US3463719A - Continuous electroplating apparatus - Google Patents

Description

Aug. 26, 1969 w, 5, BROWN ETAL 3,463,719

commuous ELECTROPLATING APPARATUS INVENTORS. WAYNE 8- BROWN ATTORNEY 2 'Sheets-Sheet 1 WILLIAM S PART'RIDGE Filed Sept. 27. 1966 Aug. 26, 1969 w. 5. BROWN ETAL CONTINUOUS ELECTROPLATING APPARATUS 2 Sheets-Sheet 2 Filed Sept. 27. I 1966 FIG. 3.

V T w INVENTORS. WAYNE S. BROWN WILLIAM S. PARTRIDGE BY f E ATTORNEY United States Patent U.S. Cl. 204-216 7 Claims ABSTRACT OF THE DISCLOSURE A continuously driven essentially vertically oriented cathode drum substantially submerged within electrolyte solution, the outer surface of which receives electrorefined metal continuously as the drum is rotated. An elongated electrolytic bath opens adjacent the drum so that the electro-refined metal is peeled from the drum and conveyed through the electrolytic bath while being continuously subjected to electrodeposition. The improved method comprises continuously electrodepositing metal along the entire circumference of the generally vertical power-rotated drum and continuously peeling the resulting metal veneer from the drum at a fixed location and conveying the veneer through the electrolytic bath and continuously electrodepositing metal upon the veneer throughout the length of the electrolytic bath.

This invention pertains to purification of metal by an electrolytic process and apparatus and more specifically to a novel apparatus for and method of continuously refining metal by electrodeposition, without interruption. The metal is first electrodeposited as a thin sheet upon a continuously driven, substantially submerged cathode drum, the orientation of which is generally vertical. Thereafter, as the thin sheet is being progressively peeled from the drum and while it is being displaced in substantially vertical submerged relation through an elongated portion of the electrolytic cell in which the drum is situated, additional metal is successively deposited as plated molecules upon the exposed periphery of the thin sheet to steadily increase its transverse dimension, the sheet continuing to act as a cathode.

In contrast, the generally accepted commercial techniques of electro-refining metals constitutes the so-called batch method. In order to use the batch method, it is necessary to separately prefabricate (a) cathode starter steets and (b) anode metal hangers. The costs of such prefabrication are very high and many man hours of time are required. Subsequently, the pre-formed cathode starters and anodes must be alternatively positioned in a large electrolytic bath. Thereafter, as the process continues, each remnant anode and each enlarged cathode, in its turn, is individually removed and replaced respectively by one of the previously mentioned performed anode hangers and cathode starters. This cumbersome procedure is, therefore, objectionable not only because of the high anode and cathode preforming costs, but likewise, because of the significant capital outlays required for the excessive factory floor space occupied by the bulky equipment used, the time required to complete the total process and the relatively high manpower requirements.

Although certain alternatives for the batch method have been suggested by the prior art (for example, see US. Patents 1,600,257 and 1,60l,691), these proposals have failed to gain commercial acceptance. The principal objections appear to be (a) the prolonged time required to form the cathode metal, (b) relatively inferior quality control, and (c) gross diificulty encountered in handling the metal as it becomes heavier with time during the refining process.

In view of the foregoing, it would be a significant and 3 ,463 ,7 l9 Patented Aug. 26, 1969 worthwhile contribution to the electro-refining art to provide a system, including process and apparatus, which (a) materially reduces the plant space requirement per unit of metal refined, (b) is essentially uninterrupted from start to finish thereby reducing the time required to complete the refining, and (c) significantly reduces the number of man hours required per unit of metal refined. The present invention was conceived to provide such a novel system.

operationally, in the presently preferred embodiment of this invention, metal is simultaneously electrodeposited as a veneer along the entire circumference of a generally vertical, rotating drum, which is substantially submerged in an electrolytic bath. The term drum as used herein means any suitable closed curved surface having substantial length in the direction of a central axis of rotation and being either open or closed at the opposite ends of the curved surface. When the ends are open the back side of the curved surface must be suitably insulated from the electrolyte so that electrodeposition will occur only at the exterior of the curved surface. The veneer is peeled continuously from the drum as: it rotates and is thereafter displaced, while immersed, through an elongated portion of the electrolytic bath, the resulting peeled sheet being suspended by hangers in a generally vertical plane during the latter step. The suspension sites of the peeled sheet are progressively strengthened by deposited metal as the thickness of the sheet increases to strengthen the sites against shear failure due to the gradual increase in the weight of the sheet. The present invention also accommodates asomewhat higher level of metal purification than is normally achieved by using the mentioned batch method, principally because with the present invention contaminate particles may be essentially isolated from the electroplating region, preferably by use of a large filter bag. Significantly, the process is. essentially uninterrupted from the initial to the final step.

With the foregoing in mind, it is a primary object of this invention to provide an efiicient, comparatively rapid, commercially superior, uninterrupted process for electrolytic purification of metals.

A further significant object of this invention is to provide a novel apparatus which accommodates continuous electro-refining of metals.

These and other objects and features of the present 1nvention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a schematic perspective representation of a presently preferred clectro-refining apparatus of this invention;

FIGURE 2 is a schematic plan view illustrating several electro-refining units of the type shown in FIGURE 1 arranged in side-by-side compact relation;

FIGURE 3 is a cross-sectional view taken along line 3-3 of FIGURE 2;

FIGURE 4 is a cross-sectional view taken along line 4-4 of FIGURE 2 and FIGURE 5 is a cross-sectional view taken along line 55 of FIGURE 1.

Reference is now made to FIGURE 1, which illustrates a presently preferred electro-refining embodiment of this invention, generally designated 28. The apparatus 28 comprises a cylindrical drum 32, the exposed circumferential surface area of which is preferably fabricated from titanium or titanium alloy, although suitably coated stainless steel and other conducting materials could be used. Significantly, the drum is supported in a generally vertical attitude so that it can be freely rotated, for example, by use of a variable speed motor 36 through a shaft 34, which is integrally joined to the drum 32. Easy rotation of the drum is accommodated by use of inert Teflon or other suitable bearings 51, 53 (FIGURE 4) which support the drum in its vertical position and are inert to electrolyte. The bearing 51 is suitably carried by a sprocketed support 66 (FIGURES l and 4), while the bearing 53 (FIGURE 4) is suitably joined to the bottom of the electrolytic tank 33.

The drum 32 is connected electrically by any satisfactory means to electrically charge the entire circumferential surface area of the drum. Thus, the circumference of the drum acts as a cathode in the present electrolytic process with the ends of the drum being suitably insulated from the circumference so that metal will electroplate only at the circumferential surface. The cylindrical drum 32 is preferably completely immersed in a bath of electrolyte solution (not shown), which solution is contained by the tank 33, so that by electrolysis a thin veneer 30 will be formed on the circumference of the drum as it is slowly rotated. Experimentally, a six-inch drum having a current of about 20 amps per square foot and one inch spacing between the cathode and the anode was plated with a copper sheet 10 mils thick during one revolution of the drum at a rate of approximately revolution per hour. But, of course, the most desirable drum speed will vary with the size of the drum, the strength of the electrolyte, the electrical current intensity and the desired veneer thickness.

Thereafter, the veneer is progressively stripped from the drum as it rotates and is displaced down the elongated portion 41 of the tank 33 for purposes and in a manner which will subsequently become more fully apparent.

At least two receptacles 37, which receive and retain anode metal shot 38 or metal of any divided form, are also immersed in the elongated portion 41 of the bath 33 in spaced relationship with respect to each other. The metal shot 38 is suitably electrically connected so as to function as the anode in the present electrolytic process. While each receptacle 37 can be made of any satisfactory inert material, the perforated walls are preferably constructed of ceramic material in the form of louvers. The ceramic louvers 35 (FIGURE 3) are suitably spaced and orientated at predetermined acute angles with respect to the vertical so as to confine the metal shot 38 within the receptacle, even after it has been reduced in size by the electrolytic process. At the same time the construction and spacing of the louvers 35 permit more than sufficient contact between the electrolyte solution and the anode metal.

In electro-refining some types of metals it may be desirable to place a filter between the anode and cathode metal. In instances where subsequent voltage drops which may be undesirably incurred by such filters, the filters may be eliminated. In the embodiment depicted in FIGURES l, 3, and 4 the cylindrical drum 3-2 and subsequently the electroplated metal sheet 29 may be separated from the anode metal in each receptacle 37 by a gravity-suspended filter such as a fabric bag 54- (FIGURES 3 and 4). The gravity-suspension of the filter 54 in the electrolyte solution substantially prevents contaminate particles from reaching the peeled sheet 29 and veneer 30. Thus, the metal refined by the present process may attain a slightly greater purity, due to the lack of contaminating particles, than is normally achieved by the prior art.

When the veneer 30 has attained a suificient thickness so that, inter alia, it will not tear or otherwise fracture during subsequent handling, it is peeled from the drum 32 along an essentially vertical line at the circumference of the drum. Any suitable technique can be used to effectuate such peeling, one preferred way being illustrated in FIGURES l, and 3, i.e., by use of a knife edge 58, peeling being accomplished by rotation of the drum 32 against the knife edge 58. Under conditions where the surface of the drum 32 is titanium or titanium alloy where a suitable release agent is used, the knife edge 58 may be unessential.

As the veneer 30 is progressively separated from the drum 32, the resulting sheet 29 is periodically penetrated by a depending hook 59", of serially disposed non-conducting hangers 42, preferably by piercing or by insertion through a punched or otherwise fabricated aperture 43 (FIGURE 3) disposed in the sheet 29 near the top thereof. Thus, the weight of the peeled sheet 29 is carried by the series of spaced hangers 42 While the sheet is retained in an essentially vertical orientation.

The spaced, non-conducting hangers 42 are suspended from an overhead conveyer cable 44 preferably constructed of wound metal strands.

With particular reference to FIGURE 5, which depicts a cross section of the cable 44 and one hanger support 50 with a hanger 42 suspended therefrom, the proximal T end 78 of the hanger support 50 is securely interposed between the flexible strands of the cable 44. The hanger support 50 has a vertically disposed slotted aperture 72 in the distal end 80 of the hanger support 50 which projects essentially horizontally from the cable. A downwardly extending projection 48 (FIGURE 5) of a hanger 42 fits Within each aperture 72 to suspend the hanger from the cable 44. Hanger 42 is shaped such that the downward force caused by the weight of the suspended veneer is essentially directly beneath the cable 44 thereby minimizing any possible twisting of the cable.

The cable 44 is moved by an essentially horizontally disposed driven wheel 47 that is non-rotatably joined to an intermediate portion of the shaft 34 and driven by the motor 36. The simultaneous rotation of both the cylindrical drum 32 and the cable drive wheel 47 by the motor 36 through shaft 34 inherently synchronizes the speeds of the hangers 42 and the sheet 29. The cable 44 is further suspended in a movable manner by generally vertically disposed idler wheels or pulleys 49 and horizontal idler 63. The hanger 42 may be removed from its suspended relation with the cable by elevating the hanger to remove the depending portion 48 of the hanger 42 from the aperture 72 disposed in the hanger support 50 (see FIGURE 5).

As can be seen by reference to FIGURES 3 and 4, the filter 54, when used, not only shields the veneer 30 on the drum 32 from contaminating particles in the solution, but likewise shields the peeled sheet 29 from such particles along the entire length of the linear cell 41.

Ignoring small losses, the electric current applied to the circumference of the drum 32 will also be present over the entire length of the sheet 29. Therefore, sheet 29 will also act as the cathode. If it is desired, additional electric current may be transferred along the hangers 42 to the peeled sheet 29 with appropriate conductive material. Also, the metal shot 38, disposed in the receptacle 37 along both sides of the linear cell 41, is electrically connected at one or more locations so as to function as the anode. Thus, additional metal will be continuously electro-deposited on the sheet 29 as it traverses along the linear cell 41 (contrast the thickness of the sheet 29 shown at the left with the sheet 29 shown at the right of FIGURE 3).

As the sheet 29 increases in thickness and becomes heavier, the weight load thereof becomes materially greater. However, the portion of the sheet disposed immediately above each hanger hook 59 also becomes thicker such that shearing out at the hanger locations about the apertures 43 is substantially obviated.

s used during the electrolytic process. Any suitable technique may be employed t compllsh such replenishment. One suitable and presently preferred technique is depicted in FIGURES 1 and 3, Spec1fically, a center dump, track-guided car 52, shown schematically for purposes of illustration may be used to selectively replenish the shot. Suitable prime mover means may be employed to mechanically or electrically propel the car 52 to and fro. Wheel flanges 70 longitudinally maintain the center dump car 52 generally as illustrated in FIGURE 3 and the ceramic louvers 35 thereby sustaining the car whether the car is being longitudinally displaced or unloaded. The car 52 will be periodically loaded with shot, manually or mechanically, preferably at a fixed location along the track, following dumping of each load of shot from the car 52.

Reference is now made to FIGURE 2, which schematically depicts a plurality of drums of the type previously described in conjunction with FIGURE 1 along with a comparable series of linear cells and electrolytic equipment as previously explained. By arranging several of the devices 28 in side by side longitudinally placed relationship, a significant saving in factory space requirements is achieved. Structurally, each apparatus 28 is preferably substantially identical with the apparatus 28 previously described in conjunction with FIGURE 1. Hence, each apparatus 28 preferably comprises an essentially vertically disposed drum 32 which turns continuously against a knife edge or stripper 58 to form and then peel metal veneer tangentially from the drum at the circumference thereof. It is to be appreciated that any intermediate electrolytic unit shares a common anode receptacle 39. Ceramic louvers 35 disposed at each side of the central cells 39 accommodate fluid displacement of the electrolyte therethrough for purposes of replenishment. Otherwise, the construction of the bath of the apparatus shown in FIG- URES 2 and 3 is essentially the same as that previously described.

It is normally necessary for continuous electrolytic processing that the sludge, which accumulates in the bath, as a result of decomposition of the metal shot, be removed. FIGURE 3 depicts one embodiment for removing the sludge. The sludge will settle as sedimentation through a grating 55 composed of non-conducting material, and will be removed from the cell 41 by operation of one or more screw conveyors 56. Moreover, as mentioned earlier, the gravity suspended filter 54 may be used to envelop each sheet 29 to minimize contact between the sheet 29 and any contaminate material carried with the molecules being deposited upon the sheet through the electrolyte solution 31. The filter 54 is preferably in the form of a bag which totally separates the sheet from the anode material but accommodates solution flow therethrough.

The filter 54 is preferably attached as by bonding at 74 to the inside portion of the anode receptacle 37 and to the Teflon bearing 53 at 76.

Keeping in mind that the ultimate thickness of the sheet 29 is determined by the length of the linear cell 41 the strength of the electrolyte, the magnitude of the current utilized and the speed at which the veneer traverses the linear cell 41, the presently preferred operation of the apparatus shown in FIGURE 1 will now be described.

Specifically, as electric current is applied (a) to the cylindrical surface of the essentially submerged cathode drum 32, as it is being rotated, and (b) also to the anode metal shot 38, charged metal molecules migrate from the anode 38 through the electrolyte solution 31 and are deposited on the surface of the slowly rotating drum 32, being carried to such position by action of the electric current. Extraneous contaminate material may be filtered out by filter 54 when used to thereby substantiall eliminate contamination of the metal being purified as it accumulates on the surface of the drum 32.

As the drum 32 rotates, the veneer is peeled from the drum and displaced along the linear cell 41 essentially submerged in the solution at a uniform rate equal to the rate of rotation of the drum. Since the peeled sheet 29 also functions as the cathode, there is a continuous electric current flowing from the anode through the elec trolyte solution to the sheet. Thus, additional metal is progressively deposited not only at the circumferential surface of the drum but also upon all exposed portions of the purified metal sheet which are submerged in the electrolytic solution. Serially, the hook 59 of each hanger will be forced to penetrate the metal sheet near the top edge so that the sheet is essentially vertically suspended in the electrolyte approximately equidistant between the spaced anode receptacles 37. Synchronous movement of the hanger drive cable 44 and the drum 32 will normally uniformly displace the metal sheet 29 along the length of the cell 41, the sheet increasing in thickness with time. Preferably, the level of the electrolyte solution 31 is maintained at a level slightly above the top edge of the sheet 29 both as it is being formed upon the drum 32 and as it is being displaced longitudinally along the linear cell 41. This accommodates increase in the size and, accordingly the strength of the portion of the sheet disposed above each hanger hook 59 so as to prohibit shearing out of these areas due to the increasing weight of the sheet. The metal sheet is displaced generally linearly from the linear cell 41 through the opposed elastomeric squeegees 81 and out the exit 82. Using the illustrated embodiment, it is preferred that the hangers 42 be serially detached from their supports 50 at idler 63 and that the hooks 59 thereafter be removed from the sheet. The scrubbing action of the Squeegees tends to retain all solution in the tank except for a small residual amount left at the surfaces of the sheet. The surfaces of the sheet are thereafter washed preferably with water and the sheet is severed into desired lengths or sizes for subsequent fabrication into suitable products.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In an apparatus for continuous electro-refining of metals comprising at least one generally vertically axially oriented power-driven cylindrical cathode drum having axial shaft structure associated with the drum, the shaft structure projecting beyond each end of the drum; driving means coupled to the drum which rotates the drum; support means to maintain said drum in said orientation and comprising means journalling the shaft structure at each end of the drum to accommodate drum rotation; means connecting a source of electrical power directly to the drum to supply electrical current to the exterior curved periphery of said drum before and after electrorefining occurs; a tank for receiving electrolyte solution, the tank containing said drum in substantially immersed relation; a supply of relatively impure: anode metal disposed in the electrolyte solution; means to supply electric current to said impure anode metal whereby cathode metal is deposited as a veneer upon the exterior curved periphery of the drum; means for tangentially peeling electro-refined metal from the drum :in the form of a vertically-disposed sheet.

2. An apparatus as defined in claim 1 further comprising an elongated extension of said bath having substantial length likewise adapted to receive electrolyte solution and being in communication with said impure metal, means to guide the displacement of the sheet generally vertically through the elongated extension.

3. An apparatus as described in claim 1 wherein said impure metal is confined within at least one receptacle having spaced louvers of a non-conducting material situated on at least one side of said receptacle, said louvers being disposed outwardly and upwardly whereby anode metal is substantially prevented from escaping from the receptacle between the louvers.

4. An apparatus as described in claim 2 further comprising a porous filter enveloping the veneer and the sheet and serving to partition the veneer and the sheet from the impure metal to thereby substantially isolate the submerged cathode metal from impurities in the anode metal.

5. An apparatus as described in claim 2 wherein said guiding means comprises an overhead conveyor including (a) a driven mechanism the movement of which is synchronized with the rotating drum, (b) spaced hangers removably suspended from the conveyor, and having means for coupling to the metal sheet by which the sheet is supported and guided through the elongated bath extension during displacement.

6. An apparatus as described in claim 2 further comprising means for supplying additional impure metal to the electrolyte solution and wherein said impure metal is in the form of relatively small metal units.

7. An apparatus as described in claim 1 further comprising means for removing waste material from the elec trolytic bath including at least one conveyor disposed in the bottom of the bath.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner H. M. FLOURNOY, Assistant Examiner US. Cl. X.R. 204-43, 28, 20s

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