JPH0754062A - Aluminum scrap refining method - Google Patents

Abstract

(57) [Summary] [Purpose] To purify an aluminum material having a target composition from molten metal of aluminum scrap by utilizing segregation solidification. [Structure] A molten aluminum raw material 2 contained in a rotatable refining vessel 1 is maintained at a temperature equal to or higher than the freezing point of α-Al,
The molten metal 2 is cooled by the cooling body 7 arranged at the bottom of the purification container 1, while stirring the raw material molten metal 2 with the stirrer whose rotating shaft 3 or the vertical axis is deviated from the rotation center C of the purification container 1. Purified aluminum is obtained as a solidified body 8 in which impurities are crystallized and separated. The stirring bar may be moved in the horizontal direction simultaneously with the rotation of the purification container 1. [Effect] Since no stagnation portion is formed below the rotating shaft 3 or the vertical shaft, the crystallized impurities and the impurity concentrated liquid are carried away from the solidification interface to the mother liquor, and purified aluminum having high purity as a whole is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refining method for obtaining an aluminum material having a target composition while crystallizing and separating impurities contained in a molten raw material.

[0002]

2. Description of the Related Art Fe contained in molten aluminum,
To separate and remove impurities such as Mn, a method utilizing segregation solidification is adopted. When the molten metal is transformed from the liquid phase to the solid phase, impurities in the molten metal are discharged into the liquid phase, and the purity of the obtained solidified body is increased. In this method, in order to increase the purity of the purified aluminum, various means for preventing impurities from being mixed into the solidified body are adopted. A typical method is to stir the molten metal and diffuse the crystallized impurities and the impurity concentrate into the mother liquor from the solidification interface. The stirrer used for stirring the molten metal is immersed in the molten metal 2 housed in the refining vessel 1 from above, as shown in FIG. 1, so that the stirring shaft extending horizontally in the rotating shaft 3 extending in the vertical direction. It has a structure with blades 4 attached. Instead of the rotating method, a stirrer having a vertical shaft that moves vertically in the vertical direction or a rotatable vertical shaft is also used. As a refining method using a stirrer, for example, in Japanese Unexamined Patent Publication No. 56-146838, a stirrer is arranged in the vicinity of the solidification interface, and impurities that tend to concentrate on the solidification interface are diffused into the molten metal by the stirrer. Further, in Japanese Patent Laid-Open No. 57-160568, a stirrer having a large number of holes is immersed in the molten metal, and the stirrer is moved up and down to stir the molten metal.

[0003]

Regardless of which stirrer is used, the stirring flow 5 spreads outward of the purification container 1 around the rotary shaft 3 or the vertical shaft. Therefore, the molten metal 2 below the rotary shaft 3 or the vertical shaft is weakly stirred as compared with the molten metal 2 around it, and may not be stirred in an extreme case. As a result, impurities 6 crystallized from the molten metal 2
Tend to collect in the center of the purification container 1. Even if the impurities 6 do not deposit, a region having a high impurity concentration is formed in a portion where the stirring effect is weak. Under this circumstance, when the molten metal 2 is cooled by the cooling body 7 arranged in the lower part of the refining vessel 1 and the solidified body 8 is grown, the deposited impurities 6 and the impurity concentrated liquid are solidified in the solidified body 8.
It is easy to be taken in by. As a result, the concentration of impurities in the solidified body 8 located below the rotary shaft 3 or the vertical axis increases, and the overall purification efficiency decreases.

In order to increase the purity of purified aluminum, it is necessary to diffuse the impurities 6 into the molten metal 2 from the solidification interface of the solidified body 8. However, with conventional stirrers,
It is unavoidable that the crystallized impurities 6 and the impurity-concentrated region locally gather and stay at the solidification interface of the solidified body 8. Therefore, there is a limit to the increase in the purity of the purified aluminum obtained as the solidified body 8. The present invention has been devised in order to solve such a problem, by locally moving the stirrer with respect to the refining vessel, to locally agglomerate the crystallized impurities and the retention of the impurity concentrate. The purpose is to solve this problem and obtain highly purified aluminum.

[0005]

In order to achieve the object, the refining method of the present invention holds the molten aluminum raw material contained in a refining vessel that continuously or intermittently rotates at a temperature not lower than the freezing point of α-Al. Then, while stirring the raw material molten metal with a stirrer whose rotation axis or vertical axis is deviated from the rotation center of the purification container, the molten metal is cooled by a cooling body arranged at the bottom of the purification container, It is characterized in that purified aluminum is grown as a solidified body from the bottom surface. As the stirrer, a stirrer equipped with a stirring blade near the lower end of a vertically extending rotary shaft or vertical shaft is used, and the stirrer is rotated or moved vertically while being immersed in the molten metal. Further, the stirring bar may be moved in the horizontal direction simultaneously with the rotation of the purification container.

[0006]

[Operation] When the molten aluminum is cooled and solidified,
There is a phenomenon in which the impurity concentration near the solidification interface rapidly increases as the solidification progresses. The increase in the impurity concentration lowers the purity of the purified aluminum obtained as a solidified body and reduces the purification efficiency. The increase of the impurity concentration is avoided by moving the impurities discharged near the solidification interface away from the solidification interface. Further, the higher the efficiency of moving away, the higher the efficiency of purification. The present inventors have variously investigated and studied the relationship between the stirring form and the purification efficiency based on such a premise. When the molten metal is simply stirred by the stirrer immersed in the molten metal, the liquid at the solidification interface is replaced with the mother liquor by the stirring flow 5 as described with reference to FIG. 1, but the stirring is performed in the portion located below the stirrer. The effect is smaller than the surroundings. In particular, since the rotary stirrer produces the stirring flow 5 by the rotary motion of the molten metal 2, it becomes relatively stationary in the central portion of the purification container 1, which is below the rotary shaft 3.
When the aluminum scrap is refined as a melting raw material in this state, the crystallized intermetallic compound particles are collected in the central portion of the solidification interface and taken into the solidified body 8.

In the present invention, in order to prevent the impurities 6 from gathering in the central portion of the purification container 1, the purification container 1 is rotatably provided as shown in FIG. 3 is offset and a stir bar is arranged. For the stirrer, graphite, graphite-silicon carbide fired body, or the like, which has excellent resistance to corrosion by molten aluminum, is used. As shown in FIG. 2A, the refining vessel 1 is placed on a rotating disk 9 with a cooling body 7 interposed therebetween. A rotary drive shaft 10 that is rotated by receiving power output from an appropriate drive source is fixed to the rotary disk 9. Therefore, the purification container 1 rotates about the rotation drive shaft 10.

As shown in FIG. 2 (b), the rotating shaft 3 of the stirring bar is set at a position deviated from the rotation center C of the refining vessel 1 by a distance d. The deviation distance d is 1 of the diameter of the rotating shaft 3.
/ 2 or more is preferable. However, if the deviation distance d is set too large, the opposite side to the rotation center C, as shown in FIG.
In this case, the stirring effect on the right side becomes smaller, and the stirring action given to the molten metal 2 is weakened as a whole. Under normal operating conditions, the deviation distance d falls within 1/2 of the distance between the stirring blade 4 and the inner wall of the purification container 1 when the rotary shaft 3 is set at the center of the purification container 1.
Is preferably defined. When the molten metal 2 is agitated by the deflected stirrer, the agitated flow 5 whose center position is displaced according to the displacement distance d is generated in the molten metal 2. At this time, the rotary drive shaft 1
Since the purification container 1 is rotated by 0, the stirring flow 5
Moves circularly around the center of rotation C. Therefore, the portion located below the rotary shaft 3 as described with reference to FIG. 1 does not become stationary. Therefore, the impurities crystallized as the intermetallic compound from the molten metal 2 are carried on the stirring flow 5 and carried away from the entire solidification interface of the solidified body 8.

Although FIG. 2 shows a stirring bar in which the stirring blade 4 is attached to the rotating shaft 3, the present invention is not restricted to this, and the stirring blade is attached to the shaft that moves up and down instead of the rotating shaft 3. It is also possible to use a stirrer. In this case, by displacing the vertical axis from the rotation center of the refining vessel 1, the crystallized impurities can be similarly diffused into the molten metal 2. The rotary shaft 3 or the vertical shaft may rotate or move vertically at a fixed position, or may be arranged so as to be relatively movable in the horizontal direction. The relative movement in the horizontal direction changes the stirring flow 5 from the steady flow to the unsteady flow in combination with the rotation of the purification container 1 and the stirring by the stirring blade 4. Unsteady state stirring flow 5
Makes the action of winding impurities from the solidification interface of the solidified body 8 into the molten metal 2 irregularly fluctuate, and makes the removal of impurities at the solidification interface more effective.

After the stirrer is immersed in the molten metal 2, the stirrer and the refining vessel 1 are started to rotate. The timing of starting the rotation of the stirring bar and the timing of starting the time point of the purification container 1 may be either first or the same. The relative movement of the stirrer with respect to the horizontal direction is performed by a method of moving the stirrer together with the holding device in the horizontal direction, a method of moving the rotating disk 9 on which the purification container 1 is placed, or a combination of these methods. be able to. It is preferable that the purification container 1 is continuously rotated at a constant speed. However, it is of course possible to rotate the purification container 1 intermittently or change the rotation speed. The rotation speed of the stirrer is preferably set in the range of 1 to 8 m / sec as the peripheral speed on the outer circumference of the stirring blade 4 in order to obtain a good stirring effect.

[0011]

【Example】

Example 1: As the purification container 1, a graphite crucible having an inner diameter of 400 mm and a height of 800 mm was used. As a stirrer, a stirring blade 4 with a diameter of 200 mm is used as a rotating shaft 3 with a diameter of 50 mm.
I used it. Rotation center C of the purification container 1
The rotation axis 3 at a position displaced from the deviation distance d = 50 mm from
Set 150 kg of molten aluminum to the purification container 1
Charged into. The purification container 1 is rotated at a rotation speed of 2 r. p. m. While rotating at 1, the stirring bar was rotated at an outer peripheral speed of 1.3 m / sec. Further, the stirring bar was moved left and right at a moving speed of 100 mm / min within a range of 50 mm from the center of rotation C to the left and right. The molten metal 2 is a cooling body 7 arranged at the bottom of the refining vessel 1.
Was cooled at a cooling rate of 1 ° C./min. As a result, the solidified body 8 grew upward from the bottom surface of the purification container 1. In addition,
The height from the solidification interface to the lower end of the stir bar is a constant value of 50 mm
The stir bar was raised according to the growth of the solidified body 8 so as to be maintained at.

About 3 of the aluminum charged under these conditions
The growth of the solidified body 8 was continued until 5% by weight solidified. When the target amount of solidification was obtained, the stir bar was taken out of the purification container 1 and the molten metal 2 remaining in the purification container 1 was solidified together with the solidified body 8. After completion of cooling, the aluminum block was taken out of the purification container 1 and vertically divided into two. When the cross section was observed, as shown in FIG. 3, the refining section 11 corresponding to the solidified body 8 and the impurity concentrating section 12 were clearly distinguished by the boundary line 13. The refining section 11 was cut along a cutting line 14 slightly deviated from the boundary line 13 to the refining section 11 side, and samples for analysis were collected from the refining section 11 at measurement points P _{1 to} P ₃ . The measurement point P ₁ is located at the center of the refining section 11, the measurement point P ₂ is located at a position 80 mm away from the center point, and the measurement point P ₃ is also located at a position 160 mm apart. Table 1 shows the impurity concentrations at the measurement points P _{1 to} P ₃ . In addition, Table 1 shows, as a comparative example, a case where aluminum is refined while stirring the molten metal 2 with a stirrer arranged at the center of the refining vessel 1 without rotating the refining vessel 1.

[0013]

[Table 1]

As is clear from Table 1, in the comparative example in which the eccentricity of the stirrer and the rotation of the purification container 1 did not occur, the impurity concentration of the sample collected from the measurement point P ₁ corresponding to the center of the solidified body 8 was Si. , Fe and Cu are significantly higher than the impurity concentrations of the samples taken from the other measurement points P ₂ and P ₃ . This is because the deposited and concentrated impurities 6 described in FIG. 1 are taken into the solidified body 8. On the other hand, in the embodiment in which the stirring bar is eccentric and the purification container 1 is rotated according to the present invention, the difference in impurity concentration between the measurement points P _{1 to} P ₃ is extremely small, and the purified aluminum is highly purified as a whole. Has been obtained.

[0015]

As described above, in the present invention, when aluminum is refined by the segregation solidification of the molten metal, the refining vessel containing the molten metal is rotated and the rotary shaft or the vertical shaft is rotated from the rotation center of the refining vessel. The molten metal is stirred by a stirrer that is offset. The stirring flow generated by the stirring bar moves circularly around the rotation center of the purification container. Therefore, the crystallized impurities and the impurity concentrate are carried away from the solidification interface to the mother liquor without forming a region where the impurities are easily aggregated or concentrated under the stirring bar. Therefore, purified aluminum having a high degree of purity can be obtained as a solidified body without the crystallized impurities and the concentrated impurity solution being taken into the solidified body.

[Brief description of drawings]

FIG. 1 Conventional refining device

FIG. 2 Purification device according to the invention

[Fig. 3] Longitudinal section of a cooled and solidified aluminum block

[Explanation of symbols]

1: Purification container 2: Molten metal 3: Rotating shaft 4: Stirring blade 5: Stirring flow 6: Deposited impurities 7: Cooling body 8: Solidified body
9: rotating disk 10: rotary drive shaft 11: refining unit
12: Impurity enrichment part 13: Boundary line 14: Cutting line C: Center of rotation of the purification container d: Eccentric distance of the rotation axis
P _{1 to} P ₃ : Measurement points

Claims (3)

[Claims] 1. A rotary or vertical axis is deviated from the rotation center of the refining vessel by holding the molten aluminum raw material contained in a refining vessel that continuously or intermittently rotates at a temperature equal to or higher than the freezing point of α-Al. While stirring the raw material molten metal with a stirrer, the molten metal is cooled by a cooling body arranged at the bottom of the refining vessel, and purified aluminum is grown from the bottom surface of the refining vessel as a solidified body of aluminum scrap. Purification method. 2. The purification method according to claim 1, wherein an agitator having an agitating blade attached near the lower end of a vertically extending rotary shaft or a vertical shaft is used. 3. The refining method according to claim 1, wherein the stirring bar is relatively moved in the horizontal direction simultaneously with the rotation of the refining vessel.