JP7724100B2 - METAL REFINING METHOD AND METAL REFINING APPARATUS - Google Patents

Description

This invention relates to a metal refining method and apparatus for refining metals, and more specifically to a metal refining method and apparatus that utilizes the principles of segregation solidification to refine a high-purity substance from a substance containing eutectic impurities by reducing the eutectic impurity content to a level lower than that of the original substance.

When a metal contains impurities such as Fe, Si, or Cu that form a eutectic 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, then selectively extract the primary crystals as it cools and solidifies.

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 then rotating the cooling body to crystallize high-purity metal on its surface. 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 cooling body's periphery.

Patent Document 1 below proposes a metal refining method in which the cooling body is positioned at a position offset 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. This intentionally creates narrow and wide areas in the flow path of the swirling molten metal, causing the molten metal to flow radially around the crucible, thereby slowing the circumferential flow rate of the molten metal and increasing its relative velocity.

JP 2008-163420 A

However, the metal refining method described in Patent Document 1 above has the problem that the flow rate can become too fast in narrow parts of the flow path, and centrifugal force can cause the molten metal surface to rise excessively locally, which can easily lead to problems such as molten metal splashing (molten metal splashing).

This invention was made in consideration of the above-mentioned problems, and aims to provide a metal refining method and metal refining device that can achieve excellent refining efficiency and suppress the scattering of molten metal.

To achieve the above objectives, the present invention comprises the following means:

[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] The metal refining method described in paragraph 1, wherein the axis of the cooling body is tilted 10° to 40° with respect to the vertical axis when the cooling body is rotated within the molten metal.

[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 described in any one of the preceding paragraphs 1 to 3, wherein the cooling body is rotated within the molten metal while the inclination angle of the axis of the cooling body relative to the vertical axis is changed.

[5] A metal refining method as described in paragraph 4, in which the inclination angle of the axial core of the cooling body relative to the vertical axis is gradually decreased.

[6] A metal refining method according to any one of items 1 to 5, 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 around 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] The metal refining device described in paragraph 7 above, wherein the angle of inclination of the cooling body rotating within the molten metal relative to the vertical axis can be changed.

According to the metal refining methods of inventions [1] and [2], tilting the cooling body creates narrow and wide areas between the outer surface of the cooling body and the inner 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 surface of the cooling body relative to the molten metal and enabling 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 on the outer periphery of the cooling body is prevented from becoming extremely narrow or wide. This stabilizes the surface of the molten metal without disturbance and prevents the molten metal from splashing.

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. This means that the cooling body is positioned at the center of the molten metal at the molten metal surface, and the width of the flow path around the cooling body at the molten metal surface is approximately constant over the entire circumference, making the molten metal surface even more stable and more reliably preventing the molten metal from splashing.

The metal refining method of invention [4] allows the tilt angle of the cooling body to be changed appropriately depending on the progress of the refining process, making it possible to refine metal ingots of even higher purity.

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, more reliably eliminating 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.

The metal refining method of invention [6] refines aluminum, allowing the desired aluminum product to be obtained.

Inventions [7] and [8] specify a metal refining device that can implement the above-mentioned metal refining method invention, and therefore can achieve the same effects as above.

FIG. 1 is a schematic diagram showing the configuration of a metal refining apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II-II in FIG.

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

In the present invention, the shape of the crucible 1 is not limited to a cylinder, and it is preferable that the inner circumferential surface be curved whenever possible. Furthermore, the heating method for the furnace that constitutes the crucible 1 is not particularly limited, and for example, electric heating or a gas burner can be suitably used.

The temperature of the molten metal 10 needs only to exceed 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.

The metal refining apparatus of this embodiment is provided with a cooling body 2 that can be immersed in the molten metal 10 in the crucible 1. The 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 the cooling body 2 is not limited, and it may be cylindrical or have other shapes.

The rotating shaft 3 is tubular, with a hollow duct formed inside, and a space is 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 allows the cooling body 2 to be cooled from the inside.

A gas or liquid is used as the refrigerant. It is desirable to use a material with high thermal conductivity, such as metal or graphite, for the surface of the cooling body 2.

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

The rotation axis 3 is also configured so that its tilt angle relative to the vertical axis can be freely changed by a tilt drive means (not shown). 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 (which serves as the vertical axis) can be freely changed.

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

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, resulting in a high-purity metal ingot. The metal ingot adhering to the cooling body 2 can be removed and recovered by applying mechanical force or by reheating.

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

In this embodiment, suitable examples of refined metals include metals such as aluminum, silicon, magnesium, lead, and zinc, which contain eutectic impurities.

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 gap between the outer circumferential surface of the cooling body 2 and the inner circumferential surface of the crucible 1 exists in relatively narrow and wide areas. For example, at the lower end of the cooling body 2, the gap L1 between the outer circumferential surface of the cooling body and the inner circumferential surface of the crucible on the left side of FIG. 1 is narrower than the gap L2 between the outer circumferential surface of the cooling body and the inner circumferential surface of the crucible on the right side of FIG. 1. Because there are narrow and wide gaps between the outer circumferential surface of the cooling body and the inner circumferential surface of the crucible in this way, as the molten metal 10 flows from the narrow gap to the wide gap, the gap widens, 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 from the cooling body 2 acts in the radial direction (outer diameter direction), changing the direction of the flow of the molten metal 10. Even if the flow size 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 to the molten metal 10 can be increased, allowing for the refinement of a higher purity metal ingot.

Furthermore, the flow of the molten metal 10 also has a radial component, which promotes the outward diffusion of the concentrated impurity layer that forms at the solidification interface of the metal ingot that adheres to and grows on the outer surface of the cooling body 2, resulting in the production of a metal ingot with higher purity.

In addition, 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 described above, high-purity metal ingots adhere to and grow 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. This means that 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. This allows the molten metal to flow smoothly in the circumferential direction at the surface of the molten metal without being disturbed, thereby suppressing the scattering of the molten metal 10 and preventing the occurrence of so-called molten metal splashing (liquid splashing).

In particular, in this embodiment, the inclination angle θ of the cooling body 2 is set within a specific range, so the width of the flow path for the molten metal 10 does not become significantly narrower or wider around the outer periphery of the cooling body 2. Therefore, the surface of the molten metal remains stable without being disturbed, which also effectively prevents the molten metal 10 from splashing.

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 on the outer periphery of the cooling body 2 cannot be sufficiently ensured, the relative velocity between the outer surface of the cooling body and the molten metal 10 cannot be increased, and the flow of the molten metal 10 cannot be sufficiently guided radially, which may result in the purity of the metal ingot that adheres and grows being insufficiently high, which is undesirable. Conversely, if the inclination angle θ of the cooling body 2 is greater than 50°, there will be locations where the flow path width between the outer surface of the cooling body 2 and the inner surface of the crucible 1 becomes significantly narrow, which will cause a local rise in the molten metal surface (liquid level), which will promote the scattering of the molten metal 10 and may cause 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°.

The metal refined in this embodiment is highly pure, and can be used in a variety of processes and applications to demonstrate excellent properties and functionality. For example, the refined metal may be used in casting to produce castings, or these castings may be rolled and used as various metal plates or metal foils. Furthermore, these metal foils may be used, for example, as electrode material for aluminum electrolytic capacitors.

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. 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 surface of the cooling body 2 and the inner surface of the crucible 1 gradually increases, thereby reliably eliminating the problem of metal chunks adhering to and growing on the outer surface of the cooling body 2 coming into contact with the inner surface of the crucible 1.

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

Example 1
As shown in Table 1, a molten aluminum (original molten aluminum) 10 made of an 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:

As shown in Figure 1, 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. The cooling body 2 was made of graphite and had an inverted truncated cone shape with a larger diameter at the top end, and an outer diameter d at the top of the molten metal of 220 mm.

Then, 1,200 liters/minute of compressed air was circulated inside the cooling body 2 as a cooling medium, and the cooling body 2 was rotated at a constant peripheral speed of 4,400 mm/s while the refinement was carried out for 6 minutes.

During this refining process, the inclination angle θ of the axis X2 of the cooling body 2 relative 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 at the surface of the molten metal 10.

The Fe impurity concentration and Si impurity concentration of the refined aluminum ingot of Example 1 obtained in this manner were measured, and the refining efficiency was calculated. The refining efficiency is determined by 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.

<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.

Example 5
For the original molten metal having the impurity concentration 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 gradually decreased during refining so that the inclination angle θ of the cooling body 2 was 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 determined in the same manner.

<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.

<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 of the molten metal was observed at all, "Excellent", almost no splashing was observed, "Good", and some splashing was observed, "Good".

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 splashing. For the overall evaluation, a "Good" was given if all three of the following conditions 1 to 3 were met, and a "Poor" was given if any one of them was not met. These evaluation results are also shown in Table 1.

Condition 1: Fe refining efficiency is 0.13 or less. Condition 2: Si refining efficiency is 0.23 or less. Condition 3: Splash evaluation is "◎" or "〇".
As can be seen from Table 1, the refining methods of Examples 1 to 5 had better refining efficiency than Comparative Example 1, and no molten metal splashing occurred, making it possible to highly efficiently refine metal while suppressing molten metal splashing. Furthermore, the refining method of Comparative Example 2 had high refining efficiency, but was unable to sufficiently suppress molten metal splashing, and this was found to be a problem.

The metal refining method of this invention can be used, for example, to refine a high-purity material from a material containing eutectic impurities by utilizing the principles of segregation solidification, thereby reducing the eutectic impurity content compared to the original material.

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

Claims (8)

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. The metal refining method described in claim 1, wherein the axis of the cooling body is tilted 10° to 40° relative to the vertical axis when the cooling body is rotated within the molten metal. A metal refining method according to claim 1 or 2, wherein the axial center of the cooling body and the axial center of the molten metal holding vessel intersect at the surface of the molten metal. A metal refining method according to any one of claims 1 to 3, in which the cooling body is rotated within the molten metal while the inclination angle of the cooling body's axis relative to the vertical axis is changed. The metal refining method described in claim 4, wherein the inclination angle of the axial core of the cooling body relative to the vertical axis is gradually decreased. The metal refining method according to any one of claims 1 to 5, wherein the molten metal is aluminum. 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. The metal refining apparatus described in claim 7 is configured so that the angle of inclination of the cooling body rotating within the molten metal relative to the vertical axis can be changed.