US1910150A - Apparatus for electrodeposition of metals - Google Patents

Description

May 23, 1933- s. o. cowPER-coLEs 1,910,150

APPARATUS FOR ELECTRODEPOSITION OF METALS I l l I I if. Il

May 23, 1933 s. o. cowPER-coLEs 1,910,150

APPARATUS FOR ELECTRODEPOSITION 0F METALS Filed May 6, 1950 2 Sheets-Sheet .2

. ment in the circumferential direction of the.

Patented May 23, 1933 UNITED STATES PATENT OFFICE F. C. METAL PROCESSES LIMITED, OF LONDON, ENGLAND,

A.- BRITISH COMPANY APPARATUS FOR ELECTRODEPOSITION METALS Application led May 6, 1930, Serial No. 450,180, and in Great Britain May 15, 1929.

My invention has for its object the rapid and economical electro-deposition of metals, especially copper, of a quality superior to any hitherto attainable and in what I believe to be a new physical condition such that the deposited metal is at once and withoutfurther treatment suitable for the manufacture of a variety of industrial products as hereinafter indicated. The metal is of exceptional purity, density and hardness; thus, inthe case of copper, a hardness numeral of 130 or more on the Brinell scale and a. breaking stress in tension of 35 tons per square inch are obtainable. The process results in uniformity of structure owing to the fact that the metallic crystals are, to a large extent at least, broken down; any remaining crystals all lie in one direction, thus also conducing to uniformity. The metal may be obtained as sheet, strip or Wire or in the form of cylinders or tubes of any desired diameter.

According to the invention the cathode employedfor the electro-deposition of the desired metal is constituted by a horizontal mandrel rotated at a speed resulting in 'turbulence of the electrolyte suiiicient to break up the` film of exhausted electrolyte in proximity to the mandrel, rollers or discs free to revolve and capable of a limited movemandrel being arranged to bear on the metal deposited thereon. The rollers are mounted on a carriage or the like which is moved to and fro in a direction p-arallel tothe axis of the mandrel, the arrangement preferably roimay be varied by altering the pressure exbeing such that the rollers are operative during motion in one direction only. The abovementioned qualities of the metal deposited erted by the rollers or discs or the number of to-and-fro movements performed in unit prior 'English specification No..

1898, inthat in the latter case there 1s emtime, or by changing both these factors.

It will be realized that this invention differs essentially from that disclosed in my 21,971 of ployed a vertical mandrel-wholly immersed androtated at a speed suiiciently high to throw olf by centrifugal force the cathodic film of exhausted electrolyte containing hydro,D n bubbles, whereas in the present case the n andrel is only partially immersed and the speed is merely sufficient to lift, at the point at which the rotating surface of the mandrel emerges from the electrolyte, a small quantity of the electrolyte a few inches above the normal surface of the liquid, from which height it falls back giving the appearance of a cascade, producing agitation of the liquid and breaking up the cathodic film. The fact of the rollers being operative during axial travel in one direction only results in equality of treatment over the whole surface of the mandrel and causes the metal ,to

be deposited in such a manner that any crystals which in the process are not broken down lie substantially in one direction, producing uniformity in the metallic structure hitherto, I believe, unattained. The rollers are preferably so mountedas to bear on the mandrel solely by their own weight, such pressure determining to a large extent the density and other 'qualities of the deposlted metal; in order to vary the pressure rollers of different weights are preferably employed, but obviously such variation may be secured by means of spring pressure or weights applied to the frame or the like carrying the rollers.

In describing my invention I w1ll take copper as the metal to be deposited from a suitable electrolyte such per and in the first place I will describe the process as adapted for the manufacture of copper sheet. In a suitable vessel contaming the electrolyte I mount the rotatable mandrel, so that about half of the circumference of the mandrel is below the surface of the electrolyte. Below the mandrel I place the anode which may consist of copper bars placed i continuous semi-cylindrical conductor adjacent to and following the contour of the cylindrical surface of the mandrel, the space between the cathode and anode being about one quarter of an inch. The mandrel consists of a cylinder or drum whlch may be wholly or partly made of metal, but which as sulphate of copside by side so as to form a treated in any known manner to prevent the adhesion of the deposited metal. A special method of treating the surface to prevent adhesion forms a subsidiary feature of my present invention. Suitable arrangements are made for rapidly rotating the mandrel at the critical speed above referred to, which, however, is not so high-I that any substantial part of the li uid is carried up and over the drum, but s cient to cause the turbulence in the electrolyte necessary to break up the cathodic film as above described.

Bearing upon that portion of the mandrel which is not immersed in the electrolyte there are arranged revoluble rollers or discs of metal or glass or any other suitable material. In copper deposition I have found a very suitable material is a high-percentage ferro-silicon alloy Awhich is not attacked by copper sulphate solution. The rollers or y discs are so arranged that they exert a comparatively hea pressure per unit area of contact on the eposited metal owing to the fact that that area is very small. In practice I have found it desirable to deposit a thin layer of copper before allowing the rollers or discs to be applied. The rollers or discs are free to rotate by frictional contact with the surface of the mandrel, (it being understood that in this term I include the metal deposited there0n,) and are also capable of a limited movement in the circumfer? cntial direction of the mandrel: I refer to them accordingly as floating rollers. Further, they are arranged and mounted so that they can be moved in contact with the mandrel transversely inv a direction parallel its axis. The transverse movement of the rollers ordiscs is a reciprocating movement, but they should only contact with the mandrel when moved in on'e direction; the return -movement should be out of contact therewith. Thefunction of these rollers or discs is (l) still further to ensure the film of electrolyte on the mandrel being broken up and (2) at .the Sametime through their rolling pressure and rubbing action, due to the transverse motion, to produce a deposit of' copper which'possesses an extraordinary degree of toughness.. The consolidating effect of the rollers or-discsalso assists in eliminating any nodules or roughness which the deposited copper may tend to form, with the result that Athe latter presents throughout an unusually smooth and even surface.

One or more-rows of rollers or discs may be iitted -to bear upon the mandrel and in the case of long thin mandrels which have a tendency to sag I may lind it expedient to arrange a row of rollers or discs underneath the mandrel and two rows on the top. In order to prevent the deposition of metallic excrescences at the edges of the mandrel ess, I place secondary electrodes at both ends of the mandrel. These secondary electrodes are semi-circular plates made of lead or other inert electrical conductors, or of wood, vulcanite or other insulating material or a combination of an insulating and conducting material capable of withstanding the electrolyte, so arranged that they are in close proximity to the mandrel and preferably provided with a flange to overlap a portion of its depositing surface. The effect of these secondary electrodes is that they reduce the rate of deposit at the extreme ends of the mandrel and instead of the metal building up at the ends, the deposit can be so regulated that the ends are just as smooth and the thickness of the deposited metal the same as on the other parts of the mandrel, or it can be arranged so that the deposit slightly tapers off. Again a medium applied to facilitate stripping or to other causes, I may find it desirable, after deposition for a comparatively short time and, before application of the floating rollers or discs, to cause a rapidly revolving brush to travel over the surface of the mandrel, whereby the thin deposit is levelled up and further depositis free from iaws and blemishes. Preferably the mandrel is provided with a transverse groove or an insertion of a material of higher specific resistance than that on the mandrel surfaceas a whole, with the result that the deposit is locally thinner or even entirely absent, thereby furnishing a line along which stripping of the deposited sheet from the mandrel may'be started.

Metal sheet produced in this way is so homogeneous and smooth that it is capable of being advantageously used for prmtlng plates or gramophone discs or other purposes for which electro-deposited copper 1s not normally'adapted.

The process of electro-deposltlon have described is applicable to the production of tubes or cylinders. In the deposition of metal in the form ofseamless tubes greater difficulty is sometimes experienced in detaching the tube from the mandrel than in the case where the removal ofthe deposited metal 1s effected by stripping it off from: the mandrel as a sheet or strip.. I have foundthat 1n order to ensure the ready detachment of a tubular deposit it is advantageous to use copper or brass-coated mandrels which have their surfaces highly polished and are then coated With a solution containing 0.05% to 0.5% of beeswax dissolved in turpentine, to which solution 1% of carbon bisulphide is added. The same composition may be used, if desired, to facilitate the detachment of sheets or strips.

In order to obtain a surface on the mandrel which at reasonable cost will ensure that the inner surface of the deposited sheet, (that is the surface in contact with the mandrel), is perfectly smooth and free from imperfections, I construct the mandrel or drum of welded steel or iron sheet or cast iron, which is then turned and polished. On this surface I then electro-deposit copper, having first made the surface passive `by treatment with nitric acid or other well-known means so as to ensure the adherence of the copper deposited. Upon a mandrel having a surface so prepared, polished and treatedwith a preparation for facilitating detachment I am then able to deposit copper according to the process herein described to produce sheets,

tubes or cylinders whose inner surface is mir-` Vror-llke and whose outer surface also 1s un` usually smoothl and free from imperfections. I produce copper strip or wire having the special characteristics obtainable in accordance with the present invention in the following way. I form upon lthe surface of the mandrel a helically disposed V-shaped groove as described in my prior specification No. 21,568 of 1904,-the pitch of the helix corresponding with the width of the strip which it is desired to produce. The V-shaped groove forms a Weak line of cleavage in the deposited metal, enabling it to be removed from the mandrel in the form of a continuous strip, which may then be rolled or drawn through draw plates or dies to form wire.

The copper strip as Aunwound from the mandrel has a small iin on'either edge due to fission along the line of cleavage in the metal deposited in the Vshaped groove. Unlessv special means are taken to eliminate this fin it is apt to result in imperfect wire. I find that the best means to eliminate it is to run the strip in the process of stripping off from the mandrel between rollers which are so shaped or are set at such an angle that they press the small fins into the body of the strip so that when it is drawn through a round die there is no fear of the fins turning over and forming lines or imperfections in the finished wire. i

For the purpose of my invention I use any of the electrolytes ordinarily used for the deposition of the metals to which my invention relates. I find, however, that in depositing copper according to my invention an advantageous electrolyte for certain purposes consists of a strong, almost saturated, solution of the sulphate of aluminium, mag- ,nesium or other alkaline metal, to each gallon instance at 100 amperes or more per square foot, the voltage at the terminals of the cell being in the order of 0.8. The solution is preferably Worked hot at a temperature of about 90o C. If a copper anode is used in such a solution it dissolves away evenly leaving a smooth surface.

It will be realized that in the case of all the above described operations the anode constitutes the source of the metal which is deposited on the revolving cathode, the electrolyte merely acting as a vehicle for the transfer of this metal. It is, however, possible to employ the electrolyte as the source of the deposited metal, the anode, if desired, being made of lead, carbon, ferro-silicon or other electro-chemically inert material. The possibility is thus afforded of obtaining by an electrolytic method a metal directly from a compound containing it provided that such process; for example, in order to recover copper from a sulphide ore in this manner I may proceed as followsz- The ore is first concentrated by any of the wellfknown methods and if such method has necessitated the use of oil this must be removed by treatment with a suitable solvent or by applying the necessary heat. The concenti-ated ore is then mixed with a sodiuln chloride solution of a strength of about 10% and the sludge and the ore from the solution are circulated through a tank in which, as above described, is a horizontall revolving cathode andan anode composed of Igraphite or other suitable material. The solution with the ore in lsuspension is caused to circulate in the intervening annular space so that the copper sulphide is attacked by the nascent chlorine and converted into a cuprous copper chloride-the copper being deposited on the revolving cathode. In this Way lit is found possible to work at 'a very high current density-say, 200 amps. per square foot-with a low voltage and, on account ofthe solution ing reducedwith evolution of sulphuretted hydrogen and the sulphur finally recovered.

In the case of an ore containing different metals, it may be possible, by what might be termed fractional electrolyzation, that is to say, by altering the conditions under which the electrolytic process is carried out, successively to obtain a deposit of each of the metals in a pure state. For example, in treating a sulphide ore containing nickel 4%, copper 9% and cobalt 2% the ore or concentrate is first roasted in a suitable furnace to a bright red heat with constant stirring until the sulphate state is reached. The roasted ore is leached first with water and then with 10% sulphuric 4acid solution, the temperature not beingallowed to rise above 30 C. After the desired extraction has been obtained, the solution is decanted and contains the copper and cobalt, the nickel remainingin the residue. -The latter is subjected to a 1:further leaching operation with 10% sulphuric acid at 90 C. to extract the nickel and the solution is then electrolyzed in the manner above described at a temperature of 80 C.; an insoluble anode is used and a voltage applied suilicient to result in a current density of about 60 amps. per square foot, whereupon the nickel is deposited as a cylinder which may be stripped off in the form of sheet.

The first leaching solution containing the copper and cobalt salts is electrolyzed at a temperature of 30 C. and current density about 10 amps. per square foot with acidity 6% free acid and, using an insoluble anode, the cobalt is deposited on a suitable revolving cathode. When all the cobalt has been removed another revolving cathode 'is substituted, the current density is raised to 30 amps. per square foot, the temperature to 60 C. and the acidity to about 940% free acid, when copper is obtained by deposition on the cathode,vthe iron in solution being crystallized out from time to time.

In all cases I have found it possible to operate economically at a higher current density than has hitherto been commercially employable; such current density is obtainable by the application of voltages substantially lower than those used heretofore, due largely to the eilicient depolarization and continual renewal of the cathodic film secured by running the rotating cathode at -the critical speed above mentioned.

The mechanical features of the apparatus required for carrying out my invention may take various forms. A form" of apparatus which I have found suitable is one in which the mandrel is supported by means of trunnions mounted in bearings outsidethe de` positing tank. As current, which is of considerable magnitude, passes from the mandrel or drum throughwthese bearings I pro-- vide for their being Water-cooled and lubricated by means of graphite or other electrical 5- 'understood and readily carried into effect it will now be described more fully with reference to the accompanying drawings which illustrate various forms of apparatus for depositing metal having the uniquequalities attainable in accordance with the invention,

'and wherein F' res 1 to 3 show respectively in side view, end view and plan apparatus suitable for depositing metal on a mandrel of comparatively large diameter with a view to its subsequently being stripped off inthe form of a sheet.

Figures 4 and 5 respectively illustrate in section two forms of floating rollers or for bearing on the mandrel,

-Figures 6 and 7 depict an alternative mechanism for producing the to-and-fro transverse movement of the rollers or discs,

Figures 8 and 9`show in section and diagrammatic plan respectively apparatus suitable for the manufacture of tubes,

Figures 10 and 11 depict respectively in side view and end view rollers whereby the fin existing on a strip which has been deposited on the helically grooved mandrel and subsequently stripped olf may be disposed of, Figures 12 and 13 being respectively sections of the said strip before and after treatlnent by the rollers.,

Referring to Figures 1 to 3, the mandrel 1 is mounted within a suitable vat or the like 2, which is preferably lead lined, by means of a shaft 3 supported in bearings 4 vertically adjustable by means of screws 5 passing through suitably threaded supports 6. As indicated, the 'bearings 4 are preferably open-topped to facilitate ready removal and replacement of the mandrel l'and, on account of the fact that current is fed to the mandrel through the bearings, they are lubricated with graphite, or other electrically conductive lubricant, being preferably, also in view of the large current to be transmitted, water-cooled by means of ducts 7 connected by pipes 8 with a water supply. To relieve pressure on the bearings, the mandrel may be made hollow and watertight, so that a portion of its weight Y is taken byflotation in the electrolyte,the level of which is conveniently about as indicated in Figure 2. The mandrel is rotated by means of a pulley 9, or analogous driving member, from a counter-shaft 10, which also, by means of worm gearing '11, serves to rotate a cam -shaft 12 the purpose of which will be hereinafter described. The anode 13 constituted by a copper casting or sheetor, as indicated in Figure 2, by a series of copper bars is in the form of an arc of a cylinder surrounding the lower portion of the mandrel which constitutes the cathode, being Lsupported 'in this i position by means of cradles or like members vproximity to the ends shown, with inwardly directed flanges of lead yor other inert material which protrude be- .tween the edge of themandrel and the anode 13. The secondary electrodes 15 are supportedby means of rods or like members 16 which are .attached toy the bearings 4 by means' of adjusting nuts 17; thusthe distance of each secondary electrode from the end of the many idrel may be varied in order to produce the different effects as regards the thickness of the deposit above mentioned It-will be' Vseen that, as the secondary electrodes are supendwise '35.

`ported.from the bearings 4, they partake in any vertical adjustment of the position of the mandrel 1 relatively to the anode 13 which may be given effect to in order to obtain the desired current density or to compensate for wastage of the anode 13.

The floating rollers or discs 18 bearing on the mandrel are carried on a spindle 19 supported by two bars 20 adapted to rock on a pivot bar 21 but vprevented from moving thereon by collars 22 fixed on the bar. A wiper 23 is also preferably loosely pivotedto the spindle 19 in such a position as to make contact with the mandrel just before it asses under the rollers 18 for the purpose o removing any grit, dirt or other extraneous matter which might have found its way into the electrolytel The pivot bar 21 is journalled in bearings 24 supported in uprights 25 so that it is free to move in an axial direction for the purpose of producing the desired transverse travel of the rollers or kdiscs 18 across the mandrel 1. To ez'ect this movement the cam shaft 12 is provided with `a snail cam 26 adapted to co-operate with a roller 27 provided on a lever 28 pivoted at 29 and connected by a linkV 30 with the pivot bar 21; thus rotation of the`cam'26 results in travel of the rollers or discs 18 at a uniform rate across the mandrel 1 in a direction from left to right as seen in upon reaching the right-hand end of the ,mandrel the lever 28 together with its assoi rapidly toward the left by ciated members, is allowed to be drawnback the action of a weight 31 connected with the pivot bar 21 by a cord.or the like 32 33 a`s indicated: excefsslve shock due to rapid motion of the lever,- pivot bar and rollers may be prevented by the provision of a suitable spring buffer 34. In order that, on the return stroke, the rollers or discs'18 shall be Figure 1, and

passing over a pulley.

out of contafct with the mandrel 1, they are lifted by means of 'a second cam 35 o erat-A ing through'a lever 36 pivoted at 37 an c onnected by a link 38, having a double knuckle Joint 39, with a tipping bar 40v supported in arms 41 hinged around the pivot bar 21, the said tipping bar 40 bearing on the upper side of the rear end of the bars 20. rThe cam 35 is, as indicated, so shaped that during ashort period of its revolution the lever 36 is depressed with the result that the rollers or discs 18 are raised from contact with the mandrel this action being timed to take place synchronously with `the return transverse movement of the rollers or discs. Asindicated, the vat2 is preferably supported by Ainsulators 42 and suitable means, not shown, are providedl for making'electrical supply connections respectively with the bearings 4 and the anode 13.

In order that the rollers or discs 18 may individuall have freedom not only to revolve but o movement in the circumferential direction of the mandrel, the constructions shown by way of example in Figure 4 or Figure5 may be adopted. Referring to Figure 4, each roller 18 is formed^with a central aperture 43 of a diameter larger than that of the splndle 19, the rollers vbeing preferably separated by distance-pieces 44. According to the construction depicted in Figure 5, the

vspindle 19 is surrounded by a bush 45 free to revolve thereon and the spaces enclosed within the apertures 43 in the discs 18 and the bush are lled with sponge rubberr46 whereby the desired freedom of movement of the individual rollers is permitted.

Y In the alternative form of transverse travel mechanism shown iniFigures 6 and 7, the pivot-bar 21 is stationary and the bars 20 are capable of sliding movement along it. Parallel to and on each side of the pivot bar 21 are screwed spindles 47 and 48 which are either rotated in opposite directions, as de- A scribed'y below, or formed with oppositely handed threads. The bars 20 are provided with half- nuts 49 and 50 adapted respective- 'ly to co-operate alternatively with the spin- v dles 47 and 48, the engagement of one half- ',nut or the other with itsco-operating spin-v dle being determined by the lie of` a pivoted weight 51 adapted to oscillate between pins 52 litted between the bars 20. The spindle 47 is the one whereby the operative transverse movement of the rollers 18 is produced, th' spindle 48 being employed to"efect the return stroke: consequently, it is desirable that the latter spindle shalll revolve more rapidly than the former. The spindle 48 may be driven from the counter-shaft 10 or from any other suitably placed shaft by means of a cord or chain 53 passing over a pulley 54 on the s' indle48. A second pulley 55 on this spin 1e serves 'to drive, by means of a cross cord or belt 56, a pulley 57 of larger diameter tted on the spindle 47. In order to effect reversal at the ends of the forward and return strokes stationary cam plates 58 are provided to engage the pivoted arm on which the weight 51 is mounted, thereby throwing over this weight from contact with one of the pins 52 to contact with the other pin and so rocking the bars 20 to disengage the halfnut in operative relation with one of the screwed spindles and engage the other halfnut with its spindle. The bars 20 are preferably provided with a counterweight 59 so that the pressure of the rollers or discs 18 on the mandrel 1 is determined wholly or to any desired extent by the weight of the rollers themselves.

In the apparatus shown in Figures 8 and 9, two mandrels are employed each having a corresponding set of floating rollers 18 carried by a common frame 60 resting on a pivot bar 2l and adapted to be tilted on the return stroke by means of a tipping` bar 40 as in the'modification above described. As, however, in the manufacture of tubes the length of the mandrels 1 may be very con siderable, it is possible that sagging might be produced as a result of the pressure of the rollers 18. Consequently, a supplementary set of floating rollers 61 isprovided on the underside of the mandrels in order to afford them some degree of support. The set of rollers 61 is supported by means of a rod 62 adapted to slide vertically through the frame 60 and provided 'with a wing-nut or the like 63 whereby the upward pressure of a spring 64 serving to support the rod 62 and rollers 61 may be deposed. In order that, on the return stroke, the rollers 18. may be lifted from their respective mandrels by the tilting of the frame 60, it is obviously `necessary that the rollers 61 shall be lowered out of contact with the mandrels 1 and this result is attained automatically by means of a collar 65 fitted on the rod 62 and provided with an inclined surface 66 adapted to co-operate with a .similarly shaped surface on a sleeve 67 loose on the rod 62 aud bearing against a fixed abutment 68 in such a manner that rotation of the sleeve 67 results in depression 0f the rollers 61. The sleeve 67 is provided with an outwardly projecting rod 69 which, on the forward or operative stroke of the rollers 18 and 61, occupies the position relatively to the frame 60 shown in full lines in Figure 9.' On approaching the end of the operative stroke however, the rod 69 encounters a stop pin 70 and thereby, on account of the continued transverse travel of the frame 60, the rod 69 is retarded and brought to the position shown in dotted lines so rotating the sleeve 67 and depressing the rollers 61. The tippingbar 40 then operates to tilt the frame 60 and the reversing mechanism comes into action to perform the return stroke, whereupon the rod 69 on approaching the end of that stroke 'encounters a second stop pin, not shown, which-restores it to its original full-line position, thereby allowing the spring 64 to raise the rollers 61 into contact with the mandrels 1 at/the same moment as the tipping b ar 40 is operated to allow the rollers 18 to bear on the mandrels.

The apparatus for removal of the fins ywhich essentially exist on a strip or w1re produced by depositing metal as above on a helically grooved mandrel and subsequently stripping it olf, depicted in Figures 10 and 11, comprisesessenti'ally two rollers 71 and 72, the former. of which is provided with a. rectangular groove to accommodate that side 'of the strip or wire on which the fins. do not exist, that is to say, the lower portion of the wire a section of which before treatment is shown in Figure 12. The second roller 72 is formed with a groove, the bottom ofwhich `is bevelled, as indicated at 73 in Figure 11, so that wire of a section 'shown in Figure 12 when passed between the rollers has its section altered to that depicted in Figure 13. The outline of the original section is indicated in Figure 11 in dotted lines and it will be seen that between that portion of the upper surface of the wire intermediate of the fins and the opposing bottom of the groove in the roller 72 there is a space, this being provided to enable the fins to be squeezed by the bevelled portions 73 of the groove into the body of the wire rather than folded over on the outside thereof. The result is that the above mentioned intermediate surface of the wire is forced outwards to lill the space above referred to as that the section of the Wire, as illustrated in Figure 13, corresponds with the space between the rollers 72 and 73 constituted by the respective grooves in these rollers. It willbe realized that instead of employing a single roller 72, two rollers set at an'angie andl adapted to operate one on each lin may be employed, the peripheries of the rollers being shaped so that their combined action in co-operation with the roller 71 in disposing of the fins is similar to that above described.

While the process and apparatus have been described more particularly in their application to the production of copper sheet, tubes, strip or wire, the invention is also applicable to the deposition of other metals such, for example as zinc, nickel, cobalt or silver, whether from their ores or other compounds as above indicated or by transfer from an anode of the metal in question.

lVhat I claim and desire to secure by Letters Patentof the United States is 1. Apparatus for the electrosdeposition of metal comprising a vat for containingthe electrolyte, an anode immersed therein and a cathode in the form of'a rotating mandrel on which rollers, free to revolve and capable of a limited movement in the circumferential ment of the rollers is comparatively slow in one direction followed by a rapid return movement.

3. Apparatus as in claim 1, wherein the transverse to and fro motion of the rollers is produced by cam-and-lever mechanism.

4. Apparatus. as in claim 1, wherein the transverse to and fro motion of the rollers is produced by reversing screw mechanism.

5. Apparatus as in claim 1 in which camand-lever mechanism is provided for lifting the rollers out of contact with themandrel during their transverse motion in one direction.

6. Apparatus as in claim 1, in which the rotating mandrel is provided with a shaft mounted in bearings located outside the vat and vertically adjustable by such means as a screw.

7. Apparatus as in claim 1, wherein the rollers are supported by a frame constituted by bars transverse to the axis of the mandrel and carried by a pivot bar about which it may rock and which permits of its transverse movement across the mandrel and the frame is extended on the side of the pivot bar remote from the rollers and is adapted to co-operate with a tipping bar whereby, on the return transverse stroke, the rollers are aisled from contact with the rotating man- 8. In apparatus as in claim 1, means'for permitting the circumferential movement of the rollers according to which they are mounted on a common spindle which passes through an aperture in each roller substantially larger in diameter than that of the spindle.

9. In apparatus as in claim 1, means for permitting the circumferential movement of the rollers according to which they are mounted on a common spindle surrounded by a bush free to revolve, the spindle and bush passing through an aperture in each roller of substantially greater diameter than the external diameter of the bush and filled veith resilient material such as sponge rub 10. Apparatus as in claim 1, in which a set .of rollers is arranged to bear on the underside of the mandrel.

11. Apparatus for the electro-deposition of metal, comprising a vat for containingtthe electrolyte, an anode immersed therein, a cathode in the form of a rotating mandrel on the upper surface of which rollers, free to revolve and capable of a limited movement in the circumferential direction of the mandrel, are adapted to bear, a set of rollers arranged to bear on the underside of the mandrel, means for automatically lowering the set of rollers bearing on the underside of the mandrel and subsequently raising the rollers bearing on the upper side of the mandrel, and a common frame capable of transverse motion for supporting the rollers bearing on the upper side of the rotating vmandrel and those bearing on the underside thereof.

12. Apparatus as in claim 11, wherein a spindle supporting the rollers bearing on the underside of the mandrel is provided with a collar having a cam surface adapted to co-operate with a corresponding surface on a member which is automatically moved as each end of the transverse stroke is approached, whereby the spindle is depressed and the rollers lowered out of contact with the mandrel.

SHERARD OSBORN COWPER-COLES.

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