JPH0754070A - Refining method for aluminum scrap - Google Patents

Abstract

PURPOSE:To produce refined aluminum having low concns. of the impurities from the melt of aluminum scrap by utilizing segregation solidification. CONSTITUTION:The molten metal M having a compsn. in which a part of impurities are crystallized as primary crystals of intermetallic compds. is housed into a refining vessel 10 where the molten metal M is cooled down to a temp. right above the solidification point of alpha-Al to settle the impurities as the intermetallic compds. I of Al-Si-Fe-Mn, etc., on the bottom of the refining vessel 10. A cooling medium g is then fed to a rotary cooling body 30 or this rotary cooling body 30 is immersed into the molten metal M and the purified aluminum is crystallized and solidified as a solid A on the surface of the rotary cooling member 30. As a result, the intermetallic compds. I is not taken into the solid A and, therefore, the lowering in the purity of the molten metal M by the intermetallic compds. I does not arise and the refined aluminum having the low concns. of Fe and Mn is obtd.

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]

In the refining method using an additive such as Mn, only Fe and Mn can be removed, and the Fe concentration of the obtained refined aluminum is 0.5.
The limit is about wt%. Moreover, when impurities are separated and removed by adding Mn, it is necessary to add an excessive amount of Mn. Therefore, a large amount of Mn is added to the purified aluminum material.
Is included. Further, when the aluminum raw material is refined by the method introduced in JP-A-57-82437, the crystal strength of aluminum crystallized is weak in a system in which an intermetallic compound is crystallized as a primary crystal. Therefore, when the rotation speed of the cooling pipe is increased to an outer peripheral speed of 2.5 to 8 m / sec, part of the aluminum crystallized on the surface of the cooling body is released and transferred to the molten metal, and the apparent solidification speed is reduced. In the worst case, an upper limit may be added to the thickness at which the solidified body can grow.

Moreover, the crystallization temperature of the intermetallic compound crystallized as the primary crystal is usually several tens of degrees Celsius as compared with the freezing point of α-Al.
high. Therefore, the impurities crystallize and solidify on the surface of the cooling body as an intermetallic compound prior to the crystallization of aluminum.
This solidified layer causes a decrease in the purity of the purified aluminum crystallized on the solidified layer, and thus involves a problem in the purification process both in principle and practically. The present invention has been devised to solve such a problem, and by incorporating a step of precipitating and separating impurities as an intermetallic compound from the molten metal, impurities that crystallize on the surface of the cooling body are contaminated with aluminum. The purpose is to avoid the mixture and to obtain purified aluminum with a high yield.

[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, By holding the molten metal in a temperature range that is 10 ° C. higher than the freezing point of α-Al, the intermetallic compounds are crystallized and settled at the bottom of the refining vessel, and then the rotary cooling body is immersed in the molten metal to form the rotary cooling body. It is characterized in that the molten metal is cooled while being rotated to grow purified aluminum as a solidified body on the surface of the rotary cooling body. The rotary cooling body immersed in the molten metal has an outer peripheral speed of 0.5 to 2 m in which the intermetallic compound settled at the bottom of the refining container does not mix with the solidified body of the refined aluminum.
It is preferable to rotate at a speed of 1 / second. The rotary cooling body can be immersed in the molten metal from the start stage of refining. In this case, when the molten metal is cooled to a temperature range that is higher than the freezing point of α-Al by a maximum of 10 ° C., a cooling gas is fed into the rotary cooling body to grow purified aluminum as a solidified body on the surface of the rotary cooling body.

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. A heating mechanism 20 is arranged on the outer periphery of the purification container 10 so as to surround the outer container 12. The heating mechanism 20 includes a heater block 22 made of refractory brick with a heater 21 attached to the inner circumference side.
It is preferable that each of the heater blocks 22 to 24 is independently controlled so that the amount of heat of each heater block 22 to 24 is controlled. The heater block 25 is also arranged at the bottom of the purification container 10. The aluminum scrap to be purified is charged into the refining vessel 10 and then melted by heating from the heater blocks 22 to 25,
It is maintained at a temperature slightly above 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 body 13,
It is connected to an output shaft 35 of a motor 34 via a coupling 33. The arm 36 extending from the motor 33 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 a gap 3 is formed between the outer pipe 32 and the lower end of the inner pipe 31.
9 is formed. Cooling medium g sent from the inner pipe 31
Are emitted from the outer tube 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 molten metal M is cooled through the tube wall of the outer tube 32, and the solidified body A grows around the outer tube 32. The temperature of the molten metal M and the growth rate of the solidified body A are optimally maintained by controlling the flow rate of the cooling medium g. According to the temperature drop of the molten metal M, Al-Si
Impurity I crystallizes out as an intermetallic compound such as a —Fe—Mn system. The crystallized impurity I has a larger specific gravity than the molten metal M, and therefore descends in the molten metal M and deposits on the bottom of the refining vessel 10. The amount of the intermetallic compound I deposited increases as the molten metal M is cooled.

The temperature T at which the molten metal M starts to solidify is predetermined based on the components and content of the molten raw material, the amount of impurities crystallized in the cooling process, and the like. Molten metal M is T ~ (T + 10
When the temperature is lowered to a temperature range of (° C.), the rotary cooling body 30 is immersed in the molten metal M, or the rotary cooling body 3 already immersed.
The cooling medium g is supplied to 0. As a result, the molten metal M in which the impurities are crystallized and separated is cooled by the rotary cooling body 30, and crystallized as a solidified body A on the surface of the rotary cooling body 30. At this time, since the rotary cooling body 30 is rotating, the impurity concentration gradient generated between the molten metal and the mother liquor in the vicinity of the solidified body A is eliminated, the crystallization of the intermetallic compound is promoted, and the molten metal M The cooling rate can be increased.

The rotary cooling body 30 diffuses the impurity element discharged by the segregation action during solidification into the molten metal M from the solidification interface. As a result, the purification efficiency for the solidified body A that crystallizes and solidifies on the surface of the rotary cooling body 30 is improved. However, when the rotary cooling body 30 rotates at a high speed, a part of aluminum crystallized at the solidification interface of the rotary cooling body 30 is separated by the centrifugal force and scattered into the molten metal M, so that the solidification rate is reduced. Therefore, as the rotation speed that does not adversely affect the purification efficiency and does not significantly reduce the solidification speed, the peripheral speed at the outer circumference is 0.5.
It is preferable to rotate the rotary cooling body 30 at a speed of 2 m / sec.

When the temperature of the molten metal M reaches near the freezing point of α-Al, the supply of the cooling medium g is stopped and the rotary cooling body 30
Rotation of the rotary cooling body 30 is stopped by driving the motor 37.
Is taken out from the purification container 10. Immediately thereafter, the refining vessel 10 is tilted and the residual hot water is transferred to separate it from the deposited intermetallic compound I. The solidified body A is separated and collected from the rotary cooling body 30 by mechanical scraping, remelting, or the like. The separation of the intermetallic compound I can be performed before the purified aluminum is crystallized as the solidified body A instead of performing the purification after the purification. In this case, a temperature control furnace and a refining furnace are separately provided, the temperature of the molten metal is lowered to just above the temperature at which solidification is started in the temperature control furnace, then the molten metal is transferred to the refining furnace, and the rotary cooling body is added to the molten metal stored for refining. To immerse and refine. Alternatively, the intermetallic compound I deposited on the bottom of the purification container 10 may be removed by suction with an appropriate metal pump, and then the refrigeration using the rotary cooling body 30 may be performed.

[0012]

Function: For example, a large amount of Si, Fe, M as impurities
When the molten metal M in which aluminum scrap containing n or the like is melted is cooled, impurities are first crystallized as an Al-Si-Fe-Mn-based intermetallic compound. Crystallized intermetallic compound I
Due to the difference in specific gravity, the molten metal descends and deposits on the bottom of the refining vessel 10. As a result, the remaining molten metal M becomes high-purity aluminum from which impurities have been removed. Therefore, molten metal M
When solidified on the surface of the rotary cooling body 30, purified aluminum is obtained as a solidified body A. In this way, by shifting the timing at which the impurities are crystallized as the intermetallic compound I and the timing at which the purified aluminum is crystallized and solidified on the surface of the rotary cooling body 30, the molten aluminum can be purified by a simple operation. It The timing at which the purified aluminum crystallizes on the surface of the rotary cooling body is set to the temperature immediately above where the molten metal M starts to solidify. When the molten metal M is about to start solidification, the rotary cooling body 3 is added to the molten metal M.
0 is immersed, or the cooling medium g is sent to the rotary cooling body M which is already immersed. The timing of immersing the rotary cooling body 30 in the molten metal M can be easily known by continuously measuring the temperature of the molten metal M. The purified aluminum solidifies on the surface of the rotary cooling body 30 while being separated from the impurities crystallized as the intermetallic compound I.

[0013]

EXAMPLE A graphite crucible having an inner diameter of 200 mm and a height of 600 mm was mounted on the refining apparatus shown in FIG. 1 to refine the molten metal. As the rotary cooling body 30, a graphite tube having an outer diameter of 100 mm was used. Table 1 shows the impurity concentration of α-Al, the freezing point of the aluminum scrap raw material molten metal of about 595 ℃ 35k
g was placed in a crucible and heated to 640 ° C. When the melting is completed, the rotary cooling body 30 is placed in the melt M to a depth of 160 mm.
The molten metal 30 was gradually cooled by natural cooling.
At this stage, the cooling medium g was not supplied to the rotary cooling body 30. When the temperature of the molten metal M was lowered to a temperature of 603 ° C., cooling air was supplied to the rotary cooling body 30 as a cooling medium g at a flow rate of 400 liters / minute. After 40 minutes, the supply of cooling air was stopped, and the rotary cooling body 30 was taken out of the purification container 10.
The solidified body A formed on the surface of the rotary cooling body 30 was separated and collected from the rotary cooling body 30 by heating and melting. The purified aluminum thus obtained had the impurity concentrations shown in Table 1. The recovery rate at this time was 20%. In addition, at the bottom of the purification container 10, 3.4 kg of Al-Si-Fe-M is used.
The n-type intermetallic compound I was deposited.

For comparison, the rotary cooling body 30 is immersed in the same melt M at a temperature of 620 ° C. at which the intermetallic compound I crystallizes,
Immediately after the immersion, the molten metal M was cooled while supplying cooling air at a flow rate of 400 liters / minute. The impurity concentration of the purified aluminum obtained at this time is also shown in Table 1 as a comparative example. As is apparent from Table 1, when the cooling by the rotary cooling body 30 is started at a temperature just above the freezing point (about 595 ° C.) of α-Al, the Fe concentration and the Mn concentration in the refined aluminum are significantly lowered. I understand. This indicates that the intermetallic compound I that first crystallized from the molten metal M was not taken into the solidified body A, but was precipitated and separated at the bottom of the purification container 10. Further, even when the rotary cooling body 30 was immersed in the molten metal M at the time when the molten metal M was cooled to 603 ° C., refined aluminum in which Fe and Mn concentrations were similarly reduced was obtained.

[0015]

[Table 1]

[0016]

As described above, according to the present invention, when the molten aluminum scrap having the composition in which the primary crystal is an intermetallic compound is segregated and solidified to refine aluminum, impurities are removed from the molten metal as an intermetallic compound. After settling, purified aluminum is solidified on the surface of the rotary cooling body. Therefore, purified aluminum with high purity can be obtained under stable operating conditions without being affected by the intermetallic compound crystallized during the cooling process of the molten aluminum.

[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 metal A: solidified body g: cooling medium 10: refining vessel 20: heating mechanism 30: rotary cooling body

Claims (3)

[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 contained in a refining vessel, and the melt is kept at a temperature range higher than the freezing point of α-Al by at most 10 ° C. By crystallizing the intermetallic compound and allowing it to settle at the bottom of the refining vessel, immersing a rotary cooling body in the molten metal, and cooling the molten metal while rotating the rotary cooling body to solidify purified aluminum. A method for refining aluminum scrap, characterized by growing as a body on the surface of the rotary cooling body. 2. A rotary cooling body is immersed in a molten metal at the start of refining, and impurities are crystallized and precipitated as intermetallic compounds on the bottom of the furnace by cooling the molten metal to obtain a temperature 10 ° C. higher than the freezing point of α-Al at the maximum. A method for refining aluminum scrap, characterized in that, when the molten metal is cooled to a range, a cooling gas is sent to the rotary cooling body to grow purified aluminum as a solidified body on the surface of the rotary cooling body. 3. An outer peripheral speed of 0.5 at which an intermetallic compound settled at the bottom of a refining vessel is not mixed into a solidified body of refined aluminum.
The refining method according to claim 1 or 2, wherein the rotary cooling body immersed in the molten metal is rotated at a speed of 2 m / sec.