FI114924B - Method for providing a good contact surface in an electrode holder arm and holder arm - Google Patents

Description

114924

METHOD FOR GETTING A GOOD CONTACT SURFACE IN THE ELECTRODE SUPPORT BAR AND THE SUPPORT BAR

The invention relates to a method of forming a good contact surface 5 on an electrode support bar, at least part of which is copper. In the method, a conductive layer is formed at least at one end on the copper portion of the support bar. The highly electrically conductive layer forms a metallic bond with the support bar of copper and is preferably achieved either by thermal injection-lo coating or by soldering. The invention also relates to the copper rod electrode support, either partially or completely, at least one end of which is coated with a highly conductive material.

Production of many metals such as copper, zinc and nickel involves an electrolytic step in which the pure metal produced is deposited on the cathode by an electric current and impurities remain in solution. Electrolytic: The recovery is carried out, for example, with an electrolyte containing sulfuric acid ·: · in filled electrolysis pools and immersed alternately in electricity; electrodes made of rope conducting material; anodes and cathodes.

20 The anodes and cathodes generally consist of a plate portion that is submerged in a basin: and a support bar or ears attached to the top of the plate portion. The electrode rests in the electrolysis pool on support bars or ears supported on the sides of the pool. Rods or ears connect the electrodes to the electrical circuit via bus rails located at the sides of the pool. The other end 25 of the support bar is generally located on the insulating rail. In one method, the other end of the support bar is also located on a conducting and leveling rail. The metal to be produced is introduced into the process either as soluble anodes, ··· 'electrorefining' or the metal is in the electrolyte ·: ··; dissolved, whereby the anodes used are insoluble or passive anodes (electrowinning).

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The electrode carrier rods for electrolysis may, for example, have a steel core and a copper sheath. Such a support bar is described, for example, in U.S. Patent No. 4,871,436. The end of the support bar acts as a contact surface against the busbar rail.

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Whole copper support bars can be used, for example, in electro-refining, where copper seed plates are used as cathodes. In these, the end of the support bar is automatically in contact.

ίο Electrode support bars can also use a copper core, whereby the bar shield is made of another metal or metal compound. Depending on the situation, a sheath made of steel, titanium, or lead, to which the electrode plate itself is attached, is used, as the case may be. Steel and titanium sheaths are used in particular in cathodes and 15 lead sheaths in anodes such as zinc electrolysis, which operates on an electro-winning principle. Contact surface of support bar with shield _. formed, for example, by machining the copper sheath open ... at the end of the support bar, or by using a casting technique to expose the surface of the copper core. The copper core is thus used as a contact surface, which is placed on top of the busbar even by electrolysis.

WO 00/17419 describes a method for manufacturing a permanent cathode hanging rod, wherein the hanging rod is made of a rigid metal outer jacket and a highly conductive core attached thereto. According to the publication, the outer-25 sheath is made of stainless steel and the core is copper or aluminum. The parts of the pendulum rod are joined to each other either by pulling with a mandrel, by hammering or by casting. The steel rod is removed from the finished rod at the end of the rod ... ... so that the exposed copper core is exposed and can be used as a contact surface.

.. WO 02/40749 discloses another method for making an electrode hanging rod. According to this method, an electrically conductive core member, as well as a connecting material, is placed inside the jacket member and the suspension rod 3 114924 is heat treated. During the heat treatment, a metallurgical bond is formed between the core member and the jacket member by means of a bonding agent. Tin is mainly used as a bonding agent. The publication does not specify how the contact surface is formed at the end of the suspension rod.

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For brackets with a copper contact surface, rapid wear of the contact surface is a problem. The main reason is probably the oxidation of copper to the oxide and the corrosion of the oxide to copper sulfate by the electrolyte. The copper sulphate formed on the contact surface further weakens the electrical conductivity of the supporting 10 bar. Oxidation causes an increase in voltage drop because the electrical conductivity of copper oxide is significantly lower than that of pure copper. The problems caused by oxidation are exacerbated by, for example, the lead anode with copper-containing support bars, which are otherwise quite long-lived.

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A method has now been developed to provide a good contact surface for an electrode support bar for metal electrolysis, wherein at least part of the bar is made of copper. Part of the support bar may be made of other material, such as steel, titanium or lead, or the support bar 20 is entirely made of copper. According to the developed method, at least the area on the underside of one end of the support bar, the contact surface which comes into contact with the busbar of the electrolysis pool, is coated with a highly conductive metal such as silver or silver alloy. Copper and silver are bonded together by means of a transmission layer. By forming a metallic joint between the copper portion of the support bar 25 and the transmission layer formed on its underside and the coating material, problems caused by wear or oxidation of the contact surface are avoided. The invention also relates to a method for producing an electrode support rod for electrolysis, the electrically conductive layer of which is formed at least at one end of which has a copper conductive contact surface.

What is claimed is essential to the invention.

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It is important that the contact surface on the electrode support bar is conducting well. The use of a highly conductive metal such as silver or an alloy of silver as a coating material ensures efficient power supply to the electro-5. The metallurgical basis for the use of silver is that, although it forms an oxide on its surface, at relatively low temperatures the oxides are no longer stable but decompose back to the metallic form. Em. therefore, the silver coating on the contact surface of the support bar does not form oxide films in the same way as, for example, on the copper surface, ίο The coating ensures that the electrolysis quality level remains high in the long run.

The silver does not form a metallurgical, highly adherent bond directly onto the copper, but rather, a thin transfer layer must first be formed on the copper surface, preferably consisting of tin or a tin-plated alloy. The text then refers only to tin for the sake of simplicity, but also refers to other tin-dominated alloys. The tin layer can be formed in many ways such as pre-heating, tin-plating, electrolytic plating, or thermal injection prior to the actual plating directly on the surface of the object. The tin surface is then coated with silver or silver alloy.

. ' · The coating of the copper contact surface of the bracket with silver is advantageously carried out by means of, for example, thermal injection or soldering.

The copper portion acting as a contact surface at the end of the support bar is deoxidized prior to forming the coating.

"It is also advantageous to carry out the operation on new rods, but especially when the method is applied to improve the electrical conductivity of the used rods..., Deoxidation is necessary. Removal, for example by sandblasting. The contact surface may also consist of a notch formed on the underside of the copper part of the rod 5 114924. In this case, the conductive rods can be extended in a simple manner by the need for a contact surface at the ends of the rod. the coating is renewed, the contact surfaces should be straightened out because the wear of the contact surfaces may have caused the contact to no longer have the desired geometry. this reduces the power supply to the cathode.

ίο Another advantageous way of coating the contact surfaces of the support bar is silver plating using thermal injection technology, since the melting point of silver is 960 ° C. AgCu alloy may also be used as coating material, for example in the form of wire or powder. The melting point of the eutectic AgCu alloy is even lower than the melting point of silver and is thus suitable for coating the contact surfaces in question. technique.

In practice, thermal injection techniques include at least gas combustion.

Mileage-based technologies have proven to be useful. Of these, High Velocity Oxy-Fuel (HVOF) is based on the continuous combustion of fuel gas or liquid and oxygen at high pressure and the rapid flow of gas through a spray gun. The coating material is fed in powder form, by carrier gas, most commonly axially to the gun nozzle. In the nozzle, the powder particles heat up and produce a very high speed of motion (several hundred m / s) and are applied to the body to be coated.

'In conventional flame spraying, the combustion gas / oxygen mixture, when burned, melts the coating material in wire or powder form. Acetylene is the most commonly used gas for combustion,. · · 30 because of its extremely hot flame.

The coating material wire is guided through the wire nozzle by means of a feeding device operated by a compressed air turbine or an electric motor. In front of the wire nozzle 6 114924, a flaming gas flame melts the end of the wire and the melt is blown by compressed air into the metal spray coated body. The particle velocity is in the order of 100 m / s.

5 Thermal spraying technology melts the coating material and, because of the high temperature of the droplets of silver-containing coatings, metallurgical bonding between the copper, tin and the coating material is created by coating the copper end of the supporting rod. Thus, the electrical conductivity of the joint is good. The method of bonding metals produces a eutectic rubber formed by a ternary alloy of silver, tin and copper in the bonding region, for example, at a temperature between 380 and 600 ° C. If necessary, a separate heat treatment may be performed after injection to facilitate the formation of a metallurgical joint.

When the soldering technique is used to form a coating on the contact surface of the support bar, the surface to be treated is cleaned and a tin layer, preferably less than 50 µm, is formed. After that ... the silver plating is carried out using a suitable burner.

· The tin layer melts and when placed on a molten tin, it is easily positioned in its 20 position.

The invention also relates to a copper-containing support bar for an electrode used in electrolysis. In particular, an electrically conductive layer is formed on the copper surfaces at the ends of the support bar, in particular in the area on the underside thereof, the contact surface which comes into contact with the busbar of the electrolysis pool. As a conductive metal or alloy, silver is used, or a silver alloy such as silver copper.

The coating of the contact surface is preferably carried out, for example, by soldering or thermal injection technology, whereby there is, between the contact surface and the coating. '30 formed metallurgical joint.

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The method of the invention is further illustrated by the following figures and examples, wherein Figure 1 shows the relative voltage drops of new cathodes as a function of relative compressive force, and Figure 5 shows the relative voltage drops of used cathodes as a function of relative compressive force.

Example

Copper electrolysis (cathode) cathodes of the size 10 production scale were kept in the test vessel during the normal production period. Some of the cathode support bars were conventional, i.e. having a common copper contact surface. In some cases, a silver coating was formed on the contact surface of the support bars by spray coating. The contact surfaces of the busbars of the electrolysis pools were copper.

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Figure 1 is a graph showing the results of electrolysis of new cathodes. Relative voltage of conventional copper contact surfaces:. Losses are significantly higher than those of silver plated ·. voltage drops of contact surfaces as a function of relative compressive force.

·· 20 Compressive force means the force exerted by the cathode on the busbar.

The relative compression force takes into account the increase in cathode weight as the electrolysis cycle progresses, and the value 100 corresponds to the average cathode weight at the end of the cycle.

Figure 2 shows the results of the test corresponding to Figure 1 when the test is carried out with commercially used spent cathodes. The relative voltage drop is calculated to be 100, its worst value when the electrolysis cycle begins with the copper cathode contact cathodes used.

·; ·: The relative voltage drop and the relative compressive force of Figure 1 are on the same scale as Figure 2. The pictures also show that in all cases, the voltage drop is greatest when the cathode weight is the smallest, but as the cathode weight rises, contact with the busbar is improved. The figures also show that the voltage drop of the 8114924 bars treated in accordance with the invention is clearly less than that of conventional contact surfaces. The difference is particularly evident in the cathodes used. The example also shows that the silver contact surface is not as dependent on the compression force as the copper contact surface.

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Claims (18)

114924 A method for providing a good contact surface at the end of an electrode support bar for use in metal electrolysis, wherein the electrode consists of a plate portion submerged in an electrolysis basin and a support bar in which at least a portion of the bar is formed of copper. a transfer layer is formed on the underside of the copper end of the supporting rod, the contact surface, after which the contact surface is coated with silver or a silver alloy forming a metallurgical connection with the copper and transfer layer, whereby the coating is formed by soldering or thermal injection technology. 15 Method according to Claim 1, characterized in that the transmission layer is tin or a tin-predominant alloy. Method according to claim 1 or 2, characterized in that: ·. 20 silver alloy is silver-copper. ··; Method according to one of the preceding claims, characterized in that the copper core part of the support bar is surrounded by a sheath made of stainless steel, titanium or lead, which is removed at least from the underside of one end of the support bar. A method according to any one of claims 1 to 3, characterized; . because the backing is made entirely of copper. Method according to one of Claims 1 to 3, characterized in that the sheath portion of the support bar is made of copper. 114924 Method according to claim 1, characterized in that the thermal injection technique is based on the combustion of gas. A method according to claim 1 or 7, characterized in that the thermal injection technique is high-speed flame spraying. Method according to one of the preceding claims, characterized in that the highly conductive coating material is in powder form. Method according to Claim 1, characterized in that the thermal spraying technique is flame spraying. Method according to one of claims 1 to 7 or 10, characterized in that the highly conductive coating material is in the form of a wire. Method according to one of the preceding claims, characterized in that the contact surface is subjected to a heat treatment: *. 20 after coating. 13. Electrode support bar for metal electrolysis; . wherein the plate portion of the electrode is intended to be submerged in an electrolysis pool and the electrode support bar is supported at its ends at the edges of the electrolysis pool, wherein at least a portion of the support bar is formed of copper and at least one of the support bar; forming a contact surface on the busbar, characterized in that a contact layer is formed on the contact surface of the support bar, after which the contact surface is coated with silver or a silver alloy coated by soldering or thermal injection, whereby the copper, transfer layer and metallic material are formed. 114924 Support bracket according to claim 13, characterized in that the transmission layer is of tin or a tin-predominant alloy. 15. Support bracket according to claim 13 or 14, characterized in that the highly conductive coating layer is a silver-copper alloy. Carrier bar according to one of Claims 13 to 15, characterized in that the copper core of the carrier bar is surrounded by a sheath made of stainless steel, titanium or lead, which is removed at least from the underside of one end of the carrier bar. Support bar according to one of Claims 13 to 15, characterized in that the jacket part of the support bar is made of copper. Support bar according to one of Claims 13 to 15, characterized in that the support bar is entirely made of copper. 1