JPS5832236B2 - Cathode and suspension rod assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to cathodes, particularly but not exclusively to cathodes for copper refining.

Copper refining by electrolysis has been known for a long time, and in this method the anode is usually an impure copper sacrificial anode that is consumed during electrolysis.
Pure copper is electrodeposited on the cathode of the electrolytic cell.

In the first step, a thin layer of pure copper is electrodeposited on a specially prepared mother plate, in the second step the newly deposited pure copper in the form of a thin or thick plate is peeled off from the mother plate, and in the third step this master plate is It is common practice to use copper as the cathode in other electrolytic cells where another thick layer of pure copper is electrodeposited on the cathode.

Recently, titanium has been used as the base plate for this method.

Another development is to make a thick deposit of pure copper directly on the titanium cathode and then peel off the slab, eliminating the first and second steps of the previously described method.

When titanium is used as the material for either the first step mother plate or the second step cathode, each mother plate or cathode is connected to a suspension rod that extends across the electrolytic cell (thus connecting to the power supply busbar and connecting the electrolytic cell). contact with busbars placed on one side (or both sides) of the

Until now, these suspension bars have been made of copper, and the connection between the copper and the titanium mother plate or cathode has been by bolts or rivets.

Electrical contact between the mother plate or cathode (hereinafter referred to simply as the cathode) and the suspension rod has been considered to be contradictory.

The cathode and suspension rod are held tightly together near the bolt or rivet, but the surfaces elsewhere are slightly separated.

This separation can occur as a result of mechanical deformation or various thermal expansions.

If a separation is formed between the suspension rod and the plate, droplets of electrolyte will force their way into this gap and leave crystals, such as copper sulfate, in this gap and dry out.

If this gap is sealed by other deformations, these crystals prevent complete closure.

Another move is to build up other materials in the gap (konari,
As a result, this gap is enlarged by a ratchet-type action.

A decrease in surface contact area clearly results in an increase in the electrical resistance of the joint.

Japanese-style copper-to-copper joints have excellent properties, and electrolyte droplets have a cleaning effect on copper, but electrolyte does not have a cleaning effect on titanium. The resulting surface oxide film prevents electrical contact.

This surface film tends to increase the resistance across the titanium-copper interface as a result of heating the titanium.

With currents used to date, this electrical contact problem was solved by using multiple bolts or rivets to improve the electrical contact.

However, over the past five years or more, the use of high currents in electrolytic refining has led to the development of serious problems of contact resistance.

If a number of cathodes are used in parallel and the applied current is constant and the resistance of one of the cathodes increases, the cathode will receive less current.

This not only results in a lower rate of deposition on the cathode, but also increases the current through the remaining cathodes.

This overloads the next highest resistance cathode, causing it to overheat, become distorted and increase its resistance.

This further increases the current flow to the remaining cathode groups, which in turn causes damage.

Heating of the cathode further increases the load on the remaining cathodes, and the small amount of distortion that distorts the cathode is compensated for by hyperlocal growth as the cathode is brought closer to the anode, which in turn causes deposits to form on the cathode. The rapid formation of the precipitate causes a spherical growth of the precipitate onto the cathode and shortens the distance between the cathode and the anode.

This factor also has important implications for the economics of electrolytic refining, since current loss due to heating of the joint between the cathode and the suspension is a waste of energy and therefore cost.

Valve metal, as used herein, refers to an oxide film-forming metal selected from the group of titanium, niobium, zirconium, tantalum, hafnium, or alloys of these metals.

The present invention comprises an aluminum or copper suspension rod at least partially sheathed with valve metal by explosive bonding and a continuous plate of valve metal welded along one edge of at least a portion of the length of the suspension rod. A cathode and suspension rod assembly is provided.

The edges are preferably bent like a crank and have staggered legs, which may be spaced apart so that they can be easily added or removed.

Preferably, the legs are spot welded to the suspension rod.

Preferably, the end of the suspension rod is abraded to expose the core material along at least a portion of at least one side thereof.

At least 1 on the core material at the end or both ends of the hanging rod.
A current lead-in portion is provided at several locations.

The suspension bar may have reinforcing means.

The invention also relates to an aluminum or copper suspension rod that is at least partially coated with valve metal by explosive bonding and a valve that is welded along only one end for at least a portion of the length of the suspension rod. An electrolytic cell having a cathode and an anode made of continuous metal plates is also provided.

The suspension rod and cathode can be designed as described above.

A suspension bar is preferably located at each end of the electric busbar, the suspension bar having the valve metal sheath removed where it contacts the busbar.

Embodiments of the present invention will be described in further detail based on the accompanying drawings.

In FIG. 1 two copper plates 1 are shown connected to a titanium plate 2 by rivets 3.

Rivets 3 are placed in the holes passing through plates 1 and 2 in order to hold the rivets in place.

This compression tends to bulge the center of the rivet so that it is pressed into intimate contact with the drilling of the hole through the plate 2.

The rivet head is also pressed into intimate contact with the surface 5 of the plate 1.

The flow path of the current from the titanium plate 2 to the copper plate 1 is through the mutual plane between the perforation in the plate 2 and the surface of the rivet 3, along the rivet, into the copper plate 2 through the surface 5, and along the direction of the arrow 6. There is a tendency to pass.

Thermal cycling of the rivet tends to loosen the rivet, thus increasing contact resistance.

The bolted connection shown in FIG. 2 has another aspect.

It is shown that plates 1 and 2 are bolted together by bolts 7 and nuts 8.

The action of tightening the bolt tends to tension the bolt and tend to thin it, creating a gap 9 along the length of the bolt between the bolt and the borehole.

The current path between titanium 2 and copper 1 increases along the line of arrow 6a.

It can be seen that the current flows largely between the copper and titanium in the compressed area under the head of the bottle 7 and the nut 6.

Thermal cycling of the joint is slow in the bolt and copper and gradually diminishes, creating tension in the bolt.

The pressure across the titanium and copper mass below the head of the bolt 7 and below the nut 8 is therefore reduced.

Therefore, the resistance of the bond also tends to increase over time.

In both cases, the bond between copper 1 and titanium 2 terminates at a point as shown in FIG.

There tend to be voids at the ends, and droplets of electrolyte are naturally found in the voids, and the electrolyte tends to form crystals such as copper sulfate and dry out.

The differential expansion of the copper and titanium during part of the thermal cycle displaces the copper from the titanium, creating a deposit as shown at 10 in FIG.

When this joint is cooled, the copper holds a wedge of salts 10,
Unable to fully shrink onto titanium.

The next thermal cycle therefore pushes the copper further away from the titanium,
A further deposition of the electrolyte salt forming the wedge 10 prevents it from returning again.

There is therefore a ratcheting effect that tends to separate the copper from the titanium, thus increasing the contact resistance of the joint.

This thermal cycling, of course, tends to build up an oxide layer on the titanium and affects the oxide which increases the surface contact resistance of the joint.

Although copper layers 1 are shown on both sides of the titanium core 2, it is clear that there could be only a single layer of copper 1 using riveted or bolted joints and the same principles would apply.

In FIG. 4, the suspension rod 11 is welded to a titanium plate 12.

At its upper end, the titanium plate is bent like a crank and has alternating legs 13, 14 and 15, two of which are on one side of the suspension rod 11 and the other leg 14. is on the other side of the hanging rod.

The alternating legs 13, 14 and 15 are spaced apart to leave gaps 16 and 17 to facilitate handling of the cathode assembly in use.

Legs 13, 14 and 15 are spot welded to the suspension rod as shown at 18.

The suspension rod 11 has a central copper core 19 as shown in FIG.
has.

The copper core 19 is surrounded by a titanium sheath 20.

The titanium legs 13, 14 and 15 thus weld themselves to the titanium surface and provide good electrical contact.

The ends 21 and 22 of the suspension rods are machined to remove the titanium sheath, exposing the copper surface 23.

The copper surface 23 rests on each fine earth busbar 24 of the electrolytic cell 25, as is clear from the partial perspective view of FIG.

When using a cathode, the current path is between the copper busbar 24 and the surface 2.
3, between the copper core materials 19, through the mutual surface between the core material 19 and the exterior 20, and through the welded portion 18 to the cathode 12.

The use of the welded structure described above uses staggered legs at the cathode end in contact with the copper suspension rod, and the weld 18 is replaced by a bolt passing through the titanium cathode and the suspension rod as described above. can be compared with that of

Figure 8 shows the expected millivolt drop across the suspension rod/cathode interface in service versus time, line 26.27.28
and 29 indicate the millivolt drop of the bolted structure,
Line 30 shows the millivolt drop of the welded structure.

The scattering of the voltage drop across said mutual plane is very severe in bolted structures, where some voltage drops remain constant or only increase by a small amount, but when the voltage increases rapidly, as in the case of line 29, It can be seen that overheating can occur and the joint becomes useless.

In such a case, the cathode is pulled out from the place of use, the hanging persimmon and the surface bolts are removed, and the joint is remanufactured.

However, the voltage drop across the welded surfaces is extremely small and constant at the start of operation, since this is not a mechanical connection and does not deteriorate.

Although the legs 13, 14 and 15 are shown staggered, such an arrangement is not necessary and the legs can all be on one side, in which case the plates The main body of the suspension rod can be placed below the center line of the suspension rod to form a crank shape, or it can be installed directly downward from the line of the spot weld 18 or tilted.

Consider another arrangement in which the air gaps 16 and 17 are omitted and the plate edges are welded directly to the titanium sheath 20.

Although spot welding was used in the foregoing, other types of welding such as stitch welding or other electrical resistance welding or fusion bonding may be used if desired.

The core 19, as previously described, is made of copper, but can be made of aluminum if desired.

Although the suspension bar described above has a continuous sheath of titanium that completely surrounds the suspension bar, it is clearly within the scope of the present invention to have only a partial sheath.

Another simple way in which titanium or other valve metal plates may be metallurgically bonded to copper is by explosive welding or bonding, where a thin plate of titanium is placed on the steel and then explosively bonded in a known manner. It is.

If necessary, the hanging can also be reinforced with high-strength steel inserts as a floor to support the weight of the coated cathode in use or the weight of the operator walking over the cell surface using the hanging. .

[Brief explanation of the drawing]

Fig. 1 is a partial sectional view of the rivet joint, Fig. 2 is a partial sectional view of the bolt joint, Fig. 3 is a partial sectional view of the end of the copper/titanium mutual surface, and Fig. 4 is the suspension rod and cathode part. A perspective view of
Figure 5 is a plan view taken from the direction of the arrow ■ in Figure 4, Figure 6 is an enlarged side view taken from the direction of the arrow ■ in Figure 4, Figure 7 is a partial perspective view of the electrolytic cell and cathode assembly, and Figure 8 is a partial perspective view of the electrolytic cell and cathode assembly. The figure is a graph of millivolts versus time, where 1 is a copper plate, 2 is a titanium plate,
3 is a rivet, 7 is a bolt, 8 is a nut, 9 is a gap, 1
0 is a precipitate, 11 is a suspension rod, 12 is a titanium plate, 13
, 14.15 is a leg, 16.17 is a gap, 18 is a spot weld, 19 is a copper core, 20 is a titanium exterior, 21,
22 is an end, 24 is a bus bar, and 25 is an electrolytic cell.

Claims (1)

[Claims] 1. An aluminum or copper suspension rod with a copper or aluminum core material at least partially covered with a valve metal sheath or partial sheath by explosive welding, and one edge of at least a portion of the length of the valve metal sheath of the suspension rod. A cathode and suspension rod assembly consisting of a continuous plate of valve metal welded along only one section.