JPH0551660A - Method for dehydrogenating molten aluminum - Google Patents

Abstract

PURPOSE:To remove hydrogen from molten aluminum without blowing the bubles of an inert gas into molten aluminum, to obviate the generation of dross in the process, to eliminate loss of molten aluminum, to prevent the splashing of molten aluminum and to make the maintenance of a crucible easy or needless. CONSTITUTION:Molten aluminum A is held in an inert gas atmosphere having <=-25 deg.C dew point and agitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dehydrogenation for removing hydrogen as impurities dissolved in molten aluminum when aluminum is melted in a production line of various aluminum primary products such as casting, extrusion and rolling. Regarding the method.

In this specification, the term "aluminum" includes aluminum alloy in addition to pure aluminum.

[0003]

2. Description of the Related Art Conventionally, as a method of removing dissolved hydrogen gas as described above, an inert gas is blown into the molten aluminum in the form of fine bubbles while stirring the molten aluminum to diffuse hydrogen into the bubbles. There is known a method of floating hydrogen gas together with bubbles (Japanese Patent Publication No. 60-497).
00, Japanese Patent Publication No. 61-40737 and Japanese Patent Publication No. 52-36487).

[0004]

However, in the conventional method, when the bubbles of the inert gas float on the surface of the molten aluminum and burst, the molten metal scatters and the amount of dross leading to the loss of aluminum increases. There was a problem. In particular, when processing expensive 99.99 wt% or higher high-purity aluminum, the loss of the molten aluminum becomes a serious problem. Further, since the scattered molten metal adheres to the inner wall of the peripheral wall and ceiling of the treatment crucible, there is a problem that it takes time and cost to maintain the treatment crucible for removing the deposits.

An object of the present invention is to provide a dehydrogenation method from molten aluminum which solves the above problems.

[0006]

The method of dehydrogenation from the molten aluminum according to the present invention is to keep the molten aluminum in a dry air atmosphere having a dew point of -25 ° C or lower,
The method is characterized by stirring the molten aluminum.

In the dehydrogenation method from the molten aluminum, the dew point of the dry air is set to -25 ° C. or below.
For the following reasons. That is, in order to perform dehydrogenation from the molten aluminum to obtain a low hydrogen concentration of, for example, 0.30 cc / 100 g Al or less, it is necessary to set the water vapor partial pressure in the atmosphere to 7 × 10 ⁻⁴ atm or less. Unless the dew point is -25 ° C or lower, the water vapor partial pressure in the atmosphere is 7
This is because it cannot be made less than or equal to × 10 ^-4 atm.

[0008]

According to the method of the present invention, the molten aluminum is kept in a dry air atmosphere having a dew point of -25 ° C. or lower, and the molten aluminum is stirred, so that the partial pressure of water vapor in the atmosphere is lowered. It is possible to effectively perform dehydrogenation treatment from the molten aluminum. The reason is considered as follows. That is, the equilibrium hydrogen concentration is determined on the surface of the molten metal which is in contact with dry air in accordance with the partial pressure of water vapor in the atmosphere. When the hydrogen concentration in the molten aluminum is higher than the equilibrium hydrogen concentration on the molten metal surface, the hydrogen in the molten metal diffuses to the molten metal surface and escapes as hydrogen gas from the molten metal surface into the atmosphere, reducing the hydrogen concentration in the molten metal. However, the decrease in hydrogen concentration in the molten metal due to this diffusion requires an extremely long time, as expected from the diffusion equation. However, when the molten metal is stirred to generate forced convection in the molten metal,
The decrease in hydrogen concentration in the molten metal due to diffusion is accelerated, and dehydrogenation from the molten metal can be effectively performed.

Furthermore, according to this method, it is not necessary to blow the inert gas in the form of bubbles into the molten aluminum.

[0010]

The method of the present invention will be described below.

FIG. 1 shows an apparatus for carrying out the method of the present invention.
A specific example is shown.

In FIG. 1, a dehydrogenation apparatus for molten aluminum (A) is a treatment chamber (3) having a closed structure arranged in a heating furnace (1) in which a heater (2) is embedded in a peripheral wall (1a). Is equipped with. The processing chamber (3) is made of, for example, stainless steel and has an open upper end (4).
And a lid body (5) which is also made of stainless steel and is detachable. An annular groove (6) for filling the sealing material is provided at the upper end of the outer peripheral surface of the chamber body (4) over the entire circumference. The annular groove (6) is filled with a sealing material (7) made of, for example, sand. A dry air supply port (8) is formed in the lower part of the peripheral wall (4a) of the chamber body (4), and a dry air supply pipe (9) is connected to the supply port (8).

The peripheral portion of the lid body (5) projects outwardly from the peripheral wall (4a) of the chamber body (4), and an annular downward projecting wall (5a) is integrally formed on this portion over the entire circumference. There is. The lower part of the downward protruding wall (5a) is inserted into the sealing material (7) in the annular groove (6). A through hole (11) is formed in the center of the lid (5). A shield device (12) is provided around the through hole (11). The shield device (12) has a double inner and outer tubular surrounding wall (13) (14) fixedly provided on the upper surface of the lid (5) so as to surround the through hole (11) and projecting upward. In addition, the upper walls of both surrounding walls (13) and (14) are closed to form a dry air passageway (15) inside. Inner wall (1
A plurality of dry air outlets (16) are formed in 3). A dry air supply pipe (18) for shielding is connected to the outer surrounding wall (14). Further, a dry air discharge pipe (20) for discharging excess dry air in the processing chamber (3) is penetratingly fixed to the lid body (5). Although illustration is omitted, the lid (5) is formed with an insertion port for the temperature detector, and the temperature detector is inserted into the processing chamber (3) through this insertion port.

A crucible (21) made of alumina, for example, is arranged in the processing chamber (3). Crucible
On the inner surface of the peripheral wall (21a) of (21), a plurality of baffle plates (22) are arranged at intervals in the circumferential direction. The upper end of the baffle plate (22) projects upward from the surface of the molten aluminum (A), and the lower end is at a position approximately half the depth of the molten aluminum (A). Inside the molten aluminum (A) in the crucible (21), the lid
A disk-shaped stirring member (24) fixedly provided is immersed at the lower end of the vertical rotation shaft (23) passed through the through hole (11) of (5). A plurality of stirring blades (24a) are formed on the circumferential surface of the stirring member (24) at intervals in the circumferential direction.

In such a structure, in order to perform dehydrogenation treatment from the molten aluminum (A), the molten aluminum (A) to be treated is put in the crucible (21) and heated to a temperature higher than the melting temperature by the heater (2). Keep heating. At the same time,
The dew point of the dry air supply pipe (9) into the processing chamber (3) is −
Dry air at 25 ° C. or lower is supplied to keep the chamber (3) in a dry air atmosphere. Further, the same dry air as above is supplied from the dry air supply pipe (18) of the shield device (12) into the dry air passageway (15), and blown out from the blowout port (16), thereby the vertical rotation shaft (23). Shield between the through hole (11). Then, the vertical rotating shaft (23) and the stirring member (24) are rotated to stir the molten aluminum (A). Then, hydrogen in the molten aluminum (A) is removed.

Next, a more specific embodiment of the method of the present invention performed by the apparatus shown in FIG. 1 will be described.

Concrete Example 1 A molten metal (A) of high-purity aluminum having a purity of 99.99 wt% was placed in a crucible (21) and kept at 700 ° C. by a heater (2). 0.39cc / in this molten metal (A)
It contained 100 g of hydrogen. And the processing chamber
(3) Inside the dew point -40 ℃ (steam partial pressure 1.5 × 10 ^-4 atm
), And the vertical rotating shaft (23) and the stirring member (24) were rotated at a rotation speed of 500 rpm.

The amounts of hydrogen in the molten aluminum (A) after 10 minutes and 40 minutes were measured and found to be 0.23 cc / 100 g and 0.07 cc / 100 g, respectively.
Met. In addition, when checking for the occurrence of dross,
It didn't happen at all.

Concrete Example 2 A molten metal (A) of high-purity aluminum having a purity of 99.99 wt% was placed in a crucible (21) and kept at 750 ° C. by a heater (2). 0.55 cc / in this molten metal (A)
It contained 100 g of hydrogen. And the processing chamber
(3) Inside the dew point -40 ℃ (steam partial pressure 1.5 × 10 ^-4 atm
), The vertical rotation shaft (23) and the stirring member (24) were rotated at a rotation speed of 400 rpm.

The amount of hydrogen in the molten aluminum (A) after 20 minutes and 40 minutes was measured and found to be 0.30 cc / 100 g and 0.10 cc / 100 g, respectively.
Met. In addition, when checking for the occurrence of dross,
It didn't happen at all.

Concrete Example 3 A molten metal (A) of high-purity aluminum having a purity of 99.99 wt% was placed in a crucible (21) and heated and held at 675 ° C. by a heater (2). 0.30cc / in this molten metal (A)
It contained 100 g of hydrogen. And the processing chamber
(3) Inside the dew point -25 ℃ (steam partial pressure 6.9 × 10 ^-4 atm
), And the vertical rotating shaft (23) and the stirring member (24) were rotated at a rotation speed of 600 rpm.

The amounts of hydrogen in the molten aluminum (A) after 10 minutes and 30 minutes were measured and found to be 0.18 cc / 100 g and 0.12 cc / 100 g, respectively.
Met. In addition, when checking for the occurrence of dross,
It didn't happen at all.

[0023]

According to the method for dehydrogenating molten aluminum of the present invention, hydrogen can be removed from the molten aluminum as described above. Moreover, since it is not necessary to blow bubbles of inert gas into the molten aluminum as in the conventional case, it is possible to prevent the generation of dross due to the burst of the inert gas bubbles on the surface of the molten metal. Therefore, the loss of the molten aluminum can be prevented.
Further, since it is possible to prevent the molten aluminum from scattering due to the burst of the inert gas bubbles on the surface of the molten metal, maintenance of the treatment crucible becomes simple or unnecessary, and the cost thereof becomes low.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing one specific example of an apparatus for carrying out the dehydrogenation method for molten aluminum according to the present invention.

[Explanation of symbols]

 A molten aluminum

Claims (1)

[Claims] 1. A method for dehydrogenating an aluminum melt by keeping the aluminum melt in a dry air atmosphere having a dew point of -25 ° C. or lower and stirring the aluminum melt.