JPH0873959A - Method for refining aluminum and device therefor - Google Patents

Abstract

PURPOSE: To efficiently refine aluminum by utilizing the fact that the impurities crystallized as intermetallic compds. have the sp. gr. larger than the sp. gr. of the aluminum. CONSTITUTION: The molten aluminum M in which the impurities are crystallized as the intermetallic compds. from the melt is housed into a refining vessel 10 and is kept in a state of having a prescribed temp. distribution by a heater 20. The molten aluminum M is cooled by a rotary cooling body 30 disposed in the upper part of the refining vessel 10 to allow the refined aluminum α-Al to solidify and grow. The intermetallic compds. crystallized from the molten aluminum M gather at the bottom of the refining vessel 10 by settling together with the concd. liquid of the impurities, thereby yielding the flocculated and concd. liquid I. The rotary cooling body for crystallizing the α-Al on the rear surface 37 of the cooling body accelerates the crystallization and sepn. of the impurities as the intermetallic compds., thereby improving the refining efficiency of the resulted aluminum.

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 efficiently purifying an aluminum melt in which impurities are crystallized as an intermetallic compound.

[0002]

2. Description of the Related Art There is known a method of purifying aluminum by adding impurities such as Fe and elements forming an intermetallic compound to a molten aluminum and separating the crystallized intermetallic compound. For example, JP-A-57-2134
In Japanese Patent Laid-Open No. 59-12731, Mn or Al-Mn and M are added.
g or Al-Mg is added together. In either method, Fe as an impurity is separated and removed as an Al-Fe-Mn-based intermetallic compound. When the impurities are separated and removed by adding Mn, an excessive amount of Mn is added, so that the purified aluminum material contains a large amount of Mn as impurities. Further, impurities such as Fe that do not form an intermetallic compound with Mn cannot be separated and removed from the aluminum material. Moreover, it is very difficult to separate and remove the crystallized intermetallic compound from the aluminum material, and the recovery rate itself is low, which is not a practical purification method.

By the way, JP-A-57-92148 introduces a method of purifying an aluminum material by utilizing segregation solidification. In this method, the molten aluminum contained in the crucible is cooled and solidified from the bottom of the crucible while stirring the molten aluminum with a stirrer.
The high-concentration impurity solution at the solidification interface diffuses upward from the solidification interface without being caught in the solidified body by the stirring flow of the molten aluminum given by the stirrer. Therefore, a high-purity aluminum material is produced as a solidified body at the bottom of the crucible.

[0004]

The high-concentration impurity solution released from the solidified body diffuses throughout the molten aluminum. Therefore, as the solidified body grows, impurities are concentrated in the remaining molten aluminum. When the impurity concentration is high, it is impossible to prevent the impurities from being taken into the solidified body. Therefore, JP-A-57-9214
In the case of purifying an aluminum material by the method described in Japanese Patent Publication No. 8, the remaining aluminum melt must be discharged from the crucible when about half of the molten amount of the aluminum material injected into the crucible is solidified. That is, the whole amount of the aluminum material charged in the crucible is not purified as a solidified body, and the purification method is poor. Further, since the aluminum material that is not refined as a solidified body is also heated and melted, wasteful heat energy is consumed.

The present inventors have developed a refining method for solving such a drawback by developing a method of crystallizing refined aluminum on the lower surface of the cooling body set on the upper part of the container.
It was introduced in Japanese Patent Publication No. 295465. In this method, the intermetallic compound crystallized along with the refining of aluminum falls to the bottom of the container to improve the refining efficiency. The present invention was discovered in the course of research to further enhance the action of the cooling body on the crystallization separation of the intermetallic compound, and further promotes the crystallization separation of the intermetallic compound by rotating the cooling body. And to purify aluminum with higher efficiency.

[0006]

In order to achieve the object, the aluminum refining method of the present invention contains, in a refining vessel, an aluminum melt in which impurities are crystallized as intermetallic compounds from a melt, and the upper part of the refining vessel It is characterized in that the molten aluminum is cooled by a rotary cooling body inserted from the above to obtain purified aluminum, and the crystallized intermetallic compound is dropped by gravity onto the bottom of the purification container. Further, the aluminum refining apparatus includes a refining container in which molten aluminum is stored, a rotatable cooling body mounted in an upper opening of the refining container, and a heater which is arranged around the refining container and which can control heating. It is characterized in that the intermetallic compound crystallized from the molten aluminum is aggregated in an impurity concentration portion formed at the bottom of the purification container.

A method in which the intermetallic compound crystallized and separated is solidified together with purified aluminum and then the intermetallic compound is separated, or the impurity concentrated liquid accumulated at the bottom of the refining vessel is continuously or intermittently supplied by a metal pump or the like. Purified aluminum is recovered by any method, such as a method of refining while pumping out. In the case of solidifying together with purified aluminum, the intermetallic compound or impurity concentration part is cut off by cutting separation or the like. Further, purified aluminum may be drawn out from the refining container while the molten aluminum remains at the bottom of the container to separate the crystallized intermetallic compound. When the refined aluminum adheres to the inner wall of the refinement container, the refined aluminum is easily taken out from the refinement container by slightly heating and melting the surface layer of the refined aluminum. When the impurity concentrate is pumped out continuously or intermittently by a metal pump or the like, it is preferable to replenish the refining vessel with the molten metal raw material in accordance with the discharge amount of the impurity concentrate. Purified aluminum can also be continuously withdrawn by removing the furnace lid during the refining operation. Also in this case, it is preferable to add the molten metal raw material to the refining vessel according to the refining amount.
When the refining aluminum drawn from the refining container is blown with a cooling medium such as cooling air, the refining operation is speeded up.

The purification method according to the present invention is shown in FIG.
It is carried out using the device having the equipment configuration shown in. As the refining vessel 10, a graphite crucible or a crucible obtained by mixing and firing graphite and SiC is usually used. Crucible body 11
Is put in the outer container 12, and the lid 13 is attached. A burner 14 for temperature control may be attached to the lid 13. The bottom of the refining vessel 10 preferably has the lowest center at the bottom and an inclined surface that is inclined upward toward the periphery so that impurities crystallized from the molten metal M are easily deposited. Purification container 1
On the outer periphery of 0, the heating mechanism 20 is arranged so as to surround the outer container 12. The heating mechanism 20 has a heater 21 on the inner peripheral side.
Heater block 22-24 made of refractory brick with attached
It is preferable that the heat quantity of each of the heater blocks 22 to 24 is independently controlled. At the bottom of the purification container 10,
The heater block 25 is arranged. By adopting the independently controllable heater blocks 22 to 24, the vertical temperature distribution of the molten metal M in the refining vessel 10 can be adjusted.

The aluminum scrap to be refined is charged into the refining vessel 10 and then melted by heating from the heater blocks 22 to 25, and is maintained at a temperature slightly higher than the freezing point of α-Al. Molten metal M held in a molten state
The rotary cooling body 30 is dipped in. The rotary cooling body 30 is
It has a double pipe structure in which the outer pipe 32 is fitted to the inner pipe 31. The inner pipe 31 and the outer pipe 32 are provided at their lower end portions with flanges 33 and 34 which are spread in the axial direction.
Plural orifices 35 are formed in the flange 33. In the case of FIG. 1, the inner pipe 31 and the outer pipe 32 are made of stainless steel, but a graphite block having a predetermined gas passage may be used.

The flanges 33 and 34 have a circular shape, and a cylindrical heat insulating material 36 is attached to the peripheral edges thereof. A bottom wall 37 is attached to the bottom surface of the heat insulating material 36 at a constant distance from the flange 33. A cooling medium 40, such as air or an inert gas, is sent from the supply port 41 to the outer pipe 32, passes through the annular passage 42 formed between the inner pipe 31 and the outer pipe 32, and between the flanges 34 and 33. It is introduced into the distribution chamber 43 formed in. Then, the cooling gas flows into the cooling chamber 44 via the orifices 35, 35. At this time, the cooling gas once flows from the annular passage 42 into the distribution chamber 43 having a large internal volume and is then sent to the cooling chamber, so that the flow rate distribution in the radial direction is made uniform.

The cooling gas in the cooling chamber 44 cools the molten metal M through the bottom wall 37. Since the heat removal ability of the cooling gas is made uniform within the surface of the bottom wall 37, α-Al crystallizes uniformly from the cooled melt M on the lower surface of the bottom wall 37. The cooling gas whose temperature is raised by heat exchange with the molten metal M is discharged from the cooling chamber 44 to the outside of the system through the exhaust passage 45 in the inner pipe 31 and the exhaust hole 46. The outer tube 32 penetrates through the lid 13 and extends upward, and the output shaft 53 of the motor 52 is interposed via the coupling 51.
It is connected to the. Arm 54 extending from motor 52
Is fitted into a feed screw 56 rotated by a motor 55. As a result, the rotary cooling body 30 rotates in the refining container 10 so as to be vertically movable.

The cooling medium 40 includes air, non-oxidizing gas,
Air containing mist-like water is used. Due to the flow of the cooling medium 40, the molten metal M is cooled through the bottom wall 37, and α-Al grows on the lower surface of the bottom wall 37. Temperature of molten metal M and α
The Al growth rate is optimally maintained by controlling the flow rate of the cooling medium 40. When the temperature of the molten metal M decreases, in a system in which the primary crystal is an intermetallic compound, for example, Al-Si-Fe-M.
The n-based intermetallic compound crystallizes on the surface of the bottom wall 37. With the crystallization of the intermetallic compound, the remaining molten metal M is purified and the temperature further decreases. Therefore, the α-Al layer is crystallized on the surface of the intermetallic compound. At this time, Si, F discharged to the interface between α-Al and the molten metal M by the rotation of the rotary cooling body 30.
Impurities such as e and Cu crystallize out as an intermetallic compound I having a larger specific gravity than the molten metal M, and thus fall in the molten metal M as schematically shown in FIG. Intermetallic compound I is
By the stirring flow of the molten metal M generated by the rotation of the rotary cooling body 30,
Collect in the center of the bottom of the crucible body 11 (Fig. 1).

In the case of a molten metal whose primary crystal is α-Al, α-Al first crystallizes on the surface of the bottom wall 37. α-
The impurities concentrated in the residual liquid due to the crystallization of Al become intermetallic compounds and fall in the molten metal M. The rotary cooling body 30 is
The α-Al rotates at a peripheral speed for diffusing the impurity element and the intermetallic compound I crystallized in the molten metal M when the α-Al solidifies. At an excessively high rotation speed, the vortex generated by the rotation of the rotary cooling body 30 becomes large, and not only the oxidation of aluminum, which causes a decrease in yield, progresses, but also the molten metal M scatters, which causes safety and operational inconvenience. Occurs. Further, the solidified α-Al layer scatters in the molten metal M due to the centrifugal force, and the solidification efficiency deteriorates.

Specifically, the rotation speed of the rotary cooling body 30 is preferably set at an outer peripheral speed of 0.2 to 8 m / sec. Also,
In order to prevent the oxide film floating on the surface of the molten metal M from being entrained, it is preferable to rotate the rotary cooling body 30 in one direction, but the rotary cooling body 30 may be periodically rotated alternately.
When the α-Al layer has grown to the set value, the supply of the cooling medium 40 and the rotation of the rotary cooling body 30 are stopped, and the motor 55 is rotated to take out the rotary cooling body 30 from the crucible body 11. Immediately thereafter, the entire refining vessel 10 is tilted, and the remaining molten metal M and the intermetallic compound I deposited on the furnace bottom are discharged. Then, α crystallized on the bottom wall 37 of the rotary cooling body 30
-The Al layer is transferred to a refining metal recovery furnace arranged on the refining furnace side, melted and recovered. When the primary crystal is an intermetallic compound and is crystallized in a two-layer structure with α-Al on the bottom wall 37, the primary crystal is melted by heating to a temperature at which the intermetallic compound is not dissolved, and
Separate Al. In some cases, the α-Al layer can be mechanically scraped and separated from the intermetallic compound.
After the start of crystallization, it is also possible to gradually raise the rotary cooling body 30 to expose the cooling body portion above the surface of the molten metal, and to continue the crystallization process in the state where only α-Al is in the molten metal. In this case, the corrosion of the rotary cooling body 30 due to the molten aluminum is suppressed.

[0015]

Example A graphite crucible having an inner diameter of 400 mm and a height of 800 mm was mounted on the refining apparatus shown in FIG. 1, and the primary crystal was α-Al.
150 kg of aluminum raw material having a composition of A rotary cooling body having a diameter of 300 mm was set so that the bottom wall 37 was positioned at a depth of 20 mm from the surface of the generated molten aluminum. The molten aluminum was cooled through the cooling body by sending air into the rotating cooling body at a flow rate of 1000 l / min while rotating the cooling body at a speed of 100 rpm. With cooling, α-Al began to crystallize from the molten aluminum. The crystallization start time could be measured based on the thermal analysis curve. Crystallization was continued until 30 minutes passed from the start of crystallization.

The refined metal crystallized on the lower surface of the cooling body was separated from the cooling body by pulling up the cooling body after the crystallization reaction and taking it out from the furnace and melting it in another refined metal recovery furnace. A sample for analysis was sampled from the metal thus melted, and the composition was analyzed. Table 1 showing the analysis results
As can be seen from the above, the eutectic impurities such as Si, Fe, Cu and Mg were reduced, and 12 kg of aluminum having high purity was obtained. The refining efficiency is the reduction rate of impurities contained in the refined metal based on the impurities contained in the source metal, that is, [(impurity concentration in the source metal)-(impurity concentration in the refined metal)]. It was expressed as / (impurity concentration in raw material metal) × 100 (%). In addition, the content of impurities concentrated in the residual hot water after separating the refined metal was also measured and is also shown in Table 1.

[0017]

[Table 1]

On the other hand, except that the cooling body was not rotated, the aluminum raw material was melted and purified under the same conditions to obtain 13 kg of purified metal. An analytical sample was sampled from the purified metal. Table 2 shows the analysis results of impurities contained in the residual hot metal after separating the analytical sample and the purified metal.

[0019]

[Table 2]

As is clear from the comparison between Table 1 and Table 2,
Si, Fe, Cu, Mg, etc., which are typical impurities, are significantly reduced by rotating the cooling body, and it can be seen that the refined metal is refined to a higher purity.

Example 2: Using the same apparatus as in Example 1,
150 kg of an aluminum raw material having a composition in which the primary crystal is an intermetallic compound was melted. The rotary cooling body 30 was set under the same conditions as in Example 1. The rotation speed of the rotary cooling body 30 and the flow rate of the cooling air were also set to the same values as in Example 1. Crystallization was continued until 2 hours had elapsed from the start of crystallization that could be measured based on a thermal analysis curve. At the end of crystallization, the rotary cooling body was pulled out of the refining furnace, the rotary cooling body was transferred to another recovery furnace, and the atmosphere was raised to 750 ° C., so that the entire crystallized substance separated from the bottom wall 37 of the rotary cooling body 30. fell down.

Since the separated crystallized substance was still in the form of lumps, the ingot obtained by cooling as it was was investigated. The recovered weight at this time was 23 kg. An intermetallic compound was crystallized as a primary crystal on the contact surface of the bottom wall 37 with a thickness of about 3 mm, and then α-Al was crystallized downward. Table 3 shows the results of analysis of the raw material molten metal, the residual liquid at the end of crystallization, the intermetallic compound crystallized as the primary crystal, and the α-Al crystal.
The residual hot water at this time was stirred and mixed with the deposits deposited on the bottom of the furnace to obtain an analytical sample. Further, the primary crystal intermetallic compound was separated from the obtained ingot by cutting. As is clear from Table 3, the primary intermetallic compound is Si-Fe-Mn.
-Cu system, the purification efficiency of α-Al crystals is 5 except Zn.
It was 0% or more.

[0023]

[Table 3]

Example 3: With the same raw material composition as in Example 2 in which the primary crystal was an intermetallic compound, the intermetallic compound was first dropped into the furnace bottom without being crystallized as the primary crystal on the bottom wall 37. In this case, the raw material melt was held at 610 ° C. for 1 hour to crystallize and drop the intermetallic compound to the furnace bottom, and then the rotary cooling body was immersed.
Crystallization of α-Al was started. Rotating speed of the rotating cooling body is 2
00 revolutions / hour, cooling air flow rate 2000 liters /
Min, and the α-Al crystallization treatment time was set to 1.5 hours.
Then, by the same operation as in Example 2, the crystallized ingot was investigated. The obtained ingot was 22 kg. Unlike Example 2, no intermetallic compound was crystallized on the contact surface of the bottom wall 37, confirming the effectiveness of the intermetallic compound treatment effect by holding the molten metal. Table 4 shows the analysis results in this case.

[0025]

[Table 4]

When comparing the compositions of the molten metal raw materials before and after the intermetallic compound crystallization treatment shown in Table 4, it is found that the Fe-Mn-based intermetallic compound is precipitated at the furnace bottom due to the intermetallic compound crystallization treatment. It is confirmed. When the raw material melt after the separation of the intermetallic compound is to be purified, the purification time is shortened in comparison with Example 2. That is, by increasing the flow rate of cooling air and increasing the rotation speed, α-A
The crystallization time of 1 was shortened by 30 minutes, and almost the same amount of purified aluminum was obtained. This made it possible to improve the recovery rate. However, the purification efficiency of Example 2 was slightly higher.

[0027]

As described above, according to the present invention, the crystallization separation of impurities crystallized as an intermetallic compound having a larger specific gravity than that of molten aluminum causes α-Al to crystallize on the lower surface of the cooling body, and The crystallization reaction is accelerated by the rotation of the cooling body to obtain purified aluminum having a higher purity. The crystallized intermetallic compound is collected at the bottom of the refining vessel as a coagulation concentrate and efficiently separated from the refined aluminum at the top of the refining vessel. According to this method, the crystallization of impurities is efficiently performed, and purified aluminum with high purity is produced with a high yield.

[Brief description of drawings]

FIG. 1 is a refining apparatus adopted in an embodiment of the present invention.

FIG. 2 α-Al growing on the bottom surface of a rotary cooling body

[Explanation of symbols]

M: Molten aluminum I: Crystallized intermetallic compound 10: Purification vessel 20: Heating mechanism 30: Rotating cooling body 40: Cooling medium

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Kato 161 Kambara, Kambara-cho, Anbara-gun, Shizuoka Nihon Metal Co., Ltd. Kambara factory

Claims (9)

[Claims] 1. A molten aluminum in which impurities are crystallized as an intermetallic compound from a melt is contained in a refining vessel, and the molten aluminum is cooled by a rotary cooling member inserted from the upper part of the refining vessel to obtain purified aluminum. An aluminum refining method, characterized in that the intermetallic compound is dropped onto the bottom of the refining vessel by gravity. 2. The method for purifying aluminum, wherein the intermetallic compound according to claim 1 is solidified integrally with purified aluminum and then cut and separated. 3. The purified aluminum according to claim 1, which is drawn out from the refining vessel with the molten aluminum remaining at the bottom of the refining vessel and separated from the crystallized intermetallic compound. Purification method. 4. The method for purifying aluminum according to claim 1, wherein the intermetallic compound according to claim 1 is discharged together with the impurity concentrated liquid through an impurity suction pipe opened at the bottom of the purification container. 5. An aluminum refining method, wherein the molten metal raw material is replenished in a refining vessel in accordance with the discharge of the impurity concentrated liquid according to claim 4. 6. The refined aluminum according to any one of claims 1 to 3, which is cooled in a furnace after completion of refining and then heated to melt a surface layer in contact with an inner wall of the refinement vessel, and then the refinement vessel. A method for purifying aluminum, which is characterized in that it is extracted from the aluminum. 7. A refining container containing the molten aluminum, a cooling member rotatably provided at an upper opening of the refining container, and a heater disposed around the refining container and capable of controlling heating, An aluminum refining apparatus characterized in that an intermetallic compound crystallized from the molten aluminum is agglomerated in an impurity concentration section formed at the bottom of the refining vessel. 8. A refining vessel containing a molten aluminum, a rotatable cooling body mounted on an upper opening of the refining vessel and moving upward as the refining aluminum solidifies and grows, and around the refining vessel. The cooling device includes a heater that is arranged and controllable for heating, an impurity suction pipe that opens to an impurity concentration portion formed at the bottom of the purification container, and a molten metal raw material supply pipe that opens to an inner surface of a side wall of the purification container. The purified aluminum was continuously drawn out of the purification container by moving the body, and a route was provided for replenishing the molten metal raw material to the purification container in an amount commensurate with the extracted amount of the purified aluminum and the discharge amount of the impurity concentrate. An aluminum refining device characterized in that 9. An aluminum refining apparatus, characterized in that a refrigerating jet nozzle is arranged so as to face a side surface of the refined aluminum drawn out from the refining container according to claim 8.