DEVICE FOR ELECTROLYTICALLY COATING A WIRE

Description

[0001] The invention relates to a device for the continuous electrolytic coating of a wire in a continuous process.

[0002] It is well known to electrolytically coat metallic objects such as wires in a galvanic system, for example, by tinning them. The wire and the coating material are immersed in an electrolyte bath, thereby creating an electrically conductive bond. If the wire and the coating material are then connected to opposite poles of a direct current source, an electric current flows at a sufficiently high voltage, causing the ions in the electrolyte to migrate toward the wire or coating material (electrolysis).

[0003] The wire is connected to the negative terminal of the direct current source and forms the cathode. The positively charged metal ions migrate in the electrolyte to the cathode and absorb electrons there (electrochemical reduction), forming metal atoms that attach to the wire to be coated. A distinction is made between soluble anodes and insoluble anodes. With soluble anodes, the anode metal dissolves, releasing electrons into the circuit (electrochemical oxidation) and enters the electrolyte (usually a salt solution) as a metal ion. Insoluble anodes, on the other hand, do not dissolve but only serve to contact the electrolyte to form the metal ions within the electrolyte (usually a metal-salt solution). In the case of soluble anodes, these ions dissolve over time; in the case of insoluble anodes, the electrolyte becomes depleted of metal over time.

[0004] In acidic electrolytes, such as methanesulfonic acid-based tin electrolytes, there is always a difference between the anodic and cathodic current efficiency when using soluble anodes. The anodic current efficiency is typically close to 100%, while the cathodic current efficiency, for example, in the case of methanesulfonic acid-based tin electrolytes, is typically between 95% and 97%. The cathodic current efficiency depends particularly on the coating material, the electrolyte, and the operating parameters (bath temperature, bath agitation, current density, etc.).

[0005] The difference between anodic and cathodic current efficiency described above results in an increase in the metal concentration in the electrolyte in conventional electroplating systems, which must be corrected when a predetermined upper threshold is reached. To keep the metal concentration in the electrolyte within a predetermined range, the electrolyte can be regenerated regularly or continuously, for example.

[0006] On the other hand, when using insoluble anodes, it is necessary to correct the metal concentration when a predetermined lower threshold is reached. To maintain the metal concentration in the electrolyte within a predetermined range, it is also possible in this case to regenerate the electrolyte regularly or continuously. For example, DE 195 39 865 A1 discloses a continuous electroplating system with insoluble anodes in the electrolytic cell, wherein the electrolyte is continuously enriched with metal ions in a regeneration chamber.

[0007] Furthermore, DE 195 39 865 A1 describes the use of insoluble anodes in the electrolytic cell, which are shielded from the electrolyte by diaphragms, and of soluble anodes in an external regeneration chamber to supplement the metal content of the electrolyte.

[0008] US 5,100,517 discloses an apparatus for depositing a metal layer on a wire in an electrolyte bath with an insoluble electrode, the apparatus also having a soluble electrode.

[0009] It is the object of the present invention to provide an improved device for electrolytically coating a wire.

[0010] This object is achieved by the teaching of the independent claims. Particularly preferred embodiments of the invention are the subject of the dependent claims.

[0011] The device according to the invention for electrolytically coating a wire comprises an electrolyte container containing an electrolyte; a first direct current source; at least one soluble anode, which is at least partially immersed in the electrolyte in the electrolyte container and is electrically connected to a positive pole of the first direct current source; and at least one cathode terminal, which is electrically connected to a negative pole of the first direct current source and to which a wire to be coated, immersed in the electrolyte in the electrolyte container, can be electrically and movably connected. This device is characterized by a second direct current source, which can be operated independently of the first direct current source; and at least one insoluble anode, which is at least partially immersed in the electrolyte in the electrolyte container and is electrically connected to a positive pole of the second direct current source.

[0012] In the device according to the invention, the metal concentration in the electrolyte can be controlled by the at least one insoluble anode. Since the second direct current source can be operated independently of the first direct current source, with appropriate operation of the two direct current sources, it is possible to compensate for the difference between the anodic and cathodic current yield for the at least one soluble anode via the at least one insoluble anode, thus keeping the metal concentration constant within a predetermined range.

[0013] The second DC power source is preferably operated continuously or is only switched on as needed.

[0014] The term "electrolyte" in this context refers to a liquid that can dissociate into ions and is therefore suitable for electrolysis, particularly in a galvanic plant. The chemical composition of the electrolyte depends in particular on the material of the wire to be coated, the material of the anodes, especially the soluble anodes, and the desired coating material. A methanesulfonic acid electrolyte is preferably used for tinning a (copper) wire.

[0015] In this context, the term "DC power source" refers to any type of device capable of providing a DC voltage at its output and thus supplying a connected load with DC current. Batteries, accumulators, fuel cells, and particularly preferably rectifiers are preferably used as DC power sources. The rectifiers are preferably connected downstream of an AC power source such as an AC generator or a power grid. A DC power source is preferably composed of a DC voltage-providing device or of several (preferably essentially identical) DC voltage-providing devices connected in parallel.

[0016] In this context, a "soluble anode" refers to an anode that dissolves over time in the electrolyte through electrochemical oxidation. The metal forming the coating material passes into the electrolyte as a metal ion, releasing electrons into the circuit. A tin anode is preferably used for tinning a (copper) wire.

[0017] In this context, the "insoluble anode" refers to an anode that essentially does not dissolve in the electrolyte over time, but serves only to electrically contact the electrolyte. Insoluble anodes can also be referred to as dimensionally stable or inert anodes. Insoluble anodes preferably consist essentially of stainless steel, titanium, or platinum and / or are provided with a protective layer of titanium, platinum, iridium, ruthenium, or the like.

[0018] The device has at least one soluble anode and at least one insoluble anode, which are at least partially immersed in the electrolyte. In the device according to the invention, both anode types are immersed in the same electrolyte into which the wire to be coated is also immersed. One, two, three, four, or more soluble anodes are used; in the case of a continuous electroplating system, a larger number of soluble anodes is used depending on the size of the continuous electrolyte container. In addition, one, two, three, four, or more insoluble anodes are used. The effective total surface area of ​​all soluble anodes is preferably larger than the effective total surface area of ​​all insoluble anodes. The soluble and insoluble anodes are preferably of substantially equal dimensions. In this case, the number of insoluble anodes is preferably smaller than the number of soluble anodes.

[0019] The wire to be coated, which is immersed in the electrolyte in the electrolyte container, can be connected to a cathode terminal of the device, which is electrically connected to a negative pole of the first direct current source. In this context, the cathode terminal is a device suitable for establishing an electrically conductive connection with the wire to be coated. This connection is preferably detachable to allow easy replacement of the wire to be coated. For a continuous electroplating system, this connection is designed to be movable according to the invention. The cathode terminal is preferably also electrically connected to the negative pole of the second direct current source, so that both direct current sources are at the same potential.

[0020] According to the invention, the current intensity of the second direct current source can be adjusted independently of the current intensity of the first direct current source. By regulating the current intensity in the circuit of the at least one insoluble anode, the difference between the anodic and cathodic current efficiency for the at least one soluble anode can be compensated via this at least one insoluble anode, thus keeping the metal concentration constant within a predetermined range.

[0021] According to the invention, a control device is provided for controlling the first direct current source and the second direct current source depending on at least one electrolytic parameter of the electrolyte in the electrolyte container. According to the invention, both direct current sources are controlled to regulate the current intensities in both circuits. In this context, an "electrolytic parameter" is understood to mean an operating parameter of the device that influences the electrolysis in the electrolyte and thus the electrolytic coating of the wire to be coated. The electrolytic parameters in this context include, in particular but not exclusively, the metal (ion) content, the acid content, the pH value, and the conductivity of the electrolyte, as well as the current intensity and the flow rate. According to the invention, at least one of the electrolytic parameters is the metal ion content.

[0022] According to the invention, a measuring device is provided for detecting at least one electrolytic parameter, namely at least the metal ion content, of the electrolyte in the electrolyte container. This measuring device is preferably a measuring device separate from the electrolyte container, to which electrolyte samples, preferably regularly taken from the electrolyte container, are fed for analysis, or a measuring device in contact with the electrolyte in the electrolyte container in order to be able to perform a substantially continuous analysis.

[0023] The device according to the invention is designed as a continuous device for the continuous electrolytic coating of a wire.The continuous device can be used for coating wire. A method for the continuous electrolytic coating of a wire in a continuous process, which is described for a better understanding of the invention, comprises the steps of: immersing a wire to be coated in an electrolyte container containing an electrolyte, into which at least one soluble anode, which is electrically conductively connected to a positive pole of a first direct current source, and at least one insoluble anode, which is electrically conductively connected to a positive pole of a second direct current source, are at least partially immersed; electrically connecting the wire to be coated to a negative pole of the first direct current source and a negative pole of the second direct current source; and operating the second direct current source independently of the first direct current source.

[0024] With this method, the same advantages can be achieved as with the device of the invention described above. Regarding the advantages, definitions, and preferred embodiments, reference should therefore be made only to the above statements in connection with the device according to the invention.

[0025] In a preferred embodiment of the method, the current intensity of the first direct current source and the current intensity of the second direct current source are set differently from one another.

[0026] According to the invention, a total current strength of the first direct current source and the second direct current source is kept substantially constant.

[0027] According to the invention, the first direct current source and the second direct current source are controlled as a function of at least one electrolytic parameter of the electrolyte in the electrolyte container, namely at least the metal ion content.

[0028] In yet another embodiment of the method, the at least one electrolytic parameter of the electrolyte in the electrolyte container is recorded regularly or continuously.

[0029] It should be noted at this point that the device of the invention and the method are not limited to any specific wire to be coated, any specific electrolyte, any specific coating material, any specific soluble anodes, and any specific insoluble anodes.

[0030] The above and other features and advantages of the invention will become more apparent from the following description of a preferred, non-limiting embodiment with reference to the accompanying drawings, in which the sole Fig. 1 , largely schematically, the structure of a continuous electroplating system according to a preferred embodiment of the present invention.

[0031] The electroplating system has a large, elongated electrolyte tank 10 for holding a suitable electrolyte 12. For wire tinning, for example, a methanesulfonic acid electrolyte 12 is used.

[0032] A plurality of soluble tin anodes 14 are arranged in the electrolyte container 10. As shown in Fig. 1 As indicated, these are preferably arranged in two rows, each in pairs opposite each other. The tin anodes 14 are each immersed in the electrolyte 12 in the electrolyte container 10.

[0033] The tin anodes 14 are all electrically connected to a positive terminal of a first direct current source 16. The first direct current source 16 is, for example, a rectifier connected to a power grid or an alternating current generator. The first direct current source 16 is designed, for example, for a total current of approximately 6,500 A.

[0034] The wire 18 to be coated is immersed in the electrolyte 12 in the electrolyte container 10 in a continuous process. For this purpose, appropriate conveying devices are available, which are Fig. 1 are not shown. The conveying speed of the wire 18 through the electrolyte 12 is adjusted to the desired coating thickness.

[0035] The wire 18 to be coated is electrically connected to a cathode terminal 20, which is electrically connected to the negative pole of the first direct current source 16. This creates a closed circuit from the positive pole of the first direct current source 16 via the soluble tin anodes 14, the electrolyte 12, the wire 18, and the cathode terminal 20 to the negative pole of the first direct current source 16.

[0036] In addition to the soluble tin anodes 14, insoluble anodes 22 are provided in the electrolyte container 10 in such a way that they are also immersed in the electrolyte 12. As in Fig. 1 As indicated, the soluble anodes 14 and the insoluble anodes 22 are essentially the same size and shape, but the number of insoluble anodes 22 is significantly smaller than the number of soluble anodes 14. The effective total surface area of ​​all soluble anodes 14 immersed in the electrolyte 12 is thus significantly larger than the effective total surface area of ​​all insoluble anodes 22.

[0037] The insoluble anodes 22 are all electrically connected to a positive pole of a second direct current source 24. Similar to the first direct current source 16, the second direct current source 24 is, for example, a rectifier connected to a power grid or an alternating current generator. The second direct current source 24 is designed, for example, for a total current in the range of approximately 50 to 150 A.

[0038] The cathode terminal 20 contacting the wire 18 to be coated is also connected to the negative pole of this second DC power source 24. Thus, the negative poles of the first and second DC power sources 16, 24 are at the same potential.

[0039] According to the invention, the first DC power source 16 and the second DC power source 24 can be operated independently of one another. In particular, the current strengths of the two DC power sources 16, 24 can be adjusted independently of one another.

[0040] For this purpose, a control device 26 is provided which controls the first direct current source 16 and the second direct current source 24.

[0041] This control device 26 is connected to a measuring device 28, which is designed to detect at least one electrolytic parameter of the electrolyte 12 in the electrolyte container 10. This can be done, for example, continuously by directly measuring the parameter in the electrolyte container 10 or by regularly taking samples from the electrolyte container 10 and subsequently analyzing them separately from the electrolyte container.

[0042] The electrolytic parameter is an operating parameter that influences the electrolysis in the electrolyte and thus the electrolytic coating of the wire 18 to be coated. Electrolytic parameters measured by the measuring device 28 include, for example, the metal (ion) content, the acid content, the pH value, and / or the conductivity of the electrolyte 12, but according to the invention, at least the metal ion content. Further operating parameters that can be measured by the measuring device 28 in this context are the current intensity and the throughput speed, which also influence the electrolytic coating of the wire 18.

[0043] The current calculated for the coating process, for example, corresponds to 100%, meaning that the metal ions required for the desired coating thickness pass from the soluble anodes 14 into the electrolyte solution 12. The cathodic current efficiency, in contrast, is only approximately 97%. Therefore, the metal (ion) concentration in the electrolyte 12 would increase over time.

[0044] To prevent this, in the device according to the invention, the second direct current source 24 can be switched on by the control device 26, thus compensating for the missing 3% of the cathodic current yield. Since the insoluble anodes 22 do not release metal ions into the electrolyte, but only serve to supply current, the metal concentration in the electrolyte can be kept essentially constant or constant within a predetermined range.

[0045] This is illustrated in more detail using the example of wire tinning in a methanesulfonic acid electrolyte. With a wire diameter of approximately 1.6 mm and a desired tin coating thickness of approximately 5 µm, the wire 18 is conveyed through the electrolyte 12 at a speed of approximately 10 m / s.

[0046] At a tinning current of approximately 3,000 A (corresponding to an anodic current efficiency of the soluble tin anodes 14 of approximately 100%) and a cathodic current efficiency of approximately 97%, the control device 26 controls the second direct current source 24 in such a way that it compensates for the current efficiency difference of approximately 3%, ie provides a current of approximately 90 A (= 3% × 3,000 A).

[0047] In addition to keeping the metal (ion) concentration in the electrolyte 12 constant, the invention also makes it possible to correct an excessively high metal content in the electrolyte 12. If the metal (ion) concentration in the electrolyte 12 is too high, which is detected by the measuring device 28, the current intensity of the first direct current source 16 can be reduced and the current intensity of the second direct current source 24 can be increased accordingly by the control device 26 in the device according to the invention. If the increase in the current intensity of the second direct current source 24 is greater than the reduction in the current intensity of the first direct current source 16, the metal content in the electrolyte 12 can be reduced again over time.

Claims

1. Device for continuously electrolytically coating a wire (18) using a throughput process, comprising: an electrolyte container (10) with an electrolyte (12); a first DC power source (16); at least one soluble anode (14) which is at least partially immersed into the electrolyte (12) in the electrolyte container (10) and which is electrically conductively connected to a positive pole of the first DC power source (16); and at least one cathode terminal (20) which is electrically conductively connected to a negative pole of the first DC power source (16) and to which a wire (18) to be coated which is immersed into the electrolyte (12) in the electrolyte container (10) can be electrically conductively connected, a second DC power source (24), which can be operated independently of the first DC power source (16); and at least one insoluble anode (22), which is at least partially immersed into the electrolyte (12) in the electrolyte container (10) and which is electrically conductively connected to a positive pole of the second DC power source (24), a measuring device (28) for detecting at least one electrolytic parameter, namely at least a metal ion concentration, of the electrolyte (12) in the electrolyte container (10); a control device (26) for driving the first DC power source (16) and the second DC power source (24) as a function of the at least one electrolytic parameter, namely at least of the metal ion concentration, of the electrolyte (12) in the electrolyte container (10), characterized in that the second DC power source (24) can be operated in such a way that the total current of the first DC power source (16) and the second DC power source (24) is kept substantially constant, in that the control device (26) is adapted to reduce the current of the first DC power source (16) and to increase the current of the second DC power source (24) accordingly in order to correct a metal ion concentration in the electrolyte (12) that is too high.

2. Device according to claim 1, characterized in that a plurality of soluble tin anodes (14) is provided, the soluble tin anodes (14) and the insoluble anodes (22) being substantially equally dimensioned and the number of insoluble anodes (22) being smaller than the number of soluble tin anodes (14), so that the effective total surface area of all soluble tin anodes (14) is greater than the effective total surface area of all insoluble anodes (22).