JPH0754072A - Method and device for refining aliminum scrap - Google Patents

Abstract

PURPOSE:To produce aluminum having high purity by refining raw material molten metal by segregation solidification. CONSTITUTION:A stirrer 3 immersed in the raw material molten metal 2 is rotated to entrain intermetallic compds. 6 crystallized near the solidification boundary and the impurities thickend liquid in stirring flow 7 so as to float on the mother liquor at the time of crystalling alpha-Al from the raw material molten metal 2 by the segregation solidification and obtaining the refined aluminum as the solid. The intermetallic compds. 6 are captured by a capturing member 8 disposed in mid-way of the flow route of the stirring flow 7. The solid grows on the base of a refining vessel 1 when the raw material molten metal is cooled by a cooling body 4 arranged in the bottom of, for example, the refining vessel 1. The molten metal is segregated and solidified while the intermetallic compds. 6 are captured and, therefore, the amt. of the intermetallic compds. to be trapped in products is decreased and the purity of the refined aluminum obtd. in such a manner is improved. The residual molten metal is usable as a material for aluminum alloys as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for obtaining purified aluminum while crystallizing and separating impurities contained in a raw material molten metal as an intermetallic compound.

[0002]

2. Description of the Related Art As a method for separating and removing impurities such as Fe contained in an aluminum raw material, Mn for purifying an intermetallic compound between the impurities and Al-Fe-Mn is added.
The method of crystallization separation is adopted as an intermetallic compound such as. For example, in JP-A-57-2134, Al
-Mn intermetallic compound was added to the method described in JP-A-59-12731.
In the publication, Mn or Al-Mn and Mg or Al-Mg
Is added together. In either method, Fe, which is a part of the impurities, is separated and removed as an Al—Fe—Mn-based intermetallic compound. However, these methods
It cannot be applied to aluminum raw materials containing. The obtained purified aluminum also contains Mn in an excessive amount, so that its use as an aluminum alloy is restricted.

Fe is the only impurity that can be removed by the Mn addition method. In this respect, other impurities are also removed by the refining method utilizing segregation and solidification. For example, in a system in which impurities are crystallized as primary crystals of intermetallic compounds, impurities are crystallized and separated in the process of gradually lowering the temperature of the raw material molten metal, and purified aluminum with increased purity is obtained as a molten metal or a solidified body. Further, in a system in which α-Al crystallizes as a primary crystal, purified aluminum is obtained as a solidified body and separated from the residual liquid in which impurities are concentrated. This type of purification method is introduced, for example, in Japanese Patent Laid-Open Nos. 61-3385 and 2-228432.

[0004]

When obtaining purified aluminum by segregation and solidification, it is important to prevent impurities crystallized as intermetallic compounds from being incorporated again into purified aluminum. However, the crystallized intermetallic compound is likely to remain at the solidification interface and is taken into the purified aluminum as it is, which causes a decrease in product purity. The crystallized intermetallic compound has a large specific gravity and precipitates in the molten metal. Therefore, in the method of growing purified aluminum as a solidified body on the bottom surface of the purification container, the intermetallic compound precipitated on the surface of the solidified body is easily incorporated into the purified aluminum. It is also possible to immerse the stirrer in the molten metal and put it on a stirring flow to remove the intermetallic compound from the solidification interface. However, since the precipitation rate increases with the grain growth of the crystallized intermetallic compound, the incorporation of the intermetallic compound by purified aluminum is still unavoidable. Even in a system in which α-Al crystallizes as a primary crystal, the impurity concentration of the residual liquid increases with the growth of the solidified body, and the intermetallic compound actively crystallized from the residual liquid is taken into the solidified body.

In the conventional refining method, the intermetallic compound that crystallizes during refining floats in the raw material melt. Unless the amount of the floating intermetallic compound is reduced, the amount of the intermetallic compound taken into the purified aluminum cannot be suppressed. However, a practical method for removing the floating intermetallic compound from the molten metal has not yet been developed. Therefore, there is a limit in improving the purity of the obtained purified aluminum. The present invention has been devised to solve such a problem, and captures an intermetallic compound that floats in a molten metal on an agitated flow and prevents the intermetallic compound from reaching the solidification interface again. By preventing it, it is intended to suppress an increase in the substantial impurity concentration of the molten metal and obtain purified aluminum with high purification efficiency.

[0006]

In order to achieve the object, the aluminum scrap refining method of the present invention is such that when a purified aluminum is obtained by crystallizing α-Al from a raw material molten metal by segregation solidification, it is immersed in the raw material molten metal. The stirrer was rotated, and the intermetallic compound and impurity concentrate crystallized near the solidification interface were placed on the stirring flow to float on the mother liquor, and the intermetallic compound was removed by the trapping member provided in the middle of the flow path of the stirring flow. It is characterized by collecting. For example, a raw material melt having a composition in which some of the impurities crystallize out as primary crystals of intermetallic compounds is placed in a refining vessel, and the raw material melt is cooled by a cooling body placed at the bottom of the refining vessel to solidify the refined aluminum. Grow as a body on the bottom of the purification container. At this time, since the crystallized intermetallic compound rides on the stirring flow and is carried away from the solidification interface, the crystallization reaction of the intermetallic compound is also accelerated. Moreover, since the crystallized intermetallic compound is collected by the trapping member, the effective impurity concentration of the molten metal does not increase.

Even in a system in which α-Al crystallizes as a primary crystal, the trapping member removes the intermetallic compound crystallized from the residual liquid in which impurities are concentrated. Therefore, as a result of suppressing the increase of the effective impurity concentration of the residual liquid, α-A
l preferentially crystallizes to obtain highly productive purified aluminum. The stirrer is rotated at an outer peripheral speed of 1 m / sec or more in order to carry the intermetallic compound and the impurity concentrated liquid on the stirring flow away from the solidification interface. Further, in order to obtain a constant stirring flow, it is preferable to rotate the stirring bar in one direction. Further, it is desirable to control the stirrer at a relatively high speed when the crystallization of the intermetallic compound is actively performed, and to control the rotation speed to be decreased when the crystallization rate of the intermetallic compound decreases. The refining equipment used is a refining vessel containing the raw material melt, a stirrer immersed in the raw material melt, a cooling body provided at the bottom of the refining vessel, and a stirrer flow generated by the rotation of the stirrer. And a captured member.

As the trapping member, a baffle plate having a container at the lower end is used, and the intermetallic compound colliding with the baffle plate is deposited in the container due to the difference in specific gravity. In this case, the baffle plate may be made of fiber and the container may be filled with the fibrous filter material.
The fibrous filter material attached to the inner wall of the purification container with a jig can also be used as the capturing member. The present invention will be specifically described by taking as an example a case where a part of impurities is crystallized as a primary crystal of an intermetallic compound. The amount of crystallization of the intermetallic compound generally depends on the temperature of the molten metal, and is determined according to the temperature difference at which the temperature of the molten metal drops to a temperature slightly higher than the solidification temperature. However, in the actual operation, the crystallized intermetallic compound and the concentrated impurity solution are likely to stay at the solidification interface, which is different from the theoretical crystallized amount calculated based on the phase diagram.

The stagnation of the crystallized intermetallic compound and the impurity concentrate at the solidification interface is eliminated by stirring the molten metal. That is, as shown in FIG. 1, the stir bar 3 is immersed in the raw material melt 2 contained in the refining vessel 1, and the raw material melt 2 is stirred while being cooled. Since the raw material melt 2 is cooled by the cooling body 4 provided at the bottom of the purification vessel 1, α-Al grows as a solidified body 5 from the bottom surface of the purification vessel 1. When α-Al solidifies, impurities crystallize out of the raw material melt 2 as intermetallic compounds 6. The intermetallic compound 6 and the impurity concentrate at the solidification interface are carried away from the solidification interface by the stirring flow 7 generated by the stirrer 3, and new molten metal is sent to the solidification interface.
Therefore, the impurity concentration of the molten metal is suppressed from locally increasing near the solidification interface, and the intermetallic compound 6 and α-Al are suppressed.
Crystallizes under conditions similar to the phase diagram.

At this time, the stirrer 3 having a directional blade is provided so that a downward flow is generated below the stirrer 3 and an upward flow is generated on the side wall of the refining vessel 1. 1
It is preferable to rotate at m / sec or more. If the peripheral speed is less than 1 m / sec, the action of removing the intermetallic compound 6 from the solidification interface becomes weak. The intermetallic compound 6 is given a large inertial force by the agitated flow 7 as much as the specific gravity is larger than that of the raw material melt 2. Therefore, it is carried to the vicinity of the inner surface of the side wall of the purification container 1 in which the capturing member 8 is provided. The intermetallic compound 6 is collected by the trapping member 8, and the molten metal having no intermetallic compound, in other words, having a low effective impurity concentration is the stirring flow 7 as the refining vessel 1
Circulate inside. Therefore, new crystallization of the intermetallic compound 6 and growth of the solidified body 5 are promoted.

As the catching member 8, for example, as shown in FIG. 2, a tubular body with a bottom whose peripheral surface is partially cut out in the axial direction is used. The cutout portion of the peripheral surface serves as the baffle plate 8a, and the tubular body portion serves as the container 8b. Further, the latch bar 8c may be fixed to the back surface of the baffle plate 8a by means such as welding. The latch bar 8c is locked to the support portion of the stirring bar 3 and the upper end of the side wall of the purification container 1. When the latch bar 8c is hooked on the support portion of the stirring bar 3, the capturing member 8 moves up and down in synchronization with the stirring bar 3. A heat-resistant material such as stainless steel having resistance to molten aluminum is used for the tube forming the capturing member 8. The trapping member 8 is the baffle plate 8
The inner surface of a is installed in the refining container 1 in a positional relationship in which it faces the stirred flow 7. The crystallized intermetallic compound 6 has a specific gravity of 4 or more, and has grown to a particle size with a large sedimentation rate due to the stirring effect. When the agitated flow 7 in which the intermetallic compound 6 is suspended collides with the baffle plate 8a, the flow velocity of the agitated flow 7 decreases and the intermetallic compound 6 settles due to the difference in specific gravity. The precipitated intermetallic compound 6 is stored in the container 8b below the baffle plate 8a.

When the fibrous filter medium is filled in the container 8b, the precipitated intermetallic compound 6 is captured by the filter medium,
It will not be sent out again from the container 8b into the refining container 1. Further, when the baffle plate 8a or the entire trapping member 8 is made of fibrous material, the intermetallic compound 6 is trapped by the baffle plate 8a, and the liquid-phase agitated flow 7 from which the intermetallic compound 6 is removed passes through the baffle plate 8a. It circulates in the purification container 1. As the capturing member 8, as shown in FIG. 3, a net basket 8d made of a heat-resistant material,
It is also possible to use a press-molded body of stainless steel cutting scraps 8e. Also in this case, the stirring flow 7
When passing through the trapping member 8, the floating intermetallic compound 6 is trapped by the cutting chips 8e, and only the liquid phase circulates in the purification container 1. In order to efficiently collect the intermetallic compound 6, the capturing member 8 is preferably arranged with the lower end as close to the surface of the solidified body 5 as possible. However, if they are brought too close to each other, they may be taken into the growing solidified body 5. Therefore, as the solidified body 5 grows, the capturing member 8
Is preferably raised. Further, in the stationary trapping member 8, the lower end is arranged above the solidification interface by 1 to 2 cm.

[0013]

In this way, the solidified body 5 is grown while the crystallizing intermetallic compound 6 is removed by the trapping member 8, so that the solidified body 5 and the residual hot water are efficiently separated. That is, the intermetallic compound 6 crystallized at the solidification interface has a specific gravity of 4 or more,
The particle size may grow to 100 μm or more due to the stirring effect. Therefore, even if the stirring strength is increased and the intermetallic compound 6 is placed on the stirring flow 7 to be suspended in the raw material molten metal 2, the sedimentation speed is high and the solidified body 5 may be taken in. In this respect, in the present invention, before the intermetallic compound 6 does not grow to a large particle size, it is carried on the stirring flow 7 and carried away from the solidification interface, and is collected by the trapping member 8. for that reason,
Less intermetallic compound 6 is brought into the solidified body 5,
The purity of the obtained purified aluminum is improved. Further, since the intermetallic compound 6 has a large specific gravity and a large particle size, a large inertial force is applied by the agitated flow 7 and the intermetallic compound 6 moves to the inner surface of the side wall of the purification container 1 at a high rate. Since the trapping member 8 is provided on the inner surface of the side wall, the trapping efficiency of the intermetallic compound 8 is high. Moreover, since the increase in the impurity concentration of the residual hot water is suppressed, the residual hot water can be used as a material for aluminum alloy depending on the application.

[0014]

【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. In the stirrer 3,
A graphite stirrer with a blade diameter of 200 mm was used. A trapping member 8 (FIG. 3) in which a net basket was filled with stainless steel cutting chips was suspended from the support of the stirring bar 3, and the height from the bottom surface of the purification container 1 to the lower end of the stirring bar 3 was set to 50 mm. At this time,
The lower end of the capturing member 8 is 100 mm from the bottom surface of the purification container 1.
Located at the height of. 150 kg of a raw material melt at a temperature of 640 ° C. in which aluminum scrap containing 8% by weight of Si, 0.8% by weight of Fe, 3% by weight of Cu and 0.4% by weight of Mn was melted was charged into the refining vessel 1. While rotating the stirrer 3 at the peripheral speed of the peripheral edge of the blade of 0.5 m / sec, cooling air was fed into the cooling body 4 at a flow rate of ³ m ³ / min, and the raw material melt 2 was cooled from the bottom surface of the purification container 1. By this cooling, the solidified body 5 becomes the purification container 1 at an average solidification rate of 50 mm / hour.
Grew from the bottom of the. The stirrer 3 and the trapping member 8 were raised according to the solidification speed, and the distance from the lower end of each to the solidification interface was kept constant.

35% by weight of the total amount of aluminum charged
When the solidification occurs, the rotation of the stirring bar 3 is stopped and the capturing member 8
Was pulled up from the purification container 1 together with the stirrer 3. afterwards,
Immediately, the purification container 1 was tilted, and the residual hot water in which impurities were concentrated was discharged. The purified aluminum obtained as the solidified body 5 contains Si: 4.8 wt%, Fe: 0.34 wt%, C
Although the content of u: 1.8% by weight and Mn: 0.16% by weight was contained, no incorporated intermetallic compound was detected. The trapping member 8 recovered 2.2 kg of the intermetallic compound 6 mainly composed of Al-Si-Fe-Mn system. When the refining vessel 1 was tilted, the amount of the intermetallic compound discharged together with the residual hot water without being captured by the capturing member 8 was 1.5 kg. For comparison, when purified under the same conditions except that the trapping member 8 was not used, the obtained solidified body 5 had a trace of the intermetallic compound 6 being trapped at the solidification interface in the center of the solidified interface. Was detected as. The amount of intermetallic compound discharged together with the residual hot water was 3.2 kg.

Example 2: Inner diameter 60 mm, container height 60
mm and baffle plate height 400 mm (Fig. 2)
The molten aluminum raw material was purified under the same conditions as in Example 1 except that The impurity concentration of the obtained purified aluminum was Si: 4.9% by weight, Fe: 0.36% by weight,
Cu: 2.0% by weight and Mn: 0.18% by weight. The intermetallic compound 6 recovered by the capturing member 8 is 2.6 k
The amount of the intermetallic compound that was not collected by the capturing member 8 and was discharged together with the residual hot water was 1.6 kg.

[0017]

As described above, in the present invention, when the molten aluminum is purified by segregation solidification,
Impurities that crystallize out as intermetallic compounds are carried on the stirring flow and carried away from the solidification interface, and the floating intermetallic compounds are collected by the trapping member. Therefore, purified aluminum can be obtained with high purification efficiency without impurities being excessively concentrated in the raw material molten metal circulating in the purification container. Further, since the residual liquid also has a reduced impurity concentration, it is used as a material for aluminum alloy according to the application. In this way, the two types of desired products are efficiently produced from aluminum scrap.

[Brief description of drawings]

1 is a vertical section (a) and a horizontal section (b) of a purification vessel fitted with a capture member according to the invention.

FIG. 2 is a perspective view (a) and a sectional view (b) of a capturing member.

[Fig. 3] Another capturing member packed with stainless steel cutting chips

[Explanation of symbols]

1: Purification container 2: Raw material melt 3: Stirrer 4:
Cooling body 5: Solidified body 6: Intermetallic compound 7: Stirred flow 8: Capture member
8a: baffle plate 8b: container 8c: hanging bar
8d: mesh basket 8e: cutting scraps of stainless steel

Claims (8)

[Claims] 1. A raw material melt containing α-Al by segregation solidification
When crystallizing to obtain purified aluminum, the stirrer immersed in the raw material molten metal is rotated, and the intermetallic compound and the concentrated impurity solution crystallized in the vicinity of the solidification interface are floated on the mother liquor by being placed on the stirring flow, and the stirring flow A method for purifying aluminum scrap, characterized in that the intermetallic compound is collected by a trapping member provided in the middle of the flow path. 2. A raw material melt having a composition in which a part of impurities are crystallized as primary crystals is contained in a refining vessel, and the raw material melt is cooled by a cooling body arranged at the bottom of the refining vessel.
The purification method according to claim 1, wherein purified aluminum grows as a solidified body on the bottom surface of the purification container. 3. The purification method according to claim 1, wherein the rotation speed of the stirrer is controlled according to the precipitation state of the intermetallic compound. 4. The purification method according to claim 1, wherein the stirring bar is rotated in one direction at a peripheral speed of 1 m / sec or more. 5. A refining container for containing the raw material melt, a stirrer immersed in the raw material melt, a cooling body provided at the bottom of the refining container, and a stirring flow generated by rotation of the stirrer. And a trapping member provided on the trapping member, the intermetallic compound floating on the stirring flow and floating from the solidification interface is repaired by the trapping member. 6. The capturing member according to claim 5, further comprising a baffle plate and a container provided at a lower end of the baffle plate, wherein the intermetallic compound precipitates from a stirring flow colliding with the baffle plate due to a difference in specific gravity. Purification device housed in a container. 7. A refining apparatus in which the container according to claim 6 is filled with a fibrous filter material. 8. A purifying device, wherein the capturing member according to claim 5 is a fibrous filter material attached to a lifting mechanism of a stirring bar by a jig.