Copper wire and method and equipment for the production of copper wire

Abstract

A copper wire has an average copper content of at least 99.95 wt.% and at least one accompanying element alloyed with the copper. The ratio of the percentage by weight of the accompanying element and the percentage by weight of the residual oxygen concentration has a value in the range of 0.8 to 1.7. The percentage by weight of the accompanying element varies along a length of wire by a maximum of 25%, based on the maximum percentage by weight of the accompanying element. The copper wire is produced by a process that includes a casting operation followed by further processing. The copper melt is protected from the surrounding atmosphere until it has solidified. To guarantee exact alloying of the accompanying element, the equipment for the production of the copper wire has an automatic metering control system connected to a metering device.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to copper wire with an average copper content of at least 99.95 wt.% and at least one accompanying element alloyed with the copper.

2. Description of the Related Art

The invention also relates to a method for the production of copper wire with an average copper content of at least 99.95 wt.%, in which at least one accompanying element is alloyed with the copper and in which the production process comprises a casting operation and possibly subsequent rolling and/or drawing operations.

Finally, the invention relates to equipment for the production of copper wire, which comprises at least a furnace for the production of a copper melt and a casting machine. Machines for rolling and/or drawing can be added downstream and can be interlinked.

In a typical production process for copper wire, the copper is first melted down and then fed to a continuous casting installation, in which it solidifies into a strand. This copper strand is shaped downstream (depending on the application, by rolling, extrusion, or drawing) to produce copper wire with a predeterminable diameter or a profile with a predeterminable cross-sectional geometry. This can also be followed by heat treatments to produce a desired combination of strength and deformability. In a final finishing step, the copper wire or profile that has been produced is typically wound on reels, in drums or similar supporting devices. The copper wire or profile produced in this way is used principally for electrical applications.

Apart from the special case of the production of resistance wire, a typical requirement is the achievement of the highest possible electrical conductivity of the wire or profiles. This typically requires, above all, the production of a high-purity copper melt with the greatest possible exclusion of accompanying elements.

One method for reducing the fraction of accompanying elements in the copper melt consists in presetting a suitable oxygen concentration of the copper melt and in this way systematically removing any accompanying elements that may still be present by reacting them with the oxygen. A portion of the resulting oxides of the accompanying elements floats on the copper melt as dross and can be removed from the surface. The remaining portion of the oxides is precipitated at the grain boundaries with no adverse effect on the electrical conductivity, so that the accompanying elements bound in the oxides are no longer dissolved in the copper matrix.

However, products produced from high-purity copper melts (e.g., wire or profiles) have the disadvantage that with increasing purity of the material and the increasing crystallite size that accompanies increasing purity, the combinations of strength and deformation properties that can be realized and the fatigue-strength properties become less favorable. This results, for example, in increased risk of fracture of the copper wire or profiles.

Furthermore, wire/profiles produced from high-purity copper have a relatively low recrystallization temperature after cold working. Although this is desired in some applications, in many applications it has adverse effects, since the production-related or process-related thermal stability requirements (i.e., retention of mechanical properties even at elevated temperatures) cannot be fulfilled.

Independently of this, under certain circumstances the resistance of the copper wire/profiles to hydrogen penetration decreases at oxygen concentrations ³ 5 ppm (=g/t), since the hydrogen can be oxidized by the oxygen to water vapor, which damages the grain boundaries. Therefore, conventional oxygen-containing copper wire tends to be susceptible to so-called hydrogen damage, which damages the wire material.

SUMMARY OF THE INVENTION

The object of the present invention is to produce copper wire of the aforementioned type in such a way that an optimum combination of the specified material properties is achieved. In particular, a hydrogen-resistant wire with high electrical conductivity is to be produced, which offers favorable combinations of mechanical properties after the necessary production steps due to its homogeneous microstructure. In addition, the thermal stability is to be systematically adjusted.

In accordance with the invention, this object is achieved in that, based on a high-purity copper melt, the ratio of the percentage by weight of the accompanying element and the percentage by weight of oxygen, which is adjusted within narrow tolerance limits, has a value in the range of 0.8 to 1.7, and that the percentage by weight of the accompanying element varies along a length of wire by a maximum of 25%, based on the maximum percentage by weight of the accompanying element.

A further object of the invention is to improve a method of the aforementioned type in such a way that the production of copper wire with optimized material properties is assisted or made possible.

In accordance with the invention, this object is achieved by protecting the copper melt from the surrounding atmosphere until it has solidified and by adding the accompanying element in an amount such that the ratio of the percentage by weight of the accompanying element and the percentage by weight of the systematically adjusted oxygen concentration of the copper melt is adjusted to a value in the range of 0.8 to 1.7, and the ratio is maintained at an essentially constant value along the length of the wire.

An additional object of the invention consists in designing equipment of the aforementioned type in such a way that it assists the production of copper wire with material properties that are optimized and essentially constant even in the case of large production amounts.

In accordance with the invention, this object is achieved by connecting a metering device for metering the accompanying alloying element to an automatic metering control system, which is connected to at least one sensor for detecting the furnace weight and a device for measuring the casting output.

In accordance with the invention, the relation between the percentage by weight of the accompanying element and the residual oxygen concentration makes it possible to achieve both high conductivity and a good combination of mechanical properties (strength, elongation, fatigue strength), as well as hydrogen resistance of the copper wire. The fraction of the accompanying element in accordance with the invention makes it possible, upon solidification of the copper melt, for the grain boundaries that form to be optimized with respect to both electrical conductivity and mechanical properties and at the same time for the average grain size to be small.

To achieve hydrogen resistance and the optimum compromise between a good combination of high mechanical strength and high deformability, on the one hand, and good conductivity, on the other hand, it is advantageous for the accompanying element to be phosphorus.

The use of boron as the accompanying element is also advantageous.

It is also possible to use lithium as the accompanying element.

The desired material optimization can be achieved especially if the copper contains the accompanying element in a concentration of 5 ppm to 60 ppm.

A good combination of optimum conductivity and strength and at the same time the highest possible deformability can be achieved, e.g., in the soft state, if the average grain size has a maximum value of 30 micrometers.

In a typical realization, the accompanying element bound in the reaction product is at least partly deposited at the grain boundaries.

Furthermore, it is also possible for the accompanying element to be at least partly incorporated in elemental form in the atomic lattice of the corresponding grains.

For large-scale industrial applications, it has been found to be advantageous for the percentage by weight of the accompanying element to vary along the length of the wire by a maximum of 20%, based on its maximum percentage by weight.

The amount of the accompanying element contained in the copper can be measured by the use of at least one test probe for determining the accompanying element in the copper.

Simple measurement can be accomplished by using a test probe to determine the concentration of the accompanying element in the molten copper zone.

Measurement in the final product can be accomplished by using a test probe to determine the concentration of the accompanying element in the solidified wire zone. In a typical process sequence, the conductivity of the copper is adjusted by the concentration of the accompanying element in the copper.

To compensate for at least partial binding of the alloyed accompanying element by oxygen contained in the copper melt, it is proposed that an increased proportion of the accompanying element be added to the copper according to a suitable algorithm when there is an increased oxygen concentration.

One production variant consists in producing the copper wire by direct casting.

Moreover, it is also possible for the copper wire to be produced from a cast strand by subsequent hot working.

Another process variant, especially with the inclusion of a heat treatment after the deformation, consists in producing the copper wire by cold working.

A typical site for adding the accompanying element to the copper is in the region of a runner.

It is also possible for the accompanying element to be added to the copper in the region of a lower crater.

In accordance with another process variant, it is also possible for the accompanying element to be added to the copper in the region of a casting trough.

It is also possible for the accompanying element to be added in the region of an upper crater.

In accordance with an alternative embodiment, it is possible for the accompanying element to be added to the copper in the region of a holding furnace.

Finally, it is also possible for the accompanying element to be added to the copper in the region of a molten stream.

A relatively small delivery amount in the area of the metering device can be achieved by adding the accompanying element to the copper essentially in the form of a pure substance.

Exact metering and rapid distribution of the accompanying element in the copper melt are assisted by adding the accompanying element to the copper essentially in the form of a prealloy.

Further equalization of the material quality can be achieved by measuring the oxygen concentration of the copper melt and supplying the result of the measurement to the automatic metering control system.

Uniform material quality even in the case of varying input parameters is promoted by measuring the proportion of the accompanying element contained in the copper and maintaining it at an essentially constant level along the length of the wire in a closed-loop control system with the use of the automatic metering control system and the metering device.

A common effect of several accompanying elements contained in the copper melt can be taken into account if the total content of all of the accompanying elements in the copper is taken into account by the automatic metering control system to determine the amount of the selected accompanying element to be metered.

The casting output can be determined by installing the furnace on a weighing device and measuring the amount of wire cast or the length of wire cast.

In a typical embodiment of the invention, the furnace is designed as a melting furnace.

In accordance with another embodiment of the invention, it is also possible for the furnace to be designed as a casting furnace.

The oxygen concentration of the copper melt can be measured by connecting the automatic metering control system to a sensor for detecting the oxygen concentration of the copper melt.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing

FIG. 1 shows a graph illustrating the electrical conductivity of a copper wire as a function of the proportions of various accompanying elements;

FIG. 2 shows a graph illustrating the electrical conductivity of a copper wire as a function of its iron concentration;

FIG. 3 shows a graph illustrating the electrical conductivity of a copper wire as a function of its phosphorus concentration at two different oxygen concentrations;

FIG. 4 shows a modified version of the graph in FIG. 3 with the specific conductivity plotted as a function of the phosphorus concentration, including higher phosphorus concentrations;

FIG. 5 shows a graph with four recrystallization curves illustrating the increase in the recrystallization threshold for different alloying elements and concentrations;

FIG. 6 shows an example of the grain structure of a copper wire in accordance with the present invention after the test for hydrogen resistance;

FIG. 7 shows the grain structure of a copper wire with destroyed grain boundaries with the use of an oxygen-containing material in accordance with the state of the art after the test for hydrogen resistance; and

FIG. 8 shows a schematic representation of equipment for the production of copper wire.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the electrical conductivity of copper as a function of added amounts of various accompanying elements. The graph shows the general significant decrease in conductivity with increasing concentration of the accompanying element. The strength of the decrease depends on the particular accompanying element. Of the accompanying elements shown here as examples, phosphorus causes the strongest decrease in conductivity, and cadmium causes the smallest decrease.

FIG. 2 shows the electrical conductivity of a copper wire made of recrystallized copper with a phosphorus concentration of less than 1 ppm as a function of the iron concentration. Within the usual scattering range, there is an approximately linear relationship between the electrical conductivity and the iron concentration for the illustrated range of iron concentrations.

FIG. 3 shows the electrical conductivity of a copper wire made of recrystallized copper as a function of its phosphorus concentration at an oxygen concentration of less than 5 ppm and at an oxygen concentration of 30-40 ppm. An essentially linear relationship also exists here for the illustrated range of phosphorus concentrations.

FIG. 4 illustrates the specific conductivity of a copper wire as a function of the phosphorus concentration. Furthermore, the functional relationship is explicitly stated.

FIG. 5 illustrates the change in tensile strength of a cold-worked copper wire as a function of the temperature of a preceding annealing treatment in the presence of various accompanying elements and various concentrations of accompanying elements (recrystallization curves). The curve for oxygen-free pure copper is shown for comparison. The graph shows that an increasing concentration causes a significant increase in the recrystallization temperature, especially in the case of phosphorus as the accompanying element.

In accordance with one embodiment, high-purity electrolytic copper with a copper content of greater than 99.95 wt.% is used, and phosphorus is added as the accompanying element in concentrations of 5 ppm to 60 ppm. As shown by the graph in FIG. 3, a phosphorus concentration in this range causes only a relatively small decrease in the electrical conductivity, but as the graph in FIG. 5 shows, it produces a significant increase in tensile strength after certain types of cold working and heat treatment. As an alternative to the use of phosphorus, the use of boron or lithium as the accompanying element has also been found to be advantageous. A portion of the accompanying element that is alloyed with the copper is deposited at the grain boundaries of the individual crystallization grains of the copper (as oxide or even partly in elemental form), while another portion of the accompanying element is incorporated in the crystal lattice. The combined incorporation of the accompanying element both within the lattice and at the grain boundaries results in especially favorable properties with respect to subsequent processing.

The alloying of the accompanying element causes the formation of Cu—P—O nuclei in the copper melt, which bring about homogeneous and at the same time fine-grained solidification with stable grain boundaries. In the embodiment described above, an average grain size with a diameter on the order of 30 micrometers or less can be realized after hot working or after cold working with a subsequent recrystallization heat treatment. FIG. 6 shows an example of the grain structure of a copper wire produced according to this embodiment after a heat treatment in a reducing atmosphere of 100% hydrogen at a treatment temperature of 850° C. and a treatment time of 30 minutes. FIG. 7 shows a conventional oxygen-containing material after a similar treatment. FIG. 6 thus illustrates the clearly smaller grain structures and the spatially less extensive dimensioning of the grain boundaries.

FIG. 8 illustrates the arrangement of equipment for the production of the copper wire. A copper melt 2 produced in a furnace 1 is fed to a casting machine 3. A rough profile 4 produced by the casting machine 3 is worked into copper wire 6 in a downstream processing machine 5. The furnace 1 is installed on a weighing device 8 equipped with a sensor 7. The weighing device 8 is connected to an automatic metering control system 9, which controls a metering device 10 for the accompanying element. The automatic metering control system 9 is also connected to a device 11 for measuring the casting output.

The accompanying element can be alloyed with the copper, for example, in a runner between a melting furnace and a holding furnace. It is also possible to add the accompanying element to the copper in a lower crater or in a casting trough. Moreover, it is possible to carry out the alloying operation in the upper crater or in the holding furnace itself. It is also conceivable for the copper charged to the melting furnace already to contain the desired proportion of the selected accompanying element. The copper with the desired proportion of the accompanying element can be fed, for example, as broken charge material in the form of scrap. In another variation, the alloying can be carried out directly in a molten stream above the bath in the mold or in the casting nozzle itself.

The accompanying element can be supplied by the metering device 10 in pure form or in the form of a prealloy. For example, copper that contains the accompanying material in amounts of 10% to 50% can be used as a prealloy. The accompanying element or the prealloy is supplied in lump form or in fine-grained form. The addition of spherical particles has been found to be especially effective. Alternatively, alloying wire or pigs can be added.

The weighing device 8 shown as an example in FIG. 8 and the device 11 for measuring the casting output allow continuous determination of the volume throughput of the melt at the alloying site. Based on the current measured values, the automatic metering control system 9 can determine a quantitative balance and the required metering amount. Continuous supplying of the accompanying element with sufficient mixing of the materials before solidification is preferred, but it is also possible to supply the accompanying element discontinuously.

In addition, when the oxygen concentration of the copper melt is unknown or fluctuates, it has been found to be advantageous to measure the oxygen concentration at the alloying site continuously or at least discontinuously. An elevated oxygen concentration within the tolerance limits makes it necessary to increase the amount of the accompanying element being added to realize the predetermined proportion of the accompanying element in the solidified product.

Further improvement of the uniformity of the proportion of the accompanying element along the length of the wire can be realized by continuously or at least discontinuously determining the actual concentration of the alloying element in the solidified wire, e.g., by spectrometry. In accordance with a simplified variant of the method, the concentration of the alloying element is determined in the melt by probes before the wire solidifies.

The small grain sizes achieved by the method of the invention also result in more stable grain boundaries, which allow greater true strain and higher strain rates. This has great importance, especially in cold working. Furthermore, due to the smaller grain sizes, a small segmental chip forms during machining, which allows optimized process management. Cut edges that are produced also show less pinching, smaller gradation, and a smaller shear stress fracture zone than conventional materials.

Another advantage of the smaller grain structures is that fewer distinct Luders lines form on the surface of the casting during cold working. The accompanying element content also results in improved corrosion resistance.

In accordance with an embodiment in which phosphorus is added to the copper in a concentration of 55 ppm, the recrystallization temperature can be increased by about 80-100° C. This results in both high conductivity and increased high-temperature strength.

In accordance with another embodiment, a copper melt is used in which the copper content is greater than 99.995% and the oxygen concentration in the pouring basin is less than 5 ppm. The phosphorus concentration is set at 5-10 ppm. This makes it possible to achieve a conductivity of at least 101% IACS with small grain sizes. To achieve a conductivity of at least 100% IACS, a phosphorus concentration of 5-20 ppm and preferably 15-20 ppm is used. To achieve a conductivity of at least 98.3% IACS, a phosphorus concentration of 5-30 ppm and preferably 25-30 ppm has been found to be effective.

In addition, the small grain sizes realized with the proposed proportions of the accompanying element in the copper melt have the advantage that the copper reacts insensitively to errors during a heat treatment. In particular, when annealing times are too long, a secondary recrystallization does not occur until significantly later.

Claims

1. A copper wire comprising an average copper content of at least 99.95 wt.% and at least one accompanying element alloyed with the copper, wherein a ratio of the percentage by weight of the accompanying element and the percentage by weight of the residual oxygen concentration has a value in the range of 0.8 to 1.7, and wherein the percentage by weight of the accompanying element varies along a length of wire by a maximum of 25%, based on the maximum percentage by weight of the accompanying element.

2. The copper wire in accordance with claim 1, wherein the accompanying element is phosphorus.

3. The copper wire in accordance with claim 1, wherein the accompanying element is boron.

4. The copper wire in accordance with claim 1, wherein the accompanying element is lithium.

5. The copper wire in accordance with claim 1, wherein the concentration of the accompanying element in the copper is 5 ppm to 60 ppm.

6. The copper wire in accordance with claim 1, wherein an average grain size is a maximum of 30 micrometers.

7. The copper wire in accordance with claim 1, wherein the accompanying element is at least partly deposited at grain boundaries.

8. The copper wire in accordance with claim 1, wherein the accompanying element is at least partly incorporated in the atomic lattice of the grains.

9. The copper wire in accordance with claim 1, wherein the percentage by weight of the accompanying element varies along the length of the wire by a maximum of 20%, based on its maximum percentage by weight of the accompanying element 10.

10. A method for the production of copper wire having an average copper content of at least 99.95 wt.%, in which at least one accompanying element is alloyed with the copper, and in which the production includes a casting operation, the method comprising protecting the copper melt from a surrounding atmosphere until the copper has solidified, and adding the at least one accompanying element is added in an amount such that a ratio of the percentage by weight of the accompanying element and the percentage by weight of a residual oxygen concentration of the copper melt is adjusted to a value in the range of 0.8 to 1.7, and the ratio is maintained at an essentially constant value along the length of the wire.

11. The method in accordance with claim 10, comprising determining the concentration of the accompanying element in the copper by at least one test probe.

12. The method in accordance with claim 10, comprising determining the concentration of the accompanying element by the test probe in a molten copper zone.

13. The method in accordance with claim 10, comprising determining the concentration of the accompanying element by the test probe in a solidified wire zone.

14. The method in accordance with claim 10, comprising adjusting the conductivity of the copper by the concentration of the accompanying element in the copper.

15. The method in accordance with claim 10, comprising, when the oxygen concentration is elevated, adding an increased amount of the accompanying element to the copper.

16. The method in accordance with claim 10, comprising producing the copper wire by direct casting.

17. The method in accordance with claim 10, comprising producing the copper wire by casting and hot working.

18. The method in accordance with claim 10, comprising producing the copper wire by cold working.

19. The method in accordance with claim 10, comprising added the accompanying element to the copper in the region of a runner.

20. The method in accordance with claim 10, comprising added the accompanying element to the copper in the region of a lower crater.

21. The method in accordance with claim 10, comprising added the accompanying element to the copper in the region of a casting trough.

22. The method in accordance with claim 10, comprising added the accompanying element to the copper in the region of an upper crater.

23. The method in accordance with claim 10, comprising added the accompanying element to the copper in the region of a holding furnace.

24. The method in accordance with claim 10, comprising added the accompanying element to the copper in the region of a molten stream.

25. The method in accordance with claim 10, comprising added the accompanying element to the copper essentially in the form of a pure substance.

26. The method in accordance with claim 10, comprising added the accompanying element to the copper essentially in the form of a prealloy.

27. The method in accordance with claim 10, comprising measuring the oxygen concentration of the copper melt and supplying the result of the measurement to an automatic metering control system.

28. The method in accordance with claim 27, comprising measuring the proportion of the accompanying element contained in the copper and maintaining the concentration at an essentially constant level along the length of the wire in a closed-loop control system with the use of the automatic metering control system and the metering device.

29. The method in accordance with claim 10, wherein the total content of all of the accompanying elements in the copper is taken into account by the automatic metering control system for determining the amount of the selected accompanying element to be metered.

30. Equipment for the production of copper wire, comprising at least a furnace for the production of a copper melt and a casting machine, further comprising a metering device for metering at least one accompanying element connected to an automatic metering control system, which control system is connected to at least one sensor for detecting a furnace weight and a device for measuring a casting output.

31. Equipment in accordance with claim 30, wherein the furnace is installed on a weighing device.

32. Equipment in accordance with claim 30, wherein the furnace is a melting furnace.

33. Equipment in accordance with claim 30, wherein the furnace is a casting furnace.

34. Equipment in accordance with claim 30, wherein the automatic metering control system is connected to a sensor for detecting the oxygen concentration of the copper melt.