JPS6354052B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a treatment method for removing inclusions contained in molten aluminum. In recent years, quality requirements for aluminum materials have become increasingly strict. For example, in order to make the base of a magnetic disk from aluminum, the aluminum material is required to be clean enough to contain non-metallic inclusions such as various oxides of several μm or less. In order to remove such minute inclusions, various in-line molten metal processing apparatuses have been developed and are being put into practical use. One method for removing inclusions contained in molten aluminum is to filter the molten metal through a filter. According to this removal by filtration, the size of the inclusions that can be removed is determined by the pore size of the filter. However, when using a filter with a correspondingly small pore size to filter minute inclusions of several micrometers, the pressure required to pass the molten metal through the filter, especially the initial pressure, becomes extremely high, making it difficult to use with a normal gravity filtration device. Moreover, efficient removal is not possible. In addition, a flotation-type removal treatment technique in which chlorine gas or the like is blown into the molten metal to collect and float away minute inclusions has also been used in practice.
In addition to chlorine gas, nitrogen gas, argon, or a mixture thereof is generally used as the gas to be blown. For example, Japanese Patent Application Laid-Open No. 52-32811 describes a method for reducing the aluminum carbide content from contaminated aluminum molten metal containing a large amount of aluminum carbide produced by the carbothermic method. It has been disclosed that aluminum carbide is separated as a floating fraction by blowing carbon, water vapor, chlorine, nitrogen gas, etc. However, even if this flotation method is used, if the size of the inclusions is minute, the collection effect may not be obtained effectively, and it is difficult to achieve reliable removal of such minute inclusions. It was strongly desired. Under these circumstances, the inventors of the present invention conducted numerous experiments and found that when water vapor is blown into molten aluminum and then filtered, a filter with a large pore diameter through which the molten metal can easily pass has been developed. The present invention was completed based on the knowledge that it is possible to remove inclusions that are much smaller than the diameter of this material, and the purpose is to remove inclusions that are much smaller than the diameter of An object of the present invention is to provide a method for treating molten aluminum that can reliably, easily, and efficiently remove aluminum. That is, the present invention is a method for treating molten aluminum, which is characterized by blowing steam into molten aluminum and then subjecting it to overtreatment. The inventors have conducted various studies on the phenomenon that when water vapor is blown into molten aluminum and filtered, even inclusions much smaller than the diameter of the filter can be removed even if a filter with a large pore diameter is used. When water vapor comes into contact with molten aluminum, γ-Al ₂ O ₃ is produced by a reaction, and this reaction product has the effect of strongly collecting minute inclusions, and the minute inclusions become γ-Al2O3. It was considered that the inclusions grow together with Al ₂ O ₃ into large inclusions and are captured by a filter with a large pore size. The method of the invention will be explained in more detail below with reference to examples. In order to examine the effects of the present invention, the following comparative tests were conducted. That is, after performing different molten metal treatments as shown in the following [Experiment 1] to [Experiment 4] (comparative example) and [Experiment 5] to [Experiment 7] (example of the present invention), samples were cast from each molten metal. , each sample was inspected for inclusions. The test materials used in each experiment were Al-Mg aluminum alloy (AA5056);
It is approximately 100Kg. [Experiment 1] A sample was cast with the molten metal left untreated. [Experiment 2] After filtering the molten metal through a ceramic filter with a filter pore size of 200 μm, a sample was cast. [Experiment 3] Chlorine gas (50 g per 100 kg of molten metal) was blown into the molten metal for degassing treatment, and then the filtration treatment of [Experiment 2] was performed, and then a sample was cast. [Experiment 4] After steam (0.17 g per 100 kg of molten metal) was blown into the molten metal, the floating inclusions were removed, and then the sample was cast. [Experiment 5] Steam (0.17 g per 100 kg of molten metal) was blown into the molten metal, and then the filtration treatment of [Experiment 2] was performed, and then a sample was cast. [Experiment 6] Add chlorine gas (50g per 100kg of molten metal) to the molten metal as a carrier gas and water vapor (0.17g per 100kg of molten metal)
was blown into the mold, followed by the filtration treatment of [Experiment 2], and then the sample was cast. [Experiment 7] Steam (0.17 g per 100 kg of molten metal) was blown into the molten metal, then chlorine gas (50 g per 100 kg of molten metal) was blown into the molten metal for degassing treatment, followed by the filtration treatment of [Experiment 2]. After that, the sample was cast. Here, when blowing in chlorine gas for degassing treatment and steam, which is a feature of the present invention, the blowing speed is such that the required amount is blown in approximately 5 minutes, and the sedation time after blowing is approximately 15 minutes. It was set as 1 minute. Furthermore, the molten metal temperature was maintained at approximately 720°C. In carrying out each of the above-mentioned experiments, a crucible device and a gas blowing device whose basic configurations are shown in FIGS. 1 and 2 were used. The experimental equipment used will be outlined below. The crucible device shown in FIG.
The test material 4 placed inside can be melted and maintained at a temperature of approximately 720°C. When filtration treatment was not required, the molten metal was directly sampled from the crucible 2 and poured into a mold. When performing filtration processing, the lid 5 is closed and a pressurized gas such as nitrogen gas is introduced from the conduit 6 into the space 7 inside the crucible 2, and by this pressurization, the molten metal 4 is passed through the required filter device 8 provided at the bottom of the crucible. The filtered molten metal was collected in a crucible 9 to receive the molten metal, and the filtered molten metal was poured into a mold. On the other hand, a gas blowing device as shown in FIG. 2 was used to blow water vapor and chlorine gas for degassing. This device includes a pipe member 10 that is inserted into the molten metal 4 of the crucible 2, a steam generator 11, and a chlorine gas cylinder 12, which are led to a mixing chamber 17 by pipes 15 and 16 via flow meters 13 and 14, respectively. It is configured as follows. The piping 15 for water vapor was equipped with a heating coil 18 as required. Valves 19 and 20 are used to supply and stop water vapor and chlorine gas.
21 etc., and can be supplied individually or together. Reference numerals 22 and 23 are safety valves and thermometers. Porous ceramics 1 are placed at the tip of the tube member 10.
0A, so that the supplied water vapor and/or chlorine gas formed small bubbles 30 as shown in FIG. 1 and rose in the molten metal. A conventional inclusion inspection was performed on each of the cast samples obtained in Experiments 1 to 7 as described above, and the presence of inclusions obtained as a result is shown in Table 1.

[Table] From the results in Table 1, the examples of the present invention ([Experiment 5] to [Experiment 7]), which include the step of blowing water vapor and then filtering, are compared to the comparative examples ([Experiment 1] to [Experiment 4]). It can be seen that minute inclusions are significantly reduced. As mentioned above, this is because γ-Al 2 O ₃ is generated when steam is blown into contact with the molten aluminum, and this γ- _{Al 2 O 3} has the effect of adhering to and collecting minute inclusions. It is considered that γ-Al ₂ O ₃ and minute inclusions grow together into large inclusions and are captured by a filter with a large pore size. However, the gas content after casting tends to increase due to the injection of steam. It is clear from [Experiment 6] and [Experiment 7] that blowing chlorine gas is effective in reducing this gas content. As described above, the present invention is highly effective in removing minute inclusions by injecting water vapor into molten aluminum and then filtering it. Furthermore, although there is a tendency for the gas content to increase due to the injection of water vapor, this can be sufficiently reduced by injection of a degassing agent such as chlorine gas. Therefore, it is also advantageous to combine other degassing treatments, such as vacuum casting or reduced pressure casting. In this way, the treatment method of the present invention
It can be very easily combined with conventional processing methods, making it possible to produce aluminum materials with higher purity. Moreover, the equipment required for this purpose is extremely simple, and has the advantage that it can be immediately applied to existing processing equipment. Note that the injection of water vapor can be performed simultaneously with the injection of chlorine gas, etc. That is, water vapor can be easily blown in using chlorine gas or the like as a carrier gas.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a crucible device, which is an experimental device used to examine the effects of the present invention. FIG. 2 is a schematic diagram of an experimental apparatus for injecting steam, which is a feature of the present invention. 1... Container body, 2... Crucible, 3... Electric heating coil,
4... Molten metal, 5... Lid, 6... Pipe, 8... Ceramic filter, 9... Pot for receiving molten metal, 10... Pipe member, 1
1... Steam generator, 12... Chlorine gas cylinder, 1
3, 14... Flowmeter, 15, 16... Tube, 17... Mixing chamber, 18... Heating coil, 19, 20, 21... Valve, 22... Safety valve, 23... Thermometer.

Claims (1)

[Scope of Claims] 1. A molten aluminum treatment characterized in that in order to remove minute inclusions contained in the molten aluminum, steam is blown into the molten metal, the minute inclusions are collected, and then filtered. Method. 2. The method for treating molten aluminum according to claim 1, wherein a degassing gas such as chlorine gas, nitrogen gas, or argon gas is also blown in as a carrier gas for the purpose of blowing in the water vapor. 3. The molten aluminum processing method according to claim 1, wherein a degassing treatment is performed after the steam is blown into the molten aluminum.