US3501385A - Process for stripping metal from a cathode - Google Patents

Description

March 17, 1970 P. M. JAS BERG 3,501,385

7 PROCESS FOR STRIPPING METAL FROM A CATHODE Filed May 8, 1967 2 Sheets-Sheet 1 INVENTOR. PETER M. JHSBERG March 1970 P. M. JAS aBERG 3,501,385

PROCESS FOR STRIPPING METAL FROM A CATHODE Filed May 8, 1967 2 Sheets-Sheet 2 INVENTOR. PETfR IZ JRSBERG HTTYS.

United States Patent O f 3,501,385 PROCESS FOR STRIPPING METAL FROM A CATHODE Peter M. Jasberg, Kellogg, Idaho, assignor to The Bunker Hill Company, Kellogg, Idaho, a corporation of Delaware Filed May 8, 1967, Ser. No. 636,797

Int. Cl. C23b 7/08 US. Cl. 204-42 10 Claims ABSTRACT OF THE DISCLOSURE The disclosure herein is directed to the Stripping of electrolytically deposited sheets from a plate cathode in metal recovery processes. It is particularly described with respect to recovery of zinc. The sheets are stripped by application of fluid jets at the interface between sheet surfaces. Auxiliary mechanical rapping and Wedging steps to facilitate stripping is also described.

BACKGROUND OF THE INVENTION This invention relates to a novel process for stripping electrolytically deposited metal from a reusable cathode in electrolytic metal recovery systems such as are used in the production of zinc.

The conventional method of stripping sheets of zinc from a cathode of aluminum or aluminum alloy is carried out manually, the sheet being chipped gradually with a chisel to pry it from the aluminum surface. The aluminum cathode, being relatively soft, also deteriorates in such use and sometimes is damaged to an extent which makes stripping more difficult and eventually further use of the cathode is impossible. Other alternatives previously proposed for facilitating this operation utilize rollers to deflect the metal surfaces, mechanical impaction of the metal layer or utilize mechanical or vacuum pressure gripping devices to pull the sheets from the cathode. Besides the complicated and expensive mechanisms required for such operations, all such mechanical processes include the hazard of physical damage to the cathode as Well as to the sheet of metal being removed from it. In addition, many of these processes are slow and consume a working period equal to or even greater than conventional manual chipping methods.

According to the process described below, the deposited metal layer is removed from the cathode by hydraulic jets directed against the metal layer along the boundary between the coated and uncoated cathode areas. The use of hydraulic jets in this manner eliminates mechanical damage both to the cathodes and to the removed sheets of deposited metal. It has been found to accomplish superior results in a fraction of the time required for manual removal of such sheets. Various equipment alternatives and accessory process steps are described as practical adjuncts to the basic hydraulic stripping process.

It is a first object of this invention to provide such a process which can be automated to effectively strip metal from cathodes in a continuous operation.

Another object is to provide a versatile process of releasing deposited metal sheets applicable to cathodes lowing disclosure taken together with the accompanying drawings which schematically illustrate the process and 3,501,335 Patented Mar. 17, 1970 ice DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic perspective view showing a portion of a conveyor assembly and progressive stripping of metal from cathodes on the conveyor assembly;

FIGURE 2 is an end elevation view showing a cathode and the fluid nozzles prior to stripping of the metal from the cathode, progressive stripping of the metal being illustrated in dashed lines;

FIGURE 3 is a schematic sectional view taken along line 33 in FIGURE 2 showing the nozzles and a typical stream pattern;

FIGURE 4 is a view similar to FIGURE 1 illustrating the use of accessory process steps to facilitate stripping in a modified form of the process;

FIGURE 5 is a plan view of a device for maintaining initial separation of the metal from the cathode; and

FIGURE 6 is a fragmentary side elevation view showing the device in FIGURE 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGURE 1 illustrates generally the basic steps of the instant process. At the left in this drawing is a typical rectangular cathode 10 coated about most of its surface area by a zinc layer 11. The side edges of the zinc layer 11 are defined by insulating strips 8 on the cathodes 10 which prevent accumulation of zinc across the vertical cathode edges. The zinc layer 11 is deposited electrolytically on the cathode 10, the deposited metal being located between strips 8 along an area bounded by a boundary line 9 formed at the zinc-aluminum interface created on the cathode 10 at the level at which cathode 10 is immersed in the electrolytic bath. Along the boundary line 9 is a short area (about /2 inch) of zinc having a tapering thickness leading to the constant thickness of zinc in the bulk of the zinc layer 11. The stripping of the .zinc from the aluminum is normally found to be most difiicult along the boundary line 9.

The zinc-coated cathodes 10 are mechanically handled by a continuous trolley conveyor shown generally at 13. Each cathode 10 is held by a clamp 12. suspended from the conveyor 13, the cathodes 10 being in a vertical position.

In the area at :which the zinc layers 11 are to be stripped from cathode 10, a manifold 14 is located on each side of the conveyor 13 with one or more nozzles 15 connected to the liquid manifold 14. The nozzles 15 are directed toward the adjacent cathode surfaces at each end of cathode 10, preferably with the central axis of each nozzle in a plane perpendiuclar to the wide cathode surface planes. The jet from each nozzle is preferably in alignment with the boundary line 9 and is angulary directed toward the zinc layers 11. Impingement of a high pressure water jet from the nozzles 15 on the zinc-aluminum interface (at boundary line 9) breaks the bond between the deposited zinc layer 11 and the aluminum cathode 10. Further subjection of the cathode 10 to the high pressure jet permits the jeis to penetrate between the zinc layer 11 and the cathode 19 and progressively break the bond between them from top to bottom. The deposited zinc layer is removed by simply peeling the zinc from the aluminum cathode 10, leaving separate zinc layers 11 and a clean cathode 10 as they emerge from the area between the nozzles 15 as shown to the right in FIGURE 1.

In FIGURE 2 there is illustrated the progressive removal of the zinc layers 11 by nozzles 15 at each side of the cathode 10. The three nozzles 15 are shown directed toward the solution line 9 at an angle of approximately 25 relative to the plane of cathode 10. Angles of 0 to 25 have been found most suited to this process and individual nozzles can be set at differing angles. As the cathode 10 moves past the nozzles 15, the zinc layers 11 initially separate from cathode 10 adjacent the upper edges of the respective layers 11. This initial position of the free upper edges of the strips 11 is designated in FIGURE 2 by the reference number 11a. As movement of cathode 10 continues and subjection of the cathode 10 and zinc layers 11 to the high pressure jets from nozzle 15 is maintained, the strips 11 are freed from cathode 10 to the point illustrated by the reference numeral 11b in FIGURE 2, wherein each zinc layer 11 is almost free to fall from the cathode 10. In actual practice, this process requires handling devices (not shown) to receive the layers 11 and to convey them from the the stripping area for further processing.

A typical manifold and nozzle arrangement is shown in FIGURE 3, where the liquid streams produced in the high pressure jets are indicated by the numeral 16. As the cathode 10 enters the stripping area shown in FIGURE 3, it is first subjected to a straight jet from the first nozzle 15a. The stream 16a from the nozzle 15a is controlled so as to be straight, thereby insuring maximum hydraulic impact against the cathode 10 and zinc layer 11. This maximum hydraulic impact created by the straight nozzle 15a better insures freeing of the zinc layer 11 at the area adjacent to the solution line, where the bonding forces joining the two sheets are found to be strongest. Following this jet, the next two jets produced by nozzles 15b and 150 are shown flat jets with a spray angle from 25 to 80. The liquid streams from nozzles 15b and 15c are designated at 16b and 160 respectively. The fan-shaped configurations of liquid streams 16b and 16c distributes the hydraulic pressure required to continue peeling of the zinc layer 11 along the interface until it is finally free from contact with cathode 10.

While many variations in operating pressure are possible, it has been found that effective stripping of the zinc layers is best obtained by using manifold pressures from 4000 to 6000 p.s.i. depending upon the size and thickness of the materials being handled. After the peeling of zinc has begun, pressure is less significant. Subsequent jets at 300-600 p.s.i. (and larger volumes) could effectively continue peeling the sheet, if directed at the interface exposed initially by a high pressure jet. Many different nozzle types and arrangements have been tried experimentally in developing this process and all have been found to work effectively in the pressure range of 4000 to 6000 p.s.i., with a flow rate of approximately 10 gallons per minute of Water.

In one typical arrangement, the three nozzles such as shown in FIGURE 3 were spaced on 8-inch centers from one another and the nozzle outlets were located /8 of one inch from the surface of the cathode 10. The arrangement successfully removed layers of zinc deposited on 24 x 36 inch aluminum cathodes during periods of both eight hours and 24 hours and left clean cathodes with no residue of zinc along the original solution line 9. The stripping time for each cathode was approximately two seconds and at this rate, the pressure and flow rate of the water jets caused no excessive erosion of the cathode plates or deformation of either the cathode plate or the zinclayer. The resultant projected cathode life is 2-3 years.

This process does not require the use of any particular nozzle or stream configuration. A single nozzle operating in the pressure ranges indicated above has beenfound to be adequate, although combinations of up to five nozzles have been used successfully. The single nozzle used in an actual test was a Spraying Systems Co., Nozzle No. 0010, with a 0 spray angle, and a 0.078 inch orifice diameter, operating at a pressure of 5500 p.s.i. and a flow rate of 10 gallons per minute. In another test, a Spraying System Co. flat jet No. 1510 with a 0.078 inch orifice diameter and 15 spray angle performed eifective stripping of zinc at an operating pressure of 4700 p.s.i. and flow rate of 10 gallons per minute. Many variations in selection of nozzle and jet stream pattern can be made in adapting the instant process to particular operating conditions to obtain optimum results.

Tests also have been carried out with a modified process using jets operating at substantially lower pressures. Operating pressures as low as 600 p.s.i. to 1200 p.s.i. have been used with auxiliary equipment as illustrated in FIG- URE 4 with varying degrees of success. This auxiliary equipment comprises a vibrating rapper device 17 for mechanically loosening the bond between the zinc layers 11 at each Side of the cathode 10. The rapper is provided with a contacting roll 18 and is supported on a movable support 20 so that it can be positioned adjacent to the cathode 10 or pulled back when necessary. Support 20 is guided by stationary frame guides 21 on the same general framework assembly 23 that anchors a cylinder 22 used to position the support 20 and rapper apparatus 17. The use of rapping devices for this purpose has been known previously in this industry and no further description of the details of this apparatus is believed necessary in order to understand the inclusion of this additional step in the basic process. The loosening of the bond between the zinc layer 11 and cathode 10 might be accomplished by other mechanical devices, such as olfset rolls to produce reverse bending of the zinc layers and cathode along the solution line 9. In any event, such mechanical loosening of the bond along solution line 9 assists, in some instances, in insuring greater effectiveness of stripping by the hydraulic jets, particularly where the jets are utilized at pressures below the high pressure'range (4000 to 6000 p.s.i.) indicated above.

One other useful accessory step in stripping the zinc by the basic process involves the use of mechanically positioned wedges 28 as shown in FIGURES 5 and 6. Following initial loosening of the upper edges of each zinc layer 11, it has been found that, in some instances, a vacuum is partially formed between the zinc layer 11 and cathode 10. This partial vacuum actually pulls the zinc layer 11 back toward the cathode surface. To counteract this force, wedges 28 are positioned between the zinc layer 11 and cathode 10 at each side of the cathode. The wedges 28 are fixed to lever arms 25 pivotally connected to stationary frame members 24 by a vertical pivot shaft 27. Each lever arm 25 is biased inwardly toward the cathode center line by a suitable spring 26 wound about the shaft 27. A guide roll 30 on each lever arm 25 adjacent to wedge 28 prevents unnecessary pressure against the cathode 10 by the wedges 28. The width of the rolls 30 is such that the inner faces of each wedge 28 will actually be maintained a slight distance outward from the surface of the cathode 10 following initial insertion of the wedges 28 between the layers 11 and cathode 10. The rolls 30 will simply roll along the surface of the moving cathode 10 and will not mar or disturb the normally smooth cathode surface configuration. Different wedge arrangements can be utilized, and coating of the wedges with a substance to minimize friction (such as Teflon") will lessen cathode wear.

In the process shown in FIGURE 4, the zinc layer 11 is initially rapped by the vibrating rapper 17 at each side of the conveyor 13 to loosen the zinc layers 11 along the solution line 9. The moving cathode '10 is then subjected to the hydraulic stripping operation previously described and, when necessary, the upper edges of the partially removed zinc layers 11 are mechanically held apart from the cathode 10 by the wedges 28 during completion of the stripping process.

It is to be understood that the illustration in FIGURE 4 is schematic in nature. The spacing between the various devices is not necessarily accurately portrayed. The process involved herein obviously requires elfective timing between the various steps, and the time between rapping of the solution line initiation of hydraulic stripping, mechanical holding of the upper edge of the partially removed layers, and completion of the stripping operation obviously must be varied to meet operating conditions by proper location of the devices along the conveyor 13. Such proper positioning to achieve maximum effectiveness at a particular operating pressure, flow rate and conveyor speed is believed to be obvious.

In actual practice, a high percentage (9099%) of all cathodes run at the high pressure range indicated above (4000 to 6000 p.s.i.) have been effectively stripped using the hydraulic Stripping process shown in FIGURE 1, with no auxiliary solution line breaking or other devices being used. Where difficult stripping is encountered, rapping of the plates to break the bond at the solution line has been found to increase the effectiveness of the process and hydraulic stripping is then more easily accomplished. The use of spreading wedges in conjunction with the hydraulic jets increases the effectiveness of the process and better utilizes the available energy from the high pressure water jet insuring that it is directed between the adjacent zinc and aluminum surfaces.

Many variations in operating conditions will depend upon the particular requirements of an individual installation. Changes envisioned within the above disclosure include:

(1) Nz zlesany number of nozzles can be used.

(2) Nozzle characteristicscan be varied individually or as a group. Variations are possible in orifice size, spray pattern and spray angles, volume-pressure relationships, impingement angles and distance from orifice to impingement point.

(3) Direction of plate travel-can be changed when related to nozzles.

(4) Fluid-water, other liquids or gases can be used, with or without additives which can vary laminar flow and effectiveness of nozzle arrangement.

(5) Point of impingement-must only be along boundary line between cathode and zinc.

(6) Stripping speedno-t restricted, although higher stripping speeds result in less cathode wear and more effective stripping. Must also relate to loading and unloading rate of cathodes.

(7) Flow charcteristicsdevices to straighten flow between manifold and nozzle increase effectiveness.

Many other modifications could be made in the process without deviating from the basic steps described above. The process as set out in this description is practical and strips aluminum cathodes effectively while the cathodes are hung from the moving conveyor 13. The time involved (less than 2 seconds) is much less than the time required to manually strip the zinc by chisels (about 11 seconds). The process minimizes the possibility of mechanical damage to the vulnerable cathodes. By providing the hydraulic stripper apparatus at two sides of the cathodes hung vertically from a conveyor, the forces exerted against the cathode along each of its sheet faces serve to oppose and balance one another. The method described, since it eliminates manual operations, can be automated and applied continuously in a zinc recovering process.

Having thus described my invention, I claim:

1. A process for stripping a deposited metal layer from a cathode previously dipped in an electrolytic solution and coated wtih deposited metal along anarea bounded by a solution line, comprising the following step:

impinging a fluid jet on the cathode and deposited metal layer along an exposed interface with the jet angularly directed toward the coated area of the cathode to thereby separate the deposited metal layer from the cathode in the form of a sheet.

2. The process as set out in claim 1 wherein the deposited metal layer is mechanically impacted along the solution line prior to impingement by the fluid jet.

3. The process as set out in claim 1 wherein the deposited metal layer is mechanically held apart from the cathode after initial disengagement from the cathode.

4. The process as set out in claim 1 as applied to a flat sheet cathode wherein a series of successive fluid jets successively impinge on the sheet and deposited metal in oppositely directed streams against the two sheet faces.

5. The process as set out in claim 1 as applied to a flat sheet cathode moving in a direction parallel to its sheet faces wherein a series of successive fluid jets successively impinge on the sheet and deposited metal in oppositely directed streams against the two sheet faces.

6. The process as set out in claim 1 wherein the cathode and deposited metal layer are successively impinged by a straight fluid jet and then by a succeeding fluid jet with a widening spray angle.

7. The process as set out in claim 1 wherein the jet comprises a liquid jet and the jet pressure is between 4000 to 6000 psi.

8. The process as set out in claim 1 wherein the fluid jet to initially break the bond of the deposited metal layer is a liquid jet having a jet pressure between 4000 to 6000 p.s.i., and subsequent liquid jet pressure applied to the interface between the deposited metal layer and cathode is above 300 psi.

9. The process as set out in claim 1 wherein the jet is directed toward the cathode at an angle of no more than 25 degrees from the cathode surface.

10. The process as set out in claim 1 wherein the cathode is aluminum, the metal layer is zinc and the fluid is water.

References Cited W. H. Safranek, Product Engineering, June 5, 1961, pp. 609-614.

JOHN H. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner

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