JP3237330B2 - Purification method of aluminum alloy scrap - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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 the crystallized intermetallic compound is separated. The method has been adopted. For example, in Japanese Patent Publication No. 57-2134, an Al-Mn intermetallic compound is added, and in Japanese Patent Publication No. 59-12731, Mn or Al-Mn is added in combination with Mg or Al-Mg. In either method, Fe, which is a part of the impurity, is used.
Is separated and removed as an Al-Fe-Mn intermetallic compound.

[0003]

In the refining method using an additive such as a Mn-based additive, only Fe and Mn can be removed, and the Fe concentration of the obtained purified aluminum is also 0.5%.
Weight percent is the limit. In addition, when impurities are separated and removed by the addition of Mn, an excessive amount of Mn needs to be added.
Is included. Further, when an aluminum raw material is purified by a method introduced in JP-A-57-82437, in a system in which an intermetallic compound is crystallized as a primary crystal, the crystal strength of aluminum crystallized is low. Therefore, when the rotation speed of the cooling pipe increases 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 separated and transferred to the molten metal, and the apparent solidification speed decreases. In the worst case, an upper limit may be added to the thickness at which the solidified body can grow.

In addition, the crystallization temperature of the intermetallic compound crystallized as a primary crystal is usually several tens of degrees Celsius compared to the freezing point of α-Al.
high. Therefore, the impurities crystallize and solidify on the surface of the cooling body as an intermetallic compound before the crystallization of aluminum.
This solidified layer causes a reduction in the purity of the purified aluminum crystallized thereon, and thus involves a problem in the purification process in principle and practically. The present invention has been devised in order to solve such a problem. By incorporating a step of preliminarily crystallizing and separating impurities from the molten metal as an intermetallic compound, the impurities crystallized on the surface of the cooling body are free from impurities. An object of the present invention is to obtain purified aluminum with high yield while avoiding mixing.

[0005]

According to the purification method of the present invention, in order to achieve the object, Fe, M
n, Cr-containing Al-Si based aluminum alloy scrap melt is accommodated in a purification vessel, and the Fe, Mn, and Cr are retained by maintaining the melt in a temperature range that is at most 10 ° C. higher than the solidification point of α-Al. After forming an intermetallic compound with Al and Si in the aluminum alloy and allowing it to settle to the bottom of the purification vessel, a rotating cooling body is immersed in the molten metal, and the molten metal is cooled while rotating the rotating cooling body. The α-Al crystal is crystallized and grown on the surface of the rotary cooling body. The rotary cooling body immersed in the molten metal is preferably rotated at an outer peripheral speed of 0.5 to 2 m / sec so that the intermetallic compound settled at the bottom of the refining vessel does not mix in the crystallized α-Al crystals. The rotary cooling body can be immersed in the molten metal from the beginning of refining. In this case, when the melt is cooled to a temperature range that is at most 10 ° C. higher than the solidification point of α-Al, a cooling gas is sent to the rotary cooling body to crystallize and grow on the surface of the rotary cooling body as α-Al crystals. Let it.

[0006] The purification method according to the present invention is, for example, shown in FIG.
It is carried out using the equipment having the equipment configuration shown in FIG. As the purification vessel 10, a crucible made of graphite or a crucible obtained by mixing and firing graphite and SiC is usually used. Crucible body 11
Into 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 a refractory brick having a heater 21 mounted on the inner peripheral side.
To 24, and the amount of heat of each of the heater blocks 22 to 24 is independently controlled. A heater block 25 is also arranged at the bottom of the purification vessel 10. The aluminum scrap to be purified is melted by heating from the heater blocks 22 to 25 after being charged into the purification container 10,
The temperature is kept 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 tube 32 fitted near the tip of an inner tube 31 having a gas passage in the axial direction. The inner tube 31 extends upward through the lid 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 inserted into a feed screw 38 rotated by the motor 37. Thereby, the rotary cooling body 30 is rotatable up and down inside the purification vessel 10. The outer tube 32 has a bottom surface closed as shown in FIG.
9 is formed. Cooling medium g sent from inner pipe 31
Is discharged from the outer tube 32 through the gap 39. Alternatively, instead of the double structure of the inner tube 31 and the outer tube 32, a graphite block having a predetermined gas passage may be used.

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 α-Al crystals are crystallized around the outer tube 32, and the solidified body A grows. The temperature of the melt M and the growth rate of the solidified body A are optimally maintained by controlling the flow rate of the cooling medium g. As the temperature of the molten metal M falls, the impurity I is crystallized as an intermetallic compound such as an Al-Si-Fe-Mn system. The crystallized impurity I has a higher specific gravity than the molten metal M, and therefore descends in the molten metal M and deposits on the bottom of the purification vessel 10. The deposition amount of the intermetallic compound I increases as the molten metal M is cooled.

[0009] The temperature T at which the molten metal M starts to solidify is determined in advance based on the components and content of the molten raw material, the amount of impurities crystallized in the cooling process, and the like. Melt M is T ~ (T + 10
° C), the rotating cooling body 30 is immersed in the molten metal M, or the rotating cooling body 3
0 is supplied with cooling medium g. Thereby, the molten metal M in which the impurities are crystallized and separated is cooled by the rotary cooling body 30, and α-Al crystals are 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 concentration gradient of impurities 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 is also increased.

[0010] The rotary cooling body 30 diffuses impurity elements discharged by segregation during solidification from the solidification interface into the molten metal M. As a result, α which crystallizes and solidifies on the surface of the rotary cooling body 30
-The purification efficiency of the coagulated body A of the Al crystal is improved. However, when the rotating cooling body 30 rotates at a high speed, the rotating cooling body 3
Part of the α-Al crystals crystallized at the solidification interface of 0 is separated by the centrifugal force and scattered in the molten metal M, so that the solidification speed is reduced. Therefore, it is preferable to rotate the rotary cooling body 30 at a peripheral speed of 0.5 to 2 m / sec on the outer periphery as a rotational speed that does not adversely affect the purification efficiency and does not significantly reduce the solidification speed.

When the temperature of the molten metal M reaches the vicinity of the solidification point of α-Al, the supply of the cooling medium g is stopped,
Is stopped, and the motor 37 is driven to rotate the cooling body 30.
From the purification vessel 10. Thereafter, the refining vessel 10 is immediately tilted, and the remaining hot water is decanted to be separated from the deposited intermetallic compound I. The solidified body A crystallized as α-Al crystals is separated from the rotary cooling body 30 by mechanical scraping, re-melting, etc., and collected as purified aluminum. The separation of the intermetallic compound I may be performed before the α-Al crystal is crystallized as the solidified body A, instead of performing the separation after the purification. In this case, the temperature adjusting furnace and the refining furnace are separately provided, and the temperature of the molten metal is lowered to just above the temperature at which solidification starts in the temperature adjusting furnace. And immersion for purification.
Alternatively, the intermetallic compound I deposited on the bottom of the purification vessel 10
Is removed by suction with an appropriate metal pump,
Purification using 0 can also be performed.

[0012]

For example, when cooling a molten metal M in which Al-Si-based aluminum alloy scrap containing a large amount of Fe, Mn, etc. as impurities is cooled, first, Al-Si-Fe-Mn
Impurities are crystallized as a system intermetallic compound. The crystallized intermetallic compound I descends from the molten metal due to a difference in specific gravity and deposits on the bottom of the purification vessel 10. As a result, the remaining molten metal M becomes a high purity aluminum alloy molten metal from which impurities have been removed. Then, when the molten metal M is solidified on the surface of the rotary cooling body 30, α-Al crystals are obtained as the solidified body A. As described above, by shifting the timing at which the impurities are crystallized as the intermetallic compound I and the timing at which the α-Al crystals are crystallized and solidified on the surface of the rotary cooling body 30, the molten aluminum is purified by a simple operation. You. The timing at which the α-Al crystals crystallize on the surface of the rotary cooling body is set to a temperature immediately above the temperature at which the molten metal M starts to solidify. Immediately before the molten metal M starts to solidify, the rotary cooling body 30 is immersed in the molten metal M,
Alternatively, the cooling medium g is fed into the rotary cooling body M already immersed. The timing at which the rotary cooling body 30 is immersed in the molten metal M can be easily known by continuously measuring the temperature of the molten metal M. The α-Al crystals are separated from the impurities crystallized as the intermetallic compound I, and
Solidifies on the surface of Then, it is separated from the rotary cooling body 30 and recovered as purified aluminum.

[0013]

EXAMPLE A graphite crucible having an inner diameter of 200 mm and a height of 600 mm was mounted on a purifying apparatus shown in FIG. 1 to purify a molten metal. As the rotary cooling body 30, a graphite tube having an outer diameter of 100 mm was used. A crucible was charged with 35 kg of an Al-Si-based aluminum alloy scrap raw material melt having an α-Al solidification point of about 595 ° C, which has an impurity concentration shown in Table 1, and heated to 640 ° C. When the melting is completed, the rotary cooling body 30
Was immersed at a depth of 160 mm, and 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 dropped to 603 ° C., cooling air as a cooling medium g was supplied to the rotary cooling body 30 at a flow rate of 400 L / min. After 40 minutes, the supply of the cooling air was stopped, and the rotary cooling body 30 was
Removed from The solidified body A formed on the surface of the rotary cooling body 30 was separated and recovered from the rotary cooling body 30 by heating and melting. The resulting purified aluminum had the impurity concentrations shown in Table 1. The recovery at this time was 20%. In addition, 3.4 kg of Al
-Si-Fe-Mn intermetallic compound I was deposited.

For comparison, the rotary cooling body 30 is immersed in the same molten metal 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 L / min. The impurity concentration of the purified aluminum obtained at this time is also shown in Table 1 as a comparative example. As is clear from Table 1, when the cooling by the rotary cooling body 30 is started at a temperature just above the solidification point of α-Al (about 595 ° C.), the Fe concentration and the Mn concentration in the purified aluminum are significantly reduced. I understand. This indicates that the intermetallic compound I first crystallized from the melt M was sedimented and separated at the bottom of the purification vessel 10 without being taken into the solidified body A. Further, even when the rotary cooling body 30 was immersed in the molten metal M when the temperature of the molten metal M dropped to 603 ° C., purified aluminum having similarly reduced Fe and Mn concentrations was obtained.

[0015]

[Table 1]

[0016]

As described above, in the present invention, Fe and M which form an intermetallic compound with Al and Si are used.
When segregating and solidifying a melt of an Al-Si-based aluminum alloy scrap containing n and Cr as impurities, and purifying aluminum, the impurities Fe, Mn, and Cr were precipitated from the melt as intermetallic compounds and then purified. Aluminum is solidified on the surface of the rotating cooling body. Therefore, highly purified aluminum can be obtained under stable operating conditions without being affected by intermetallic compounds crystallized in the process of cooling the molten aluminum.

[Brief description of the drawings]

FIG. 1 shows an example of a purifying apparatus for performing a purifying method according to the present invention.

[Explanation of symbols]

M: molten metal A: solidified body g: cooling medium 10: purification vessel 20: heating mechanism 30: rotary cooling body

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-105940 (JP, A) JP-A-64-73027 (JP, A) JP-A-60-190531 (JP, A) 162823 (JP, A) JP-A-5-295465 (JP, A) JP-A-6-299265 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22B 1/00-61 / 00 C22C 1/02

Claims (3)

(57) [Claims] 1. Fe, Mn, Cr as part of impurities
The Al-Si-based aluminum alloy scrap melt contained is contained in a refining vessel, and the melt is maintained at a temperature range that is at most 10 ° C. higher than the solidification point of α-Al, thereby pre- heating the melt.
Fe, Mn, and Cr were converted to Al and S in an aluminum alloy.
i, an intermetallic compound is formed and settled at the bottom of the refining vessel. Then, a rotary cooling body is immersed in the molten metal, and the molten metal is cooled while rotating the rotary cooling body to form an α-Al crystal.
Purification method of an aluminum alloy scrap, characterized in that to the crystallization grown on the surface of the rotary cooling member. 2. A rotary cooling body is immersed in a molten metal at a refining start stage, and impurities are crystallized and separated at a furnace bottom by cooling the molten metal as an intermetallic compound, and the temperature is at most 10 ° C. higher than the solidification point of α-Al. when the melt is cooled to a range, the aluminum, characterized in that the the rotary cooling body feeding a cooling gas to crystallization grow alpha-Al crystals on the surface of the rotary cooling body
Method for refining scrap of aluminum alloy . 3. An outer peripheral speed of 0.5 to 2 m at which intermetallic compounds settled at the bottom of the purification vessel are not mixed with the α-Al crystallized product.
The refining method according to claim 1 or 2, wherein the rotary cooling body immersed in the molten metal is rotated at a rate of / sec.