BACKGROUND ART The process of extracting metals from an electrolytic solution by electrodeposition of the metal onto an electrode is well known. Metals that are extracted in this manner include copper, zinc, nickel and lead. In electro- refining, an impure anode is made from the metal of interest. In the presence of an electric current, the metal in a purified form is deposited onto the cathode. In electrowinning, there is a pure anode and the metal of interest is in a dissolved form in the electrolyte solution. In the presence of an electric current, the metal from the electrolyte solution is deposited onto the cathode.

The cathodes used in electrowinning and electro-refining are typically thin, stainless steel sheets of uniform thickness. A bank of sheets is typically placed within an electrolyte solution for electrodeposition. After the metal has been deposited, the cathodes are removed from the electrolyte solution, washed and the electrodeposited metal is mechanically stripped from both sides of the cathode. The stripped cathode is then returned to the electrolytic solution and the process is repeated.

In order for the deposited metal to be able to be stripped from the cathode, it is important that there is no electrodeposition about the edges of the cathode. To prevent such deposition, it is known to place protective edge strips of a non-conductive material that mask the edges of the cathode from deposition. Conventional edge strips are extruded thermoplastic strips having a U-shaped cross section having arms that fit about the edges of the

cathode. Such edge strips may be attached to the cathode by means of bolts or pins passing through holes that have been drilled in the cathode and the edge strip. Fixing the edge strip to the cathode in this manner is labour intensive and costly.

It has also been observed, that even though the arms of the strip are designed to fit snugly about the cathode edge, it does not completely prevent ingress of the electrolyte between the edge strip and the cathode.

This results in electrodeposition of the metal beneath the edge strip. The amount of metal electrodeposited beneath the edge strip builds up over time.

Eventually, this deposition may result in the edge strip becoming loosened and ultimately the edge strip is prone to removal during the metal stripping process. A further disadvantage of attaching the edge strips to the cathodes by pins or bolts is that there is little allowance for thermal expansion of the thermoplastic strip. Thermal expansion of the strip occurs when the cathodes are washed of electrolyte prior to stripping. This typically occurs at temperatures of about 90°C.

In an attempt to address this problem, different methods of attachment of edge strips to electrodes have been investigated. When proposing new methods, it is of course desirable that any new attachment means is applicable to existing electrodes.

One known system has an edge strip which has a continuous longitudinal groove along each arm. A series of pins are inserted or moulded onto the cathode. To fit the strip to the cathode, the strip is pushed onto the cathode such that the longitudinal groove receives the pin (s). Such a strip provides some advantages in the fitment of the strip to the cathode over the method described above. However, these strips are still susceptible to ingress of electrolyte between the strip and the cathode.

Another proposal for use with electrodes having holes drilled therein is to provide an edge strip retainer in the form of a continuous length

of an injection moulded thermoplastics material having a series of spaced studs extending there from. The studs are spaced so as to be received by and pass through existing holes in an electrode. In use the retainer is mounted to an electrode by placing the studs through the holes in the electrode such that a continuous strip of material extends along one side of the electrode with studs projecting through and from the other side of the electrode. An edge strip having opposed longitudinal grooves located in the internal faces of the jaws is then slid onto the electrode such that one groove receives the continuous strip and the other groove receives the projecting ends of the studs. The edge strip is retained on the edge of the electrode by engagement of the studs and strip with the respective grooves.

In practice, it has been observed that the studs on the retainer are susceptible to shearing under a load. When this occurs, the edge strips can become dislodged from the electrode and in particular during the stripping process.

It would therefore be desirable to manufacture edge strip retainers which are more resistant to shearing forces.

In order to reduce the ingress of electrolyte between the edge strip and the cathode, it has also been proposed to increase the clamping pressure of the arms of the strip against the cathode surface by modifying the rear portion of the edge strip. Such proposals include inserting expansion members in the rear portion of the strip. It has also been proposed to thicken and enlarge the rear portion. However, cathodes are made according to precise dimensions and there is little tolerance permitted in these dimensions during the electrodeposition and stripping processes. Thus, any increase in the dimensions of the edge strips is limited by such tolerances. Also, in practice it has been observed that such edge strips still allow ingress of the electrolyte.

In order to facilitate stripping of metal from electrodes, it is also

desirable to avoid electrodeposition along the bottom edge of the electrode.

Traditionally high temperature wax has been applied to the bottom edge of an electrode. More recently, it has become accepted practice to machine a fine groove along the bottom edge of the electrode. It has been surprisingly discovered that as a result of the mechanism of crystal formation during electrodeposition, metals such as copper will not deposit into and bridge this narrow groove. As these grooves are very narrow (the width of an electrode being between about 2 to about 3 mm), they are subject to damage during use, which in turn may lead to metal depositing across the bottom edge of the electrode. For this reason, it is generally a tank house requirement to provide a bottom plug in the edge strip to project below the electrode to protect the groove. Typically, the plugs project about 3 mm below the bottom of the cathode. The most common approach is to low pressure injection mould a plug into the edge strip. However, this process is expensive. Further, the injected material can be pushed into the electrode slot, thereby blocking the strip. It is also known to provide a separate plug which is pushed into the end of the edge strip. However these plugs are all attached to the edge strip which requires the edge strip to have a special design to lock with the end plug. It is important that the end plug does not fall off. Existing plugs also do not assist to increase the clamping pressure of the arms of the strip against the cathode surface.

OBJECT OF THE INVENTION It is an object of the invention to provide an edge strip and/or a clamping pin which may at least partially overcome the abovementioned disadvantages or provide the public with a useful or commercial choice.

According to a first broad form of the invention there is provided an edge strip for protecting an edge surface of a sheet or plate electrode, the edge strip having a substantially rigid elongate non-conductive body with a longitudinal slot defined by opposing electrode contact portions (which can be jaws) for receiving an edge of the electrode, and means to clamp the

electrode contact portion against the electrode.

The edge strip can have a body made of a non-conductive material so as to mask the edge of the electrode for an electrolyte solution.

The strip is typically formed from an extruded thermoplastics material which is relatively rigid and hard and stable under the conditions of use. These conditions include the low pH of the electrolyte solution and the high temperatures used in washing the cathodes prior to stripping. Suitable materials include polyvinyl chloride, acrylic polyvinyl chloride and acrylonitrile- butadiene-styrene.

Preferred materials are those having a low melt flow index and good heat resistance. Low heat materials having a higher melt flow index, such as PVC may also be used but this can result in widening of the electrode slot at higher temperatures.

The edge strip can be formed of multiple parts. Suitably, the edge strip comprises 3 parts being a pair of side parts between which the electrode can pass, and a top part. Each side part can have the electrode contact portion which can comprise a jaw or like member.

The means to clamp the electrode contact portion against the electrode can comprise a separate member which is attached to the edge strip. The separate member can be an end plug which can be inserted in a bottom end of the edge strip (when the edge strip is in the vertical position).

The separate member can comprise attachment means to attach to the electrode, and this can comprise a hooked finger, projection and the like which uses the opening on the electrode for attachment.

Thus the end plug can be attached to the plate electrode which has not hitherto been achieved, can also plug the bottom end of the edge strip and can also assist in modifying the clamping pressure of the jaws on the electrode. Typically, the plugs are injection moulded from a suitable

thermoplastics material.

A further seal may be provided to seal the internal cavity of the edge strip from the electrolyte solution. The seal may be provided on each jaw member and on an upper part of each side part. The seal on each side part may comprise a thin flexible rib which is attached to the side part via a groove or recess in the side part.

According to a second broad form of the invention, there is provided a clamping pin for an electrode of the type which is provided with at least one opening, the clamping pin adapted for clamping engagement with the opening, the clamping pin comprising a main pin portion and a wedging portion, the main pin portion comprising a main body portion which has a width which is less than the width of the at least one opening in the electrode such that the main body portion can pass through the opening, the main body portion having a length which is greater than the thickness of the electrode such that when the main body portion passes through the opening, a portion of the main body portion extends outwardly from at least one side of the electrode, the main body portion having at least one end shoulder portion, the shoulder portion having a size to allow it to pass through the opening in the electrode, the wedging portion adapted to extend over at least part of the main body member and able to be pushed into the opening to wedge the clamping pin in said opening.

In this second broad form of the invention, an edge strip can be attached to the clamping pin to keep the edge strip attached to the plate electrode. The edge strip may be as described above.

The end plug as described above can also be used in this second broad form of the invention.

The electrode can be provided with an array of pins to assist in holding the edge strip, and the pins can be simply and easily attached to the

electrode via the openings. Moreover, the clamping pin can be mass produced inexpensively.

Typically, the clamping pin is provided with a pair of main pin portions and wedging portions which means that a clamping pin can be used to clamp into two openings.

Suitably, the main pin portion and a wedging portion are attached to respective arm members and the arm members are attached to each other. In this manner, the main pin portion and a wedging portion can be formed integrally, typically from plastics material.

The main body portion has a length which is greater than the thickness of the electrode. For instance, if the electrode has a thickness of approximately 3 mm, it is preferred that the main body portion has a length of approximately 6-20 mm and typically approximately 10 mm.

The main body portion has a width which is less than the width or diameter of the opening in the electrode. The opening in the electrode is typically circular and typically has a diameter of about 8 mm. Thus, it is preferred that the main body portion has a width of approximately 4-6 mm such that it can easily slide through the opening and still provided gap for the wedging portion. The main body portion is typically oval in cross section although other cross sections are also envisaged such as circular and polygonal.

The main body portion is provided with at least one end shoulder portion. Typically, a pair of said shoulder portions is provided one at each end of the main body portion. The shoulder portion typically comprises a shape which is substantially the same as the shape of the opening through the electrode. Thus, if the opening in the electrode is circular (which is common), the shape of the shoulder portion is also circular which means that the shoulder portion may be substantially dislike in configuration. The size of the shoulder portion is suitably such that it can pass through the opening

but as it is preferred that the shoulder portion is quite sturdy, and the size of the shoulder portion is preferably only slightly smaller than the size of the opening. This allows the shoulder portion to be as large as possible while still passing through the opening in the electrode.

Suitably, the, or each shoulder portion extends substantially at right angles from the main body portion and in such a manner that the combination is roughly U-shaped in cross section.

The wedging portion typically comprises an elongate arcuate member which has a length approximating the length of the main body portion. The wedging portion is typically arcuate to conform to the curved outer body of the main body portion. However, if the outer body of the main body portion has a different configuration, the wedging portion typically has a configuration to complement the different configuration of the main body portion.

The wedging portion is designed to press over the top of the main body portion, and the wedging portion has a thickness such that when attached over the top of the main body portion, the total size is larger than the opening in the electrode. This will be described in greater detail below.

In another form, the invention resides in an edge strip for an electrode, the edge strip comprising 3 parts being a pair of side parts between which the electrode can pass, and a top part, the side parts each having an electrode contact portion, a longitudinal groove adjacent the electrode contact portion, and a top part engaging portion, the top part comprising a channel into which the edge of the electrode can pass, and a pair of outer arm members adapted to engage with the top part engaging portion contact in each side part.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be described with reference to the following drawings in which: Figure 1. Illustrates a clamping pin according to an embodiment of the invention.

Figure 2. Illustrates in greater detail the main pin portion and the clamping portion of the clamping pin of figure 1.

Figure 3. Illustrates part of an edge strip attached to the edge of an electrode and a clamping pin of the type illustrated in figure 1 and figure 2.

Figure 4. Illustrates the edge strip of figure 3 from the other side of the electrode.

Figure 5. Illustrates an end view from one side of the edge strip illustrated in figure 3.

Figure 6.. Illustrates an end view from the other side of the edge strip illustrated in figure 5.

Figure 7. Illustrates the edge strip from the opposite side.

Figure 8. Illustrates the clamping pin next to an opening in the electrode.

Figure 9. Illustrates the clamping pin of figure 8 with the main pin portion inserted through the opening and the wedging portion still outside of the opening.

Figure 10. Illustrates the clamping pin of figure 9 with the wedging portion partially pushed through the opening in the electrode.

Figure 11. Illustrates the clamping pin of figure 10 with the wedging portion in position and where the pin is clamped in the opening in the electrode.

Figure 12. Illustrates a"double headed"pin to attach an edge strip to a plate electrode and according to another embodiment of the invention.

Figure 13. Illustrates the pin of figure 12 attached to a plate electrode in two places.

Figure 14. Illustrates the pin of figure 13 with an edge strip partially extending over the pin Figure 15. Illustrates an edge strip and a locking plug and according to

another embodiment of the invention.

Figure 16. Illustrates the locking plug in greater detail.

Figure 17. Illustrates an end view of a preferred edge strip which comprises three parts.

Figure 18. Illustrates attachment of the locking plug to an opening in a plate electrode.

Figure 19. Illustrates the edge strip of figures 15 and 17 attached over the edge of a plate electrode and having the locking plug partially in the locking position.

Figure 20. Illustrates an end view of figure 19.

Figure 21. Illustrates a close up side view from one side of one end of the clip of figures 12-14.

Figure 22. Illustrates a close up side view from the other side of the clip of figure 21.

Figure 23. Illustrates a plan view of the clip of figures 21-22.

Figure 24. Illustrates a plan view from the other side of the clip of figures 21-23.

BEST MODE Referring to figures 1-11 there is illustrated a clamping pin and an edge strip according to a further embodiment of the invention. Referring initially to figure 1 there is illustrated a clamping pin 60 according to a preferred embodiment of the invention. Clamping pin 60 is manufactured from plastics material as an integral unit. In the embodiment, the length of the clamping pin is. approximately 110 mm from one end to the other end, this length being determined by the spacing of the openings in the electrode.

Clamping pin 60 is a"double pin"which means that it can pin into a pair of openings in the electrode. Clamping pin 60 comprises a main pin portion 61 and a wedging portion 62. These portions 61,62 are attached to arm members 63,64 which are connected to each other at a distal point 65 such that the entire clamping pin is an integral unit.

Main pin portion 61 has a main body portion 66 (best illustrated in figure 2). The main body portion has a length of approximately 9 mm which means that it passes entirely through an electrode having a thickness of approximately 2-3 mm and projects from each side of the electrode. Of course, the length of the main body portion can vary depending on the thickness of a particular electrode. Main body portion 66 has a somewhat oval configuration when viewed in cross section and comprises a curved upper part 67 to mate with the arcuate wedging portion 62 which will be described in greater detail below. The width of main body portion 66 is significantly less than the diameter of the opening in the electrode. For instance, if the opening in the electrode has a diameter of approximately 8 mm, the width of the main body member is approximately 3-4 mm. Each end of main body portion 66 is provided with a shoulder portion 68. Each shoulder portion 68 is disk like in configuration having a diameter which is only slightly smaller than the diameter of the opening in the electrode, and having a thickness of approximately 2 mm. The shoulder portions 68 offset to the longitudinal axes of the main body portion is illustrated in figure 10 to define what can be seen as a U-shaped channel defined by the walls of each shoulder portion 68 and main body portion 66.

The arrangement is such that main pin portion 61 can pass through opening 70 (see figure 3) in electrode 71, and can then be pushed against the internal wall of opening 70 to provide a gap between curved outer body 67 (caused by the main body portion 66 having a width which is substantially less than the diameter of opening 70) and the wall of opening 70.

The main pin portion 61 is held in this position by wedging portion 62. Wedging portion 62 has an arcuate inner face 70 to which is adapted to overlie the arcuate outer face 67 of main body portion 66.

The stepwise clamping arrangement is best illustrated with reference to figures 8-11. Referring initially to figure 8, the main pin portion 61 and wedging portion 62 are not connected and are positioned next to opening 70. Referring to figure 9, main pin portion 61 has been pushed through opening 70 and has been then pushed downwardly in the direction of arrow 73 such that the shoulder portions 68 at least partially overlap the side wall of electrode 71. Referring to figure 10, wedging portion 62 is being pushed through opening 70 to keep main pin portion 61 in the position illustrated in figure 9. Referring to figure 11, this illustrates the clamping pin in the clamped position. The pin cannot be slid out of opening 70 by virtue of shoulder portions 68 being pushed downwardly by wedging portion 62 to overlie the side wall of electrode 71. To remove the clamping pin, it is necessary to initially slide wedging portion 62 out of opening 70 after which the main pin portion 61 can be lifted in opening 70 such that shoulder portions 68 can now be slid out of opening 70.

Referring to figures 5-7, there is illustrated an edge strip according to an embodiment of the invention attached over the each of electrode 71 and held in place inter alia by the clamping pin.

Specifically, the edge strip according to this embodiment is formed of three parts best illustrated in figure 6, the parts comprising a pair of side parts 80,81 and a top part 82. Each part is formed of plastics material.

The side parts 80,81 extend over each side of the electrode. Each side part 80,81 is formed with an outer electrode contact portion which comprises an elongate foot 83,84 adapted for clamping engagement or sealing engagement with the surface of the electrode. Adjacent foot 83,84 is a longitudinal recess or groove 85,86 in which is located the disk shaped shoulder portion 68 of the clamping pin. Each side part is provided with a top part engaging portion which in the embodiment comprises a thickened head portion 87,88 below which extends a longitudinal groove 89,90.

Top part 82 is provided with a central channel 91 which extends

over the edge of the electrode 71. Top part 82 further comprises a pair of outer arm members 92,93 which extend over the thickened head portion 87, 88 of each side part and where each arm member 92,93 has a small inwardly extending terminal lip 94,95 which extends at least partially into the longitudinal groove 89,90.

As the edge strip is formed of three parts, and because it is important to ensure that no electrolyte passes into the edge strip, the edge strip is provided with additional seals to prevent ingress of electrolyte. In the particular embodiment (and best illustrated in figure 17), each side wall 12,13 is provided with a small groove 25,26 (groove 25 also being illustrated in figure 5 and figure 6). A small co-extruded seal made of softer plastics material 27 is attached into each groove. Seal 27 comprises a thin flexible member which seals the spacing between the respective side wall 12,13 and top wall 14. Thus, a separate seal is provided on each side wall. A further seal 28 is co-extruded on the front face of each jaw 15,16 to seal against the electrode. Thus, the edge strip contains four additional seals being two upper seals 27 and two lower seals 28.

Referring to figures 12-14 and 21-24, there is described another type of pin for attaching an edge strip to a steel plate electrode. Pin 102 is made of plastics material and comprises a pair of pin heads 103,104 separated by a thin filamentary body 105. Body 105 is not linear but instead has a"wave like"formation (see figure 13), which allows the entire pin to stretch somewhat to engage into openings 70 on the steel cathode plate.

Each pin head 103,104 has a substantially cylindrical shape having a length of about 10 mm, and a diameter of about 5 mm. The pin heads 103,104 are not exactly cylindrical but instead have a cylindrical mid section 106 (see figure 23) and a squarish top and bottom section 107,108. Each pin head 104,103 is provided with a small arrow shaped projection 109 (figure 23) which allows the pin head to be wedged into the hole 70 in the steel cathode plate. In use, the pin extends into a pair of holes in the steel cathode plate and an edge strip 110 (figure 14) can be slid over the edge of the cathode

plate and held by the pin. The edge strip 110 has an internal profile to accommodate the pin and in particular the squarish sections 107 and 108 on each pin head extend into the opposed channel like cutouts 111,112 (not illustrated) of edge strip 111.

This particular pin is suitable for use with conventional edge strips of the type illustrated in figure 14. Known pins are relatively weak and do not wedge or lock into the hole of the cathode plate. The pin illustrated in figures 12-14,21-24 is provided with the wedge shaped projection 109 which allows it to be wedged or locked into the hole. This now allows the edge strip to be attached to the edge of the steel cathode when the cathode is in the vertical position which has previously not been possible. Previously, the pins could not be locked into the hole and therefore the edge strips had to be assembled while the cathode plate was in a horizontal position. The pin according to the embodiment is a stronger pin as the pin head can be substantially the same diameter as the hole in the cathode plate.

Conventional pins have a pin head which is smaller than the diameter of the hole in the cathode plate to allow for tolerances.

The dual pin retainer as illustrated in figures 12-14,21-24 is stronger than the conventional retainer which typically comprise a strip having five pins extending there along and which extends into five openings on a plate like electrode. The retainer according to this embodiment is stronger because the shorter flow requirements, stronger engineering plastics can be used which give a substantially better results than the conventional polypropylene plastic which must be used for the longer 5 pin retainers. Also, the pin of the embodiment is thicker (i. e. a larger diameter) to match the slots 70 in the edge strip. To explain, the hole size in the plate electrode is 8 mm.

An early form of attachment had a 6 mm pin solvent welded into the edge strip and passing through the 8 mm opening. The oversize hole allows for expansion and contraction of the edge strip and prevents the pin from being sheared off (it being appreciated that during electroplating, there are quite significant temperature changes on the plate electrode). The pin according to

this embodiment has a centre diameter of 7.8 mm thereby making it thicker and therefore stronger than the conventional 6 mm pin. Each side has the squarish flat ends 107,108 (see figure 23) these ends having a cross-section of 6 mm. These ends are offset to ensure the correct positioning to locate the edge strip slots and to ensure that the internal slots will not bottom out on the cathode plate.

Figures 15-20 illustrate an edge strip 11 and a locking plug 50 which is in inserted into one end of the edge strip to lock the edge strip onto a plate electrode 71 and also to provide an end seal.. The edge strip 11 is similar to that of figure 3,5, 6. The edge strip 11 is best illustrated in figure 17 and is made of three parts being a first sidewall part 12 an opposed sidewall part 13 and a connecting top part 14. When the parts are attached, an internal passageway is formed. Also, each sidewall part terminates with a gripping jaw 15,16. A steel plate electrode 71 (see figures 19-20) is inserted between jaws 15-16 and is pushed such that the edge of the electrode extends in U-shaped passageway 17. At this stage, jaws 15-16 lightly touch the opposed sides of the electrode but do not yet clamp the electrode in place. Locking plug 50 is then pushed into the bottom end of edge strip 11 (it being appreciated that in practice edge strip 11 may be several metres long to cover the entire edge of a large plate electrode.) Locking plug 50 has an end face 18, a pair of upstanding locking nibs 19,20 and a pair of extending hooked fingers 21,22. The hooked fingers are designed to lock into the bottom most hole in the cathode plate. A pair of fingers 21,22 is provided to accommodate different types of electrodes which may have the holes 70 in different places. Figure 18 shows locking plug 50 attached to electrode 71 by having the longer hooked finger 21 extending through a hole 70 in the electrode. The other hooked finger 22 is not used for this particular electrode.

Locking plug 50 can be pushed into the end of edge strip 14.

Figure 19 illustrates locking plug 50 almost entirely pushed into the end of

edge plate 14, and in practice, locking plug 50 is then pushed or hammered further in place. Figure 20 illustrates locking plug 50 almost fully inserted into the end of edge strip 14. In this figure, there is illustrated how locking nibs 19, 20 pass into the channel shaped passages 23-24 (best illustrated in figure 17) of edge strip 14. The spacing between locking nibs 19,20 is slightly less than the spacing between passages 23,24. Thus, as locking plug 50 is pushed or hammered into place, locking nibs 19,20 pass into passages 23,24 and cause jaws 15,16 to clamp more tightly to each face of the electrode 71.

To ensure a good seal, a two-part silicone mixture is introduced into the pin cavity while the plate is in the vertical position. This mixture flows down to encapsulate the pin locking nibs and also completely seals the base against ingress of fluid during the electrodeposition process.

It should be appreciated that various changes and modifications can be made to the embodiment described without departing from the spirit and scope of the invention.