JP2008075170A - Molten aluminum treating agent and treating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a treating agent which is easy to handle and requires no post-treatment in removing gas and inclusions from molten aluminum and further has no toxicity and can minimize influence on global warming or also to provide a treating method. <P>SOLUTION: A molten aluminum treating agent composed of a gaseous mixture of fluoroketone and inert gas is used. The treating agent filled into a treating agent container 1 is blown, via a pipe 3, using an injection pipe 6 into molten aluminum A filled into a melting furnace 7 to cause bubbling. Fluoroketone concentration in the treating agent is made to 0.01 to 10 mass%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a treatment agent for molten aluminum used to remove inclusions such as gases such as hydrogen, gases, impurity elements, and oxides present in molten aluminum or aluminum alloy (hereinafter collectively referred to as aluminum in the present invention). And a processing method using the same.

In general, an inert gas such as Ar, N ₂ , or He is used to remove the gas present in the molten aluminum.
Also, halogen is often used to remove inclusions such as impurity elements and oxides and to improve the separation between dross (molten surface surface) and molten aluminum. As the halogen, a flux (powder) typified by chlorine gas (Cl ₂ ), Freon gas, sulfur hexafluoride (SF ₆ ) gas, and potassium chloride (KCl) is used.

However, chlorine gas is very active and excellent in molten aluminum treatment, but it is difficult to handle due to its toxicity and corrosivity, and it generates chlorine gas and aluminum chloride gas as exhaust gas. A large exhaust gas treatment device is required.
The chlorofluorocarbon gas also contains chlorine gas and aluminum chloride gas in the exhaust gas. Therefore, a method using a non-toxic SF ₆ has been proposed, SF ₆ is a high global warming potential gases are likely to take future use limitation.

Since flux is a powder, it is often used together with a carrier gas, but it is difficult to control the input amount, which may cause moisture contamination due to moisture absorption from the atmosphere. Since toxic gas is contained in the gas and a large amount of dust is generated, a large-scale exhaust gas treatment device is required.
JP-A-64-47822 Japanese Patent No. 2767262 JP 2004-143383 A

  Therefore, the problem in the present invention is to provide a treatment agent or treatment method that is easy to handle, does not require post-treatment, has no toxicity, and has little impact on global warming when removing gases and inclusions in molten aluminum. There is to get.

To solve this problem,
The invention according to claim 1 is an aluminum melt treatment agent comprising a mixed gas of fluoroketone and inert gas.
The invention according to claim 2 is the aluminum melt treating agent according to claim 1, wherein the fluoroketone concentration in the mixed gas is 0.01 to 10% by mass.

  According to a third aspect of the present invention, there is provided a molten aluminum treatment method, wherein the molten aluminum treatment agent according to the first or second aspect is blown into the molten aluminum and bubbled.

  According to the present invention, gas and inclusions in the molten aluminum are removed by blowing and bubbling the molten molten metal treatment agent into the molten aluminum. Moreover, since exhaust gas does not contain toxic gas, no post-treatment is required. Furthermore, since fluoroketone has a low global warming potential, it has little impact on global warming even if released into the atmosphere.

  FIG. 1 shows an example of the treatment method of the present invention, and reference numeral 1 in the figure denotes a treatment agent container. The treatment agent container 1 is a container in which a molten aluminum treatment agent (hereinafter sometimes simply referred to as a treatment agent) is filled in a pressure vessel 2 such as a gas cylinder. This treating agent consists of a mixed gas of fluoroketone and inert gas.

  As the fluorinated ketone, at least one selected from perfluoroketones is used. The number of carbonyl groups contained in one molecule of fluoroketone is preferably 1.

As the perfluoroketone, those having 5 to 9 carbon atoms are preferable. For example, CF ₃ CF ₂ C (O) CF (CF ₃ ) ₂ , (CF ₃ ) ₂ CFC (O) CF (CF ₃ ) ₂ , CF ₃ (CF ₂ ) ₂ C (O) CF (CF ₃ ) ₂ , CF ₃ (CF ₂ ) ₃ C (O) CF (CF ₃ ) ₂ , CF ₃ (CF ₂ ) ₅ C (O) CF ₃ , One or more selected from the group consisting of CF ₃ CF ₂ C (O) CF ₂ CF ₂ CF ₃ , CF ₃ C (O) CF (CF ₃ ) ₂ , and perfluorocyclohexanone is preferred. Moreover, 1 type may be used among these and 2 or more types may be mixed and used.

Among these fluoroketones, pentafluoroethyl-heptafluoropropyl ketone, that is, C ₃ F ₇ (CO) C ₂ F ₅ (for example, CF ₃ CF ₂ C (O) CF (CF ₃ ) ₂ , CF ₃ CF ₂ C (O) CF ₂ CF ₂ CF ₃ ) is particularly preferred.

  The molecular weight of the fluoroketone is 250 or more, preferably 300 or more. By using a material having a molecular weight within this range, the fluoroketone in the treatment agent tends to be uniform with respect to the inert gas.

The concentration of the fluoroketone in the mixed gas is 0.01 to 10% by mass, preferably 0.05 to 5% by mass. By setting the fluoroketone concentration within this range, the gas and inclusions in the molten aluminum can be removed.
If the fluoroketone concentration is less than 0.01% by mass, the effect of the molten metal treatment with the desired fluoroketone cannot be obtained, and if it exceeds 10% by mass, excess aluminum fluoride is generated and dross increases and the cost increases. It will be.
In addition, since fluoroketone is normally a liquid at normal temperature, it needs to be vaporized in order to mix with an inert gas.

  Argon, nitrogen, helium, etc. are used for the inert gas which becomes one component which comprises the said molten aluminum processing agent, These mixed gas can also be used.

  As the pressure vessel 2, one used for storage of argon or the like can be used. In general, the pressure resistant container 2 uses a synthetic resin material for valve packing or the like. Of the members that come into contact with the processing agent when the processing agent is taken out from the pressure vessel 2, the members made of synthetic resin (valve packing, etc.) have at least a surface of chloroprene rubber, butyl rubber, fluorine rubber to prevent deterioration due to fluoroketone. , Ethylene propylene rubber, silicone rubber, nitrile rubber, Teflon (registered trademark), nylon, delrin (registered trademark), and Daiflon (registered trademark). These materials can be used not only for the valve of the pressure vessel 2 but also for any member of the system that supplies the processing agent to the melting furnace.

In order to fill the pressure-resistant vessel 2 with the treatment agent, it is preferable to first supply fluoroketone into the pressure-resistant vessel 2 and then supply an inert gas into the pressure-resistant vessel 2. By supplying the inert gas used in a relatively large amount after the fluoroketone, the inert gas and the fluoroketone can be sufficiently mixed and made uniform when supplying the inert gas.
The filling pressure of the mixed gas composed of fluoroketone and inert gas into the pressure resistant container 2 is set to about 1 to 20 MPa · G.

The processing agent in the processing agent container 1 is supplied at a predetermined flow rate to the blowing pipe 6 through the pipe 3, the on-off valve 4, and the flow meter 5.
Reference numeral 7 in the figure denotes a melting furnace such as an electric furnace which melts aluminum to form a molten metal, and the molten aluminum A is filled in the melting furnace 7.

  In the molten aluminum A, the tip of the blowing pipe 6 is inserted so as to reach the bottom of the furnace 7, and the gaseous treatment agent supplied to the blowing pipe 6 is blown into the molten aluminum A. As a result, bubbles are formed to rise in the molten aluminum A.

  The blow pipe 6 is made of a material having good heat resistance such as metal, carbon, ceramics, etc., and a tip having a plurality of small through holes through which a gaseous treatment agent is ejected is used. A pipe that has a blade formed at the tip thereof and is configured to be rotatable so that air bubbles made of a treatment agent are well dispersed in the molten aluminum A can be appropriately used.

The supply amount of the molten aluminum treatment agent to the molten aluminum A depends on the fluoroketone concentration in the treatment agent, the amount of molten aluminum A in the melting furnace 7, the gas in the molten aluminum, the degree of inclusion removal, etc. For example, when a treatment agent having a fluoroketone concentration of 0.5% by mass is used, the treatment agent integrated amount (flow rate × supply time) per 1000 kg of molten metal may be about 0.5 to ³ m ³ , and usually 1 m ³ or more is good. It is not necessary to blow into the molten metal A beyond 3 m ³ .

  The supply pressure of the molten aluminum treatment agent may be about 0.01 to 0.5 MPa · G, and in this range, bubbles are well ejected and dispersed in the molten metal A. The supply time is naturally determined once the processing agent integrated amount and the flow rate are determined, but it is usually preferable that the processing is completed within 60 minutes.

Thus, the treatment agent blown into the molten aluminum A rises as bubbles in the molten metal, and at this time, gas such as hydrogen dissolved in the molten metal is mixed with the inert gas in the treatment agent due to the partial pressure difference. , Taken into the bubbles and removed.
In addition, the fluoroketone in the bubbles reacts with molten aluminum to produce aluminum fluoride (AlF ₃ ). While this AlF ₃ floats in the molten metal together with the inert gas, it reacts with impurities in the aluminum, for example, calcium, to produce calcium fluoride (CaF ₂ ), and this CaF ₂ is formed on the molten metal surface together with the inert gas. And is removed as dross B.

Further, AlF ₃ , CaF _{2 and the} like accumulated in the dross B during the treatment are solid, and no harmful components are contained in the exhaust gas scattered from the molten metal. Therefore, it is not necessary to provide an extra exhaust gas treatment device.
Furthermore, AlF ₃ produced in the molten metal, as it reduces the surface tension of the molten aluminum, inclusions treatment agent bubble surface is easily adsorbed, the removal of inclusions becomes better Thereby.

  In addition, although the thing of batch processing was shown in the above-mentioned embodiment, the processing method of this invention is applicable also to continuous melting furnaces, such as a continuous casting line.

Specific examples are shown below.
(Example)
10 kg of aluminum alloy (AC4C, alloy component Si 6.5-7.5 wt%, Mg 0.20-0.45 wt%, balance Al) was melted in a melting furnace, and the molten metal temperature was set to 730 ° C.

Treatment was performed by blowing a molten aluminum treatment agent into the molten metal. As the treating agent, a gas in which fluoroketone was mixed with argon at a concentration of 0.5% by mass was used. Pentafluoroethyl-heptafluoropropyl ketone (C ₃ F ₇ (CO) C ₂ F ₅ ) was used as the fluoroketone.
The supply flow rate of the treatment agent was 0.7 N liter / minute, and the treatment time was 30 minutes.

Samples were taken from the melt every 10 minutes after the start of treatment and analyzed.
In the analysis, a molten sample was placed in a container, and the container was cooled and solidified by reducing the pressure inside the container. The reason why the sample is solidified under reduced pressure is to expand the gas remaining in the aluminum so that its presence can be observed. The components in the obtained sample were analyzed and the cut surface of the sample was observed to take a photograph.
For comparison, the same analysis was performed for the case where only argon was blown.

  The analysis results of the alloy components are shown in Table 1, and a photograph of the sample cut surface is shown in FIG. The notation “FK” in Table 1 and FIG. 2 indicates fluoroketone.

  From the results shown in Table 1, the amount of magnesium, which is an alloy component of the aluminum alloy (AC4C), is unchanged in both Ar and the treatment agent of the present invention. Calcium which is an impurity component of this alloy can be reduced by the treatment agent of the present invention. This shows that the treatment agent of the present invention can remove impurities without changing the alloy component of AC4C.

  Moreover, from the photograph of FIG. 2, it took 30 minutes for Ar to completely remove hydrogen in the molten metal. On the other hand, the treatment agent of the present invention was completely removed in 10 minutes, and the superiority of the degassing performance of the treatment agent of the present invention was confirmed.

  Further, the concentration of hydrogen fluoride and carbon monoxide was measured with a detector tube at a height of 50 cm from the surface of the molten metal, but it could not be detected, hydrogen fluoride was less than 0.5 ppm, and carbon monoxide was 5 ppm. It was found that there was no environmental problem.

It is a schematic block diagram which shows an example of the apparatus used for the processing method of this invention. It is the photograph replaced with drawing which shows the result of a specific example.

Explanation of symbols

1 ... Processing agent container 3 ... Pipe 6 ... Blowing pipe 7 ... Melting furnace A ... Aluminum melt

Claims (3)

  A molten aluminum treatment agent comprising a mixed gas of fluoroketone and inert gas.   The molten aluminum treatment agent according to claim 1, wherein the fluoroketone concentration in the mixed gas is 0.01 to 10% by mass.   A method for treating molten aluminum, comprising blowing the aluminum melt treating agent according to claim 1 or 2 into the molten aluminum and bubbling.

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