JPH04329841A - Ceramic member for suction type degassing and degassing method using the same - Google Patents

Abstract

PURPOSE:To offer a ceramic member for suction type degassing capable of swift sucking of a harmful gas contained in the molten metal of aluminum or an aluminum alloy by a simple equipment, furthermore, having a long service life and excellent in workability and a decassing method using it. CONSTITUTION:The molten metal 1 of an aluminum alloy is immersed in a ceramic tube 3. This ceramic tube 3 contains >=90% silicon carbide and/or silicon nitride in total, and its pore size is regulate to <=40mum. At the time of sucking, the pressure of suction space in the ceramic tube 3 is regulated to 50 to 400mmHg.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a suction type degassing ceramic member used for removing gases mainly including hydrogen gas contained in aluminum or aluminum alloys, and a degassing method using the same. .

0002

2. Description of the Related Art When aluminum or an aluminum alloy is cast, impurities contained in the aluminum base metal or moisture or hydroxide adhering to the surface of the aluminum base metal react with the molten metal during melting to generate gas. Among these gases, mainly atomic hydrogen gas is absorbed into the molten aluminum or aluminum alloy. In this case, because the hydrogen partial pressure in the atmosphere is extremely low, some of the hydrogen gas absorbed into the molten metal diffuses through the oxide film that exists at the interface between the molten metal and the atmosphere, passes through it, and is released into the atmosphere. , the molten metal is degassed over time. However, since most of the hydrogen gas remains in the molten metal, the gas contained in the molten metal during casting causes defects such as pinholes or blisters in the cast products, which inevitably reduces the quality and yield of the cast products. .

[0003] Therefore, in order to avoid the above-mentioned inconvenience,
The molten metal is modified by adding chlorine, an inert gas, a solvent, etc. to the molten aluminum or aluminum alloy, and further improvements are being made to melting methods such as vacuum melting and remelting. Further, a local vacuum degassing method has been proposed as a method for removing gas contained in the molten metal.

This local vacuum degassing method involves, for example, immersing a ceramic tube with one end closed in molten metal and reducing the pressure inside the ceramic tube using a vacuum decompression device or the like to remove gas inside and outside the tube. This method utilizes the difference in partial pressure to diffuse harmful gases in the molten metal into the pipe and suck them out. In the local vacuum degassing method, when degassing molten aluminum or aluminum alloy, Al2
A ceramic tube whose main component is O3 --SiO2 is used. For example, some ceramic tubes contain 47% by weight of Al2O3 and 49% by weight of SiO2.

[0005]

[Problem to be solved by the invention] However, Al2
Ceramic tubes mainly composed of O3 --SiO2 type components tend to react with aluminum or aluminum alloys, and therefore have an extremely short lifespan of about 3 hours. For this reason, it is necessary to frequently replace the ceramic tube, resulting in poor workability. Furthermore, since it is necessary to reduce the pressure inside the ceramic tube to, for example, 34 mmHg during suction, a pressure reducing device with a high pressure reducing ability must be used. This increases the cost of casting aluminum or aluminum alloy. Note that if the pressure reduction of the ceramic tube is insufficient, the removal of harmful gases in the molten metal will be insufficient, resulting in a decrease in the quality of the cast product.

The present invention has been made in view of these problems, and is capable of quickly sucking out harmful gases contained in molten aluminum or aluminum alloy with a simple device, and has a long service life. It is an object of the present invention to provide a ceramic member for suction type degassing which has excellent workability and a degassing method using the same.

[0007]

[Means for Solving the Problems] A suction type degassing ceramic member according to the present invention partitions a molten aluminum or aluminum alloy and a suction space, and removes gas in the molten metal by suctioning it into the suction space. A ceramic member for suction type degassing used for this purpose is characterized in that it contains silicon carbide and/or silicon nitride in a total amount of 90% by weight or more, and has a pore diameter of 40 μm or less.

[0008] Furthermore, the degassing method using the suction type degassing ceramic member according to the present invention is carried out using a ceramic member containing silicon carbide and/or silicon nitride in a total amount of 90% by weight or more and having a pore diameter of 40 μm or less. The molten aluminum or aluminum alloy and the suction space are partitioned off by a member, and the suction space is evacuated to a pressure of 50 to 400 mmHg.

[0009]

[Function] The ceramic member for suction type degassing according to the present invention has silicon carbide or silicon nitride as its main component, so it has extremely low reactivity with aluminum or aluminum alloy, has high thermal conductivity, and has high thermal shock resistance. is excellent. Therefore, even if this ceramic member for suction type degassing is used while being immersed in molten aluminum or aluminum alloy, it has a long life, so it does not need to be replaced frequently and has excellent workability. In addition, since silicon carbide or silicon nitride is porous, by evacuating the suction space to a predetermined pressure using a simple device such as a vacuum pump, harmful substances contained in molten aluminum or aluminum alloy can be removed. Gas can be sucked quickly. Therefore, if the suction type degassing ceramic member according to the present invention is used,
A local vacuum degassing method can be effectively carried out, and molten aluminum or aluminum alloy can be easily degassed.

Next, the reason for limiting the composition and pore diameter of the ceramic member for suction type degassing according to the present invention will be explained.

[0011] The total content of silicon carbide or silicon nitride is 9
When the content is less than 0% by weight, the ceramic member tends to react with molten aluminum or aluminum alloy, resulting in a shortened lifespan. Therefore, the total content of silicon carbide and/or silicon nitride is set to 90% by weight or more.

[0012] When the pore diameter becomes larger than 40 μm,
The molten aluminum or aluminum alloy penetrates into the pores and solidifies, thereby blocking the pores and reducing the ability to suck gas. For this reason, the pore diameter is set to 40 μm or less.

Further, in the degassing method according to the present invention, when removing gas in molten aluminum or aluminum alloy using the above-mentioned suction type degassing ceramic member, the suction space is heated to 50 to 400 mmHg. Reduce pressure to . Thereby, the degassing ability and degassing efficiency of the ceramic member having the above characteristics can be optimized.

However, if the pressure in the suction space is 50 mm
Since it takes a long time to reduce the temperature to less than Hg, the time required for degassing treatment becomes longer and the absolute gas content remaining in the molten metal increases. On the other hand, the pressure in the suction space is 400
When it exceeds mmHg, the efficiency for removing gas in the molten metal decreases. Therefore, in the present invention, the suction space is evacuated to a pressure of 50 to 400 mmHg.

[0015]

EXAMPLES Next, examples of the present invention will be explained in comparison with comparative examples thereof.

FIG. 1 is a sectional view showing a suction type degassing device. A molten aluminum alloy 1 is stored in a melting crucible 2 made of graphite. The closed end of the one-end closed ceramic tube 3 is immersed in the molten aluminum alloy 1. One end of a suction conduit 4 is connected to the open end of the ceramic tube 3, and the other end of this suction conduit 4 is connected to a safety tank 5. Further, one end of a suction conduit 6 is connected to the safety tank 5, and the other end of this suction conduit 6 is connected to a vacuum pump (not shown).

When removing harmful gases from the molten aluminum alloy 1 using the suction degassing device configured as described above, the vacuum pump connected to the suction conduit 5 is operated to reduce the pressure inside the safety tank 5. Then, the suction space inside the ceramic tube 3 is depressurized via the suction conduit 4. As a result, harmful gases in the molten aluminum alloy 1 are sucked through the pores of the ceramic tube 3. In this case, if ceramic tube 3
Even if molten metal is sucked into the vacuum pump along with harmful gases, the molten metal will be deposited in the safety tank 5, so the vacuum pump will not be damaged.

Next, various ceramic tubes 3 are manufactured,
After removing harmful gases from the molten aluminum alloy 1 using the vacuum degassing device described above, the condition of the ceramic tube 3 after use was examined.

First, a vacuum suction degassing ceramic tube 3 with one end closed and whose composition and pore diameter are shown in Table 1 below was prepared.

Next, an aluminum alloy ingot (Fe; 0.001% by weight, Si;
0.003% by weight, Cu; trace amount, Al; 99.94
% by weight), and the melting crucible 2 was inserted into a closed electric furnace and heated. As a result, the aluminum alloy base metal in the melting crucible 2 was melted, and a molten aluminum alloy 1 was obtained. Next, the ceramic tubes 3 according to Examples 1 to 5 and Comparative Examples 1 to 3 were each immersed in this molten aluminum alloy 1, and 1 kg
While pressurizing the molten metal 1 at a pressure of /cm2, the temperature of the molten metal 1 was maintained at 730±5°C and heated for 12 hours. During this heating, each ceramic tube 3 is heated using a vacuum pump.
By reducing the pressure inside as shown in Table 1 below,
Harmful gases contained in molten metal 1 were sucked.

[0021]

[Table 1]

[0022] Thereafter, the ceramic tube 3 was taken out from the molten metal 1, and the ceramic tube 3 was cut approximately at the center, and the penetration depth of the aluminum alloy and the amount of melting loss were measured. The results are also shown in Table 1.

As is clear from Table 1, in all of the ceramic tubes 3 according to Examples 1 to 5, there was almost no penetration or melting loss of the aluminum alloy.

On the other hand, Comparative Example 1 in which the pore diameter exceeds 40 μm
In the ceramic tube 3 according to No. 2 and No. 2, the aluminum alloy penetrated deeply, the pores were blocked, and the amount of melting loss was also large. Furthermore, the ceramic tube 3 according to Comparative Example 3, which mainly contains SiO2 and Al2O3, had a very large amount of erosion loss of 2 mm, and had a short lifespan.

Next, the results of removing hydrogen gas from the molten aluminum alloy 1 by the local vacuum degassing method using the ceramic tube 3 according to Examples 4 and 7 and Comparative Example 3 will be explained.

First, an aluminum alloy ingot (containing Fe, Si, Cu and Al) is placed in the melting crucible 2,
This melting crucible 2 was inserted into a closed electric furnace and heated. As a result, the aluminum alloy base metal in the melting crucible 2 was melted, and a molten aluminum alloy 1 was obtained. After heating this molten aluminum alloy 1 at a temperature of 750° C. for 120 minutes, the molten aluminum alloy 1 was solidified in an electric furnace. Next, the aluminum alloy solidified in the melting crucible 2 was melted again, and the temperature of the molten metal 1 was maintained at 750±5°C. Then, by immersing the ceramic tubes 3 according to Examples 4, 7 and Comparative Example 3 in this molten aluminum alloy 1, and reducing the pressure inside the ceramic tube 3, hydrogen gas contained in the molten aluminum alloy 1 is removed. was aspirated. At this time, the content of hydrogen gas contained in the molten aluminum alloy 1 was measured over time. The results are shown in Table 2 and FIG. 2 below. However, in Table 2, the unit of hydrogen gas content is cc/100g in standard state (STP). Moreover, the amount of melting loss was measured for the ceramic tubes 3 according to Examples 4 and 7 and Comparative Example 3 after use, and the appearance thereof was also observed. The results are shown in Table 3 below.

[0027]

[Table 2]

[0028]

[Table 3]

As is clear from Table 2 and FIG. 2, when the ceramic tube 3 was used to remove hydrogen gas from the molten aluminum alloy 1, Comparative Example 3 (conventional example) was compared to Examples 4 and 7. The degassing ability was low, and the degassing ability reached an equilibrium state after 210 minutes, making it impossible to obtain any further effects. In addition, in Comparative Example 3, it took about 210 minutes to reduce the hydrogen gas content to 0.115cc/100g, but in Examples 4 and 7, it took about 80 minutes and about 120 minutes, respectively. content has been reached, and the processing time is approximately 44% of Comparative Example 3 and approximately 56% of that of Comparative Example 3.
%Met. In Examples 4 and 7, the degassing ability did not reach an equilibrium state, and the hydrogen gas content could be reduced as the treatment time progressed, and an excellent degassing effect could be obtained. For example, 3 in Examples 4 and 7
The hydrogen gas contents after 00 minutes were about 1/3 and about 1/10 of Comparative Example 3, respectively, and about 3.6% and about 13% of the untreated case.

Furthermore, as is clear from Table 3, Example 4
In the ceramic tube 3 according to No. 7, there was no penetration of the aluminum alloy, no occurrence of pore clogging, and the quality remained almost unchanged even after use. Therefore, the ceramic tubes 3 according to Examples 4 and 7 were reusable and could be used even after being used 30 times or more. on the other hand,
The ceramic tube 3 according to Comparative Example 3 has a melting loss of 0.8 mm.
Moreover, a hair crack of about 20 mm was generated, so it could not be reused.

[0031] As described above, the ceramic tubes 3 according to Examples 4 and 7 have superior degassing ability and degassing efficiency as well as superior durability compared to the ceramic tube 3 according to Comparative Example 3. It was something like that.

[0032]

Effects of the Invention As explained above, the ceramic member for suction type degassing according to the present invention contains silicon carbide and/or silicon nitride as a main component and has a predetermined pore diameter, so that it does not react with aluminum or aluminum alloy. very low gender,
It has a long life and excellent workability, and can quickly suck out harmful gases contained in molten aluminum or aluminum alloy with a simple device.

Furthermore, according to the degassing method according to the present invention,
Since the suction-type degassing ceramic member described above is used and the suction space is evacuated to a predetermined pressure, the degassing ability and degassing efficiency can be optimized.

Therefore, according to the suction type degassing ceramic member and the degassing method using the same according to the present invention,
A local vacuum degassing method can be effectively implemented.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a suction type degassing device.

FIG. 2 is a graph showing the relationship between hydrogen gas concentration in molten aluminum alloy and degassing treatment time.

[Explanation of symbols]

1; Molten aluminum alloy 2; Melting crucible 3; Ceramic tube 4, 6; Suction conduit 5; Safety tank

Claims (2)

[Claims] 1. A suction-type degassing ceramic member used to partition a molten aluminum or aluminum alloy and a suction space and to remove gas in the molten metal by suctioning into the suction space, comprising silicon carbide. and/or a ceramic member for suction type degassing, which contains silicon nitride in a total amount of 90% by weight or more and has a pore diameter of 40 μm or less. 2. The suction space is partitioned from the molten aluminum or aluminum alloy by a ceramic member containing 90% by weight or more of silicon carbide and/or silicon nitride in total and having a pore diameter of 40 μm or less, and the suction space A degassing method using a suction type degassing ceramic member, which is characterized by exhausting to a pressure of 50 to 400 mmHg.