JPS6089528A - Treatment of aluminum melt - Google Patents

Abstract

PURPOSE:To remove efficiently gaseous hydrogen in an aluminum melt by spraying preliminarily borofluoride salt onto the surface of the aluminum melt and blowing a treating gas in a foaming state into the aluminum melt. CONSTITUTION:While a supply pipe 5 for a treating gas such as N2, Ar, He or the like is rotated by a motor 7, said gas is blown in a foaming state into an aluminum melt 1 put into a treating vessel 2 from a gas releasing member 6 which is attached to the top end of said pipe and vertical grooves 6a to remove gaseous hydrogen and nonmetallic inclusions from the inside of the melt 1. Borofluoride salt such as NaBF4, NH4BF4, etc. is preliminarily blown to the surface of said melt at about >=0.005g/cm<2>, more preferably, 0.01g/cm<2> in this state. The borofluoride salt sprayed by such disposition is decomposed by the heat of the melt 1 and the generated BF3 prevents intrusion of the gaseous hydrogen in the atmosphere above the melt 1 into the melt 1, by which the removing efficiency of the gaseous hydrogen from the melt 1 is improved.

Description

[Detailed description of the invention] The present invention relates to a method for treating molten aluminum.

Molten aluminum before casting contains harmful gases such as hydrogen gas and nonmetallic inclusions such as oxides of aluminum and magnesium. The hydrogen gas and non-metallic inclusions are removed from the obtained ingot and this ingot for 31 years.
What causes defects in the resulting product? Therefore, it is necessary to remove hydrogen gas and nonmetallic inclusions. Conventionally, as a method for removing these, a method has been adopted in which inert gas such as nitrogen gas or argon gas or chlorine gas is blown into the molten aluminum in the form of bubbles. However, because it contains water,
Aluminum reacts with moisture in the atmosphere on the surface of aluminum 7B 43.2A/→-3820-+Al2O3
+3hh), resulting in the problem that the generated hydrogen enters the molten metal. Therefore, the efficiency of hydrogen gas removal by blowing inert gas and chlorine gas becomes worse.

Therefore, a method of performing the above treatment in an inert gas atmosphere was considered, but this method also reduces the amount of moisture in the atmosphere to O,...
It is impossible to reduce the amount to 5 mgz# or less. Water content is 0
．． 5111 (+/1 or less, otherwise the amount of hydrogen gas generated by reacting with aluminum and penetrating into the molten aluminum will not decrease much, and the hydrogen gas removal efficiency by inert gas aj and chlorine gas injection will still be low. Not enough.

This invention was made in view of the above circumstances, and
Providing a treatment method that can prevent hydrogen generated by the reaction between moisture in the atmosphere and aluminum from penetrating into the molten aluminum, and can significantly increase hydrogen gas removal efficiency compared to conventional methods.1 In this specification, the term "aluminum" is used to include pure aluminum LSIs and aluminum base metals.

A method for treating molten aluminum according to the present invention includes blowing a treatment gas in the form of bubbles into a 1c aluminum molten lag placed in a treatment tank to remove hydrogen gas and nonmetallic inclusions from the molten aluminum. In this process, borofluoride salt is preliminarily sprinkled on the surface of the molten aluminum in J5 and d3 is carried out to perform the process described in P.

In the above, the processing scum that is blown into the molten aluminum in the form of bubbles includes inert gases such as gas, argon gas, helium scum, and mixtures thereof, and chlorine gas, which are contained in the molten aluminum. Any gas effective for removing hydrogen gas and non-metallic inclusions may be used.

Further, the reason why borofluoride salt is sprayed on the surface of the molten aluminum in advance in 43 above is as follows. In other words, the borofluoride salt is decomposed by the heat of the molten aluminum, and 1
3F3 gas is generated, but this 13 [3 gas is the place 1!
l! This is because cypress has the property of preventing hydrogen from entering the molten aluminum, which is generated by the reaction between the moisture in the atmosphere above the surface of the molten aluminum and the molten aluminum.
be.

As borofluoride salts, Na BF, , KB F, ,
, L+ o +-t, , N H/, l'3 F4
etc. are used. Defeat #D'? The color of the fluoride salt depends on the surface area of the molten aluminum = i L and 0.
0059/cm2 or more, but good J: Shiku, Poison 0.
01 o /cm2 or more is preferable.

Further, the amount of alkali metal or alkaline earth gold is further increased on the surface of the molten aluminum together with the borofluoride salt.The addition of the above-mentioned halide is carried out at a rate of 0°003 CI or more per surface area of the molten aluminum I C111'. It is preferable that the weight is 0.06 g or more, especially 0.06 g or more.

The method for treating molten aluminum according to the present invention is described in J.
: Sea urchin 47. 13F, which is generated by the decomposition of the borofluoride salt, even if hydrogen is generated by the reaction between the moisture contained in the atmosphere above the molten metal in the treatment tank and the aluminum. This action prevents hydrogen from entering the molten aluminum. Therefore, the hydrogen gas removal efficiency is dramatically increased compared to conventional methods.

Examples of the present invention will be described below with reference to the drawings along with comparative examples.

Example A3 and Comparative Examples 1 to 4 These Examples and Comparative Examples were carried out using the apparatus shown in Fig. 1. In Fig. 1, the molten aluminum (1) to be treated is In the treatment tank (2), molten metal (
1) It is placed so that the surface is slightly above the top of the tank (2). The upper end of the treatment tank (2) has a collar (3)
'rOccluded. A hole (4) is made in the center of the candy (3), and a treated waste supply pipe (5) is inserted through this hole (4) from above. The lower end of the processing gas supply pipe (5) (extends to near the bottom of the tank (2), and the bubbly processing gas discharge part 4.j (6) is attached to the tip of the pipe (5). (The waste supply pipe (5) can be rotated by the morph (7).

The processing gas discharge part (Δ(6〉) is disc-shaped, has a processing gas passage hole (not shown) formed in the center, and has a plurality of longitudinal tj'j ( 6a) is formed.Also, pass through M(3) and connect the N2 supply pipe (
8) and the exhaust pipe (9) are installed (pulled.
The 98-gas that has flowed through is supplied to the bottom surface of the discharge member (6) from the lower end opening of the processing gas passage hole. The centrifugal force generated by the rotation of the discharge member (6) and the longitudinal groove (6a
), small bubbles of process gas are created in the tank 2)
It is released so as to spread throughout the whole body.

Using such a device, melt the molten metal (1) at a temperature of 700 to 730
℃ and after spraying borofluoride salt on its surface or without spraying, treatment 4? ff (2) E-pull molten metal (1
) Surface J: From the supply pipe (8) to the atmosphere above the limo
While supplying two gases or without supplying one gas as shown in Table 1 (4U purity 99°99W [% aluminum molten 150
0 kg was subjected to hydrogen gas removal treatment. Ar gas is used as the processing gas and is blown into the molten metal (1) at a rate of 201/n1 inch. In addition, the processing gas supply pipe (5)
The rotational speed was 650 r, l], m. Each molten metal 20
0 g was collected in a red-hot iron container, and the number of bubbles generated until solidification was completed under a vacuum of 2 TOrr was counted. In this way, the relationship between the hydrogen scum removal treatment time and the number of bubbles generated was investigated.

The fewer the number of bubbles generated, the more hydrogen gas can be removed;

(Hereinafter in the margin) Table 1 (hereinafter in the F margin) The results of Examples and Comparative Examples 1 to 4 are summarized in Fig. 2.

As is clear from Figure 2, punishment! In case of spraying borofluoride salt on the surface of molten metal (1) in A3 tank (2) to remove hydrogen gas, remove hydrogen gas without spraying borofluoride salt. *I
J. has improved dramatically.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of an apparatus used to carry out the method of the present invention, and FIG. 2 is a graph showing the relationship between processing time and the number of bubbles generated when hydrogen gas removal is performed using this apparatus. . (1)... Molten aluminum, (2)... Treatment tank. Applicant: Showa Aluminum Co., Ltd. Figure 1 Figure 2 r Processing time (→

Claims (1)

[Claims] In a method for treating molten aluminum in which hydrogen scum and non-metallic inclusions are removed from the molten aluminum by blowing a treatment gas in the form of bubbles into the molten aluminum placed in the treatment tank, the molten aluminum placed in the treatment tank d3 1. A method for treating molten aluminum, characterized in that the above-mentioned treatment is carried out after spraying borofluoride salt on the surface of the aluminum molten metal.