Manufacturing method for copper castings

Abstract

The present invention provides a method for manufacturing copper castings that can efficiently process copper scrap and stably produce copper castings with low impurity levels using copper raw materials containing copper scrap. [Solution] The process comprises a melting step, an impurity element removal step, and a casting step, wherein the copper raw material contains 20% by mass or more of the copper scrap and has a copper purity of 95% by mass or more, and in the impurity element removal step, the amount of melted copper raw material is M (kg), and the surface area of ​​the molten metal in the heating furnace is S (mm 2 When the holding temperature is T (K), the holding time of the molten copper is t (sec), and the oxygen concentration in the molten copper is X (mass%), then Y = EXP(M ÷ S × 10) × T' ÷ t 0.5 ÷X ≤ 1.0 (where T' = 5 × 10) -5 ×T 2 The method is characterized by holding the copper raw material under conditions that satisfy -0.1473 × T + 110, and removing impurities contained in the copper raw material.

Description

[Technical Field]

[0001] This invention relates to a method for efficiently producing copper castings from copper scrap generated and separated from automotive parts, home appliances, etc., in which the amount of impurities such as aluminum, phosphorus, and iron has been sufficiently reduced. [Background technology]

[0002] In recent years, discussions on European ELV regulations have set a target of 25% recycling for plastics by 2030, and based on the review committee's findings, it has been decided to set a target for the recycled steel component of newly approved vehicles within three years of the regulations coming into effect. Similar surveys may be conducted for non-ferrous metals such as aluminum and copper in the future, and targets may be set for the scrap rate of the metals used.

[0003] The scrap rate for copper mentioned above applies to post-consumer recycled (PCR) and post-industrial recycled (PIR) materials, and does not include in-process scrap. Furthermore, the following formula is used to define the recycling rate R. Recycling rate R(%) = {[PCR material] + [PIR material]} / (total amount dissolved) × 100

[0004] One method to improve the scrap yield in copper is to remove impurity elements during the melting and casting process to refine the scrap into crude copper, and then obtain high-purity electrolytic copper through electrolytic refining. Alternatively, one could directly manufacture copper ingots (slabs, billets) that will serve as the raw material for copper alloy products. In existing processes, this requires feeding the material into upstream converters or refining furnaces, but this reduces the copper recovery rate and has poor thermal efficiency. From the perspective of reducing GHG (Greenhouse Gas) emissions in the manufacturing process, processing at a more downstream stage is desirable. On the other hand, in downstream processes, impurity elements introduced from copper scrap may not be sufficiently removed, potentially compromising the quality of the cast products. To address this problem, the following patents were known for manufacturing methods. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-001513 [Patent Document 2] Japanese Patent Publication No. 2005-042161 [Patent Document 3] Japanese Patent Publication No. 2012-087376 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, when attempting to reduce impurity elements in the molten copper using the aforementioned manufacturing method, it was not possible to sufficiently reduce impurity elements that were difficult to remove by simply separating and sorting the scrap, resulting in productivity problems. Furthermore, when using a gas reactor, CO X This resulted in a large amount of waste being generated, making it difficult to control the atmosphere for removing impurity elements, and also creating challenges related to GHGs (Gross Heat Generators). Furthermore, when copper scrap was used in proportions exceeding a certain level, there was a risk that the copper castings would not meet the impurity element standards due to uncontrollable fluctuations in the concentration of impurity elements.

[0007] The present invention was made against the background described above, and aims to provide a method for manufacturing copper castings that can efficiently and selectively remove predetermined impurity elements contained in copper after separating, sorting, and recovering copper scrap, thereby improving the recycling rate of copper scrap and enabling the stable production of high-quality copper castings with fewer impurity elements. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the inventors of this invention conducted diligent research and obtained the following findings. When the copper purity of copper raw materials, including copper scrap, is 95 mass% or higher, it is possible to stably reduce the impurity elements contained in the copper raw materials by optimizing the conditions for melting the molten copper raw materials in a heating furnace.

[0009] The present invention has been made based on the above findings, and the method for manufacturing a copper cast product according to Embodiment 1 of the present invention comprises a melting step of melting a copper raw material containing copper scrap to obtain molten copper, an impurity element removal step of holding the obtained molten copper in a heating furnace to remove impurity elements, and a casting step of casting using the molten copper from which impurity elements have been removed, wherein the copper raw material contains 20% by mass or more of the copper scrap and has a copper purity of 95% by mass or more, and in the impurity element removal step, the amount of melted copper raw material is M (kg), and the surface area of ​​the molten metal in the heating furnace is S (mm 2 ), when the holding temperature is T (K), the holding time of the molten copper is t (sec), and the oxygen concentration in the molten copper is X (mass%), Y = EXP(M ÷ S × 10) × T' ÷ t 0.5 ÷X ≤ 1.0 (However, T' = 5 × 10) -5 ×T 2 (-0.1473 × T + 110) The method is characterized by retaining the copper raw material under conditions that satisfy the above requirements and removing impurity elements contained in the copper raw material.

[0010] According to the method for manufacturing copper cast products of Embodiment 1 of the present invention, the copper raw material contains 20% by mass or more of copper scrap and the copper purity is 95% by mass or more, so that copper scrap can be processed efficiently and high-purity copper cast products can be manufactured stably.

[0011] Then, in the impurity element removal process, the amount of copper raw material dissolved is M (kg), and the surface area of ​​the molten metal in the heating furnace is S (mm²). 2) When the holding temperature is T (K), the oxygen concentration in the molten copper is X (mass %), and the holding time of the molten copper is t (sec), Y = EXP(M÷S×10)×T´÷t 0.5 ÷X≦1.0, the conditions are set so that the impurity elements contained in the molten copper can be stably oxidized and removed, and high-purity copper casting products can be stably manufactured.

[0012] The copper scrap in the present invention refers to waste materials of members used in combination or joined with metals other than copper, such as household appliances and automobile parts, or copper alloy scrap. Specific examples of the former include those obtained by crushing these waste materials into a state separable from metals other than copper, and then performing separation and selection so that Cu≧95 mass%. The latter targets copper and copper alloys other than those in the self-process having a chemical composition of Cu≧95 mass% excluding inevitable impurity elements. Examples of the copper casting products include blister copper used in electrolytic refining, copper ingots (slabs, billets) that are materials for various drawn copper products, and the like.

[0013] The method for manufacturing a copper casting product according to Embodiment 2 of the present invention is characterized in that, in the method for manufacturing a copper casting product according to Embodiment 1 of the present invention, the heating furnace for holding the molten copper in the impurity element removal step is an induction heating furnace.

[0014] According to the method for manufacturing a copper casting product according to Embodiment 2 of the present invention, since the heating furnace for holding the molten copper in the impurity element removal step is an induction heating furnace, the stirring effect of the molten copper by electromagnetic stirring is high, promoting the reaction between the ambient oxygen and the impurity elements in the molten copper, and the impurity elements can be efficiently removed. In addition, since combustion gas is not used, the generation of CO2 can be suppressed, and the environmental load can be reduced. Furthermore, the atmosphere control during melting can be stably performed.

[0015] The manufacturing method of the copper casting product according to Embodiment 3 of the present invention is characterized in that, in the manufacturing method of the copper casting product according to Embodiment 1 or Embodiment 2 of the present invention, the Al concentration in the copper casting product is 1000 massppm or less, the P concentration is 300 massppm or less, and the Fe concentration is 1000 massppm or less.

[0016] According to the manufacturing method of the copper casting product according to Embodiment 3 of the present invention, since the Al concentration in the copper casting product is 1000 massppm or less, the P concentration is 300 massppm or less, and the Fe concentration is 1000 massppm or less, the main impurity elements are sufficiently reduced, and a high-quality copper casting product can be obtained.

[0017] The manufacturing method of the copper casting product according to Embodiment 4 of the present invention is characterized in that, in the manufacturing method of the copper casting product according to any one of Embodiments 1 to 3 of the present invention, the cooling rate from 1100 °C to 1000 °C in the casting process is 10 °C / sec or less.

[0018] According to the manufacturing method of the copper casting product according to Embodiment 4 of the present invention, since the cooling rate from 1100 °C to 1000 °C in the casting process is 10 °C / sec or less, impurity elements can be discharged to the surface side by utilizing macrosegregation.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a manufacturing method of a copper casting product that can efficiently process copper scrap and stably manufacture a copper casting product with a small amount of impurities using a copper raw material containing copper scrap.

Brief Description of the Drawings

[0020] [Figure 1] It is a flowchart showing the manufacturing method of the copper casting product which is one embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0021] A method for manufacturing a copper cast product according to an embodiment of the present invention will be described below with reference to the attached drawings. Examples of copper casting products in embodiments of the present invention include crude copper used in electrolytic refining and copper ingots (slabs, billets) that serve as materials for various copper alloy products. In this embodiment, crude copper is used.

[0022] In the method for manufacturing copper cast products according to this embodiment, as shown in the flow chart of Figure 1, the method comprises: a copper raw material preparation step S01 in which copper raw materials including copper scrap are prepared; a melting step S02 in which the obtained copper raw materials are melted to obtain molten copper; an impurity element removal step S03 in which the obtained molten copper is held in a heating furnace and impurity elements are removed from the molten copper; and a casting step S04 in which casting is performed using the molten copper from which impurity elements have been removed.

[0023] (Copper raw material preparation process S01) In this copper raw material preparation process S01, the copper raw material to be melted contains 20% by mass or more of copper scrap, and is adjusted so that the copper purity is 95% by mass or more. Here, copper scrap refers to post-consumer recycled (PCR) and post-industrial recycled (PIR) materials, and does not include scrap from the manufacturing process itself. Post-consumer recycled (PCR) materials are recycled materials that are products that consumers have used but have not discarded, while post-industrial recycled (PIR) materials are recycled materials that are generated during the manufacturing process of products before they reach the market but have not been discarded.

[0024] In this copper raw material preparation process S01, the purity of the copper in the copper raw material to be melted is set to 95 mass% or higher. If the copper purity is less than 95 mass%, the amount of impurities to be removed will increase, and the production yield will deteriorate. In addition, a large amount of slag will be generated in the impurity element removal process S03, which will be described later, and removing and processing this slag may incur significant costs. Therefore, in this embodiment, the purity of copper in the copper raw material is set to 95 mass% or higher. Furthermore, the purity of the copper in the copper raw material is preferably 97 mass% or higher, and more preferably 99 mass% or higher.

[0025] Furthermore, in the copper raw material preparation process S01, by ensuring that copper scrap accounts for 20% or more by mass of the copper raw material, it becomes possible to improve the recycling rate of copper scrap. Furthermore, a higher proportion of copper scrap in the copper raw material is preferable, and it is most preferable that the entire material be copper scrap. However, as mentioned above, it is necessary to adjust the copper purity of the copper raw material to 95 mass% or higher. In addition to copper scrap, other raw materials that can be used include, for example, pure copper materials such as electrolytic copper and self-processing scrap.

[0026] (melting process S02) In this melting process S02, the copper raw material is charged into a melting furnace and heated to melt the copper raw material and obtain molten copper. Then, this molten copper is heated to a predetermined temperature. In addition, there are no particular restrictions on the atmosphere of the melting furnace in the melting process S02, but it is preferable to use an inert gas atmosphere.

[0027] (Impurity element removal process S03) Next, the obtained molten copper is held in a heating furnace to remove impurity elements from the molten copper. At this time, the melting furnace used in the melting step S02 may be used as the heating furnace in the impurity element removal step S03, or the molten copper may be transferred from the melting furnace used in the melting step S02 to another heating furnace. In this impurity element removal process S03, impurity elements contained in the copper raw material (molten copper) are reacted with oxygen in the atmosphere to form oxides, generating slag on the molten copper. By separating this slag, the impurity elements contained in the copper raw material (molten copper) are removed.

[0028] Thus, in the impurity element removal step S03, since impurity elements are removed by oxidation, the atmosphere of the heating furnace must be an oxygen-containing atmosphere (for example, an atmospheric atmosphere). For this reason, if the melting furnace used in the melting step S02 is used as the heating furnace in the impurity element removal step S03, the atmosphere inside the furnace must be adjusted appropriately. The oxygen concentration in the molten copper can be adjusted using "heated and oxidized copper raw material," "air," or "gas with adjusted oxygen concentration." Furthermore, it is desirable that the atmosphere in the heating furnace holding the molten copper has an oxygen concentration close to that of the atmosphere.

[0029] Here, both thermodynamic and kinetic perspectives are important in removing impurity elements from molten copper. From a kinetic perspective, this has not been discussed before, and in order to properly remove impurity elements, it is necessary to consider the reaction time required for the impurity elements in molten copper to react with oxygen. Here, the parameters in the impurity element removal process S03 show the following qualitative trends:

[0030] When the amount of copper raw material dissolved increases, the volume of molten copper increases, which increases the time required for the diffusion of impurity elements, and thus the time required to remove those impurity elements. When the surface area of ​​the molten copper in the heating furnace decreases, the time required to supply oxygen from the atmosphere to the molten copper lost due to the oxidation of impurity elements increases, which may prevent the efficient removal of impurity elements.

[0031] If the holding temperature drops too low, the reaction rate between impurity elements and oxygen slows down. On the other hand, if the holding temperature is too high, there is a risk that the concentration of impurity elements remaining in the molten copper will become too high. If the holding time for molten copper is too short, there may not be enough time for oxygen to react with impurity elements, potentially preventing sufficient removal of these elements. If the oxygen concentration in the molten copper is too low, there is a risk that the concentration of residual impurity elements in the molten copper will increase.

[0032] Therefore, in the present embodiment, in the impurity element removal step S03, the molten copper is held so as to satisfy the following formula. Let M (kg) be the melting amount of the copper raw material to be melted, S (mm 2 ) be the surface area of the molten metal in the heating furnace, T (K) be the holding temperature, t (sec) be the holding time of the molten copper, and X (mass%) be the oxygen concentration in the molten copper. Y = EXP(M÷S×10)×T´÷t 0.5 ÷X ≤ 1.0 (where T´ = 5×10 -5 ×T 2 -0.1473×T + 110)

[0033] By holding the molten copper under the conditions satisfying the above formula, it becomes possible to oxidize and efficiently remove the impurity elements contained in the molten copper. Note that Y = EXP(M÷S×10)×T´÷t in the above formula 0.5 ÷X is preferably 0.8 or less, and more preferably 0.5 or less.

[0034] Also, in the present embodiment, the heating furnace used in the impurity element removal step S03 is preferably an induction heating furnace. Compared with a gas combustion furnace, an induction heating furnace has a higher stirring effect on the molten copper not only by thermal convection but also by electromagnetic stirring, and is more likely to react with atmospheric oxygen. Even if an oxide is temporarily formed between the atmosphere and the molten copper, the oxide will flow due to the stirring effect, and the reaction will proceed as the molten copper is exposed to the atmosphere. In addition, the diffusion of oxygen into the molten copper is facilitated, so that the reaction rate between the molten copper and the impurity elements also increases, making it possible to efficiently oxidize and remove the impurity elements.

[0035] Furthermore, in gas combustion, exhaust gas is generated by burner combustion during the heating and melting of the material, which has a certain impact on the atmosphere, and there are technical hurdles to maintaining a constant melting atmosphere. However, in the case of an induction heating furnace, no combustion gas or the like is generated during the heating of the material, and the control of the atmosphere, such as an oxidizing atmosphere, becomes easy. Furthermore, gas combustion inevitably generates CO2 due to the use of fossil fuels, resulting in a high environmental burden. However, induction heating furnaces can suppress CO2 emissions.

[0036] (Casting process S04) Next, the molten copper from which impurity elements have been removed is poured into a mold to obtain a copper cast product. Depending on the properties required for the copper cast product, a reduction treatment may be performed after removing impurity elements to lower the oxygen concentration in the molten copper. For example, if the copper casting is crude copper used in electrolytic refining, there is no need for any special reduction treatment. In this case, the oxygen concentration in the molten copper and the oxygen concentration in the copper casting will be approximately the same. On the other hand, when copper castings are used as slabs or billets for wrought copper products, the reduction treatment can lower the oxygen concentration in the copper castings.

[0037] Furthermore, in this embodiment, it is preferable that the cooling rate from 1100°C to 1000°C in the casting process S04 is 10°C / sec or less. As described above, slowing down the cooling rate at high temperatures promotes macrosegregation, allowing impurity elements to be discharged to the surface of the copper casting during solidification. In other words, by discharging impurity elements remaining in the molten copper to the surface during solidification, it becomes possible to further reduce the amount of impurities. Furthermore, the cooling rate from 1100°C to 1000°C in the casting process S04 is more preferably 8°C / sec or less, and even more preferably 6°C / sec or less. There is no particular lower limit to the cooling rate from 1100°C to 1000°C, but it is substantially 3°C / sec or more.

[0038] In this way, copper castings with a sufficiently reduced amount of impurity elements are manufactured from copper raw materials, including copper scrap. In the resulting copper castings, it is preferable that the Al concentration is 1000 massp / pm or less, the P concentration is 300 massp / pm or less, and the Fe concentration is 1000 massp / pm or less. Because these impurity elements are reduced as described above, the copper castings can be stably used as raw materials for crude copper and drawn copper products during electrolytic refining.

[0039] Furthermore, the Al concentration in the copper casting product is more preferably 500 mass sppm or less, and even more preferably 200 mass sppm or less. Furthermore, the P concentration in the copper casting product is more preferably 200 massp / pm or less, and even more preferably 100 massp / pm or less. Furthermore, the Fe concentration in the copper casting product is more preferably 500 mass sppm or less, and even more preferably 200 mass sppm or less.

[0040] In this embodiment of the method for manufacturing copper cast products, the copper raw material is configured to contain 20% by mass or more of copper scrap in the copper raw material preparation step S01, thus enabling efficient processing of copper scrap. Furthermore, in the copper raw material preparation step S01, the copper purity in the copper raw material is configured to be 95% by mass or more, so impurity elements can be efficiently and stably removed in the impurity element removal step S03, enabling the stable production of high-purity copper cast products.

[0041] Then, in the impurity element removal process S03, the amount of copper raw material dissolved is M (kg), and the surface area of ​​the molten metal in the heating furnace is S (mm²). 2 If the holding temperature is T (K), the oxygen concentration in the molten copper is X (mass%), and the holding time of the molten copper is t (sec), then Y = EXP(M ÷ S × 10) × T' ÷ t 0.5 Since the holding conditions for the molten copper are set to satisfy ÷X ≤ 1.0, impurity elements contained in the molten copper can be stably oxidized and removed, enabling the stable production of high-purity copper castings.

[0042] In this embodiment, when the heating furnace used in the impurity element removal step S03 is an induction heating furnace, the stirring effect of the molten copper by electromagnetic stirring is high, promoting the reaction between the atmospheric oxygen and the impurity elements in the molten copper, and enabling efficient removal of the impurity elements. Furthermore, since no combustion gases are used, CO2 emissions can be suppressed, reducing the environmental impact. In addition, stable atmospheric control can be achieved during dissolution.

[0043] In this embodiment, when the Al concentration in the obtained copper casting is 1000 massppm or less, the P concentration is 300 massppm or less, and the Fe concentration is 1000 massppm or less, the major impurity elements are sufficiently reduced, and a high-quality copper casting can be obtained. Therefore, the copper casting can be stably used as a raw material for crude copper or drawn copper products during electrolytic refining.

[0044] In this embodiment, if the cooling rate from 1100°C to 1000°C in the casting process S04 is 10°C / sec or less, macrosegregation can be promoted, allowing impurity elements to be discharged to the surface side of the copper casting product during solidification. In other words, by discharging impurity elements remaining in the molten copper to the surface side during solidification, it is possible to further reduce the amount of impurities.

[0045] Although the method for manufacturing copper cast products, which is an embodiment of the present invention, has been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. [Examples]

[0046] The results of the verification experiments conducted to confirm the effects of the present invention are described below. As shown in Table 1, copper raw materials were prepared with adjusted copper scrap content and copper purity. The copper raw material was charged into an induction heating furnace and heated and melted under an argon atmosphere. After the molten copper reached a predetermined temperature, it was held under the conditions shown in Table 1. After taking a sample for oxygen analysis, it was cast into a mold to obtain a copper casting. As shown in Table 1, the cooling rate from 1100°C to 1000°C during casting was set. Oxygen analysis samples were taken from molten copper and subjected to gas analysis to measure the oxygen concentration in the molten copper. The measurement results are shown in Table 1.

[0047] Furthermore, the Al, P, and Fe concentrations in copper castings were measured by X-ray fluorescence analysis of sample materials taken from the copper castings. The measurement results are shown in Table 2. Here, samples that satisfy all three conditions—Al concentration: 1000 massppm or less, P concentration: 300 massppm or less, and Fe concentration: 1000 massppm or less—were evaluated as "○" (○), samples that do not satisfy one of the three conditions—Al concentration: 1000 massppm or less, P concentration: 300 massppm or less, and Fe concentration: 1000 massppm or less—were evaluated as "△" (△), and samples that do not satisfy two or more of the three conditions—Al concentration: 1000 massppm or less, P concentration: 300 massppm or less, and Fe concentration: 1000 massppm or less—were evaluated as "×" (×).

[0048] [Table 1]

[0049] [Table 2]

[0050] In Comparative Examples 1-5, in the impurity element removal step S03, Y = EXP(M ÷ S × 10) × T' ÷ t 0.5 Since ÷X exceeds 1.0, the impurity elements could not be sufficiently reduced, resulting in a "×" rating. In contrast, in Examples 1 to 7 of the present invention, in the impurity element removal step S03, Y = EXP(M ÷ S × 10) × T' ÷ t 0.5Since ÷X is 1.0 or less, it is possible to sufficiently reduce the impurity elements, and the evaluation is "〇" or "△".

[0051] As described above, according to the present invention, it has been confirmed that, after separating, sorting, and recovering copper scrap, predetermined impurity elements contained therein can be efficiently and selectively removed from the copper, thereby improving the recycling rate of copper scrap and providing a method for manufacturing copper castings that enables the stable production of high-quality copper castings with fewer impurity elements.

Claims

1. The process comprises a melting step of dissolving copper raw materials including copper scrap to obtain molten copper, an impurity element removal step of holding the obtained molten copper in a heating furnace to remove impurity elements, and a casting step of using the molten copper from which impurity elements have been removed to perform casting. The aforementioned copper raw material contains 20% by mass or more of the aforementioned copper scrap, and the copper purity is 95% by mass or more. In the aforementioned impurity element removal step, the amount of copper raw material dissolved is M (kg), and the surface area of ​​the molten metal in the heating furnace is S (mm²). ２ When the holding temperature is T (K), the holding time of the molten copper is t (sec), and the oxygen concentration in the molten copper is X (mass%), Y=EXP(M÷S×10)×T´÷t ０．５ ÷X≦1.0 (However, T' = 5 × 10 －５ ×T ２ (-0.1473 × T + 110) A method for manufacturing a copper cast product, characterized by holding the copper raw material under conditions that satisfy the following and removing impurities contained in the copper raw material.

2. The method for manufacturing a copper cast product according to claim 1, characterized in that the heating furnace is an induction heating furnace.

3. A method for manufacturing a copper casting product according to claim 1 or 2, characterized in that the Al concentration in the copper casting product is 1000 mass ppm or less, the P concentration is 300 mass ppm or less, and the Fe concentration is 1000 mass ppm or less.

4. A method for manufacturing a copper cast product according to claim 1 or 2, characterized in that the cooling rate from 1100°C to 1000°C in the casting process is 10°C / sec or less.

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