current 50 to 100 amperes/sq. foot of plating surface.

What has been described herein, in accordance with the present invention, is an extremely simple replenishing or regenerating technique in an electrodeposition process. This technique enables the supplying of great quantities of metal ions to a plating electrolyte in an extremely efficient manner. Moreover, the technique involves the cyclical exposure of opposed surface areas of the regenerating electrodes and the synchronization therewith of the alternating current supply so as to obtain maximum benefits from the regeneration operation.

What is claimed is:

1. In a metal plating process for the electrodeposition of a metal using an insoluble anode spaced at a fixed distance from a cathode and wherein the plating current flows through the electrolyte between the insoluble anode and the cathode, the improvement in said process of circulating the electrolyte to a regenerating apparatus comprising an alternating current power supply electrically connected to at least one pair of consumable metal electrodes having opposed surface areas, regenerating the metal ion content of said electrolyte by cyclically exposing the opposed surface areas of the consumable metal electrodes so as to form effectively a variable area current path while synchronously applying current to said electrodes to provide maximum exposed surface area for one of said consumable electrodes and minimum exposed area for the other of said consumable electrodes at a time when the current flow between said electrodes is at a maximum.

2. In a nickel plating process for the electrodeposition of nickel using an insoluble anode spaced at a fixed distance from a cathode and wherein the plating current flows through the electrolyte between the insoluble anode and the cathode, the improvement in said process of circulating the electrolyte to a regenerating apparatus comprising an alternating current power supply electrically connected to at least one pair of consumable nickel electrodes having opposed surface areas, regenerating the nickel ion content of said electrolyte by cyclically exposing the opposed surface areas of the consumable nickel electrodes so as to form eifectively a variable area current path while synchronously applying current to said electrodes to provide maximum exposed surface area for one of said consumable electrodes and minimum exposed area for the other of said consumable electrodes at a time when the current flow between said electrodes is at a maximum.

3. The process as defined in claim 2, wherein said nickel electrodes are in the form of consumable nickel balls contained within a guide and each presenting a surface area for exposure in a direct path to its opposed electrode.

4. In a nickel plating process for the electrodeposition of nickel using an insoluble anode spaced at a fixed distance from a cathode and wherein the plating current flows through the electrolyte between the insoluble anode and the cathode, the improvement in said process of circulating the electrolyte to a regenerating apparatus comprising an alternating current power supply electrically connected to at least one pair of consumable nickel electrodes having opposed surface areas, regenerating the nickel ion content of said electrolyte by cyclically exposing the surface areas of the consumable nickel electrodes so as to form a variable area, current path, while synchronously applying current to said electrodes to provide maximum exposed surface area for one of said consumable electrodes and minimum exposed surface area for the other of said consumable electrodes at a time when the current fiow between said electrodes is at a maximum, and to provide equally exposed surface areas for both of said electrodes when said current flow is zero.

5. An electroplating apparatus comprising a plating tank for containing a plating electrolyte; an insoluble anode and a cathode in said tank; electrical means for passing a direct current between said anode and cathode; a regenerating auxiliary tank adapted to receive plating electrolyte from said plating tank, regenerate said electrolyte and return said electrolyte to the plating tank; at least one pair of consumable metal electrodes having opposed surface areas within said auxiliary tank; alternating current means connected to said pair of metal electrodes for passing an alternating current therebetween; and means operative to provide maximum exposed surface area for one of said electrodes and minimum exposed surface area for the other of said electrodes when the current flow between said electrodes is at a maximum.

6. The apparatus of claim 5 wherein said consumable metal electrodes are nickel.

7. A plating apparatus as defined in claim 6, wherein said nickel electrodes are in the form of consumable nickel balls contained within a guide, each electrode presenting a surface area for exposure in a direct path to its opposed electrode.

8. The apparatus of claim 5 wherein said means operative to provide maximum exposed surface area for one of said electrodes and minimum exposed area for the other of said electrodes when the current flow between said electrodes is at a maximum is operative to provide equally exposed surface areas for both of said electrodes when said current flow is zero.

References Cited UNITED STATES PATENTS 2,541,721 2/1951 Roehl et al. 204232 XR FOREIGN PATENTS 819,548 9/ 1959 Great Britain,

JOHN H. MACK, Primary Examiner G. L. KAPLAN, Assistant Examiner US. Cl. X.R.

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