JP3211622B2 - Purification method of aluminum 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 method for purifying aluminum scrap by crystallizing and separating impurities contained in a raw material for melting, and selectively crystallizing and growing high-purity α-Al crystals.

[0002]

2. Description of the Related Art When purifying aluminum scrap by a segregation method in which a crystal is grown on the surface of a cooling body immersed in a molten metal, the purification purity is affected by the shape of the crystal solid that solidifies on the surface of the cooling body. . Therefore, in order to increase the purification purity, various control of the shape of the crystallized product has been studied. For example, in a case where a tubular body (hereinafter, referred to as a cooling pipe) is used as a cooling body, as shown in Japanese Patent Publication No. 59-45739, heat insulating materials are attached to the outer periphery of the cooling pipe at the upper and lower metal interface depths, or As disclosed in Japanese Patent Publication No. 27423/1990, a method of controlling the shape of a crystallized solidified body by mounting heaters above and below a metal interface depth inside a cooling pipe has been proposed.

[0003] However, in the method of attaching the heat insulating material to the outer periphery of the cooling pipe, there are few suitable heat insulating materials that can withstand the molten aluminum, the heat insulating material is easily peeled off from the cooling pipe, and depending on the operating conditions, aluminum may be present on the heat insulating material surface. There is a problem that the heat insulating material is liable to break when solidifying and removing this aluminum, and there are many operational problems. In addition, the method of mounting a heater inside the cooling pipe not only complicates the power supply mechanism when rotating the cooling pipe, but also causes difficulties such as disconnection and the like due to exposure to high temperatures, which makes insulation difficult. There is a problem. As a method for preventing the solidification of purified aluminum at the bottom of the cooling pipe, Japanese Patent Publication No.
A heat insulating material is attached to the outer surface of the bottom of the cooling pipe as shown in JP-A-17008, the thickness of the bottom of the cooling pipe is increased as shown in JP-B-5-65415, and the outlet of the refrigerant in the bottom direction. There has been proposed a method of canceling. However, when the heat insulating material is attached to the outside of the bottom surface, various problems such as peeling of the heat insulating material occur. In addition, there are many cases where the bottom surface is always in constant contact with the molten aluminum in any of the methods, and there is a disadvantage that the cooling pipe is eroded.

The present inventors also investigated and studied the purification of aluminum scrap by the segregation method, and in the process, developed a method for producing molten aluminum by crystallizing α-Al crystals on the surface of the cooling body. , A part of which is Japanese Patent Application No. 7-
No. 30109 was filed. In this method, a tubular rotary cooling body 10 as shown in FIG. 1 and a disk-shaped rotary cooling body 20 as shown in FIG. 2 are used. The aluminum scrap to be refined is contained in a refining vessel 30 and is heated by a heater 31 from the outer periphery. Further, heating can be performed by a burner 33 for temperature control provided on a lid 32 attached to the purification container 30. Thereby, the molten aluminum M maintained at a temperature slightly higher than the freezing point of α-Al is prepared. The molten metal M held in the molten state is added to the rotary cooling body 10,
20 is dipped. The tubular rotary cooling body 10 has an outer pipe 12 fitted near the distal end of an inner pipe 11 having a gas passage in the axial direction. The inner tube 11 extends upward through the lid 32 and is connected to the output shaft of the motor 14 via the coupling 13. An arm 15 extending from the motor 14 is inserted into a feed screw 17 rotated by the motor 16. Thereby, the rotary cooling body 10 is rotatable up and down inside the purification vessel 30. The disk-shaped rotary cooling body 20 also rotates freely by a similar mechanism.

[0005] The tubular rotary cooling body 10 (Fig. 1)
The cooling medium g fed from 1 is cooled by being discharged from the outer tube 12 through the gap 18. 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 12. Disk-shaped rotary cooling body 2
0 (FIG. 2) has a double pipe structure in which the outer pipe 22 is fitted to the inner pipe 21, and circular flanges 23 and 24, which are radially widened at both lower ends of the inner pipe 21 and the outer pipe 22, are provided. The flange 23 has a plurality of orifices 25 formed therein. A bottom wall 27 having a fixed distance from the flange 23 is attached. Cooling medium g
Is fed into the outer tube 22, passes between the inner tube 21 and the outer tube 22, and is introduced into the distribution chamber 28 formed between the flanges 44 and 43. Next, the cooling medium g flows into the cooling chamber 29 through the orifices 25.

The cooling medium g in the cooling chamber 29 cools the molten metal M via the bottom wall 27. The heat removal ability of the cooling medium g is the bottom wall 2
7, α-Al is uniformly crystallized on the lower surface of the bottom wall 27 from the cooled molten metal M. The cooling medium g heated by the heat exchange with the molten metal M is supplied to the cooling chamber 2
From 9, it is discharged out of the system through the inner pipe 21. When the temperature of the molten metal M is lowered, if the primary crystal is an intermetallic compound, the temperature of the molten metal is first lowered before cooling the rotary cooling bodies 10 and 20, and for example, the Al-Si-Fe-Mn-based intermetallic compound is Settle to the bottom. With the crystallization of the intermetallic compound, the remaining molten metal M is purified, and the temperature further decreases. Then, when the rotary cooling bodies 10 and 20 are cooled, crystallization of α-Al crystals starts.
At this time, S discharged to the interface between the α-Al crystal and the molten metal M
Impurities such as i, Fe, and Cu are separated from the α-Al crystal by the rotation of the rotary cooling bodies 10 and 20, and a part of the impurities falls into the molten metal M as an intermetallic compound I having a higher specific gravity than the molten metal M. And the rest diffuses into the mother liquor. The precipitated and separated intermetallic compound I accumulates in the center of the bottom of the purification vessel 30 due to the stirring flow of the molten metal M generated by the rotation of the rotary cooling bodies 10 and 20.

[0007]

When the .alpha.-Al crystal is crystallized and solidified on the side surface of the tubular rotary cooling body 10 and the bottom surface of the disk-shaped rotary cooling body 20, the shape of the crystallized material is controlled by the solidification speed. Control, which in turn improves the purity of the crystallized material. In the tubular rotary cooling body 10, α-Al crystals are crystallized in a shape as shown in FIGS. 3 (g) to 3 (g) in FIG.
Α-Al crystals are crystallized in a shape as shown in (i). According to the investigations and researches of the present inventors, (e), (f) and (i) of these crystallized materials have a uniform solidification rate and a high purity of the obtained crystallized materials. It turned out to be. However, conventionally, the control of the shape of the crystallized material is achieved by improving the materials of the cooling bodies 10 and 20 themselves and the heat insulating structure. Such a response results in problems such as complicated equipment and increased production costs. The present invention controls the cooling conditions so that the shape of the crystallized substance becomes (e), (f) or (i) in FIG.
An object of the present invention is to obtain highly purified aluminum with high productivity using a conventional purification apparatus without affecting the equipment configuration itself.

[0008]

In order to achieve the object, the refining method of the present invention immerses a cooling body in a molten metal in which aluminum scrap is dissolved, and crystallizes and grows α-Al crystals on the surface of the cooling body. At this time, the temperature T of the atmosphere above the surface of the molten aluminum with respect to the α-Al crystallization temperature T ₀ (° C.)
₁ (° C.) is maintained in a range of T ₁ = T ₀ − ( _{0 to} 24). When purifying an aluminum alloy having a composition in which some of the impurities are crystallized as primary crystals of intermetallic compounds, the intermetallic compounds crystallized as primary crystals are settled and separated at the furnace bottom, and then immersed in molten aluminum. The α-Al crystal is crystallized and grown on the surface of the cooled body. About 10c above the surface
When the ambient temperature at m satisfies the condition of T ₁ = T ₀ − ( _{0 to} 24), suitable cooling conditions are obtained, and the shape of the crystallized product is (e), (f) or (i) in FIG. )become. In terms of operation, it is easier to control the shape of the crystallized product by lowering the ambient temperature than the crystallization temperature of α-Al. This is presumed to be due to the fact that lowering the ambient temperature facilitates the removal of latent heat of solidification generated when the crystallized material solidifies. As the cooling body, the tubular cooling body 10 of FIG. 1, the disk-shaped cooling body 20 of FIG. 2, and the like can be used. These cooling bodies may be of a rotary type or a fixed type without rotating. When a tubular cooling body as shown in FIG. 4 is used, a vent 42 is also formed on the bottom surface of the inner tube 11, and the blowing rate of the cooling medium at the bottom surface is set to 0.1 to 5% of the total blowing amount. Adjustment is preferred.

[0009]

The α-Al crystal has various shapes as shown in FIG. 3 and crystallizes on the cooling bodies 10 and 20. It is considered that such a difference in the shape of the crystallized product is due to the following reason. In order to obtain a purified product having a high purity, FIGS.
And the shapes of (i) are preferred. When the α-Al crystal is crystallized on the side surface of the tubular cooling body 10, if the ambient temperature is too low, a large amount of heat is dissipated from the molten aluminum M to the atmosphere, and solidification on the molten metal surface is promoted. On the other hand, in portions deep from the surface of the molten metal, latent heat of solidification is not dissipated, and solidification is delayed.
As a result, the α-Al crystallized product has a shape (a) whose diameter is reduced toward the inside of the bath on the surface of the bath. Moreover, since the solidification rate on the molten metal surface is too high, impurities or low-purity Al are taken into the crystallized material during the crystallization of α-Al crystals,
The purity of the resulting purified product is reduced. In the cooling body 10 in which the cooling rate from the bottom surface is increased by increasing the blowing rate of the bottom surface, α-Al crystallites grow largely on the lower end side of the cooling body 10 (b). At this time, if the solidification rate at the bottom surface is too fast, the crystals grown on the bottom surface may have impurities or low purity A
1 is taken in, and the purity is lower than that of a crystal grown on the side surface. Further, the crystallized substance having the shape of (b) easily falls off from the cooling body 10 during the purification, which lowers the purification efficiency.

If the ambient temperature is too high, there is no heat dissipated from the molten aluminum into the atmosphere, and the progress of solidification on the surface of the molten metal cannot be expected. As a result, the solidification rate is low, and the α-Al crystals grow thickly exclusively at the lower part of the cooling body 10 (c). Further, α-crystallized on the upper part of the cooling body 10
Al is easily peeled off. If the rotation speed of the cooling body 10 immersed in the molten aluminum M is too high, the crystallized substances attached to the surface of the cooling body 10 are separated and dropped by the centrifugal force (d). When the crystallized material has such a shape, it is required to grow a crystallized material having an appropriate shape by adjusting the rotation speed of the cooling body 10. When the ambient temperature is appropriately maintained and the cooling conditions are uniform with respect to the surface of the cooling body 10, the α-Al crystallized substance grows on the side surface of the cooling body 10 with a uniform thickness (e). Further, when the heat removal function on the bottom surface of the cooling body 10 is improved, the α-Al
Crystals grow (f). From the crystallized material grown with such a uniform thickness, a purified product with high purity can be obtained. Further, the crystallized product of the shape (f) is effective in increasing the purification efficiency.

Even when the disk-shaped cooling body 20 is used,
When the ambient temperature is too low, α-Al crystallized matter grows preferentially in the vicinity of the molten metal surface, and α-Al crystal grows on the lower surface of the cooling body 20.
The crystals are relatively reduced (g). Conversely, if the ambient temperature is too high, the solidification rate will be low, and the α-Al crystal will grow downward from the center of the lower surface of the cooling body 20 (h). In contrast,
Under conditions where the ambient temperature is properly maintained, the cooling body 20
(I), the surface of the cooling body 20 is effectively used for the purification reaction, and a purified product with high purity can be obtained. From the results of various experiments conducted by the present inventors, when a crystal having the shapes shown in FIGS. 3 (e), (f) and (i) is formed, the solidification reaction proceeds at an appropriate rate, and It was also found that the product had good shape and that a purified product with good purity could be obtained. Above all, the crystallized substance (f) obtained by using the cooling body 10 having the improved heat removal ability at the bottom is:
The amount of purification per batch is larger than that of the crystallized material (e) obtained when the cooling body 10 which does not expect the heat removal ability of the bottom is used, and the bottom of the cooling body 10 is eroded by the molten aluminum. Is also prevented.

As the cooling body 10 having an improved bottom surface heat removal ability, a cooling body having a sectional structure shown in FIG. 4 is used. A plurality of ventilation holes 4 are formed on the side of the inner pipe 11 located below the molten metal surface L.
1 as well as a vent 42 on the bottom surface.
Then, the blowing rate is adjusted by adjusting the opening areas of the ventilation holes 41 and 42. For example, 60.5m in diameter
m inner pipes 11 are used, and 54 ventilation holes 41 having a diameter of 8 mm are formed on the side surface from the position 50 mm from the molten metal surface L to the vicinity of the tip of the inner pipe 11. On the other hand, one vent hole 41 having a diameter of 5 mm is formed at the center of the bottom of the inner tube 11. At this time, the blowing rate of the cooling medium g at the bottom of the inner pipe 11 is
(Π × 2.5 ² × 1 / π × 4 ² × 54) × 100 = 0.
7%.

The blowing rate at the bottom of the inner tube 11 is zero.
%, That is, when the cooling medium g is not blown out from the bottom of the inner tube 11, the lower surface of the outer peripheral surface of the cooling tube 10 is not cooled, so that FIGS. 3 (a), (c), (d), ( As shown in e), the α-Al crystal does not crystallize or grow on the lower surface of the cooling body 10, and the efficiency of using the surface of the cooling body 10 for growing the crystallized material is reduced. Further, since the lower surface of the cooling body 10 is exposed to the molten aluminum M, the cooling body 10 is eroded by the molten aluminum M depending on the material of the cooling body 10. However, when the blowing rate exceeds 5%, the cooling effect on the lower surface of the cooling body 10 becomes too large, and a crystallized substance as shown in FIG. 3B is formed. in this case,
Since the solidification rate at the lower surface of the cooling body 10 is higher than the target value, the crystal grown on the lower surface has a lower purity than the crystal grown on the side surface of the cooling body 10. On the other hand, in the cooling body 10 in which the blowing rate is adjusted in the range of 0.1 to 5%, FIG.
As shown in (f), the side surface and the bottom surface of the cooling body 10 are utilized for the growth of the crystallized matter with high efficiency, and a crystallized material having a uniform thickness and a good shape is obtained. Further, the surface of the cooling body 10 is covered with the crystallized substance, and the erosion of the cooling body 10 by the molten aluminum M is also prevented.

[0014]

【Example】

Example 1 A tubular cooling body 10 having a diameter of 110 mm was melted in an aluminum melt M in which aluminum sapphire scrap containing 0.64% by weight of Si and 0.45% by weight of Fe was melted.
Is immersed to a depth of 300 mm from the hot water surface,
Tubular cooling body 1 while supplying at a flow rate of 2,000 liters / minute
0 to 100 r. p. m. As the tubular cooling body 10, one having a vent 42 formed in the bottom of the inner tube 11 having a diameter of 60 mm and the blowing rate at the bottom set to 0.7% was used. Since the crystallization temperature T ₀ is in the range of 654 to 652 ° C., the atmosphere temperature T ₁ in the furnace was maintained at 640 to 650 ° C. so that T ₁ = T ₀ − (2 to 14) ° C. Under these conditions, α-Al crystals were grown on the side and bottom surfaces of the cooling body 10 for 15 minutes. The obtained crystallized material has a diameter of 340 mm on the side surface located 290 mm above the bottom surface of the cooling body 10.
mm. Further, the cooling body 10 was grown with a thickness of 20 mm downward from the bottom surface. The purity of the purified product obtained from the crystallized product was 0.22% by weight of Si and 0.13% by weight of Fe.

Example 2: The same aluminum melt M as in Example 1 was used, with a diameter of 280 mm.
Of the rotary cooling body 20 of
While supplying at a flow rate of 1 liter / min, the disc-shaped cooling body 20 is supplied at 50 r. p. m. The crystallization temperature T ₀ is 654-
Since the temperature range is 652 ° C., the atmosphere temperature T ₁ in the furnace was maintained at 646 to 654 ° C. so that T ₁ = T ₀ − (0 to 8) ° C. Under these conditions, α-Al crystallized substances were grown on the lower surface and the side surfaces of the cooling body 20 for 15 minutes. The obtained crystallized product has a thickness of 35 mm and a diameter of 310 mm from the bottom of the cooling body 20.
mm. The purity of the purified product obtained from the crystallized product was 0.20% by weight of Si and 0.14% by weight of Fe.

Example 3 The same tubular cooling body 10 as in Example 1 was placed 300 mm from the surface of molten aluminum M in which aluminum scrap for automobiles containing 8.02% by weight of Si and 0.68% by weight of Fe was melted. Of the tubular cooling body 10 while supplying cooling air at a flow rate of 3000 liters / min.
r. p. m. The crystallization temperature T ₀ is 594-59
Since it is in the range of 2 ° C., the atmosphere temperature T ₁ in the furnace was maintained at 570 to 594 ° C. so that T ₁ = T ₀ − ( _{0 to} 24) ° C. Under these conditions, α and α
-The Al crystallization was allowed to grow for 15 minutes. The obtained crystallized material had grown to a thickness of 240 mm in a length of 320 mm in the axial direction of the cooling body 10. The purity of the purified product obtained from this crystallized product was 3.31% by weight of Si and F
e: 0.20% by weight.

Embodiment 4: The same disk-shaped rotary cooling body 20 as in Embodiment 2 is immersed in the same molten aluminum M as in Embodiment 3, and while cooling air is supplied at a flow rate of 3000 liters / minute, disk-shaped cooling is performed. One body 20
50r. p. m. Crystallization temperature T ₀ is 594～
Since it is in the range of 592 ° C., T ₁ = T ₀ − (4 to 24) ° C.
And so as to the ambient temperature T ₁ of the furnace five hundred seventy to five hundred and ninety ° C.
Held. Under these conditions, α-Al crystallized substances were grown on the lower surface and the side surfaces of the cooling body 20 for 15 minutes. The obtained crystallized product has a thickness of 25 mm from the bottom of the cooling body 20 and a diameter of 30 mm.
It had grown to 0 mm. The purity of the purified product obtained from this crystallized product was 3.20% by weight of Si and 0.18% of Fe.
% By weight. As a result of repeating experiments as shown in Examples 1 to 4 for various aluminum scraps, α
It was confirmed that when the ambient temperature was appropriately adjusted with respect to the crystallization temperature of -Al, a purified product having a good shape and a high purity was obtained. That is, in refining aluminum sapphire scrap, the crystallization temperature T ₀ of α-Al is 650 ° C.
64, which is lower by ₀ to 10 ° C. than the crystallization temperature T _0.
It is effective to hold the ambient temperature T ₁ of in the range of from 0 to 650 ° C.. On the other hand, in refining Al scrap for automobiles, the crystallization temperature T ₀ of α-Al is around 590 ° C., so it is 570 to 59 ° C. lower than the crystallization temperature T ₀ by ₀ to 20 ° C.
It is effective to hold the ambient temperature T ₁ of in the range of 0 ° C..

Comparative Example: A case where the same molten aluminum sapphire scrap as in Example 1 was purified using a tubular rotary cooling body 10 under conditions outside the range specified in the present invention,
FIG. 5 shows a comparison with Examples 1 and 3. In Comparative Example 1 in which the ambient temperature was too low, the solidification rate near the molten metal surface was large, and the purity of the purified product was poor. Comparative Example 2 with too high ambient temperature
Thus, although a solidified product having a low solidification rate and high purity was obtained, there was a problem in productivity. Further, in Comparative Example 3 in which the blowing rate from the bottom of the inner tube was increased, a crystallized substance having a poor shape grew and the purity of the purified product was poor. When the molten metal of aluminum sapphire scrap is purified using the disk-shaped rotary cooling body 20, the ambient temperature is set to 500 to
When the temperature was set to 530 ° C., as shown in FIG. 3 (g), a solidified product having a high solidification rate near the molten metal surface and a low purity was obtained. Conversely, when the ambient temperature was set to a high value of 720 to 750 ° C., a crystal having the shape shown in FIG. 3 (h) grew and a purified product with high purity was obtained, but the purification efficiency was low.

[0019]

As described above, in the present invention, a cooling body is immersed in a molten aluminum scrap having a composition in which primary crystals are intermetallic compounds, and α-Al When purifying aluminum by crystallizing the crystals, the ambient temperature is controlled in relation to the crystallization temperature of α-Al. By this temperature control, the solidification rate of the α-Al crystal can be made uniform over the entire surface of the cooling body, and a purified product with high purity can be obtained. In addition, when a vent hole is formed at the bottom of the inner tube of the tubular cooling body to improve the bottom cooling capacity, crystallized matter of high purity also grows on the bottom of the tubular cooling body,
The purification efficiency is improved, and the erosion of the cooling body by the molten aluminum is suppressed.

[Brief description of the drawings]

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

FIG. 2 shows another example of a purifying apparatus for performing the purifying method according to the present invention.

FIG. 3 shows several examples of α-Al crystals grown in different shapes due to the influence of the ambient temperature and the like.

FIG. 4 is a tubular cooling body having an improved bottom surface heat removal capability.

FIG. 5 is a chart comparing the effect of operating conditions on the refining results when refining aluminum melt using a tubular cooling body.

[Explanation of symbols]

M: molten metal α-Al: purified crystallized substance I: intermetallic compound g: cooling medium 10: tubular rotary cooling body 11: inner tube 12: outer tube
13: Coupling 14, 16: Motor 15: Arm 17: Feed screw 18: Gap 20: Disc-shaped rotary cooling body 21: Inner tube 22: Outer tube 23, 24: Flange 25: Orifice 2
7: Bottom wall 28: Distribution chamber 29: Cooling chamber 30: Purification container 31: Heater 32: Lid 3
3: burner 41: vent formed on the lower side of the inner tube 42: vent formed on the bottom of the inner tube

Continuation of the front page (56) References JP-A-60-190535 (JP, A) JP-A-63-162823 (JP, A) JP-A-5-295465 (JP, A) JP 2-27423 (JP) , B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22B 1/00-61/00

Claims (3)

(57) [Claims] When a cooling body is immersed in a molten metal in which aluminum scrap is melted to crystallize and grow α-Al crystals on the surface of the cooling body, the aluminum molten metal is melted at an α-Al crystallization temperature T ₀ (° C.) . Temperature T ₁ (° C) of the atmosphere above the surface of the bath
The _{T 1 = T 0 - (0~24} ) method for purifying aluminum scrap, characterized in that maintained in the range of. 2. The cooling body according to claim 1, wherein the bottom is closed.
Double tube with a closed-bottomed tube inserted into a closed tube
On the side and bottom of the inner pipe located below the
It has a cross-sectional structure with ventilation holes, and is cooled from the inner tube
The medium is fed and the cooling medium is passed through the outer pipe of the double pipe.
A method for purifying aluminum scrap using a tubular cooling body in which a discharge rate of a cooling medium at a bottom surface of an inner tube is 0.1 to 5% of a total blowout amount when the water is discharged outside . 3. An aluminum alloy having a composition in which some of the impurities are crystallized as primary crystals of an intermetallic compound is melted, and an intermetallic compound crystallized as a primary crystal is settled and separated at a furnace bottom, and then the molten aluminum is melted. Α-A on the surface of the cooling body immersed in
3. The aluminum alloy according to claim 1, wherein the 1 crystal is crystallized and grown.
Purification method of beam scrap.