US3503856A - Process for controlling electrodeposition - Google Patents

Description

March 31, 1970 BLACKMORE I 3,503,856

PROCESS FOR couw'noumue smcwnonmrosmou Filed July 10, 1968 s Sheets-Sheet 1 FIG]. i

" q I t 7 o o b o o o] 1 o o 8 2b 1 o b o o o 07 7 o o 0 8 gr: 0 o o o o 03 9 o o o 8 2d 2 o o o o o o} 7 o o o k 1 a V J PROCESS FOR CONTROLLING ELECTRODEYPOSITION Filed July 10, 1968 ets-Sheet 2 Mm 31, 1910 BLAKMR5 3,503 8 PROCESS FOR CONTROLLING ELECTRODEPOSITION Filed July 10, 1968 3 Sheets-Sheet 3 United States Patent once 3,503,856 Patented Mar. 31, 1970 1 Int. Cl. B41: 5/08,- C23b 7/00 U.S. Cl. 204-6 28 Claims ABSTRACT OF THE DISCLOSURE Electrodeposition of a metal or alloy is eifeeted from solution on workpieces, particularly electrotypes moulds or shells, whilst jets of the solution are impinged on the workpiece and one anode is shaded from another anode. A box is provided for carrying an electrotype mould or shell, the box having recesses in which edges of the mould or shell are received so as to mitigate treeing. A plating tank comprises a bank of anodes in spaced, edgeto-edge relationship, shading means between adjacent anodes, and apertured pipework on each side of the anode array to direct jets of electrolyte solution upon workpieces.

This application is a continuation-in-part of my application Electrodeposition, Ser. No. 472,772 filed July 19, 1965, and now abandoned.

The invention relates to a method of electrodeposition of electroplating and includes a method of producing an electrotype, means for supporting an electrotype mould and electrotype shells during electrodeposition and a plating tank.

It is well known that electrodeposition processes can be carried out at high speeds in agitated plating baths than in non-agitated baths and that vigorously agitated solutions act faster than gently agitated solutions. The reason for such faster rate of deposition is that the turbulence set up within the solution ensures constant replacement with fresh solution of the film of electrolyte over the cathode.

Electrotyping, a specialised branch of electroforming, requires much thicker deposits than are required in deeorative plating, making high speed deposition more than usually desirable both for economic production and quick service.

For many years electrotypers have expressed dissatisfaction with existing agitation methods which are known to be a limiting factor in the fight to accelerate production.

Among the better known methods of agitation, the following have been used in electrotyping:

In air agitation, low pressure air released in the bottom of the tank from a coil or pipework system drilled at regular intervals to break the air up into streams of bubbles which cause turbulence within the solution during their ascent to the surface. The streams of rising bubbles are usually disposed slightly in front of the vertical cathode (i.e. the electrotype or workpiece) surface where they will be most effective. Albeit a method of limited efficiency and application, air agitation is none the less the method most widely employed in electrotyping.

The limited efficiency of air agitation has been ascribed to a number of factors, possibly the most important being (i) the limited action on the cathode film of electrolyte and (ii) the replacement of a significant volume of solution between anode and cathode by a non-conductor, namely air.

The method of air agitation cannot be used with tin fluoborate and lead/tin fluoborate solutions as the air would oxidise stannous tin to stannic tin and thereby destroy, or cause serious deterioration of, the bath composition. With many solutions, the method of air agitation may only be used where tanks are fitted with fume extraction equipment since the emergent air can transport a fine mist of the solution into the workroom atmosphere and this mist may at least be an irritant if not also poisonous and corrosive.

The need to maintain a clean plating solution also calls for precautions to exclude oil from the air blower and dirt from the atmosphere.

Another disadvantage of the method of air agitation is that solutions, such as copper sulphate solution, which crystallise when the tank is idle and cooling, deposit crystals within the pipes, which deposits accumulate over a period. In order to maintain adequate air flow, the coil or ipework must be removed for cleaning periodically.

In cathode bar agitation, the bar carrying the work or electrotype is reciprocated along its axis thereby causing relative movement between the workpiece and the solution. This method is less eifective with electrotypes than is air agitation although it has hitherto been the most effective permissible method of agitating stannous fluoborate solutions or solutions with a stannous fluoborate content. The main limitation of cathode bar agitation is that only modest current densities may be employed since no more than gentle agitation is created.

Combinations of air and cathode bar agitation have been used from time to time but are little better than the method of air agitation alone.

In paddle agitation one or more propellers or paddlelike devices are rotated within the tank to move the solution over the cathode surface. The results are uneven and depend on the proximity of workpiece and paddle. Furthermore, the paddle or like devices occupy valuable tank space.

Ultrasonic agitation has met with little favour in electrotyping. The method does not appear to permit significantly higher current densities.

It is an object of the invention to provide a method of electrodeposition in which some at least of the disadvantages of the prior methods are mitigated.

According to the invention, a number of jets of the electrolyte solution are caused to impinge, preferably in a regular pattern, over substantially the whole of the area of the workpiece to be plated, particularly an electrotype, whilst one anode is shaded or shielded from an adjacent anode.

The jets of the electrolyte solution may be impinged over the whole face or area of the workpiece by forcing t: the electrolyte or plating solution at high speed into a coil, network or other arrangement of pipes which are provided at close intervals with holes facing the workpiece or cathode. In such manner, a vigorous and effective agitation can be attained with the result that high current densities can be employed. It will be understood that the jets of solution emerging from the holes in the pipework are present in a body of the electrolyte solution contained in a tank or other vessel.

The electrolyte solution forced through the holes or nozzles in the pipe. or pipes on to the cathode is preferably drawn from the tank or vessel in which the electrodeposition is being effected, by means of a pump of adequate capacity. Such pump is advantageously disposed outside the tank.

It is among the advantages of the method of agitation with jets of the solution according to the invention, that the direction of movement of the solution is on to the face of the cathode and the moving solution therefore acts most effectively on the cathode film of electrolyte. Furthermore, the conductivity and cleanliness of the bath is unaffected since no foreign medium is introduced between anode and cathode.

The edge of one anode is shaded or shielded from the edge of an adjacent anode in order to prevent or reduce the formation of tree-like growths on anode edges, particularly when the electrodeposition is carried out in a tank or other vessel which is not fully loaded with workpieces. The outer side edge of each of the two end anodes in the series of anodes is preferably also shaded or shielded. When the tank or other vessel is provided with two series or banks of anodes which are, in effect, operated back to back, the backs of the anodes are also preferably shaded or shielded from each other. This mitigates against the corrosion or wearing away which otherwise tends t occur at the anode backs.

The shading or shielding of the anode edges may conveniently be effected by disposing between the edges of each pair of adjacent anodes a sheet or film of an insulating material which is inert under the conditions of electrodeposition in the electrolyte solution. The sheet or film forms a barrier and may be made of a suitable synthetic resin, for example, rigid polyvinyl chloride. One or more similar sheets may be used between one bank of anodes and another bank of anodes to shield or shade the backs of anodes in one bank from the backs of the anodes in the other bank. When two parallel banks or series of anodes are used in back to back relation, then a barrier sheet or film between the edges of two anodes in one bank is conveniently provided of such width that it also forms a barrier sheet or film between the edges of two anodes in the other bank. The backs of the anodes in the tWo parallel banks are shielded by one or more barrier sheets or films which run between the two banks in a direction substantially parallel to the anodes.

The said barrier sheet or films are conveniently mounted in a framework on which anode bags may also be mounted to catch anode sludge. Such bags are known per se and may conveniently be provided of a woven fabric of polypropylene or polyethylene terephthalate fibres. The framework may be made of any suitable insulating material, for example bars or rods of rigid polyvinyl chloride or of rubber-covered steel. The framework may be of a size to mount 2, 3, 4 or more of the shading sheets or films. The framework may be provided with handles to facilitate its positioning in and removal from the vessel in which the electrodeposition is effected. The vessel may also contain means to locate the framework in the correct position.

The method according to the invention has been found to give rapid electrodeposition of lead/tin alloy in the backing of electrotypes. The method is also effective with other electrotyping solutions, such as solutions. of:

Copper sulphate Copper fluoborate Copper sulphate/ copper fluoborate combined Copper pyrophosphate Nickel sulphamate Nickel fluoborate Nickel sulphamate/nickel fluoborate combined Lead fluoborate, and

Tin fluoborate.

The solution is directed at the face of the cathode, for example, at the back of the shell, so as to hose it all over. The impingement of the jets or streams of solution on the cathode must, however, be controlled so as to avoid any undue, adverse effect on the structure of the electrodeposited material. For this reason it is desirable to determine that most suitable combination of solution flow rate, hole size, spacing and distance from cathode, individually for each solution. Such determination may readily be effected by simple experiment. Thus, for example, it was found in one instance that copper electrotype shells deposited from copper sulphate solution exhibited impingement effects when impact of the jets of solution was too vigorous, the deposit at the point of impact being extremely bright and brittle. Upon reducing the' flow rate and increasing the distance between the outlet holes and the cathode and increasing the number of holes in the pipes from which the jets of solution were projected at the cathode, it was possible to deposit good quality shells at greatly increased speeds.

When impingement effects have been difficult to overcome, it has been found that a combination of this method of solution agitation with cathode bar movement eliminated further problems.

A simpler method has, however, been found of overcoming impingement effects in the electrodeposition of copper, for example in the growing of copper shells on electrotype moulds. The method consists in introducing air or other gas into the lower layers of the electrolyte solution, the gas being inert to the electrolyte solution. The air may be introduced into the solution at more than one position but it has been found effective to introduce the air at only one position in quite large tanks or baths. This single position of introduction is conveniently in a corner of the tank or bath. This is in great contrast to the usual method of air agitation in which the air is intro duced at a plurality of positions below and slightly in front of the faces of all of the workpieces being plated.

It is the custom to support silvered electrotype moulds during electroplating on flat carrier sheets, commonly known as boxes, of an insulating material such as rigid plastics, glass, plastic or rubber coated metal, fibre-glass reinforced phenolic or other plastic and plastic laminates, by means of wax or such articles as single and double sided adhesive tapes, rubber bands and clips.

For the deposition of relatively thin deposits at lower current densities this method is in general adequate.

However when higher current densities are required for increased speed of shell and backing alloy deposition, the known methods of supporting the mould or shell give rise to difficulties. By way of example, an excess of copper treeing is experienced at the edges during shell deposition and while this may be trimmed off, it is to say the least an undesirable waste. To start rapid electrodeposition of backing alloy with such a shell would be pointless; indeed rapid electrobacking on to a perfect shell in the known box or carrier will run into trouble long before suflicient alloy has been deposited since severe treeing will be experienced at the exposed edges of the shell.

It is a further object of the invention to provide a method and a support or box for an electrotype mould or'shell or other workpiece whereby the disadvantage of treeing during electrodeposition is mitigated.

According to this further feature of the invention, the electrodeposition of a shell on an electrotype mould or of a backing layer on an electrotype shell or the electrodeposition of a metal or alloy on any other workpiece is carried out whilst the side and lower edges, of the mould,

shell or other workpiece are shaded or not fully and freely exposed.

According to the invention furthermore, there is provided a box or support for carrying a workpiece, particularly an electrotype mould or shell, during electrodeposition, the box having a back, two side walls and a lower end wall or floor, the two side walls and the floor having recesses to receive the corresponding edges of the mould or shell or other workpiece. The workpiece, for example a mould or mould plus shell, is preferably a free sliding fit in the recesses and for this purpose the edges of the mould may be trimmed or the recesses dimensioned accordingly.

The box is advantageously provided of a substantially rigid, synthetic material such as rigid polyvinyl chloride.

According to the invention moreover, an electrotype mould or shell or other workpiece is supported in the box during a process of electrodeposition whilst the electrolyte or plating solution is impinged over substantially the whole of the face of the work in the manner hercinbefore described.

The invention further provides a plating tank comprising a bank, series or array of anodes in spaced, edge-toedge relationship, an anode shading sheet of an insulating material disposed between the edges of each adjacent pair of anodes, two series of means for suspending workpieces in the tank, the two series being disposed one on each side of the bank of anodes, and between the bank of anodes and each of said series of suspending means an array of pipes provided with jets, nozzles or apertures, said jets, nozzles or apertures being so provided that liquid emerging from them under pressure would impinge upon workpieces suspended in appropriate positions from the adjacent series of suspending means.

The invention is diagrammatically illustrated by way of example in the accompanying drawings in which- FIGURE 1 is a longitudinal section of a plating tank showing one construction of means for agitating the electrolyte solution;

FIGURE 2 is a transverse section of the construction shown in FIGURE 1;

FIGURE 3 is a perspective view of one construction of box;

FIGURE 4 is a transverse section of the box shown in FIGURE 3 with an electrotype mould and shell shown in position;

FIGURE 5 is a diagrammatic plan view of one arrangement of agitation means, anodes and barrier or shading sheets in a plating tank, and

FIGURE 6 is a perspective view of one construction of a frame for the anode shading sheets.

The agitation means 1 (FIGURES 1 and 2) comprise two banks each of four substantially horizontal outlet pipes 2a, 2b, 2c, 2d and 3a, 3b, 3c, 3d respectively, disposed in a rubber-lined plating tank 4 of 400 imperial gallons capacity. Each of the outlet pipes is feet long and each outlet pipe is disposed approximately 5 /2 inches above or below an adjacent outlet pipe in the same bank, the two tanks being substantially parallel.

A bank or series of anodes 5 is disposed between the two banks of outlet pipes, the anodes being disposed in spaced edge-to-edge relationship, that is to say, the anodes are in line one with the other and are spaced apart. A series of workpieces or cathodes 6 is disposed on the other or outer side of the pipes 2a2b and a series of workpieces or cathodes 7 is similarly disposed in relation to the pipes 3a3d. Each of the outlet pipes 2a-2d is provided on its outer side with a series of holes 8 directed towards at least one of the cathodes 6, the holes being spaced at equal distances from each other. Each of the outlet pipes 3a3d is provided with a similar series of holes 9 directed towards at least one of the cathodes 7.

A shading or barrier sheet is disposed between the adjacent anodes, each shading sheet being of an insu ating material which is inert to the electrolyte solution. The

shading sheets are suitably of rigid polyvinyl chloride and they are of sufficient length to extend from below the level of the lower ends of the anodes to above the surface of the electrolyte. The shading sheets are of a width sufiicient to shade the edges of two adjacent anodes one from the other so that tree-like growths on anode edges is prevented or reduced, particularly when the plating tank is operated under partial load, that is, when a full complement of cathodes 6 and 7 is not present in the tank. The anode shading sheets have been omitted from FIGURES 1 and 2 for the sake of clarity, but their disposition in the tank is illustrated in FIGURE 5.

At corresponding ends, the two banks of outlet pipes 2a-2d and 3a-3d communicate with feed pipes 10 and 11 respectively, the feed pipes 10 and 11 being in communication with the pump (not shown) through a line 12. The other ends of the outlet pipes 2a-2d are in communication with a vertical pipe 14 the lower end of which communicates with the lower end of the feed pipe through a pipe 16. The ends of the outlet pipes 3a-3d remote from the feed pipe 11 are also in communication with a vertical pipe similar to the pipe 14, the lower end of such pipe being in communication with the lower end of the feed pipe 11 through a pipe 17. The upper end of the vertical pipe 14 is connected to the upper end of the similar vertical pipe associated with the pipes 3a3d.

The network of pipes 2a-2d 3a-3d, 10, 11, 12, 14, 16 and 17 are all of polyvinyl chloride. They could, however, be of another suitable material, for example, ABS

resin.

In operation, the pump draws electrolyte solution 18 from the tank 4 through its suction line (not shown) and feeds it through lines 12, 10, and 11 to the outlet pipes 2a-2d and 3a3d. The electrolyte solution emerges under pressure through the holes 8 and 9 into the body of solution in the tank 4 as a series of streams or jets directed at the work which forms the cathodes 6 and 7. The rate at which the solution is pumped into the outlet pipes, the diameter and number of the holes 8 and 9 and the distance between the outlet pipes and the corresponding cathode are so provided that electrodeposition can be effected rapidly on the cathode whilst avoiding adverse eifects on the structure of the deposited layer through too vigorous impingement of the jets or streams from the holes 8 and 9 on the work.

The box or support shown in FIGURES 3 and 4 comprises a back 30, side walls 31 and a bottom or floor 32. The back, side wall and floor are all of rigid polyvinyl chloride and are securely welded together. It will be understood that the box may be made of any other suitable insulating material, such as materials other than polyvinyl chloride which are commonly employed at present in the manufacture of electrotype boxes. The back 30 is provided at its end remote from the floor 32 with a hole 33 by means of which the box may be suspended in the electrolyte bath.

A recess 34 is provided on the inner surfaces of each of the side walls 31 and floor 32 at a position adjacent to the back 30, in which recesses the side and lower edges of the workpieces are received. By way of example, a copper shell 35 on the mould 36 on which it was grown is shown in position in the box in FIGURE 4. The back of the mould rests against the back 30 of the box and the side and lower edges of mould and shell are disposed within the recesses 34.

The heights of the side walls 31 and fioor 32 may vary. In general, however, a height which is satisfactory for use in plating with one solution may be found unsatisfactory with another solution. Thus, for example, in depositing copper shell from a copper sulphate solution on a Vinylite mould in a box of the construction shown in the drawings, the shells were grown at a fast rate when the height of the walls 31 and floor 32 was only /2" above the back 30, the recesses 34 being /a wide and /s deep. Such walls were, however, too shallow when it was sought 7 to back the electroty-pe shell at a fast rate with a lead/ tin alloy, since extensive treeing occurred. Upon increasing the height of the walls and floor to 2 inches, with the same dimensions for the recesses 34, the lead/tin alloy was satisfactorily electrodeposited at a fast rate to back the electrotype shell.

The box is secured to a conducting hanger by a bolt which passes through the hole 33 and the upper end of the hanger is secured to or is in electrical connection with the cathodes bar whilst the lower end of the hanger is electrically connected to the workpiece by a strip of copper gauze. When a shell is to be deposited on an electrotype mould, the face of the mould is sprayed with silver to render it conductive and capable of being electroplated.

In FIGURE 5 there is diagrammatically shown a rubber-lined plating tank 44 containing an array of anodes 45, two series of electrotype boxes 30 each containing, as workpiece or cathode, an electrotype mould 46 and, between the anode array and the cathodes 46, two blanks of pipes 42 and 43 each similar to the banks 2a-2d and 3a-3d shown in FIGURES l and 2. The banks of pipes are as, in the construction shown in FIGURES 1 and 2, provided with holes through which the electrolyte solution may emerge as a series of jets to impinge upon the faces of the moulds 46 in the boxes 30. Electrolyte solution is drawn from the tank 44 by a pump (not shown) and is passed by the pump into the apertured pipes of the two banks 42 and 43 through pipe 52 and arms 50 and 51.

The array of anodes 45 consists of two parallel series of anodes 45a and 45b. The side edges of the anodes are shaded or shielded by sheets 53 of rigid polyvinyl chloride. Each sheet 53 is of a length such that its lower end is disposed below the lower ends of the anodes whilst its upper end is disposed above the surface of the electrolyte solution in the tank 44. Further, each sheet 53 is of a width appreciably greater than the distance between the two parallel series of anodes, whereby each sheet serves to shade the side edge of at least one anode in each of the two series. The backs of the anodes 45a in one bank are shielded or shaded from the backs of the anodes 45b in the other bank by a series of sheets 71 of rigid polyvinyl chloride. The sheets 71 are disposed substantially parallel to the anodes 45a and 45b and extend from one sheet 53 to the next sheet 53. Further, as with sheets 53, each sheet 71 has its lower end disposed below the lower ends of the anodes and its upper end disposed above the surface of the electrolyte.

When the tank is in operation, the sheets 53 and 71 prevent or hinder the formation of tree-like growths on the side edges of the anodes and hinder or lessen corrosion on, or wearing away of the rear or adjacent faces of the anodes in the two series 45a and 45b.

The tank 44 is also provided in one corner with an air inlet pipe 54 which extends nearly to the bottom of the tank, the lower end of the pipe 54 having an elbow 55 provided with an extension pipe 56 having holes 57 through which the air emerges into the electrolyte solution, the end of extension pipe 56 remote from the elbow 55 being closed. In copper deposition, for example in the electrolytic growing of electrotype shells of copper, the feeding of air in through the pipe 54 has been found to mitigate or avoid impingement effects arising from the jets of electrolyte solution ejected from the banks of pipes 42 and 43. This method may also be used with other electrolyte solutions, for example nickel plating solutions, except those solutions which would undergo oxidation in which case nitrogen or other non-oxidising and inert gas would be used.

The anode shading sheets 53 are preferably mounted in a framework. One suitable construction of framework, with three sheets 53 and two sheets 71 mounted in position is illustrated in FIGURE 6. The composite unit of framework and sheets comprises three sheets 53 welded at their lower edges, in parallel relation to a base sheet 59 of rigid polyvinyl chloride, the base sheet 59 having along its two longitudinal edges a short upstanding wall or lip 60. Longitudinally extending rods 58 of rigid polyvinyl chloride or other inert, insulating material are welded to the side edges of sheets 53. The sheets 53 are each provided with an aperture 61 at each of the two top corners, a rod 58a of rigid polyvinyl chloride passing through each of the two sets of three holes 61 as shown. The rods 58a are removable and are secured in position by providing nuts (not shown) of rigid polyvinyl chloride on the ends of the rods 58a which are threaded to receive the nuts. It will be understood that the rods 53a may be removably secured in the position shown in any other suitable manner. Two sheets 71 are welded centrally and at right angles to sheets 53, one sheet 71 extending between each adjacent pair of sheets 53. The unit shown in FIG- URE 6 would, in the construction shown in FIGURE 5, contain four anodes within its periphery, namely two anodes 45a and two anodes 4511. An anode bag, for example a bag made of a woven fabric of polypropylene or polyester fibres, is preferably mounted around and under each such unit to retain anode sludge. The removable rods 58a facilitate mounting of the anode bag in position, the bag being preferably provided at its mouth with open-ended pockets through which the rods 58a may be passed to engage the bag.

In one example, the tank 44 was approximately 9 feet long and 2 /2 feet wide, and the extension pipe 56 was approximately 1 foot long and was provided with four holes 57. The distance between the anodes 45a and 45b was about 7 inches, that between the centres of the two banks of pipes 42 and 43 was about 10 /2 inches and that between one series of anodes and the adjacent series of cathodes or moulds 46 was about 6 inches.

The invention is further illustrated in the following examples.

EXAMPLE 1 The plating tank employed was the 400 gallon-rubberlined plating tank 4 provided with two banks of horizontal outlet pipes 2a-2b and 312-317 shown in FIGURES 1 and 2. 29 holes 8 and 9 were provided in each of the outlet pipes, each of which pipes was ten feet long, the holes being diameter and evenly spaced. The sides edges of the anodes 5 were shaded by sheets of rigid polyvinyl chloride similar to the sheets 53 shown in FIGURE 5.

The plating solution 18 in the tank was a lead/tin fluoborate plating solution of known composition.

The pump drew solution from the tank and returned it via the pipes 12, 10 and 11 at up to 300 imperial gallons per minute, equipment to a maximum of 1.3 imperial gallons per outlet hole per minute.

A number of electrotype moulds each bearing a previously deposited nickel/copper shell were inserted into a corresponding number of boxes each of the same construction as the box shown in FIGURES 3 and 4 and having walls 31 and 32 2 high and recesses 34 A wide at /8 deep. Each box was fitted with an electroplating hook and the shells were cleaned by scrubbing with a dilute solution of fluoboric acid solution. The boxes were then hung in the tank with the work facing the outlet pipes 212-201 and anodes 5 and the current was switched on, the shells forming the cathodes 6. The outlet holes 8 were approximately 2" from the face of the work.-

It was found that when plating on to the smooth shells, current densities of over 200 amps per square foot could be employed for prolonged periods (several hours if necessary). In this manner, the shells were quickly provided with a satisfactory lead/tin backing.

The solution employed is one which is particularly prone to roughness when agitation is inadequate and to treeing at the edges of the work when these are not protected. Although the tank was not full loaded, no visible treeing occurred on any of the anodes.

EXAMPLE 2 The 400 imperial gallon plating tank 4 illustrated in FIGURE 1 and 2 was employed to deposit shells on electrotype moulds, the electrolyte 18 being an acidified solution of copper sulphate. The two banks of outlet pipes, each ten feet long, had 37 holes 8 and 9 provided in each of the outlet pipes, each hole being of A" diameter and evenly distributed. The sides edges of the anodes 5 were shaded with sheets of rigid polyvinyl chloride, as in Example 1.

The pump drew solution from the tank and returned it via the outlet pipes at a rate of up to 300 imperial gallons per minute equivalent to a maximum of 1.1 imperial gallons per outlet hole 8 or 9 per minute.

It was found necessary to vary the degree of agitation from that preferred for lead/ tin alloy deposition as described in Example 1. The greater number of holes each of smaller diameter has been noted above, while the distance from the outlet hole to the cathode was increased from 2 inches to 4 inches and the rate of flow reduced to somewhat less than the maximum available. This was necessary to avoid adverse impingement effects, which revealed themselves during the deposition of the copper electrotype shells as small circular areas of brittle, lustrous deposit at the point of impact of each jet of solution. By operating as described, sound electrotype shells were quickly grown. No tree-like growths could be seen on the anodes.

EXAMPLE 3 A number of electrotype moulds, each previously sprayed with silver to render it conducting and having a copper gauze contact strip, Were inserted into a corresponding number of boxes, of the kind hereinbefore described and illustrated in FIGURES 3 and 4. The walls 31 and 32 were /2" high and the recesses 34 were /8 wide and /8" deep. Each box was provided with a gunmetal hook to support the work on the cathode bar and to make electrical contact between cathode bar and the work.

These assemblies were then suspended in a copper depositing tank of the type described in Example 2. Initially the rate of deposition was kept low to prevent burning of the deposit on the very thin silver film, but when after a few minutes sufficient copper has been deposited, the rate of deposition was increased to the maximum from one hour. The work was then removed from the tank and the copper shell on its mould thoroughly rinsed to remove all sulphate ions.

The rinsed shells and moulds were transferred to other boxes of the same kind but having 2" high walls and these boxes of work were hung in a lead/ tin fluoborate plating tank as described in Example 1. The lead/tin backing alloy was deposited at high speed (up to 300 amps per square foot current density) until a sufiicient thickness of backing alloy was deposited.

No treeing was visible on the anodes in either of the two tanks.

EXAMPLE 4 The plating tank used was the rubber-lined plating tank 44 illustrated in FIGURE 5 the electrolyte capacity of the tank being about 400 imperial gallons. The tank was employed to deposit shells on electrotype moulds, the electrolyte 18 being an acidified solution of copper sulphate. The two banks of outlet pipes 42 and 43 each ten feet long, had 37 holes provided in each of the outlet pipes, each hole being of A" diameter and the holes being evenly distributed. The sides edges and backs of the anodes 5 were shaded with sheets 53 and 71, respectively, of rigid polyvinyl chloride, the sheets 53 and 71 being mounted in several frameworks of the kind illustrated in FIGURE 6. The frameworks were made of rigid polyvinyl chloride.

Each electrotype mould, which had previously been rendered conductive, was mounted in a box 30 and each box was suspended from the cathode bar by a gunmetal hook through which electrical connection to the conduc tive face of the mould was established. A major number of, but not all of, the work stations were occupied.

The pump drew solution from the tank and returned it via pipe 52, arms 50 and 51 and the outlet pipes 42 and 43 at a rate of up to 300 imperial gallons per minute equivalent to a maximum of 1.1 imperial gallons per outlet hole per minute. The distance between the holes in the outlet pipes 42 and 43- and the cathode, that is moulds in the boxes 30, was 4 inches. The rate of flow of the electrolyte solution in the jets impinged on the work was reduced to somewhat less than the maximum available, in order to lessen adverse impingement efiects. Further adjustment of the rate of flow was not undertaken in order to avoid the residual, adverse effects of impingement. Instead, air was passed into the lower layers of the electrolyte through the single pipe 54 disposed in one corner of the tank. This step avoided the remaining adverse eifects of impingement.

In this manner, sound electrotype shells were quickly grown. No tree-like growths could be seen on the anodes and the backs of the anodes appeared unchanged.

I claim:

1. In a method of electrolytically depositing a metal or alloy from an electrolyte solution on a workpiece immersed in the said electrolyte solution, the step of impinging jets of the said electrolyte solution over substantially the whole area of the workpiece during the electrodeposition by forcing part of the said electrolyte solution through holes provided in pipework disposed between the workpiece and anodes whilst the side edge of one anode in the electrolyte solution is shaded from the side edge of an adjacent anode.

2. A method according to claim 1, in which the jets of the electrolyte solution are impinged in a substantially regular pattern over substantially the whole area of the workpiece during the electrodeposition.

3. A method according to claim 1, in which the workpiece is also subjected, independently, to movement during the electrodeposition.

'4. A method according to claim 1, in which the workpiece is an electrotype mould or shell.

5. A method according to claim 4, in which at least a portion of the peripheral edge of the workpiece is shaded during the electrodeposition to prevent treeing of the electrodeposited metal at said portion of the edge.

6. A method according to claim 1, in which the side edge of an anode is shaded from the side edge of an adjacent anode by means of a barrier sheet disposed in the electrolyte solution between and spaced from the said two side edges of the adjacent anodes, said sheet being of a material which is substantially inert under the conditions prevailing in the electrolyte solution during the electrodeposition.

7. In a method of electrolytically depositing a metal or alloy from an electrolyte solution on at least two workpieces immersed in said electrolyte solution which also contains an array of anodes, the steps of circulating part of said electrolyte solution through pipework and from positions located between the anodes and the workpieces impinging jets of said circulated electrolyte solution under pressure over substantially the whole face of each workpiece during the electrodeposition and mitigating the formation of tree-like growths on side edges of the anodes by shading said edges with sheets of an inert synthetic resin spaced from said side edges.

8. A method of electrolytically depositing a metal or alloy from an electrolyte solution on at least two workpieces immersed in said electrolyte solution, which comprises carrying out the electrodeposition with an array of anodes disposed in at least two substantially parallel series in the electrolyte solution, the anodes in each series being in spaced, edge-to-edge relationship, and impinging jets of said electrolyte solution over substantially the whole face of each workpiece during the electrodeposition whilst a sheet of an inert synthetic resin is disposed between adjacent edges of adjacent anodes in each of said series and a sheet of an inert synthetic resin is disposed between anodes in two adjacent series, whereby tree-like growths on the anode edges and corrosion of the backs of the anodes are mitigated.

9. A method according to claim 8, in which a single sheet of said synthetic resin extends between the adjacent edges of a pair of anodes in one said series and an adjacent pair of anodes in an adjacent series.

10. A method according to claim 8, in which the said synthetic resin is rigid polyvinyl chloride.

11. A method according to claim 8, in which the workpieces are electrotype moulds or shells.

12. A method according toclaim 8, in which the sheets of inert synthetic resin are mounted in one or more frames around which anode bags are provided.

13. In a method of electrodepositing backing metal from an electrolyte solution on an electrotype shell immersed in said electrolyte solution which contains two or more anodes disposed adjacent to one another, the steps of circulating part of said electrolyte solution under pressuer through pipework disposed between the electrotype shell and the anodes and containing holes through which electrolyte solution emerges as a series of jets to impinge upon substantially the whole area of the back of the electrotype shell during the electrodeposition of backing metal, and simultaneously shading the edge of one anode from the edge of an adjacent anode by means spaced from the said edges of the adjacent anodes.

14. A method according to claim 13, in which the electrotype shell is subjected to movement in a direction substantially at right angles to the direction of said impinging jets.

15. In a method of electrodepositing backing metal on an electrotype shell immersed in an electrolyte solution containing two or more anodes which are disposed adjacent to each other, the steps of shielding the side edges of the anodes by means spaced from said side edges and impinging jets of the electrolyte solution over substantially the whole area of the back of the said shell during the electrodeposition of the backing metal, said jets originating from sources disposed between the electrotype shell and the anodes and the flow rate and velocity of the electrolyte solution in said jets being such as to permit the current density employed during the electrodeposition to be improved without adverse effect on the structure of the electrodeposited metal.

16. A method according to claim 15, in which at least a portion of the edges of said electrotype shell is shaded during the electrodeposition to inhibit treeing at said portion of the edges.

17. A method according to claim 15, in which at least a portion of the edges of said electrotype shell is shaded during electrodeposition by being received in a recess in a support comprising a back and side walls, the said recess being in the side walls at a position adjacent to said back.

18. A method according to claim 15, in which said backing metal is a lead/tin alloy, said electrolyte solution containing a salt of lead and a salt of tin.

19. A method of electrolytically growing a copper or nickel shell on an electrotype mould immersed in a copper or nickel electroplating solution, which comprises growing the shell in a tank which has an array of anodes disposed in a spaced edge-to-edge relationship and from positions between the mould and the array of anodes impinging jets of the electroplating solution over substantially the whole area of the said mould during the growth of the shell, the flow rate of said jets being such as not to impair the structure of the electrodeposited copper or nickel, whilst a sheet of an inert synthetic resin is disposed between and spaced from two adjacent anodes to shade the side edge of one from adjacent side edge of the other.

20. A method of electrically depositing a metal or alloy on a plurality of workpieces immersed in an electrolyte solution, which comprises carrying out the electrodeposition in a vessel provided with a plurality of anodes disposed in spaced, edge-to-edge relationship and having a barrier sheet disposed between and spaced from the side edges adjacent anodes whereby said side edges are shaded one from the other, impinging jets of the electrolyte solution over substantially the whole face of each workpiece, and injecting a gas into the electrolyte solution during the electrodeposition, said gas being inert to the electrolyte solution under the conditions employed and the rate of injection of said gas being insuflicient in itself to effect any appreciable agitation of electrolyte solution adjacent to the faces of said workpieces.

21. A method according to claim 20, in which the electrolyte solution is readily oxidisable and said gas is nitrogen.

22. A method according to claim 20, in which the gas is injected into the lower layers of the electrolyte solution in said vessel.

23. A method according to claim 20, in which the gas is injected at only one position into the electrolyte solution.

24. A method of electrically depositing copper on a plurality of workpieces immersed in a copper electroplating solution, which comprises carrying out the elec trodeposition in a vessel provided with a plurality of anodes disposed in spaced, edge-to-edge relationship and having a barrier sheet disposed between and spaced from adjacent side edges of adjacent anodes whereby said edges are shaded one from the other, impinging jets of the electroplating solution over substantially the whole face of each workpiece, said jets originating from positions between the workpieces and the anodes, and injecting air into the electroplating solution during the electrodeposition, the rate of injection and position of injection of said air being such that the injected air is in itself insufficient to effect appreciable agitation of electrolyte solution in contact with the faces of said workpieces.

25. A method according to claim 24, in which each workpiece consists of an electrotype mould on which a shell is to be electrodeposited.

26. A method according to claim 24, in which the air is injected into the lower layers of the electroplating solution in said vessel.

27. In a method of electrodepositing metal on a workpiece immersed in an electrolyte solution containing two or more anodes which are disposed adjacent to each other in spaced edge-to-edge relation, the steps of shielding the side edges of the anodes by means spaced from said side edges and circulating the electrolyte solution through pipework through holes in which part at least of the circulated electrolyte solution emerges in the form of jets which impinge over substantially the whole area of the face of the workpiece during the electrodeposition of the metal, the said jets emerging from said pipework at positions disposed between the workpiece and the anodes, and the flow rate and velocity of the electrolyte solution in said jets being such as to permit the current density employed during the electrodeposition to be improved without adverse effect on the structure of the electrodeposited metal.

28. A method according to claim 27, in which at least some of the electrolyte solution in said jets strikes the workpiece normally to its surface and substantially all of the remainder of the electrolyte solution in the jets strikes the said surface at an angle of not more than 45 to the normal.

(References on following page) I 13 14 References Cited FOREIGN PATENTS 4,668 1905 Great Britain. UNITED STATES PATENTS 9,698 1908 Great Britain. 1, 49,787 12/1917 Leuchter 204-277 1912 GreatBrt am' 204 277 5 JOHN H. MACK, Pnmary Exammer 1423815 7/1922 Park T. TUFARIELLO, Assistant Examiner 1,587,303 6/1926 Hart 20 9 US. Cl- XR.

1,700,178 1/1929 Porzel 204279 204-23, 273, 277

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