METAL REFINING METHOD AND METAL REFINING APPARATUS

Abstract

To provide a metal refining method capable of achieving excellent refining efficiency while reducing scattering of molten metal.SOLUTION: A metal refining method includes immersing a cooling body 2 in a molten metal 10 to be purified which is stored in a molten metal holding container 1; and causing high purity metal to be crystallized on a surface of the cooling body 2 while rotating the cooling body 2 around a shaft core thereof. The shaft core X2 of the cooling body 2 is inclined at 5-50° relative to a vertical axis when rotating the cooling body 2 within the molten metal 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a metal refining method and apparatus for refining metals, and more particularly to a metal refining method and apparatus for refining a high-purity substance from a substance containing eutectic impurities by utilizing the principles of segregation solidification, thereby reducing the eutectic impurity content to a level lower than that of the original substance. [Background technology]

[0002] When a metal contains impurities such as Fe, Si, and Cu that form eutectic crystals with the metal, it is well known that an effective way to remove these impurities and obtain a high-purity metal is to melt the metal, cool it, and then selectively extract the primary crystals as it solidifies.

[0003] Various refining methods utilizing the above principle have been proposed. For example, a well-known metal refining method involves immersing a cooling body in molten metal (molten metal) in a crucible and crystallizing high-purity metal on the surface of the cooling body while rotating the cooling body. In this refining method, high-purity metal with few impurities is obtained by increasing the relative speed between the outer surface of the rotating cooling body and the molten metal swirling around the outer periphery of the cooling body.

[0004] Therefore, in the following Patent Document 1, a metal refining method is proposed in which the position of the cooling body is set at a position shifted from the center of the portion of the crucible where the molten metal is present, and the shortest distance between the inner surface of the crucible and the outer surface of the cooling body is set to a predetermined value or less relative to the longest distance between the inner surface of the crucible and the outer surface of the cooling body, thereby intentionally forming narrow and wide areas in the flow path of the swirling molten metal and causing the molten metal to flow radially around the crucible, thereby slowing the circumferential flow rate of the molten metal and increasing the relative velocity. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-163420 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the metal refining method of Patent Document 1 has the problem that the flow rate can become too fast in narrow parts of the flow path, and centrifugal force can cause localized excessive rises in the molten metal surface, which can easily lead to problems such as molten metal splashing (molten metal splashing).

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a metal refining method and a metal refining apparatus that can achieve excellent refining efficiency and suppress the scattering of molten metal. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention comprises the following means.

[0009] [1] A metal refining method in which a cooling body is immersed in molten metal to be refined contained in a molten metal holding vessel, and high-purity metal is crystallized on the surface of the cooling body while the cooling body is rotated around its axis, A metal refining method, characterized in that when the cooling body is rotated in the molten metal, the axis of the cooling body is tilted at an angle of 5° to 50° with respect to a vertical axis.

[0010] [2] The metal refining method according to the preceding paragraph 1, wherein the axis of the cooling body is tilted at an angle of 10° to 40° with respect to the vertical axis when the cooling body is rotated in the molten metal.

[0011] [3] A metal refining method according to the preceding paragraph 1 or 2, wherein the axial center of the cooling body and the axial center of the molten metal holding vessel are made to intersect at the surface of the molten metal. [4] A metal refining method according to any one of the preceding items 1 to 3, wherein the cooling body is rotated in the molten metal while the inclination angle of the axis of the cooling body relative to the vertical axis is changed.

[0012] [5] The metal refining method according to the preceding paragraph 4, wherein the inclination angle of the axis of the cooling body relative to the vertical axis is gradually decreased.

[0013] [6] The metal refining method according to any one of the above items 1 to 5, wherein the molten metal is aluminum.

[0014] [7] A metal refining apparatus comprising a molten metal holding vessel for containing molten metal to be refined, and a cooling body that is immersed in the molten metal in the molten metal holding vessel and rotates around its axis so that high-purity metal is crystallized on its surface, A metal refining device characterized in that the cooling body that rotates within the molten metal is configured so that its axis can be set to a state inclined at an angle of 5° to 50° with respect to the vertical axis.

[0015] [8] The metal refining device according to the preceding paragraph 7, wherein the cooling body rotating within the molten metal is configured to be able to change the angle of inclination relative to a vertical axis. [Effects of the Invention]

[0016] According to the metal refining method of inventions [1] and [2], by tilting the cooling body, narrow and wide areas can be formed between the outer circumferential surface of the cooling body and the inner circumferential surface of the molten metal holding vessel. As the molten metal flows from the narrow area to the wide area, the width of the area widens. As a result, the molten metal flows not only circumferentially within the molten metal holding vessel but also radially. This reduces the circumferential component of the flowing molten metal, increasing the relative speed of the outer circumferential surface of the cooling body relative to the molten metal, allowing for the refinement of higher purity metal ingots. Furthermore, because the tilt angle of the cooling body is set within a specific range, the width of the molten metal flow path at the outer periphery of the cooling body can be prevented from becoming extremely narrow or wide. This stabilizes the surface of the molten metal without disturbance and prevents the molten metal from splashing.

[0017] According to the metal refining method of invention [3], the axis of the cooling body is aligned with the axis of the molten metal holding vessel at the molten metal surface, so that at the molten metal surface, the cooling body is positioned at the center of the molten metal, and the width of the flow path around the outer periphery of the cooling body at the molten metal surface is almost constant around the entire circumference, making the molten metal surface even more stable and more reliably preventing the molten metal from splashing.

[0018] According to the metal refining method of the invention [4], the inclination angle of the cooling body can be changed appropriately depending on the progress of the refining, and metal ingots of even higher purity can be refined.

[0019] According to the metal refining method of invention [5], the shortest distance between the outer surface of the cooling body and the inner surface of the molten metal holding vessel gradually widens, which more reliably eliminates the problem of metal chunks growing on the outer surface of the cooling body coming into contact with the inner surface of the molten metal holding vessel.

[0020] According to the metal refining method of the invention [6], aluminum is refined, so that the desired aluminum product can be obtained.

[0021] Inventions [7] and [8] specify a metal refining device that can implement the above-mentioned metal refining method invention, and therefore can obtain the same effects as above. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a metal refining apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] Fig. 1 is a schematic diagram showing the configuration of a metal refining apparatus according to an embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view thereof. As shown in both figures, this metal refining apparatus is equipped with a crucible 1 as a bottomed cylindrical molten metal holding vessel, and molten metal (also referred to as "molten metal") 10 is contained and held inside this crucible 1. Crucible 1 is constructed in a heating furnace, and molten metal 10 is heated to a constant temperature.

[0024] In the present invention, the shape of the crucible 1 is not limited to a cylinder, and it is preferable that the inner peripheral surface is curved as much as possible. In addition, the heating method of the furnace that constitutes the crucible 1 is not particularly limited, and for example, electric heating, a gas burner, etc. can be suitably adopted.

[0025] The temperature of the molten metal 10 should be above the solidification temperature, but it is more desirable that it be lower than the temperature at which no solid phase exists in the molten metal while the cooling body 2 described below is immersed in the molten metal 10.

[0026] The metal refining apparatus of this embodiment is provided with a cooling body 2 that can be immersed in molten metal 10 in a crucible 1. Cooling body 2 is formed in the shape of an inverted truncated cone with a larger diameter at the upper end, and is attached to the lower end of a rotating shaft 3 that can move up and down. Note that in the present invention, the shape of cooling body 2 is not limited, and it may be cylindrical or have another shape.

[0027] The rotating shaft 3 is tubular, with a hollow duct formed inside, and a space also formed inside the cooling body 2. A refrigerant supply pipe 4 and a refrigerant discharge pipe 5 are inserted inside the rotating shaft 3, and a refrigerant is supplied from the refrigerant supply pipe 4. The supplied refrigerant is ejected into the internal space of the cooling body 2 through the refrigerant supply pipe 4, and then discharged through the refrigerant discharge pipe 5 inside the rotating shaft 3. This makes it possible to cool the cooling body 2 from the inside.

[0028] The cooling medium may be a gas or a liquid. The surface of the cooling body 2 is preferably made of a material with high thermal conductivity, such as metal or graphite.

[0029] The rotating shaft 3 is configured to be movable up and down and to be driven to rotate around its axis by a driving means (not shown), and when moved downward, the cooling body 2 is immersed in the molten metal 10, and when driven to rotate, the cooling body 2 is configured to rotate around its own axis.

[0030] In addition, the rotation axis 3 is configured so that the tilt angle relative to the vertical axis can be freely changed by a tilt drive means not shown, and by changing the tilt angle of the rotation axis 3, the tilt angle θ of the axis X2 of the cooling body 3 relative to the axis X1 of the crucible 1 as the vertical axis can be freely changed.

[0031] In this embodiment, when cooling body 3 is immersed in molten metal 10 and rotated, the inclination angle θ of cooling body 3 is set to 5° to 50° (5° or more and 50° or less). Furthermore, the axis X2 of cooling body 3 is set to intersect with the axis X1 of crucible 1 at the surface of the molten metal.

[0032] In this embodiment, the cooling body 2 is refined by rotating it at an angle within the molten metal 10, and after a certain period of time, the cooling body 2 is pulled out of the molten metal 10. This causes the refined metal ingot to adhere to the outer surface of the cooling body 2, yielding a high-purity metal ingot. The metal ingot adhering to the cooling body 2 is removed and recovered by applying mechanical force or by reheating.

[0033] When the cooling body 2 is introduced into the molten metal 10, the cooling body 2 may be placed in a vertical position with its axis X2 aligned with the vertical axis, and then tilted after introduction, or the cooling body 2 may be introduced into the molten metal 10 while still in the tilted position. When the cooling body 2 is pulled up, the cooling body 2 may be returned to a vertical position from the tilted position before being pulled up, or it may be pulled up from the molten metal 10 while still in the tilted position. Considering weight balance, etc., it is preferable to introduce and pull up the cooling body 2 in a vertical position.

[0034] In this embodiment, suitable examples of the refined metal include metals such as aluminum, silicon, magnesium, lead, and zinc containing eutectic impurities.

[0035] In this embodiment, the cooling body 2 is tilted during refining for the following reason. By tilting the axis X2 of the cooling body 2 relative to the axis X1 of the crucible 1, the distance between the outer peripheral surface of the cooling body 2 and the inner peripheral surface of the crucible 1 has both relatively narrow and wide portions. For example, at the lower end of the cooling body 2, the distance L1 between the outer peripheral surface of the cooling body and the inner peripheral surface of the crucible on the left side of FIG. 1 is narrower than the distance L2 between the outer peripheral surface of the cooling body and the inner peripheral surface of the crucible on the right side of FIG. 1. Because the distance between the outer peripheral surface of the cooling body and the inner peripheral surface of the crucible thus has both narrow and wide portions, as the molten metal 10 flows from the narrow portion to the wide portion, the width of the distance increases, increasing the degree of freedom of the flow direction of the molten metal 10 in the radial direction in addition to the circumferential direction of the cooling body 2. The centrifugal force of cooling body 2 acts in the radial direction (outer diameter direction), changing the direction of the flow of molten metal 10. Even if the magnitude of the flow remains the same, a radial component is generated in the flow of the molten metal, reducing the circumferential component of the flowing molten metal 10. As a result, the relative speed of the outer circumferential surface of the cooling body with respect to molten metal 10 can be increased, allowing for the refinement of a metal ingot with higher purity.

[0036] Furthermore, since the flow of molten metal 10 also generates a radial component, the outward diffusion of the impurity-enriched layer formed at the solidification interface of the metal block that adheres to and grows on the outer surface of the cooling body 2 is promoted, resulting in the production of a metal block of higher purity.

[0037] Furthermore, in this embodiment, the axial center X2 of the cooling body 2 is aligned with the axial center X1 of the crucible 1 at the surface of the molten metal. As a result, as described above, high-purity metal ingots are attached and grown on the surface of the cooling body 2 below the surface of the molten metal 10. However, as shown in FIG. 2, at the surface of the molten metal, the cooling body 2 is positioned at the center of the molten metal 10. Therefore, the distance between the outer peripheral surface of the cooling body and the inner peripheral surface of the crucible is approximately constant around the entire circumference. As a result, the flow of the molten metal at the surface of the molten metal flows smoothly in the circumferential direction without being disturbed, which prevents the molten metal 10 from scattering and prevents the occurrence of so-called molten metal splashing (liquid splashing).

[0038] In particular, in this embodiment, the inclination angle θ of cooling body 2 is set within a specific range, so the width of the flow path for molten metal 10 does not become significantly narrower or wider around the outer periphery of cooling body 2. Therefore, the surface of the molten metal is stable without being disturbed, and in this respect too, splashing of molten metal 10 can be effectively prevented.

[0039] In this embodiment, if the inclination angle θ of the cooling body 2 is less than 5°, the difference in the flow path width of the molten metal 10 around the outer periphery of the cooling body 2 cannot be sufficiently ensured, the relative velocity between the outer periphery of the cooling body and the molten metal 10 cannot be increased, and the flow of the molten metal 10 cannot be sufficiently guided in the radial direction, which may result in an insufficient purity of the metal ingot that adheres and grows, which is undesirable. Conversely, if the inclination angle θ of the cooling body 2 is greater than 50°, the flow path width between the outer periphery of the cooling body 2 and the inner periphery of the crucible 1 becomes significantly narrow in places, which may cause a local rise in the molten metal surface (liquid level), which may promote the scattering of the molten metal 10 and lead to equipment failure due to molten metal splashing, which is undesirable. In this embodiment, it is more preferable to set the inclination angle θ of the cooling body 2 to 10° to 40°.

[0040] The metal refined in this embodiment has high purity and can be used in various processes and applications to exhibit excellent properties and functions. For example, the refined metal may be used in casting to produce a casting, or the casting may be rolled to produce various metal plates or metal foils. Furthermore, the metal foil may be used, for example, as an electrode material for an aluminum electrolytic capacitor.

[0041] On the other hand, in this embodiment, the inclination angle θ of the cooling body 2 may be gradually changed during refining. For example, after starting refining with the cooling body 2 at a predetermined inclination angle θ, the inclination angle θ may be gradually decreased or increased, either stepwise or continuously. In particular, in this embodiment, by gradually decreasing the inclination angle θ of the cooling body 2 while the cooling body 2 is immersed in the molten metal, the shortest distance between the outer peripheral surface of the cooling body 2 and the inner peripheral surface of the crucible 1 gradually increases, thereby reliably eliminating the problem of metal chunks adhering to and growing on the outer peripheral surface of the cooling body 2 coming into contact with the inner peripheral surface of the crucible 1.

[0042] In addition, in the above embodiment, the cooling body 2 in an inclined position is positioned at approximately the center position of the molten metal surface during refining, but this is not limited to this, and in the present invention, the cooling body 2 in an inclined position may also be positioned at a position deviated from the center position of the molten metal surface during refining. [Example]

[0043] [Table 1]

[0044] Example 1 As shown in Table 1, a molten aluminum (original molten aluminum) 10 made of aluminum raw material having an Fe impurity concentration of 400 (ppm by mass) and an Si impurity concentration of 205 (ppm by mass) was placed in a crucible 1 and subjected to a refining process. The refining apparatus and refining conditions were as follows:

[0045] The crucible 1 used was a cylindrical crucible with a bottom, an inner diameter (same as the inner diameter of the opening) D at the top of the molten metal of 500 mm, a depth H of 800 mm, and a downward-facing arcuate bottom, as shown in Figure 1. The cooling body 2 used was a graphite cooling body with an inverted truncated cone shape with a larger diameter at the top end and an outer diameter d of 220 mm at the top of the molten metal.

[0046] Compressed air was circulated as a cooling medium through the cooling body 2 at a rate of 1200 liters / minute, and the cooling body 2 was rotated at a constant peripheral speed of 4400 mm / s while being refined for 6 minutes.

[0047] During this refining, the inclination angle θ of the axis X2 of the cooling body 2 with respect to the axis X1 of the crucible 1 was set to 6°. The axis X2 of the cooling body 2 was set to intersect with the axis X1 of the crucible 1 on the surface of the molten metal 10.

[0048] The Fe impurity concentration and Si impurity concentration of the refined aluminum ingot of Example 1 thus obtained were measured, and the refining efficiency was calculated. The refining efficiency was determined as the ratio of the impurity concentration of the obtained refined aluminum ingot (refined ingot) to the impurity concentration contained in the original aluminum molten metal (original molten metal). The results are also shown in Table 1.

[0049] <Examples 2 to 4> For the original molten metal having the impurity concentration shown in Table 1, refining was carried out in the same manner as in Example 1 above, except that the inclination angle θ of the cooling body 2 was set to the angle shown in Table 1, to obtain the aluminum refined blocks of Examples 2 to 4, and the refining efficiency was similarly determined.

[0050] <Example 5> For the original molten metal having the impurity concentrations shown in Table 1, the inclination angle θ of the cooling body 2 was set as follows: That is, the inclination angle θ of the cooling body 2 was changed so as to gradually decrease during refining, with the inclination angle θ of the cooling body 2 being 35° at the start of refining and 10° at the end of refining. Otherwise, refining was carried out in the same manner as in Example 1 above to obtain the refined aluminum block of Example 5, and the refining efficiency was similarly determined.

[0051] <Comparative Examples 1 and 2> For the original molten metal having the impurity concentration shown in Table 1, refining was carried out in the same manner as in Example 1 above, except that the inclination angle θ of the cooling body 2 was set to the angle shown in Table 1, to obtain aluminum refined blocks of Comparative Examples 1 and 2, and the refining efficiency was similarly determined.

[0052] <Evaluation> In each of the refining methods of the Examples and Comparative Examples, the splashing of the molten metal during refining was evaluated. The evaluation criteria for the splashing of the molten metal were as follows: no splashing at all was evaluated as "◎", almost no splashing was evaluated as "◯", and slight splashing was evaluated as "△".

[0053] Furthermore, for each refining method in the Examples and Comparative Examples, an overall evaluation was conducted based on the evaluation of refining efficiency and molten metal splash. Regarding the overall evaluation, a "good" was given to a method that satisfied all three of the following conditions 1 to 3, and a "fair" was given to a method that did not satisfy any one of them. The evaluation results are also shown in Table 1.

[0054] Condition 1: Fe purification efficiency is 0.13 or less Condition 2: Si purification efficiency is 0.23 or less Condition 3: Water splash rating is "◎" or "〇" As can be seen from Table 1, the refining methods of Examples 1 to 5 have better refining efficiency than Comparative Example 1, and no molten metal splashing occurs, making it possible to highly efficiently refine metal while suppressing molten metal splashing. Furthermore, the refining method of Comparative Example 2 has high refining efficiency, but is unable to sufficiently suppress molten metal splashing, and this is where the method presents a problem. [Industrial Applicability]

[0055] The metal refining method of the present invention can be used, for example, to refine a high-purity substance from a substance containing eutectic impurities by utilizing the principle of segregation solidification, thereby reducing the content of eutectic impurities from the original substance. [Explanation of symbols]

[0056] 1: Crucible (container for holding molten metal) 2: Cooling body 10: Molten metal X1: Crucible axis (vertical axis) X2: Axis of the cooling body θ: Inclination angle of the cooling body

Claims

1. A metal refining method in which a cooling body is immersed in molten metal to be refined contained in a molten metal holding vessel, and high-purity metal is crystallized on the surface of the cooling body while the cooling body is rotated around its axis, A metal refining method characterized in that, when the cooling body is rotated in the molten metal, the axis of the cooling body is inclined at an angle of 5° to 50° with respect to a vertical axis.

2. 2. The metal refining method according to claim 1, wherein the axis of the cooling body is tilted at an angle of 10 to 40 degrees relative to the vertical axis when the cooling body is rotated in the molten metal.

3. 3. A metal refining method according to claim 1, wherein an axial center of said cooling body and an axial center of said molten metal holding vessel are made to intersect at the surface of the molten metal.

4. 4. The metal refining method according to claim 1, wherein the inclination angle of the axis of the cooling body relative to a vertical axis is changed while the cooling body is rotated within the molten metal.

5. 5. A metal refining method according to claim 4, wherein the inclination angle of the axis of said cooling body relative to the vertical axis is gradually decreased.

6. 6. The metal refining method according to claim 1, wherein the molten metal is aluminum.

7. A metal refining apparatus comprising a molten metal holding vessel for containing molten metal to be refined, and a cooling body that is immersed in the molten metal in the molten metal holding vessel and rotates about its axis so that high-purity metal is crystallized on its surface, A metal refining device characterized in that the cooling body rotating within the molten metal is configured so that its axis can be set to a state inclined at an angle of 5° to 50° with respect to the vertical axis.

8. 8. The metal refining apparatus according to claim 7, wherein the angle of inclination of the cooling body rotating in the molten metal relative to a vertical axis is changeable.

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