Aluminium metal is generally produced by the electrolytic reduction of alumina. The reduction cells used in this process comprise an outer steel shell that is lined with a refractory layer. The refractory layer has carbonaceous material placed on top and the carbonaceous layer acts as the cathode in the electrolytic cell. A number of anodes are suspended above the cathode. In use of the cell, an electrolytic bath comprising alumina dissolved in molten cryolite is positioned between the anodes and the cathode. Passage of current through the cell causes molten aluminium metal to be deposited at the cathode. Another product of the electrolytic reaction occurring within the cell is carbon monoxide that is formed at the anodes. The cells operate at a temperature of approximately 9600C to 9800C and evolution of gases at the anodes causes the anodes to be consumed.

Anodes conventionally used in aluminium smelting cells include soderberg anodes and prebaked anodes.

Prebaked anodes essentially comprise a block of baked carbonaceous material that is attached to an anode hanger.

The anode hanger includes a rod that, in use, is attached to an anode support system located above the cell. The lower end of the rod includes a yoke that comprises a number of separate arms that extend horizontally away from the rod and then turn vertically downwardly. Each of these arms has a nipple located at their ends. In order to connect the prebaked carbonaceous block to the anode holder, the nipples are placed in preformed holes in the top surface of the anode block and molten metal, normally cast iron, is poured around the nipples in the hole. When the cast iron solidifies, the carbonaceous block is

connected to the anode holder.

As mentioned above, evolution of carbon monoxide at the anode during smelting causes the carbonaceous anodes to be consumed. Consequently, it is necessary to constantly replace the anodes during cell operation and most smelters require replacement of prebaked anodes at intervals of between 15 and 30 days. Replacement of an anode involves lifting the anode out of the cell, removing any bath or detritus that may have fallen into the hole left in the frozen layer on top of the cell, replacing the anode with a fresh anode and covering at least the perimeter of the anode with a layer of alumina or frozen bath.

Spent anodes that are removed from the cell have a small amount of carbon left on the anode holder, which is known as the anode butt. Moreover, there is generally a layer of frozen bath adhering to the upper surface of the butt. In order to reuse the anode holder, which is required for economic reasons, it is necessary to remove the frozen bath and anode butt from the anode holder and to subsequently place a fresh anode block on the anode holder.

As a first step the frozen bath must be removed from the anode butt to enable the butt to be disconnected from the yoke and to allow the carbon in the butt to be recycled.

The present invention provides a cleaning apparatus which enables this cleaning operation to be carried out mechanically rather than with hand operated tools.

DISCLOSURE OF THE INVENTION According to the invention there is provided anode cleaning apparatus for cleaning spent anodes removed from electrolytic metal electrowinning cells and comprising an anode rod and yoke having an anode butt attached thereto, said cleaning apparatus including: a fixed structure; an anode support frame pivotable on the fixed structure from a first position in which to receive an anode to be cleaned and a second position in which to

support the anode in a condition for cleaning; clamp means for clamping the anode in the frame; cleaning means mounted on the fixed structure for movement across a surface of the anode to be cleaned when the anode is clamped in the frame with the frame in its second position; and an abutment surface on the support frame which comes into engagement with a fixed abutment on the fixed structure when the frame is moved to its second position so as to support the frame against thrust forces imposed thereon through the anode by the cleaning means.

Preferably, the frame is shaped so as to receive the anode in a condition in which the anode rod is upright and the anode butt is disposed below the anode rod when the frame is in first position.

Preferably too, the frame is pivotable on the fixed structure to lay the anode down into a cleaning position in which the anode rod is generally horizontal and the normally uppermost surface of the anode butt to be cleaned is generally upright and the cleaning means is mounted on the fixed structure for substantially vertical movement across the normally uppermost surface of the anode butt to be cleaned.

The cleaning means may comprise a pair of jack hammers moveable downwardly to clean the normally uppermost surface of the anode butt one to either side of the anode yoke.

Preferably, the frame comprises a frame portion which is generally of inverted U-shape when the frame is in the first position so that the anode rod can be placed between the two limbs of the inverted U-shape with the yoke and anode butt disposed generally beneath the two limbs and the clamp means is operable to clamp the yoke and anode butt against the lower part of the inverted U-shaped frame portion.

The clamp means may comprise a clamp arm pivotally connected to the frame a location which is

disposed below the inverted U-shaped frame portion when the frame is in its first position and a clamp actuator actuable to swing the arm upwardly to engage the underside of the anode butt and to clamp the anode butt and yoke against the lower ends of the limbs of the inverted U- shaped frame when the frame is in its first position.

Preferably, the fixed abutment is located on the fixed structure generally below the position of the inverted U-shaped frame portion when the frame is in its first position and said abutment surface is located at a bottom end of one of the limbs of the inverted U-shape frame portion so as to swing downwardly into engagement with the fixed abutment when the frame is pivoted to its second position.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention will now be described with reference to the following drawings in which: Figure 1 shows a side view of an anode cleaning apparatus in accordance with the present invention with an anode positioned in the frame and the clamp in an open condition; Figure 2 shows the apparatus with the frame rotated by 30 from vertical; Figure 3 shows the apparatus of Figure 2 but with the clamp in a closed condition; Figure 4 shows the apparatus of Figures 1 to 3 with the lay down frame fully rotated to hold the anode in a substantially horizontal orientation; Figure 5 illustrates the operation of a frame rotating hydraulic cylinder unit which moves the frame between the positions shown in Figures 3 and 4; Figure 6 is a similar view to that shown in Figure 4 but with details of anode cleaning hammers included; and Figure 7 shows the apparatus of Figure 6 with the cleaning hammers extended to clean frozen bath from the

anode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figures 1 and 2 show very similar views and will be described together. In these drawings, the anode cleaning apparatus 10 includes a fixed structure 12 and an anode support frame 15 pivotally mounted on fixed structure 12 at a pivotal mounting point 18. Fixed structure 12 comprises a base 13 and an upstanding supporting portion 14. The anode support frame 15 comprises an inverted substantially U-shaped portion 15A having limbs 16 and 17 and a further portion 15B which projects from portion 15A as an extension of the limb 17.

Frame 15 is fitted with a clamp comprising a clamp arm 20 pivotally connected to frame portion 15B at a pivot mounting 19. The outer end of clamp arm 20 carries a pivoting clamp jaw 21. Operation of the clamp will be described in greater detail with reference to Figures 3 and 4.

The anode support frame 15 includes abutment means 22 mounted at the end of arm 16. Abutment means 22 has an abutment surface 23 that is designed to engage with a complementary abutment surface 24 formed on a fixed abutment 25 that is mounted on the base 13 of fixed structure 12.

Spent anodes 26 are delivered to the anode cleaning apparatus 10 via overhead conveyor 27 that includes a pneumatic indexer 28 having a hook 29 that holds the anode 26 and is connectable to and releasable from the pneumatic indexer.

With reference to Figure 1, a spent anode 26 that includes an anode rod 30, yoke 31 and anode butt 32 connected to yoke 31 via nipples (not shown) is supplied to the anode cleaning apparatus 10 by a pneumatic indexer chain arrangement 28. As shown in Figure 1, frozen bath 33 adheres to the upper surface of the anode butt 32. When the anode 26 is in the correct position, hook 29 is disconnected from the pneumatic indexer 28.

Once the anode has been indexed into the lay down frame by the pneumatic indexer 28, the support frame 15 may be rotated a small amount, such as by 30, as shown in Figure 2 to cause the anode to seat against limb 16 of the frame prior to operation of the clamp. Frame 15 is pivoted about its pivot mounting 18 by actuation of a hydraulic cylinder unit 41 pivotally connected at its lower end to the base 13 of fixed structure 12 by a pivot mounting 42 and at its upper end to the frame portion 15B at a pivot mounting 43, as is most clearly seen in Figure 5.

When the anode has been located in the frame 15 in the position shown in Figure 2, the clamp is operated by actuation of an hydraulic cylinder unit 44 connected between the clamp arm 20 and the portion 15B of frame 15 so as to pivot arm 20 upwardly towards the anode butt 32.

This causes clamping jaw 21 to contact anode butt 32, which in turn forces the anode 26 to be forced upwardly into the lay down frame until yoke 31 contacts yoke support means 34. The combination of clamping surface 21 and yoke support means 34 acts to hold the anode 26 in the lay down frame 15. By supporting the spent anode 26 at its yoke, forces are not placed on the anode rod 30, which may be susceptible to bending if it were subject to such forces.

Closure of arm 20 and clamping surface 21 onto butt 32 effectively clamps the anode in the frame 15 as shown in Figure 3, the clamp jaw 21 being free to pivot so as to self-align during the clamping movement. The frame 15 is then rotated by actuation of hydraulic cylinder unit 41 to lay the anode down into a generally horizontal orientation as shown in Figure 4. The movements of the frame and cylinder unit 41 are illustrated in Figure 5. As can be seen, as the lay down frame 15 rotates, the clamping means comprised of arm 20 and clamping jaw 21 rotates with the lay down frame to ensure that the anode remains clamped in the lay down frame. In the position shown in Figure 4, the anode is ready to have frozen bath cleaned therefrom.

The cleaning operation is shown in Figures 6 and

7, which delete some details shown in Figures 1 to 4 for the sake of clarity. As shown in Figure 6, the anode is held by frame 15 in a substantially horizontal orientation.

In this orientation, abutment surface 23 on the abutment means 22 connected to the frame 15 contacts the abutment surface 24 on the base 13 of the fixed structure 12.

In order to clean frozen bath 33 from the anode butt 32, two or more hammers 37 are mounted on fixed structure 12 so as to be moveable downwardly in parallel one to either side of the anode yoke 31 in order to clean the frozen bath 33 from the normally uppermost surface of the anode butt 32. Each hammer 37 includes a hammer end 35 that can move upwardly and downwardly by extension of hydraulic cylinder 36. Hammers 37 are of conventional construction and need not be described further.

As shown in Figure 7, in order to clean frozen bath 33 from spent butt 32, the hammer 37 is extended by cylinder 36 such that the end thereof 35 contacts the spent bath and removes it from anode butt 32.

Cleaning of the frozen bath 33 from spent butt 32 requires the application of considerable force to the frozen bath. The design of the anode cleaning apparatus 10 of the present invention ensures that the forces applied by the hammers 37 are largely borne by the anode support frame 15 and the base 13 of the apparatus. In particular, when the hammers 37 apply force to frozen bath 33, the force is transferred from the frozen bath to the yoke 31 of the spent anode and from the yoke the force is transferred into the yoke support means 34. The forces are then transferred through the frame 15 and abutment means 22 into the fixed abutment 25 on the base 13. Accordingly, the frame 15 and fixed base 13 bear most of the forces applied to the anode by the hammers 37. The pivot point 18 at which the frame 15 is mounted to the structure 12 does not have to bear the considerable force of the hammer action and accordingly any problems caused by increase wear or misalignment due to pivot point 18 bearing the force of the hammers are avoided

or minimised.

Another feature of the present invention resides in the compact design of the apparatus. As shown in Figures 6 and 7, the hammers can be mounted substantially vertically and the hammers move in the substantially vertical direction to clean the frozen bath from the anode butt. Therefore, the apparatus only has a small transverse width, which may be an important requirement for apparatus designed to be used in aluminium smelters.

Once the frozen bath has been removed from the anode butt, the anode support frame is returned to the substantially vertical position. The cleaned anode is then removed from the lay down frame by the pneumatic indexer chain and a new spent anode is positioned within the lay down frame.