FI114925B - Method of providing a good contact surface in the rail and rail of an electrolysis container - Google Patents

Description

114925

METHOD FOR OBTAINING A GOOD CONTACT SURFACE TO THE CURRENT TRACK AND CURRENT TRACK

The invention relates to a method of forming a good contact surface on a busbar of an electrolysis pool used in electrolysis of metals. The contact surface of the current rail, i.e. the surface on which the support rod or ear of the electrode to be discharged into the basin is lowered, is coated with a highly conductive metal. The invention also relates to a busbar of an electrolysis pool, the surface of which is provided with a highly conductive coating.

10

The 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 recovery is carried out, for example, in electrolysis pools filled with sulfuric acid electrolyte 15 and electrodes made of electrically conductive material are alternately immersed in the electrolyte; anodes and cathodes.

The electrode depends on the supporting rods or ears in the electrolysis pool:. '· Which are supported on the sides of the pool.

• * * 20 Electrolysis pools are grouped in series so that the anode of the previous pool is electrically connected to the cathode of the next pool by a busbar on the wall of the '' pool. The busbar is usually copper or at least copper plated. The structure typically also includes a notched insulating rail on top of the busbar that separates the previous cathode 25 cathode from the next pool anode busbar. One end of the electrode support bar is located on top of the busbar and the other end is usually on top of the insulating rail. The metal to be produced is introduced into the process either as soluble anodes, so '! . so-called active anodes (electrorefining) or the metal is dissolved in the electrolyte, whereby the anodes used are insoluble, i.e. passive anodes (electrowinning).

• I »2

11492E

The busbar geometry may vary. A uniform triangular cross-section busbar is described, for example, in U.S. Patent 3,682,809. In other cases, the positioning of the electrodes in the pool is arranged by means of a busbar design. Such is disclosed, for example, in U.S. Patent 4,035,280, wherein the electrodes 5 are disposed in bevelled grooves at the edges of the busbar.

U.S. Patent 6,342,136, in turn, describes a longitudinally continuous main busbar provided with protrusions of various heights between which an insulating profile is disposed. One end of the cathode support bar is placed over the main busbar and the other end is placed over the copper potential equalizer rail located on the dielectric profile. When the busbar is uniform, the electrode support bars or ears can be placed at the desired position on top of the rail. In this case, the entire busbar can act as a contact surface for the support bar or the ear. If the busbar is notched or otherwise shaped so that the positions of the electrodes 15 are defined, the contact surface of the bus is the notched or shaped places.

ψ

Copper busbars have a problem with fast wear on the contact surface. The reason

• I I

: <'Probably oxidation of copper to oxide and corrosion of the oxide to copper sulphate by electrolyte. The copper sulphate formed on the contact surface further weakens the conductivity of the busbar and additionally | the parisulfate is soluble in the electrolyte. Oxidation causes an increase in voltage drop because the electrical conductivity of copper oxide is significantly lower than that of pure copper. In addition, for example, in zinc electrolysis, copper soluble in bus bars 25 unnecessarily raises the copper level of cathode zinc.

Now, a method has been developed for providing a good contact surface on a busbar of an electrolytic metal used in electrolysis of metals, wherein at least the surface of the rail is made of copper. According to the developed method 30, at least the region of the busbar in which the electrode; 'Lower, contact, plated with a highly conductive metal, or. an alloy such as silver or silver alloy. Copper and silver are bonded together 114925 3 by means of a transmission layer. By forming a metal bond between the transfer layer formed on the copper surface of the busbar and the coating material, problems caused by wear or oxidation of the contact surface are avoided. The invention also relates to a busbar made of a method and used in electrolysis pools of metals 5, in which a conductive layer is formed at least at the point of contact with the electrodes, the contact surface. When used in the text, it is also referred to as a potential equalization rail in the prior art.

10

What is claimed is essential to the invention.

It is important that the contact surface on the busbar is conductive. The use of a highly conductive metal such as silver or silver alloy as a coating material ensures efficient power supply from the busbar to the electrode. 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 made on the contact surface of the current rail does not form '·' 20 oxide films in the same way as, for example, on the copper surface. The coating ensures that the electrolytic quality level of the electrolysis is maintained: high quality even in the long term.

The silver does not form a metallurgical, highly adherent bond directly on the copper 25, but rather on the copper surface a thin transfer layer, preferably consisting of tin or a tin-plated alloy, must first be formed. The text then refers only to tin for the sake of simplicity, but also refers to other tin-dominated alloys. The tin layers can be formed in many ways as above by heating. . 30 tin plating, electrolytic plating, or actual: 'pre-plating by thermal spraying directly onto the target.

'··· The tin surface can then be silver plated. Coating of the copper contact surface of the busbar 114925 4 with silver is advantageously carried out, for example, by thermal injection or soldering.

The contact strip part of the busbar is deoxidized prior to forming the coating. It is also advantageous to carry out the operation on new rails, but especially when the method is applied to improve the electrical conductivity of used rails, it is necessary to remove oxidation. For example, removal by sandblasting.

ίο The method of coating busbars depends to some extent on the rail geometry. When the busbar or potential equalizer rail is uniform in the longitudinal direction, the coating is formed over the entire length of the rail, and then it is advantageous to form the coating by thermal injection technology, although of course soldering technology can also be used. If the busbar is provided with notches or grooves as contact surfaces for the electrodes, it is of course not profitable to coat an area other than these contact surfaces. In these cases, too, soldering is the preferred method of forming the coating.

Thermal injection technology can be used to coat the busbar with 20 silver having a melting point of 960 ° C. As coating material can be. . also uses AgCu alloy, 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.

Of the thermal injection techniques, at least gas combustion techniques have proven to be practicable in practice. Of these, High Velocity Oxy-Fuel (HVOF) is based on fuel gas or liquid and oxygen in the fueling chamber of the gun. continuous high pressure combustion and fast gas flow · 30 using a spray gun. The coating material is • fed in powder form through the carrier gas, usually axially into the ··· nozzle of the gun. In the nozzle, the powder particles heat up and produce a very high 114925 5 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 5, melts the coating material in wire or powder form. Acetylene is most commonly used as the combustion gas 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, a flaming gas flame melts the end of the wire and blows the melt with compressed air into the metal spray-coated body. The particle velocity is in the order of 100 m / s.

Thermal injection 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 in the coating of the contact rail of the busbar. Thus, the electrical conductivity of the joint is good. Joints for metals. , the process produces a eutectic rubber formed by a ternary alloy of silver, tin and copper, for example, at a temperature between 380 and 600 ° C. If necessary, a separate heat treatment may be carried out after injection to facilitate the formation of the metallurgical joint.

When soldering technology is used to form a coating on the contact surface of the busbar, the surface to be treated is cleaned and a tin layer is formed which is preferably less than 50 µm. Thereafter, the silver coating is applied by means of a suitable pick-up. The tin layer melts, and when placed on a molten tin, it is easily positioned in the correct position.

..., · The invention also relates to a busbar or. Potential rail used in an electrolysis pool. In particular, an electrically conductive layer is formed on the copper surfaces of the busbar, in particular on their contact surface which comes into contact with the electrode support bar or the ear. Electricity 114925 6 silver or an alloy such as silver copper is used as the conductive metal or alloy. The coating of the contact surface is preferably accomplished, for example, by soldering or thermal injection technology, whereby a metallurgical joint is formed between the contact surface and the coating. If the busbar 5 is uniform in the longitudinal direction, the coating is preferably formed over the entire length of the busbar. If the rail is provided with contact surfaces for the electrodes by notching or grooving, only these contact surfaces are coated according to the invention.

The method according to the invention is further illustrated by the following example and the accompanying figure 1, which shows the relative voltage drops in both the busbar and the reference rails according to the invention.

15 Example

The three electrorefining pools of copper each contained 81 electrodes, which traditionally had copper contact surfaces for the busbar. One of the ponds was provided with a solution according to the invention, whereby the contact surface of the busbar rails was silver plated.

20 The other two pools had normal copper busbars. Figure 1 shows that the voltage drop of the silver plated rails is clearly smaller! . than the voltage drop of conventional busbars. The voltage drop is calculated as the average of the electrodes. The value of 100 is taken as the voltage drop of the worst-case busbar and the voltage drop of the busbars of the other pools is stated as 25.

Claims (18)

114925 7 A method for forming a good contact surface on an electrolysis busbar, in which at least a rail surface portion s is formed of copper and the contact surface is formed by a region into which the electrode is deposited, characterized in that a contact layer is formed on the copper contact surface of the busbar and, with the transfer layer, a metallurgical joint and the coating is formed by soldering or thermal injection technology. Method according to claim 1, characterized in that the transmission layer is tin or a tin-like alloy. 15 Method according to claim 1 or 2, characterized in that the silver alloy is silver-copper. A method according to any one of the preceding claims, characterized in that the electrolysis tank is provided in addition to the busbar: T; on a potential equalizer rail, whereby a transmission layer is formed on the copper-to-electrode contact surface, after which the surface is coated with a highly conductive silver or silver alloy, whereby the coating material forms a metallurgical bond with the copper and transmission layer. Method according to one of the preceding claims, characterized in that the busbar is uniform in the longitudinal direction, whereby the coating layer 'i' is formed over the entire busbar. 30 The method according to any one of the preceding claims, characterized in that the busbar contact surfaces on which the electrode 114925 8 is applied are formed by a notch or groove, whereby the coating layer is formed on the notched or grooved areas of the busbar. 5 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. 10 Method according to one of the preceding claims, characterized in that the highly conductive coating material is in powder form. 15 Method according to claim 1 or 7, characterized in that the thermal spraying technique is flame spraying. 11. A method according to any 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 after the coating. 25 13. An electrolysis for use in the electrolysis of metals, a busbar, wherein at least the surface of the rail is made of copper and the contact surface is formed by a region into which the electrode is lowered, characterized in that a contact layer is formed on the contact surface of the busbar; wherein the copper, the transfer layer, and the coating material have formed a metallurgical joint, and that the coating layer is formed by soldering or thermal injection technology. Power bus according to Claim 13, characterized in that the transmission layer 5 is tin or a tin-predominant alloy. Power bus according to claim 13 or 14, characterized in that the silver alloy is silver-copper. ίο Busbar according to one of Claims 13 to 15, characterized in that the busbar is uniform in the longitudinal direction, the coating layer being formed over the entire busbar. 15 Busbar according to one of Claims 13 to 15, characterized in that the contact surfaces of the busbar into which the electrode is lowered are made by notching or grooving, wherein the coating layer is formed on the notched or grooved areas of the busbar. . ·· '· 20> · Power bus according to any one of claims 13 to 15, characterized in that the bus is a potential equalizer rail.