JPH06299264A - Method for slagging off molten al or al alloy - Google Patents

Abstract

PURPOSE:To efficiently remove the slag floating on a molten metal surface by adding obsidian to the slag on the surface of molten Al and heating the slag to a specific temp. to foam the obsidian at the time of melting the Al by using a reflection furnace. CONSTITUTION:The obsidian is added to the slag on the molten metal surface of the Al or Al alloy and the slag is heated up to >=900 deg.C to foam the obsidian, by which the slag is removed together with the foamed obsidian at the time of melting the Al or Al alloy by using the reflection furnace. The amt. of the obsidian to be added is specified to about 0.5 to 10wt.%, more preferably 1 to 6wt.% of the Al alloy raw material. As a result, the slag removing property is improved and metal loss is decreased without generating the pollution of the atmoshere by generation of toxic gases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently removing slag floating on the surface of molten metal when manufacturing Al or Al alloy (hereinafter represented by Al alloy).

[0002]

2. Description of the Related Art Al alloys are lighter in weight, have higher specific strength, and are superior in corrosion resistance as compared with steel materials. Therefore, they are used as outer plate materials for automobiles, trains and other vehicles, parts materials, building materials, and household materials. Widely used as outer plates and cans for electrical products. The manufacturing process for obtaining these Al alloy products is as follows.

Melting raw materials (metals, scraps, etc.) → melting (mainly reverberatory furnace) → casting → soaking → hot working → cold working → heat treatment → surface treatment → inspection → shipping Here, a melting process using a reflex furnace Then, oxides (alumite, etc.) on the surface of the smelting raw material and oxides generated in the melting process float up on the surface of the molten metal as slag. This slag is a mixture of non-metal components such as oxides and metal components (Al alloy),
If this slag is left as it is, not only non-metallic components are mixed into the Al alloy molten metal to cause molten metal contamination, but also it is deposited and deposited on the furnace wall and furnace bottom after tapping to reduce the volume of the melting furnace, It also has an adverse effect on productivity.

Therefore, it is necessary to remove slag from the surface of the molten metal as soon as possible after melting the raw materials. However, since this slag contains a large amount of metal as described above and has a high affinity with the molten metal, it is difficult to separate the molten metal, and when attempting to forcibly remove it from the surface of the molten metal, a large amount of metal is accompanied. As a result, the yield of the molten Al alloy is remarkably reduced. Therefore, the currently widely used means for improving the slag removal property is to disperse a flux mainly containing chlorides or fluorides such as KCl-AlF ₃ or a halogen-based gas (Cl ₂ , Hexane chloride, chlorofluorocarbon, etc.) is blown into the slag, and the entire slag layer is heated by igniting and burning part of the metal part in the slag, melting the metal part and returning it to the molten metal. This is a method in which the oxide in the inside is changed to a high-temperature-generated oxide that has a lower wettability with the molten metal (good release from the molten metal), and then the slag is removed.

However, the refining agent used in this slag removal process is a halogen-based compound, and a large amount of harmful halogen gas and hydrogen halide gas are produced under high-temperature processing conditions, so that the work environment is significantly polluted and health hazards are impaired. Can be a factor.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to
An object of the present invention is to provide a method capable of efficiently removing slag generated in a melting step of an alloy raw material from the surface of a molten metal without using a harmful halogen-based refining agent.

[0007]

The constitution of the slag removal method according to the present invention, which has been able to solve the above-mentioned problems, is to melt Al or Al alloy in a reverberatory furnace.
The main point is that obsidian is added to the slag on the surface of the molten alloy No. 1 and the temperature of the slag is raised to 900 ° C. or higher to cause the obsidian to foam, and the obsidian is removed together with the foamed obsidian.

[0008]

In order to solve the problems pointed out in the prior art under the above circumstances, the present inventors need to develop a non-halogen type flux as a new flux for slag. I proceeded with the research along that line. Then, we focused on obsidian, which is a natural glassy volcanic rock, and examined whether or not it had an effect of improving slag removal efficiency.

That is, the inventors of the present invention have confirmed by preliminary experiments that obsidian causes a remarkable volume expansion at about 900 ° C., and has excellent wettability with respect to oxides produced in the melting process of Al or Al alloy raw materials. It is a cotton-like material that has good wettability with metal. Therefore, if these characteristics of obsidian are used effectively, only the oxides in the slag are selectively adsorbed to improve the removal of molten metal from the slag, and the metal components mixed in the slag are returned to the molten metal. It is considered possible.

However, the melting of the Al alloy raw material is usually 700-
Since it is carried out at 750 ° C, even if obsidian is added under such temperature conditions, it is not possible to effectively exert the above-mentioned slag removal improving effect due to foaming and flocculation, and the treatment temperature is at least obsidian. It is essential to raise the foaming temperature to about 900 ° C. or higher.

On the other hand, the induction melting furnace and the reverberatory furnace are currently widely used as melting furnaces for Al raw materials. In the induction melting furnace, heating is performed so that the temperature can be raised and maintained in the optimum temperature range for melting Al alloy raw materials. Since the temperature control mechanism and the like are preset, a large design change is required to raise the processing temperature to 900 ° C. or higher. On the other hand, the reverberatory furnace is a method of heating from above the molten metal surface by direct flame and radiant heat from the upper wall, and how to burn the burner (control of fuel type, supply amount, air ratio, etc.) and direct heat to the molten metal surface. The temperature of the slag can be easily raised to 900 ° C by devising a method of applying fire. Moreover, under the present circumstances, due to the problem of thermal efficiency of the raw material and the molten metal, the operation may be performed at 900 ° C. or higher. Therefore, in carrying out the present invention, the reverberatory furnace is optimal because it can be easily secured at a high temperature of 900 ° C. or higher only by changing the operating conditions without requiring a large design change of the existing equipment.

From this point of view, in the present invention, a reverberatory furnace is used as a melting furnace, and obsidian is added to the slag formed on the molten metal surface in the step of melting the Al alloy raw material, and the slag is heated to 9
The temperature is raised to 00 ° C or higher to cause obsidian to foam, and the resulting cotton-like material is removed. At this time, the cotton-like material generated by the obsidian foaming has poor wettability for metal components,
In addition, since the wettability with the oxide, which is the main slag component, is good, the oxide is trapped by the cotton-like material and forms a slag with good dewatering properties, while the metal content that has poor wettability with the cotton-like material is Since it is returned to the molten metal, the slag component having a low metal content can be easily removed from the molten metal surface together with the cotton-like material.

The time and form of addition of obsidian is not particularly limited, and it may be added before heating the slag to 900 ° C. or higher or after heating it to 900 ° C. or higher. Alternatively, it may be added in the form of lump, granule or powder. However, it is most preferable to add it in the form of granules or crushed pieces in order to spread the slag evenly while suppressing the scattering during addition.

The bubbling reaction of obsidian caused by heating is an irreversible reaction which occurs only once at about 900 ° C. When the temperature is raised to 900 ° C. or more regardless of the above-mentioned addition time, a foaming reaction occurs and changes into a cotton-like material. Since the oxide in the slag is selectively adsorbed and converted into a slag that is well separated from the molten metal, the removal from the molten metal surface is extremely easy. Also, since this cotton-like material has poor wettability with the metal component as described above, the metal component contained in the slag is
When the oxides are adsorbed on the cotton-like material, they are naturally returned to the molten metal direction so that they are squeezed out of the slag, so that the amount of metal remaining in the slag is reduced and the metal loss at the time of slag removal is greatly reduced.

The amount of obsidian added is not particularly limited,
The purpose can be sufficiently achieved by adding 0.5 to 10% by weight, more generally 1 to 6% by weight, to the Al alloy raw material.

[0016]

EXAMPLES Examples of the present invention will be shown below. However, the present invention is not limited by the following examples, and may be appropriately modified and implemented within a range compatible with the gist of the preceding and following description. It is possible and they are all included in the technical scope of the present invention.

Using a heavy oil-fired or LNG-fired reverberatory furnace, the Al alloy raw materials shown in Table 1 are heated to the temperatures shown in the same table and dissolved in the atmosphere. Next, Al is added to the slag that forms on the molten metal surface.
2 weight of obsidian (granular crushed material) was added to the alloy raw material, and the slag was heated to 1000 ± 50 ° C. by burner heating. The obsidian then foamed and changed into a cotton-like substance, and it absorbed oxides and changed into a lump that was easily removed from the hot water. Table 1 shows the metal loss generated in this slag removal process and the metal loss when slag removal was performed without adding obsidian.

[0018]

[Table 1]

As is clear from Table 1, the metal loss when obsidian is added and then slagged according to the present invention is 2/3 to 1/3 as compared with the metal loss when obsidian is not added and slagged. It can be seen that the metal loss can be significantly reduced. In addition, the slag with no obsidian added had a high viscosity and had a high affinity with the molten metal, making it difficult to separate the slag, and the slag work was extremely troublesome and it was difficult to completely remove the slag. Since the slag changed to a cotton-like lump with good spillage, the slag from the surface of the slag could be removed very easily and easily.

[0020]

EFFECTS OF THE INVENTION The present invention is configured as described above, and the existing reverberatory furnace is effectively used, and obsidian is added to the slag to heat the slag. It is possible to significantly improve the slag removal performance without improving the slag removal workability, improve the slag removal workability, and reduce the metal loss associated with the slag removal to increase the molten metal yield.

Claims (1)

[Claims] 1. When melting Al or Al alloy using a reverberatory furnace, obsidian is added to the slag on the surface of the molten Al or Al alloy, and the temperature of the slag is raised to 900 ° C. or more to foam the obsidian. A method for removing slag from a molten Al or Al alloy, characterized in that the slag is removed together with the foamed obsidian.