JPH0754073A - Refining method for aluminum scrap - Google Patents

Abstract

PURPOSE:To refine an aluminum material having an objective compdn. from the melt of aluminum scrap by utilizing segregation solidification. CONSTITUTION:The melt M of the aluminum having a compsn. in which a part of impurities are crystallized as the primary crystals of intermetallic compds. is housed into a refining vessel 10 where the molten metal M is held at a temp. above the solidification point of alpha-Al and the molten metal A is coold while a rotary cooling body 30 immersed in the molten metal M is kept rotated. The intermetallic compds. are grown as a solid S on the surface of the rotary cooling body 30 and an alpha-Al layer is grown on the surface of the solid S as the molten metal M is purified according to the crystallization of the intermetallic compds. The rotary cooling body 30 is then taken out of the molten metal M and the alpha-Al is melted and separated at a temp. at which the intermitallic comds. do not melt. The impurity concns. of the solid S and the residual molten metal are controlled by adjusting the stirring intensity and solidifying speed and, therefore, plural kinds of the aluminum materials varying in the objective compsn. are obtd. by one time of the refining stage.

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 In order to separate and remove impurities such as Fe contained in molten aluminum, Mn is added, an intermetallic compound is generated between Mn and the impurity, and a crystallized intermetallic compound is separated. The method has been adopted. For example, in JP-A-57-2134, an Al-Mn-based intermetallic compound is added, and in JP-A-59-12731, Mn or Al-Mn and Mg or Al-Mg are added together. In any method, Fe which is a part of impurities
Is separated and removed as an Al-Fe-Mn-based intermetallic compound.

[0003]

The method of removing impurities in a molten metal as an intermetallic compound by using an additive such as Mn is specified for a molten metal containing almost no Si as an impurity. It does not work with molten metal. For example, when applied to a molten metal containing a large amount of Si,
Since Si does not form an intermetallic compound with Mn, impurities such as Si cannot be crystallized and separated as an intermetallic compound. Further, in order to separate and remove impurities, it is necessary to add an excess Mn-based additive to the molten metal. As a result, the purified aluminum material contains a large amount of Mn,
Restricted to aluminum alloy applications. Moreover, the impurities to be removed are limited to the elements that form an intermetallic compound with Mn, and the impurity elements that do not form an intermetallic compound with Mn are not separated and removed.

The present invention has been devised in order to solve such a problem. It is possible to remove impurities other than Fe by utilizing segregation solidification, and Si without adding excessive Mn. Even if it contains
-Si-Fe-Mn-based intermetallic compounds, and aluminum alloys with two target compositions of solidified material and residual hot water by adjusting the number of revolutions and regulation of solidification amount, or three kinds depending on the handling of intermetallic compounds. Aim to get.

[0005]

In order to achieve the object, the refining method of the present invention contains an aluminum melt having a composition in which a part of impurities are crystallized as a primary crystal of an intermetallic compound in a refining vessel, The molten metal is held above the freezing point of α-Al, the molten metal is cooled while rotating the rotary cooling body immersed in the molten metal, and the intermetallic compound is allowed to grow on the surface of the rotary cooling body as a solidified body, Α- on the surface of the solidified body according to the purification of the molten metal accompanying the crystallization of the intermetallic compound
After growing Al, the rotary cooling body is taken out of the molten metal, and the α-Al is dissolved and separated from the intermetallic compound at a temperature at which the intermetallic compound does not dissolve.

[0006]

The molten aluminum targeted by the present invention has a composition in which some of the impurities are crystallized as primary crystals of an intermetallic compound such as an Al-Si-Fe-Mn system. The intermetallic compound crystallizes on the surface of the rotary cooling body in the course of cooling the molten metal to form a solidified body. Impurities are crystallized and separated from the molten metal as the solidified body grows, so that the purity of the molten metal increases. When cooling and solidification are continued in this state, crystallization of α-Al starts, and an α-Al layer is formed on the solidified body mainly composed of intermetallic compounds. Impurities are discharged into the molten metal by the crystallization solidification of α-Al. For example, the impurity element Fe is
Crystallized as an Al-Si-Fe-Mn-based intermetallic compound,
Fall to the bottom of the furnace. Therefore, the Fe concentration of the molten metal is maintained at a constant value during continuous solidification, and the Fe concentration of crystallized α-Al is also maintained constant from the start to the end of solidification. Other impurity elements such as Cr and W are also replaced with a part of Fe and separated from the molten metal as an intermetallic compound.

In order to crystallize the required Al-Si-Fe-Mn-based intermetallic compound, Mn of the aluminum melt /
It is preferable to maintain the Fe ratio in the range of 0.2 to 2.
If the Mn / Fe ratio is less than 0.2, the required amount of Mn is not supplied during the operation, and the Al-Si-Fe-Mn-based intermetallic compound does not crystallize. On the other hand, when the Mn / Fe ratio exceeds 2, M contained in the molten aluminum after the refining is completed.
The concentration of n becomes too high, which limits the use as an aluminum alloy raw material. The Fe concentration is not particularly limited as long as the Mn / Fe ratio is 0.2 or more. However, at an excessively low Fe concentration of less than 0.5% by weight, the crystallization temperature of the intermetallic compound drops to near the solidification temperature of the molten metal. As a result, it becomes difficult to control the temperature and a sufficient refining effect by crystallization separation cannot be obtained.

With the progress of solidification due to cooling, the Si concentration in the molten metal increases. Si concentration is 12% by weight of eutectic composition
Before and after, the solidification rate due to cooling decreases, and it becomes difficult to continue crystallization separation under stable conditions. Therefore, in consideration of operability, it is preferable that the aluminum melt as a raw material has a Si concentration regulated to 10% by weight or less. The increase in Si concentration also lowers the solidification temperature of the molten metal. Therefore, since the temperature of the molten metal is lowered to a lower temperature, the amount of crystallization of the Al-Si-Fe-Mn intermetallic compound that precipitates on the furnace bottom increases, and the Fe concentration of the molten metal decreases. Therefore, the Fe concentration in the solidified portion also decreases, and the Fe concentration in the final molten aluminum also decreases. The crystallization phenomenon of the Al-Si-Fe-Mn-based intermetallic compound is caused by S of the raw material aluminum melt.
When the i concentration is 2% by weight or more, it is effectively utilized for the crystallization separation of impurities.

As an aluminum scrap to be refined, a raw material having impurities in the concentration range described above is not always available. In such a case, Si, Mn, etc. are supplementarily added to adjust the components of the molten metal. Si and Mn
Since the adjustment accuracy is gradual, it is not always necessary to use an expensive simple metal or mother alloy. For example, if aluminum scrap whose concentration is known is
When used as an i source and a Mn source, effective use of resources and reduction of production cost are achieved. The refining method according to the present invention is carried out by using, for example, an apparatus having an equipment configuration shown in FIG. As the refining vessel 10, a graphite crucible or a crucible obtained by mixing and firing graphite and SiC is usually used. The 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.

A heating mechanism 20 is arranged on the outer periphery of the purification container 10 so as to surround the outer container 12. Heating mechanism 20
Is provided with heater blocks 22 to 24 made of refractory bricks having a heater 21 attached to the inner peripheral side thereof.
It is preferable that the calories of .about.24 are independently controlled. The heater block 25 is also arranged at the bottom of the purification container 10. Refining container 1 for aluminum scrap to be refined
After being charged at 0, it is 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. The rotary cooling body 30 is immersed in the molten metal M held in a molten state. The rotary cooling body 30 has an outer pipe 32 fitted in the vicinity of the tip of an inner pipe 31 having a gas passage in the axial direction. The inner pipe 31 extends upward through the lid 13 and is connected to an output shaft 35 of a motor 34 via a coupling 33. The arm 36 extending from the motor 33 is
It is fitted into a feed screw 38 rotated by a motor 37. As a result, the rotary cooling body 30 rotates in the refining container 10 so as to be vertically movable.

The outer pipe 32 is closed on the bottom surface side as shown in the drawing, and forms a gap 39 with the lower end of the inner pipe 31. The cooling medium g sent from the inner pipe 31 is discharged from the outer pipe 32 through the gap 39. Alternatively, the double block structure of the inner pipe 31 and the outer pipe 32 may be replaced with a graphite block having a predetermined gas passage. As the cooling medium g, air, non-oxidizing gas, air containing mist-like water, or the like is used. Due to the flow of the cooling medium g, the outer pipe 32
The molten metal M is cooled through the tube wall of No. 3, and the solidified body S grows around the outer tube 32. The temperature of the molten metal M and the growth rate of the solidified body S are optimally maintained by controlling the flow rate of the cooling medium g. When the temperature of the molten metal M decreases, first of all Al-Si
The —Fe—Mn-based intermetallic compound crystallizes as a solidified body S on the surface of the rotary cooling body 30. With the growth of the solidified body S, the remaining molten metal M is purified and the temperature further decreases. for that reason,
The α-Al layer A crystallizes on the surface of the solidified body S. At this time,
Due to the rotation of the rotary cooling body 30, the impurity element discharged to the interface between the solidified body S and the molten metal M or the intermetallic compound I that crystallizes out
Diffuses into the molten metal M.

The rotary cooling body 30 rotates at a peripheral speed at which the impurity element or the intermetallic compound I crystallized when α-Al is solidified is diffused into the molten metal M. At an excessively high rotation speed, the vortex generated by the rotation of the rotary cooling body 30 becomes large,
Not only the oxidation of aluminum, which causes a decrease in yield, progresses, but also the molten metal M is scattered, which causes safety and operational inconvenience. Further, the solidified α-Al layer A scatters in the molten metal M due to the centrifugal force, and the solidification efficiency deteriorates. The rotation speed of the rotary cooling body 30 is, specifically, an outer peripheral speed of 0.2 to
It is preferably 2 m / sec. Further, in order to prevent the oxide film floating on the surface of the molten metal M from being caught, it is preferable to rotate the rotary cooling body 30 in one direction. α-A
When the 1-layer A has grown to the set value, the supply of the cooling medium g and the rotation of the rotary cooling body 30 are stopped, and the motor 37 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 bottom of the furnace is discharged. Next, the α-Al layer A crystallized on the rotary cooling body 30 is heated and melted at a temperature at which the solidified body S is not melted, and separated from the solidified body S. In some cases, the α-Al layer A can be mechanically scraped and separated from the solidified body S.

[0013]

【Example】

Example 1: A graphite crucible having an inner diameter of 400 mm and a height of 800 mm was attached to the refining apparatus shown in FIG. 1 to refine an aluminum melt. The rotating cooling body 30 has an outer diameter of 100 m.
m graphite tube was used. Mn / F containing 8 wt% Si, 0.8 wt% Fe, 3 wt% Cu and 0.4 wt% Mn
Aluminum melt raw material 150 with e ratio of 0.5
Kg was charged into the crucible 10 and heated and held at 640 ° C.
The height of the rotary cooling body 30 from the bottom to the bottom of the crucible is 2
The peripheral speed is 1.5 at the outer circumference.
It was rotated at m / sec. Cooling air is used as the refrigerant g,
It was supplied at a constant flow rate of 3 m ³ / min throughout the operation.
Solidification was terminated at 24% of the total aluminum charge. The average solidification rate at this time was 150 mm / hour.

After solidification was completed, the rotation of the rotary cooling body 30 was stopped, and the rotary cooling body 30 was taken out of the molten metal M. Immediately, the purification container 10 was tilted, and the residual hot water in which impurities were concentrated was discharged together with the crystallized intermetallic compound I. The α-Al layer A solidified on the rotary cooling body 30 has a weight of 35 kg and an impurity concentration of Fe: 0.33% by weight, Si: 4.2% by weight, C.
u: 1.7% by weight and Mn: 0.2% by weight. On the other hand, the residual hot water contained 0.6% by weight of Fe, 8.8% by weight of Si, 3.4% by weight of Cu and 0.2% by weight of Mn. Further, the intermetallic compound crystallized as the solidified body S and the intermetallic compound I in the residual hot water are Al-Si-Fe-M.
The n-type had a total weight of 3.5 kg.

Example 2: Using the same equipment as in Example 1,
Si: 6.5% by weight under the same operating conditions. 1.2 kg of A as Mn in an aluminum raw material molten metal containing Fe: 0.8 wt%, Cu: 2.9 wt% and Mn 0.1 wt%
1-Mn alloy was added to bring the Mn concentration to 0.9% by weight and M
The n / Fe ratio was adjusted to 1.125. When the solidified amount of the adjusted molten metal reaches 20%, the cooling is terminated, the rotation of the rotary cooling body 30 is stopped, the rotary cooling body 30 is taken out of the furnace, and the residual hot water and the intermetallic compound I are immediately purified. Ejected from 10. The aluminum purified as the α-Al layer A has a weight of 30 kg and an impurity concentration of Si: 3.3% by weight, Fe: 0.29% by weight, Cu: 1.5% by weight and M.
It was n 0.4% by weight. The impurity concentration in the residual hot water is S
i: 8.5% by weight, Fe: 0.45% by weight, Cu: 3.
It was 5% by weight and Mn: 0.37% by weight. Further, the intermetallic compound crystallized as the solidified body S and the intermetallic compound I in the residual hot water were Al-Si-Fe-Mn-based and had a total weight of 4.1 kg.

Embodiment 3: A peripheral speed of the rotary cooling body 30 is set to 2.5.
The same raw material was purified under the same conditions as in Example 1 except that the rotation was carried out at m / sec and the cooling was stopped when the solidification amount reached 20%. Aluminum purified as the α-Al layer A is
The impurity concentrations were Si: 3.9% by weight, Fe: 0.30% by weight, Cu: 1.6% by weight and Mn of 0.19% by weight. The impurity concentration in the residual hot water was Si: 9.1% by weight, F
e: 0.6 wt%, Cu: 3.8 wt% and Mn: 0.
It was 18% by weight. Comparing this result with Example 1, the purity of the solidified portion is improved, and the purity of the residual hot water is F by that amount.
It can be seen that excluding e and Mn, the deterioration has occurred. From this, it is confirmed that the rotation speed of the rotary cooling body 30 affects the purification efficiency.

[0017]

As described above, in the present invention, when the molten aluminum scrap having a composition in which the primary crystal is an intermetallic compound is segregated and solidified to refine aluminum, the cooling body is rotated to rotate the aluminum molten metal. By stirring, the impurity element crystallized as an intermetallic compound is precipitated on the surface of the rotary cooling body and the bottom of the refining vessel to be separated, and the impurity content is reduced outside the rotary cooling body with good purity α- You are getting aluminum. The residual hot water is also purified by crystallization of the intermetallic compound. At this time, if the rotation speed of the rotary cooling body is controlled, three types of products including intermetallic compounds can be obtained from the same aluminum scrap raw material. Further, by adjusting the composition of the molten metal, it is possible to obtain a product in which the Fe and Mn concentrations are lowered not only in the refining portion but also in the residual molten metal portion where impurities are easily concentrated.

[Brief description of drawings]

FIG. 1 shows an example of a purification apparatus for carrying out a purification method according to the present invention.

[Explanation of symbols]

M: molten aluminum S: solidified body A: α-Al
Layer I: Crystallized intermetallic compound g: Cooling medium 10: Purification vessel 20: Heating mechanism 30: Rotating cooling body

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takaaki Murakami Inventor Takahara Murakami 161 Kambara-cho, Anbara-gun, Shizuoka Prefecture Inside the Kambara Plant of Nippon Light Metal Co., Ltd. Issue Nichiritsu Giken

Claims (6)

[Claims] 1. An aluminum melt having a composition in which a part of impurities are crystallized as a primary crystal of an intermetallic compound is placed in a refining vessel, the melt is kept at a freezing point of α-Al or higher, and immersed in the melt. Cooling the molten metal while rotating the rotary cooling body, growing the intermetallic compound on the surface of the rotary cooling body as a solidified body, the surface of the solidified body according to the purification of the molten metal accompanying the crystallization of the intermetallic compound After growing α-Al, the rotary cooling body was taken out of the molten metal,
A method for refining aluminum scrap, which comprises dissolving and separating the α-Al from the intermetallic compound at a temperature at which the intermetallic compound does not dissolve. 2. An aluminum scrap having an Fe concentration of more than 0.5 wt% is used as a melting raw material, the Fe concentration in α-Al is 0.5 wt% or less, and Fe and Fe in the residual hot water in which impurities are concentrated are contained. The refining method according to claim 1, wherein the Mn content is equal to or lower than the Fe concentration and the Mn concentration in the molten raw material. 3. The refining method according to claim 1, wherein a ratio Mn / Fe of Mn and Fe of impurity elements contained in the molten aluminum is 0.2 to 2. 4. The concentration of Si contained as an impurity element in the molten aluminum is 2 to 10% by weight, and the α-A
4. The purification method according to claim 1, wherein the freezing point of 1 is 650 ° C. or lower. 5. The Mn / Fe ratio of the molten aluminum is 0.
2 to 2 and 1 or 2 or more kinds of metal simple substance, Al mother alloy, scrap containing a large amount of Mn and / or Si, etc. are added to the molten metal so that the Si concentration becomes 2 to 10% by weight. 5. The purification method according to any one of 4 to 4. 6. A rotary cooling body immersed in a molten metal has an outer peripheral speed of 0.
The purification method according to any one of claims 1 to 5, which is rotated in one direction at 5 to 2 m / sec.