US2044415A - Method and apparatus for electrodeposition - Google Patents

Description

2 Sheets-Sheet 1 ATTORNEYS C. E. YATES Filed July 13, 1932 METHOD AND APPARATUS FOR ELEGTRODEPOSITION June 16, 1936.

Patented June 16, 1936 UNHTED. STATES FATE r OFFICE METHOD AND APPARATUS FOR ELECTRODEPOSITION of Montana Application July 13, 1932, Serial No. 622,171

35 Claims.

This invention relates to the electrolytic production of thin metallic sheets or foils by a procedure which involves plating metal on a cathode surface to the desired thickness and stripping it therefrom. More particularly, the invention is concerned with a novel method and apparatus by the use of which sheets and foils of either definite or indefinite dimensions can be produced, the deposited sheets having sharp clean-cut edges without increased thickness and the deposition being carried on under such conditions that plating of the metal on those surfaces of the cathode where it is not desired is prevented. The new method and apparatus may be used to especial advantage in the continuous production of thin copper foils and an embodiment of the invention in a form suitable for that purpose will accordingly be described in detail to make clear the principles involved, but it is to be understood that the utility of the invention is not limited to continuous production of foils ,ofindefinite length nor to that particular metal.

ihe production of copper foils by plating on a rotating drum cathode and continuously stripping the deposit therefrom was'proposed many years ago and numerous attempts have been made to develop such a process in a form which can be used commercially. These attempts, however, have heretofore not been successful because of numerous problems encountered, which up to the present have remained unsolved. One of the most importantobstacles to commercial produc tion of copper foils electrolytically is that of obtaining a product with sharp clean-cut edges and preventing deposition or sprouting on those surfaces of the drum where it is not desired.

To overcome the difiiculty, it has been proposed, for example, to apply an insulating coating to the curved surface of the drum at its ends, 40 to mount a strip of insulating material in the surface, or to apply a gasket or disc of insulating material to the ends of the drum, but while these expedicnts may function satisfactorily for a short time. they provide no permanent solution of the problem.

In the case of the insulated coating, the relaping, this deposit is torn loose, destroying the v coating. The formation of sprouts along the edge of the deposit surface results in the deposition of metal on an irregular edge surface, and when the sheet is stripped, serious troubles from tearing of the sheet arise.

When gaskets at the ends of the drum or insulating material laid in a groove in the drum surface are used, sprouting occurs as before along the edge of the deposit surface, and in addition, a thin layer of copper is deposited between the insulation and the drum, this layer remaining in place continuously. Tearing during stripping then arises from the presence both of the sprouts and the thin layer of copper under the insulation and the latter is never removed during stripping and constitutes a continual cause of sprouting.

Another difficulty encountered in the use of a rotating drum apparatus in the continuous production of metal sheets is maintaining the surface of the drum in proper condition. In my co-pending application, Serial No. 604,932, filed April 13, 1932, I discussed this problem at some length and disclosed an apparatus by means of which the surface of the drum can be kept in the desired condition for indefinite periods. That apparatus includes an element which abrades and smooths the surface of the drum after stripping and I have demonstrated that the particular apparatus disclosed is a solution of this problem. It has been proposed by others working in this field'to clean the surface of the drum by rotating brushes and various devices of that sort but all such devices, including my own, can be used only with some difiiculty in connection with a driun in which portions of the curved deposit surface are stopped off by insulating varnish or the like, since the operating element must be kept from contacting with the insulated area and at the same time all portions of the surface of the cathode on which a. deposit occurs must be treated.

The present invention is directed to a method and apparatus by which the difficultiesin producing sheets with sharp well-defined edges are overcome and sprouting on such surfaces of the drum as it is not desired to plate is prevented, the new apparatus being so constructed as to facilitate the necessary mechanical treatment of the curved surface of the drum to-keep it in proper condition.

Inthe deposition of metal on the surface of a drum cathode opposed by an anode, there is ordinarily a concentration of current along the end edges of the drum which results in the deposited sheet being built up to a. greater thicknessalong its edges than elsewhere. Such increased current density on the cathode is caused by the face, edges, and back of the anode being exposed to the electrolyte, while the ends of the drum and in some cases portions of the curved surface of the drum at its ends arestopped off by an insulating coating. Accordingly, current entering the solution from the ends and backof the anode and seeking the nearest part of the cathode, flows to the cathode edges and this produces a current density along those edges which is higher than that on any other part of the cathode with a resultant deposition at a greater rate.

In'one form of the apparatus embodying my invention, the drum may have circumferential .channels in its curved surface adjacent the ends thereof and ports leading from the bottom of 0 the channels and opening at the ends of the drum. Thetops of the channels, .at least throughout the length of those portions which lie beneath the electrolyte, are then" covered by suitable means as, for example, rubber belts, and

2 means are also employed for confining bodies of electrolyte in contact with those portions of the drum which are not to receive a plating. Such confining means may take the form of partition members'mounted at the ends of the'drum beyond the ends of the ports and extending from the drum to the tank wall. The electrolyte-thus confined is kept separate from the main body of the electrolyte except for such slight leakage as may occur beneath the belts and partitions.

35 In the confined bodies of electrolyte are placed cathodes, called sub-cathodes" for convenience, which are maintained at a potential lower than that of the drum.

With this arrangement, the belts which cover 40 the channels and also overlie the edge of the deposit surface along the channels to an extent dependent on the diameter of the belts, serve as a meansforshielding the edges of the deposit surface and preventing increased thickness -of 45 the deposit along its edges. The belts alone may be suflicient to prevent increased thickness of the edges of the deposit but the action of the belts may be made more effective by providing non-conductive shields along the edges of the an anode. If the belts and partition members made a perfect seal with the extreme edges of the deposit surface of the drum and 'with the tank wall, there would be no plating on any surface as the sub-cathodes, the latter may also cause a deplating of the deposit from the edges-of the drum and, thus assist the belts in preventing increased thickness at the edges of the deposit sheet. Ordinarily the belts with or without the 70 anode shields are sufllcient to control the thickness of the platingat the edges of the sheet and the sub-cathodes serve merely to prevent plating on those parts of the drum where no depositisdesired. 75 with the novel drum. therefore, the side edges 'deposit surface".

on which a deposit is not desired is referred to 40- of the surface on which the foil is to be deposited are so defined and shielded that there can be no sprouting along these edges, and this result is obtained without the use of insulatin coatings or the like on the surface of the cathode. 5 The cathode surface may, therefore, be maintained in proper condition by the apparatus dis ,closedin my copending application above mentioned, and the use of the present apparatus with the surface treating mechanism disclosed in that 10 application solves the problems of producing sheets of substantially uniform thickness with sharp clean edges and of maintaining the oathode surface in condition for continuous operation over long periods. 16

For a better understanding of the invention, reference may be had to the accompanying drawings illustrating one embodiment of the new apparatus. In these drawings- Fig. 1 is a vertical sectional view through the cell and drum cathode;

Fig. 2 is a view similar to Fig. 1 taken at right angles thereto;

Figs. 3 and 4 are sectional views through portions of the drum; Fig. 5 is a diagrammatic view illustrating the electrical connections in a battery of cells; and

Figs. 6, 7 and 8 are diagrammatic views illustrating the flow of current between anodes and cathodes of various constructions. Referring now to the drawings, the apparatus illustrated includes a tank III of any suitable material, the tank usually being lead lined, and mounted in bearings H at the top of the side walls of the tank is the shaft 12 of the drum cathode ll. The drum has a surface which is to receive the deposit, this surface being the cylindrical surface of the drum and referred to as the The remainder of the drum as the non-deposit surface. The drum may be of any suitable construction but preferably'includes spiders or discs I of copper constituting the ends of the drum and a cylindrical copper member l5 which provides the curved surface of the drum. The deposit surface is formed by a continuous layer I 8 of lead mounted on the curved surface I! and the ends of the drum are also provided with a lead sheathing so that the drum is completely enclosed and all its outer surfaces are covered with lead. The shaft of the drum is provided with a disc contact I! which runs in a trough ll containing mercury connected to the negative side of a source of energy.

In the bottom of the tank is a suitable support is for a pair of anodes 20, these anodes being of curved form and lying with their faces close to the cylindrical surface of the drum. The anodes are spaced apart at the bottom to provide a passage 2| and air agitation is used to maintain fresh electrolyte in the space between the anodes and cathode. For this purpose an air pipe 22 having jet openings at its top is mounted just below the passage, and the air promotes upward circulation of the electrolyte in the space between the anodes and the cathode. Each anode with shields 25 of insulating material along their lateral edges, these shields preventing current flow into the solution from the edges.

The lead plate I forming the outer cylindrical surface of the cathode projects beyond each end 7 I of the drum 9. short distance, as illustrated in Fig. 3, and lead is fllled in as at IE to provide a flange extending beyond the end of the plate IS.

The flange is then cut away to provide a circumferential channel 26 from the bottom of which ports 21 pass through the flange. A partition member 28 is mounted on the drum and extends therefrom to the wall of the cell, and I prefer to make this partition member of a preformed web of rubber and to secure it in place with a portion entering the channel 26. For this purpose, one side of the channel may be provided with a low circumferential rib 29 on flange H3 and the rubber web is placed in contact with the bottom of the channel and projects out over from the drum.

That portion of each channel which lies below the level of the electrolyte is closed by means of an endless belt 3| of rubber which is trained about pulleys 32 mounted on the tank walls and has a portion free of the drum, this portion passing, for instance, across the end of the drum from one pulley to the other. The belts which I have found satisfactory have a rubber surface and are of circular section, the diameter being considerably greater than the width of the channel so that the belts will overlie the edges of the deposit sheet .and will make good contact with the top edges of the channel.

It will be observed that the belts 3| extend out beyond the drum a substantial distance, and, as shown in Figs. 1 and 3, the size of the belts is such that they extend through a relatively large proportion of the distance between the drum and the anodes. The belts therefore reduce the openings at the ends of the drum into the space between the drum and anodes to a substantial extent, and since it is the current flowing through these openings from the back of the anode and also from the end edges thereof (if these edges are unshielded) which produces the current concentration along the edges of the deposit surface and thickening of the edges of the sheet, it will be apparent that by reducing the size of the openings between the anode and drum adjacent the ends of the drum, the belts reduce the current flow referred to and, consequently, prevent thickening of the sheet along its edges. In order that they may be used satisfactorily for this purpose, the belts must extend out beyond the cathode to a substantial extent and must provide a substantial restriction of the path of current flow. If the belts do not extend out beyond the cathode in the manner described. or the anodes are so spaced from the cathode that there is no substantial restriction of current flow by the belts,

edge thickening of the sheet will not be pre vented or reduced by the belts.

One or more sub-cathodes 36 are mounted at the endsof the drum and they may be secured to insulating bases 35 secured to the tank walls, the

' sub-cathodes at each end of the drum being immersed in a body, of electrolyte which is confined within the circular partition at that end of the drum. In the construction illustrated in Figs. 1 and 2, there are two sub-cathodes at each end of the drum. These sub-cathodes are maintained at a potential lower than that of the main cathode and this may be done by properly connecting the sub-cathodes in the electrical system to which the main cathode is connected or by providing a separate system for the sub-cathodes. Instead of mounting the sub-cathodes on the tank wall, a ring of conducting material may be mounted on an insulating base 31 on each end of the drum, the contact being made with the ring by suitable brushes.

A battery of tanks is illustrated in Fig. '5, and these tanks are advantageously connected in se-- ries, with the anodes 38 of the first tank in the series connected to the positive side of the source of energy. The main cathode in the first tank is then connected through a line 39 to the anodes a potential less than the main cathode in that tank. Similar connections are provided throughout the battery of the tanks so that current is supplied to the tanks in series and the sub-cathodes in each tank have a lower potential than the main cathode in that tank. The sub-cathodes in the last tank in the series are then maintained at their proper potentials either by being connected electrically to some point in the tank house at the proper potential or separate means for maintaining those sub-cathodes at the proper potential may be employed.

The use of the sub-cathodes with a cathode drum of the construction described prevents sprouting on the end surfaces of the drum and the formation of a deposit along the edges of the drum surface, which eventually produces ragged edges on the-sheet. The sub-cathodes'may also assist in preventing the deposit from becoming thickened along its edges. I am aware that in electroplating operations, it has been proposed to use a secondary cathode known as a thief to prevent plating on surfaces where such plating is not desired, but in the apparatus with which I am familiar, the thief is connected to the main cathode so that the two have the same potential.

The purpose of such a thief is to divide the curthat of the main cathode so that the latter has the relation of an anode to the sub-cathode, and the action of the sub-cathode is controlled by varying the difference in potential between the main cathode and the sub-cathode. The confined body of electrolyte in which the sub-cathode is immersed is in contact with those surfaces of the main cathode which are not to receive a deposit, and is substantially isolated from the main body of the electrolyte except for such leakage as may take place between the edges of the channels and the belts and between the partitions and the tank wall. In the electroplating apparatus of the general type disclosed, it is customary to employ a voltage drop of 2 volts between the anode and main cathode in each cell and with the electrical connections as illustrated in Fig. 5, there would be a voltage drop of 2 /2 volts between the main cathode and the sub-cathode in each cell assuming there is no resistance in the connections. The drop between the main cathode and the sub- .cathode, however, can be controlled by the introduction of resistance in the connections and will usually be of the order of half a volt. With that arrangement, substantially all current entering a confined body of electrolyte through a leakage path flows to the sub-cathode and causes a deposit thereon. If any metal is deposited from the confined-body of electrolyte on the end of the drum, it can be easily removed by increasingthe voltage drop from the drum to the sub-cathode but ordinarily a drop of volt serves the desired The drum illustrated in Fig. 3 has the advantage that its surface may be maintained in proper condition by the treating mechanism disclosed in my 'copending application above-identified. The,

lead clamping ring 30 which holds the rubber partition in place in the Fig. 3 construction will have its outer surface either flush with the cylindrical surface of the cathode or slightly lower and an operating element of a'size sufficient to insure proper treatment of all portions of the surface of the drum may then be used, since the contact of the element with the ring causes no trouble and if the surface of the ring lies flush with the surface of the drum at the beginning of operations, the two will be worn down equally by the treating mechanism. This construction, however, necessitates the application of the clamping rings at the ends of the drum, and the somewhat simpler drum construction illustrated in Fig. 4 may be used in processes in which stripping is elfected by the use of a stripp agent and the surface of the drum is not acted on by mechanical means whichwould wear it down.

In the Fig. 4 construction, the drum is formed with a circumferential channel 46 near each end and a rubber partition member 41 of L-sectlon is then mounted so that one leg of the L enters the channel. The partition member is held in place in any suitable way and it projects out beyond the end of the drum so as to contact with the cell wall. With this construction, the rubber belt 3| contacts directly with the partition member at one side of the channel.

In Figs. 6, 7 and 8, the current conditions at the ends of a cathode drum are diagrammatically illustrated and in Fig. 6 there is shown an anode 48 opposing the face of a cathode 49, the end of which is stopped off by means of insulating material. .The light lines extending from the anode to the cathode represent the flow of current and it will be apparent that along the edge of the cathode, there is a relatively high current density because of current entering the electrolyte from the edge and back of the anode.

In Fig. 7 current flows from the face and edge,

of anode 48 to the face of cathode 50, which is of my new construction. The presence of the belt 3| now presents a considerable obstruction to current fiow and less current enters the solution from the end of the anode because of the difiiculty of reaching the cathode, and most of the current passes directly from the face of the anode to the face of the cathode. At. the same time, a small amount of current may flow through electrolyte which seeps beneath the belt and through the confined body of electrolyte to the sub-cathode.

In Fig. 8, the cathode 50 is of the new con-- struction and the anode is provided with an insulating shield 25 along its edge which prevents current entering the solution from that edge. In this case an increase of current density along the edge of the cathode is prevented both by the belt 3| and the shield 25.

I have found that with the new method and apparatus, sheets and foils of indefinite length may be produced as a commercial operation continuing for indefinite periods. The material produced is of substantially uniform thickness from edge to edge and the edges are sharp and well defined. Also, since sprouting at the edges of the deposit surface is prevented, difiiculties in stripping, which have heretofore resulted in tearing the deposited sheet, are wholly prevented.

What I claim is:

l. A method of electrodeposition carried on in a cell containing an electrolyte, an anode, a cylindrical main cathode having its curved surface opposed to the anode, and a sub-cathode opposed to the end of the main cathode which comprises causing current to fiow through the electrolyte from the anode to the curved surface of the cathode, confining a body of electrolyte in contact with the end of the main cathode and the sub-cathode, said body of electrolyte being isolated from the remainder of the electrolyte maintaining said sub-cathode at a potential lower than that of the main cathode, and maintaining a continuous circulation of electrolyte through the space between the main cathode and the anode.

2. Apparatus for electrodeposition comprising an electrolytic cell containing an electrolyte, an anode in the cell, a main cathode in the cell having a deposit surface and a non-deposit surface. said deposit surface being opposed to the surface of the anode, a sub-cathode in the cell having its surface opposed to said non-deposit surface. means for confining a portion of the electrolyte in contact with the sub-cathode and said nondeposit surface of the main cathode and'isolating said portion of the electrolyte from the remainder, and meansfor maintaining the sub-cathode at a lower potential than that of the main cathode.

3. Apparatus for electrodeposition which comprises an electrolytic cell containing an electrolyte, an anode in the cell, a main cathode inthe cell, said cathode being of cylindrical drum form with its curved surface opposed to the anode, a sub-cathode in the cell opposed .to an end of the drum, means for confining a. body of electrolyte in contact with the main cathode and the subcathode and isolated from the remainder of the electrolyte, and means for maintaining the subcathode at a potential lower than that of the main cathode.

4. Apparatus for electrodeposition which com prises an electrolytic cell containing an electrolyte, an anode in the cell, a main cathode in the cell, said cathode being of cylindrical drum form with its curved surface opposed to the anode, a sub-cathode in the cell opposed to an end of the drum, means for maintaining the sub-cathode at a potential lower than that of the main cathode, means for confining a body ofthe electrolyte in contact with the main cathode and the sub-cathode and isolated from the remainder of the electrolyte, and means for causing a circulation of the remainder of the electrolyte between the opposed surfaces of the main cathode and the anode.

5; Apparatus for electrodeposition which comprises an electrolytic cell containing an electrolyte, an anode in the cell, a main cathode in the cell, said cathode being of cylindrical drum form with its curved surface opposed to the anode, a sub-cathode mounted on the wall of the cell in opposition to an end of the main cathode, means for confining a portion of the electrolyte in contact with the end of the main cathode and with the sub-cathode and isolated from the remainder of the electrolyte and means for maintaining the sub-cathode at a potential lower than that of the main cathode.

6. Apparatus for electrodeposition which comprises an electrolytic cell containing an electrolyte, an anode in the cell, a main cathode in the cell, said cathode being of cylindrical drum form with its curved surface opposed to the anode, a sub-cathode mounted on the end of the main cathode and insulated therefrom, means for confining a body of electrolyte in contact with the end of the main cathode and the sub-cathode and isolated from the remainder of the electrolyte and means for maintaining the sub-cathode at a potential lower than that of the main cathode.

'7. Apparatus for electrodeposition which comprises an electrolytic cell containing an electrolyte, an anode in the cell, a cylindrical drum main cathode in the cell having its curved surface opposed to the anode to receive a deposit, a subcathode in the cell opposed to the end of the drum, means extending between the end of the drum and the wall of the cell for confining a body of electrolyte in contact with the end of the drum and the sub-cathode and isolated from the remainder of the electrolyte, and means for maintaining the sub-cathode at a potential lower than that of the main cathode.

8. Apparatus for electrodeposition which comprises an electrolytic cell containing an electrolyte, an anode in the cell, a cylindrical drum main cathode in the cell having its curved surface opposed to the anode to receive a deposit, a subcathode in the cell opposed to the end of-the drum, means carried by the drum and contacting with the wall of the cell for confining a body of electrolyte in contact with the end of the drum and the sub-cathode and isolated from the remainder of the electrolyte, and means for maintaining the sub-cathode at a potential lower than that of the main cathode.

9. Apparatus for electrodeposition which comprises an electrolytic cell containing an electrolyte, a cylindrical drum main cathode in the cell, an anode in the cell said anode being curved and mounted to oppose the curved surface of the drum, a sub-cathode in the cell opposing an end of the drum, means for confining a body of electrolyte in contact with the end of the drum and the sub-cathode, means for maintaining the subcathode at agpotential lower than that of the main cathode, insulating shields extending along the lateral edges f the anode, and means for causing a continuous ow of electrolyte in the space between the main cathode and the anode.

10. In an electrolytic cell, the combination of a cylindrical drum cathode having a circumferential channel formed in its curved surface near each end thereof, ports extending through said curved surface from the bottom of each channel,

and means covering the top of each channel.

throughout at least a portion of the circumference of the drum.

11. In an electrolytic cell, the combination of a cylindrical drum cathode mounted to have a portion of its curved surface immersed in the electrolyte in said cell, a circumferential channel formed in the curved surface of the drum near each end thereof, ports extending through said surface from the bottom of each channel, and an endless belt covering the top of each channel throughout at least a portion of the circumference of the drum.

12. In an electrolytic cell, the combination of a cylindrical drum cathode mounted to have a portion of its curved surface immersed in the electrolyte in said cell, a circumferential channel formed in the curved surface of the drum near each end thereof, ports extending through said surface from the bottom of each channel, pairs of rotary guides, a pair near each end of the drum and above the level of the electrolyte in the cell, and a pair of belts, one at each end of the drum, each belt passing around one pair of guides and having a. portion covering the top of that por- 20 tion of the channel which lies beneath the electrolyte.

13. In an electrolytic cell, the combination of a cylindrical drum cathode mounted to have a portion of its curved surface immersed in the electrolyte in the cell, and an'open circumferential channel in the curved surface of the drum near at least one end thereof.

14. In an electrolytic cell, the combination of a cylindrical drum cathode mounted to have a por- 15. In an electrolytic cell, the combination of a cylindrical drum cathode mounted to have a portion of its curved surface immersed in the electrolyte in the cell, a circumferential channel near at least one end thereof, and a non-conductive partition member mounted at at least one end of thedrum and extending to the wall of the cell.

16. In an electrolytic cell,,the combination of a cylindrical drum cathode mounted to have a portion of its curved surface immersed in the electrolyte in the cell, a circumferential channel near at-least one end thereof, and a flexible web mounted at at least one end of the drum and extending edgewise toward and engaging the wall v a cylindrical drum cathode mounted to have a portion of its curved surface immersed in the electrolyte in the cell, a circumferential channel near at least one end thereof, and a partition member mounted at at least one end of the drum and extending frompne side of the channel to the wall ofthe cell.

19. In an electrolytic cell, the combination of a cylindrical drum cathode mounted to have a portion of its curved surface immersed in the electrolyte in the cell, a circumferential channel in the curved surface of the drum at at least one end thereof, a cylindrical partition member projecting beyond said end of the drum and enga ing the wall of the cell, and a ring holding said member in place.

the wall of the cell, and a. ring overlying said member to hold it in place, said ring defining a part of said channel.

21. In an electrolytic cell, the combination of Q a cylindrical drum cathode mounted to have a portion of its curved surface immersed in the electrolyte in the cell, and a partitionmember mounted on the drum and extending toward the wall of the cell. I

22. Apparatus for electrodepositlon which comprises a tank containing an electrolyte, an anode in the tank, a cathode in the tank having a surface opposing and spaced from the anode for receiving a deposit and another surface exposed to the electrolyte but on which no deposit is .desired, means for supplying current to the anode and withdrawing it from the cathode, mechanical means adjacent the edges of the deposit surface of the cathode for preventing thickening of the platingalong said edges, said means substantially restricting access of electrolyte to, the space between the anode and cathode, and electrical means for preventing deposition on the surface of the cathode on which no deposit is desired;

23. Apparatus for electrodepositlon comprising a tank containing an electrolyte, a rotating drum cathode having a portion of its cylindrical surface continuously immersed in the electrolyte, an anode in-the tank opposing the curved surface of the drum and spaced therefrom, means for supplying current to the anode and withdrawing it'from the cathode, mechanical means adjacent the ends of the drum for preventing thickening of the deposit on the curved surface of the drum, said means substantially restricting access of electrolyte to the flow of current through the openings at the ends of the drum cathode into the space between the anode and said curved surface, and electrical means for preventing deposition on the ends of the drum.

24. Apparatus for electrodepositlon comprising a tank containing an electrolyte, a rotating drum cathode having a portion of its cylindrical surface contlnuously immersed in the electrolyte, an

anode in' the tank opposing the curved surfaceof the drum and spaced therefrom, means for supplying current to the anode and withdrawing it from the cathode, members mounted on the curved surface .of the drum adjacent the ends thereof and extending from said surface toward the anode a substantial distance so as to reduce the size of the openings at the ends of said cylindrical surface into the space between the anode and said surface to a substantial extent, and electrical means for preventing deposition on the ends of the drum.

25. A method of electrodepositlon carried on in a cell containing electrolyte, an anode, a main cathode having a deposit and a non-deposit surface, and a sub-cathode, which comprises maintaintng a main body of electrolyte in contact with the anode and with the deposit surface of the main cathode, maintaining said sub-cathode at a potential lower than that of the main cathode and out of contact with said main body of electrolyte and immersed in a second body of electrolyte substantially isolated from said main trolyte in contact with the anode and with the deposit surface of the main cathode, maintaining in each cell a body of electrolyte substantially isolated from the first-mentioned body of electrolyte in said cell and in contact with the subcathode and with the non-deposit surface of the main cathode, introducing currentinto the electrolyte in each cell in theseries throughthe anode in said cell, withdrawing current from each 20 cell slmultaneouslythrough the main cathode and the sub-cathode in said cell, delivering the current withdrawn through the main cathode of each cell except the last to the anode of the next succeeding cell in the series, and delivering the current withdrawn from each cell except the last cell through the sub-cathode in said cell to the cathode of said next succeeding cell in the series.

27. Apparatus for electrodepositlon which comprises a plurality of electrolytic cells, each containing electrolyte, an anode, a main cathode having a deposit and a non-deposit surface, and a sub-cathode, means in each cell for confining a body of electrolyte therein in contact with the sub-cathode and with the non-deposit surface of the main cathode, said body of electrolyte being substantially isolated from the remainder of the electrolyte which is in contact with the anode and the deposit surface of the main cathode, means for supplying current from the positive side of a source of 'energy to the anode of the first cell in the series, means for withdrawing current from themain cathode of the last cell in the series and delivering it to the negative side of the source of energy, connections outside the cells between the main cathode of each cell except the last and the anode of the next succeeding cell in the series, and means for maintaining the sub-cathode in each cell at a potential lower than the main cathode in its cell, said means serving to withdraw current from each cell through its sub-cathode.

28. A method of electrodepositlon carried on in a cell containing electrolyte, an anode, a main cathode having a deposit and a non-deposit surface, and a sub-cathode, which comprises maintaining a main body of electrolyte in contact with. the anode and the deposit surface of the main cathode, maintaining a body of electro- 60 lyte substantially isolated from the body first mentioned and in contact with the sub-cathode and with the non-deposit surface of the main cathode, said sub-cathode being out of contact with said main body of electrolyte, introducing current into the cell through the anode, withdrawing current from the cell simultaneously through the main cathode and the sub-cathode, and varying the relative proportions of the current withdrawn from the cell through the min cathode and the sub-cathode by varying the voltage drop between the main cathode and the sub-cathode, through the substantially isolated body of electrolyte.

29. A method ofelectrodeposition carried on 76 in a cell containing electrolyte, an anode, a main cathode having a deposit and a non-deposit surface, and a sub-cathode, which comprises maintaining a main body of electrolyte in contact with the anode and the deposit surface of the main cathode, maintaining a body of electrolyte substantially isolated from the body first-mentioned and in contact with the sub-cathode and with the non-deposit surface of the main cathode, said sub-cathode being out of contact with said main body of electrolyte introducing current into the cell through the anode, withdrawing current from the cell simultaneously through the main cathode and the sub-cathode, andshielding the lateral edges of the deposit surface on the main cathode to prevent increased current density thereon.

30. Apparatus for electrodeposition comprising a tank containing an electrolyte, an anode in the tank, a cathode in the tank having a deposit surface and a non-deposit surface both exposed to the electrolyte, means for confining a portion of the electrolyte in contact with the non-deposit surface of the cathode and substantially isolated from the remainder of the electrolyte which is in contact with the anode and the deposit surface of the cathode, means for supplying current to the anode, mechanical means for preventing thickening of the plating along the edges of the deposit surface of the main cathode, and electrical means for preventing deposition on the non-deposit surface of the cathode, said electrical means also withdrawing current from the confined body of electrolyte only,

31. Apparatus for electrodeposition comprising a tank containing an electrolyte, a rotating drum cathode, this cathode having a deposit surface and a non-deposit surface, both of which have portions continuously immersed in the electrolyte, means for confining a body of electrolyte in contact with the non-deposit surface of the cathode and substantially isolated from the remainder of the electrolyte which is in contact with the deposit surface of the cathode, an anode in the tank, means for supplying current to the anode and withdrawing it from the oathode, mechanical means for preventing thickening of the plating along the edges of the deposit surface of the cathode, and electrical means for preventing deposition on the non-deposit surface of the cathode, said means also serving to withdraw current from the confined body of the electrolyte only.

32. A method of electrodeposition ,carried on in a tank containing electrolyte, an anode, a main cathode having a deposit surface and a non-deposit surface, and a sub-cathode, which comprises circulating electrolyte in contact with the deposit surface of the main cathode and a.

with the anode, maintaining a portion of the electrolyte substantially st nant and isolated from the remainder of the electrolyte, said isolated electrolyte being in contact with the subcathode and the non-deposit surface of the main cathode, maintaining the sub-cathode out of contact with said circulating electrolyte and 5 at a potential lower than that of the main cathode, introducing current into the tank through the anode, and withdrawing current from the tank simultaneously through themain cathode and the sub-cathode.

33. Apparatus for electrodeposition which comprises a tank containing electrolyte, an anode in the tank, a main cathode in the tank having a deposit surface and a non-deposit surface,

means for circulating the electrolyte in contact with the anode and the deposit surface of the cathode, means for confining and keeping out of circulation a portion of the electrolyte in con tact with the non-deposit surface of the main cathode, a sub-cathode in contact with said portion of the electrolyte and out of contact with the circulating electrolyte, means for introducingcurrent into the tank through the anode, and means for withdrawing current from the tank simultaneously through the main cathode 25 and through the sub-cathode.

34. In a metal plating operation, the method of controlling the deposition of metal on a selected. area of an object which comprises, immersing the object in an electrolyte in a cell containing an anode, attaching the object as a cathode to a source of current to effect deposition of metal upon a part of the surface of said object, isolating from the main body of electrolyte that portion of the electrolyte which contacts with another area on said object upon which the deposition is to be controlled,immersing an electrically conducting member in said isolated portion of the electrolyte, said member being out of electrical contact with said object, 40 and maintaining said member at a potential lower than that of the object.

35. Apparatus for electrodeposition which comprises, a tank containing an electrolyte, an anode in the tank, a cathode in the tank having a surface upon which metal is to be deposited and a second surface upon which the deposition is to be controlled, means for supplying current to the anode and withdrawing it from the cathode, means for isolating from the main body of electrolyte a portion of the electrolyte which contacts with said second surface, the deposition on which is to be controlled, an electrically conducting member in said isolated portion of electrolyte, said member being out of electrical contact with said cathode, and means for maintaining said member at a potential sufficiently lower than that of said cathode to control the deposition on said surface of the cathode.

CHARLES E. YATES.

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