JPH0343224B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improvements in refractories for lining aluminum melting furnaces, aluminum holding furnaces, and the like for producing aluminum light alloy products such as die castings and castings. Conventionally, high alumina bricks with low silica content have been used as refractories for lining aluminum melting furnaces, etc. However, if they contain silica, the aluminum that has penetrated into the pores of the bricks during use will This is because when it comes into contact with silica, the silica is easily reduced by the reducing power of aluminum, resulting in significant corrosion of the bricks. Therefore, recently there has been a shift towards high alumina bricks with even lower silica content. In addition, the silica content is Si ~ at the contact interface with the molten aluminum.
High alumina bricks are also being used because of problems such as the formation of Al to Al ₂ O ₃ complexes that adhere to lining refractories or mix into molten aluminum. However, the higher the alumina content of high alumina bricks, the lower their spalling resistance tends to be. Under such usage conditions, cracks occur in the bricks due to spalling, and the molten metal subsequently penetrates into the cracks, causing the bricks to break down. Furthermore, the higher the alumina content of the high alumina brick, the higher the raw material cost, and the need for firing at a high temperature for sintering the brick, which is economically disadvantageous. This invention was made in order to improve the refractory lining of conventional aluminum melting furnaces, etc., as described above. The present invention provides a method for producing a refractory that is a dense brick with a low porosity that is heat-treated at a relatively constant temperature, has low molten metal permeability, and has excellent spalling resistance. Hereinafter, the method for manufacturing a refractory of the present invention will be explained in detail. The aggregate used is one or more of corundum, mullite, zircon, silica glass, and spinel (MgO.Al ₂ O ₃ ). Aggregates containing various minerals in one raw material are also suitable aggregates for the present invention, such as those containing corundum as a main component such as sintered alumina, or those containing corundum and mullite as main components such as calcined bauxite. The above-mentioned aggregate does not undergo abnormal expansion and contraction due to crystal transition during the heating process, unlike, for example, quartz or zirconia, and has high volume stability. Furthermore, these aggregates do not react with aluminum phosphate, which is a constituent material of the present invention, at room temperature, so they are particularly suitable as aggregates of the present invention. As for the kaolin clay, commercially available water elutriated Kibushi clay is suitable. Fireclays with a JIS refractory rating of SK32 or higher and mainly composed of clay minerals such as kaolinite and halloysite are suitable, but clays containing large amounts of feldspar, quartz, mica, etc.
and those with poor plasticity are not suitable. Kaolin clay is used in an amount of 7 to 15 parts by weight per 100 parts by weight of the aggregate. If it is less than 5 parts, it must be molded under as high a pressure as possible, and it has the disadvantage that it will not sinter unless it is fired at a high temperature of 1300°C or higher. The ordinary high alumina bricks can withstand high operating temperatures;
As mentioned above, the amount of kaolin clay is reduced as much as possible (usually 2 to 4 parts by weight), and after kneading with a small amount of water, high-pressure molding and high-temperature firing (usually
1300℃ or higher). However, the high alumina bricks obtained in this way cannot be said to be sufficiently suitable for use in aluminum melting furnaces, etc., as shown in the resistance test of sample 12 in Table 3 of Examples below. Furthermore, if the kaolin clay content is 15 parts or more, there are disadvantages such as structural defects such as cracks occurring during the heat treatment stage and a decrease in corrosion resistance against molten metal. Aluminum phosphate is used in an amount of 1.5 to 6.5 parts by weight in solid terms. By using aluminum phosphate in combination with kaolin clay, heat treatment at a relatively low temperature increases the strength of the molded product, reduces the porosity of the molded product,
Moreover, the structure can have an extremely low air permeability on the order of 10 ^-4 cm ² . Therefore, since penetration of molten metal can be reduced, corrosion resistance can be significantly improved. Aluminum phosphate is 1.5
If the amount is less than 6.5 parts by weight, the above effect will be small, and if it is more than 6.5 parts by weight, lamination may occur during molding, cracks may occur during firing, etc., which is unfavorable in terms of manufacturing. The above-mentioned materials are mixed, kneaded with water, pressure-molded, and then heat-treated at 600 to 1200°C. At temperatures below 600°C, the heat-treated body may be deformed or deteriorated due to moisture absorption, which is not sufficient from the standpoint of spalling resistance. When fired at temperatures above 1,200°C, mullite and a liquid phase are generated inside the clay due to thermal decomposition of the kaolin clay, increasing the elastic modulus of the brick. Therefore, the spalling resistance decreases, which is not preferable. Next, embodiments of the invention will be described. Examples Table 1 shows the raw materials used as aggregate and the raw materials used as binder. All of these are commercially available products. Of these, most of the aggregates (a to g) each have 4
Consists of sized products that are crushed and sieved into particle sizes of -1 mm, 1-0.3 mm, 0.3 mm or less, and 0.044 mm or less,
Synthetic spinel (h) and zircon sand (i) are simply 0.3mm
The following is a sized product that has been sieved. Kaolin clay (j) as a binder is an elutriated dried Kibushi clay that has been crushed to an apparent particle size of 0.3 mm or less, and aluminum phosphate (k) is a 50% aqueous solution of aluminum monophosphate. As for sodium silicate (l), a powder product (0.3 mm or less) equivalent to JIS No. 3 product (Na ₂ O / SiO ₂ molar ratio 3) was used.

[Table] Various formulations were prepared using these raw materials, and the aggregate combinations shown in Table 2 were prepared. The formulations of these aggregates combined with kaolin clay and aluminum phosphate as binders are shown in Tables 3 to 5 in relation to the test specimen No. (sample No.). Each compound (test No. 1 to 10, 13 to 24) was mixed with a commercially available experimental kneader of the so-called Mitsukumar type, which can knead up to 50 kg, and a small amount of water was added for every 40 kg of each compound (average external addition amount: 3.5 parts by weight). Add and knead for 20 minutes. After kneading,
Using a friction press for manufacturing firebrick (commercially available), five pieces of each brick, including a spare, were molded into JIS standard brick shapes. Each molded body is placed on a trolley for 4 hours in a tunnel kiln type drying oven that heats up to 150℃ for drying firebricks.
It was dried by passing it through an oven for several days. After drying, it is inserted into a large silicon carbide heat-generating electric furnace with an upper and lower furnace body and an internal volume of 0.2 ^m3 , and the temperature is raised at a rate of 5°C/min, maintained at the specified temperature for 4 hours, and left to cool. The heat treatment was performed using the following methods. However, sample No. 22 was only dried and not heat treated.
Sample No. 23 is at 300℃, sample Nos. 1 to 10 are at 800℃
So, sample Nos. 13 to 21 are at 1100℃, and sample No. 24 is
were heat-treated at 1200°C.

【table】

[Table] For each heat-treated body, dried body, and comparative bricks (high alumina and clay bricks for lining conventional aluminum melting furnaces), the height was set to 65 mm using a water-cooled diamond coring machine, and the diameter was 30 mm (1 pieces), 50mm
(2 pieces) and 80mm (1 piece) cylindrical specimens were collected.
For those with a diameter of 30mm, use a diamond cutter.
It was cut into pieces with a height of 30 mm, and one piece was used as a test piece for measuring air permeability, and the other piece was used as a test piece for measuring apparent porosity. In addition, one of the specimens with a diameter of 50 mm was used for the spalling test, and the other specimen was used for measuring the compressive strength. The 80 mm diameter specimen was hollowed out using a 40 mm diamond core and a chisel or hammer to create a crucible so that the wall and bottom walls were 20 mm thick to create a specimen for erosion testing. These specimens were placed in an electrically heated hot air drying oven, dried again at 150°C for a day and night, and then used for each test. The spalling test, which is one way to evaluate resistance related to durability, involves inserting a cylindrical specimen with a diameter of 50 mm and a height of 65 mm into an electric furnace with a silicon carbide heating element kept at 1000°C. After holding for 20 minutes, it was taken out and put into water for rapid cooling. The specimen was taken out of the water, left at room temperature for 10 minutes, and then heated again to 1000°C. Rapid quenching was repeated five times, and the spalling resistance was evaluated based on the occurrence of cracks in the specimen. The erosion test, which is another important evaluation test for resistance, uses the above-mentioned crucible-shaped specimen with an external diameter of 80 mm, inserts 15 g of pure aluminum (99.9% purity) into the crucible, and heats it at 900°C. A certain silicon carbide heating element was inserted into an electric furnace, held for 200 hours to melt, and after cooling, the crucible was removed from the furnace and cut into two with a diamond cutter to determine the wear and tear on the inner wall of the crucible-shaped specimen. Corrosion resistance was evaluated by examining the maximum depth of molten metal (erosion loss), the presence or absence of penetration of molten metal into the refractory, and the maximum depth of penetration. As for the physical properties, compressive strength, apparent porosity, and air permeability were measured, and the measurement methods were as follows. Maximum compressive strength is obtained by hydraulically applying a cylindrical specimen with a diameter of 50 mm.
The strength was determined by crushing it using an Amsler testing machine that can pressurize 100 tons. The air permeability was measured using a cylindrical specimen with a diameter of 30 mm and a simple commercially available air permeability measuring device using a so-called decompression method, which absorbs air with an aspirator. Apparent porosity was determined using a cylindrical specimen with a diameter of 30 mm.
It was measured by the water boiling method according to JIS R 2205 method for measuring the apparent porosity of refractory bricks. Table 3 shows the results of resistance and physical property tests on the types of aggregates according to the present invention using specimens heat-treated at 800℃ using kaolin clay and aluminum phosphate as binders. This is shown in contrast to clay and high alumina bricks commonly used for industrial purposes. The results show that the aggregates that fully satisfy both the spalling resistance and corrosion resistance properties that govern the durability of furnace materials are sintered alumina (corundum)...No. 1 and calcined bauxite (corundum + mullite)...No. .
2.Synthetic mullite (mullite)...No.3, Silica glass (silica glass)...No.7, Sintered alumina and spinel (corundum + spinel)...No.8, Silica glass and zircon sand (silica glass + zircon)
…No. 9, calcined bauxite and sintered alumina (corundum + mullite) … No. 10, and the chemical composition is
Silica-based No. 6, which is composed of SiO ₂ and is common to No. 7,
In addition, No. 5 of the low stone type and No. 4 of the fired shamoto type.
Although the specimen is comparable to clay brick, it shows that it is of poor quality. The difference between quartz glass and silica stone is not in chemical composition but in mineral composition; the former is silica glass and the latter is α-type quartz, and fired siyamoto and silica stone contain α-type quartz, making them more resistant. is expected to decline. These results indicate that the aggregate used in the present invention is corundum, mullite,
This indicates that the aggregate must be composed of one or more of silica glass, zircon, and spinel. In addition, compared to clay and high alumina bricks, which are conventionally used aluminum melting furnace materials, specimens Nos. 1 to 3 and Nos. 7 to 10 according to the present invention have
Despite being heat-treated at a relatively low temperature of 800℃, the corrosion resistance and spalling resistance were significantly improved in the resistance test, and the strength was at least twice as strong as that of clay brick in the physical property test. This shows that it has the effect of improving strength. Regarding the corrosion resistance of furnace materials against molten metal,
The structure of the furnace material is important, and it was conventionally thought that it could be improved by reducing the apparent porosity, but these results show that although it is necessary to have a small apparent porosity, ventilation This proves that the permeability is more closely related to corrosion resistance, and that if the air permeability is small, on the order of 10 ^-4 cm ² , there will be no penetration of molten metal, and it is possible to create a furnace material with extremely low erosion loss. Table 4 shows that 1100
The results of resistance and physical property tests regarding the kaolin clay according to the present invention, the amount of aluminum phosphate, etc., are shown on specimens heat-treated at °C. This result shows that as the amount of kaolin clay increases (No. 13 to No. 16), the spalling resistance tends to improve, but if it is too large (No. 16), the corrosion resistance slightly decreases. This shows that the best way to fully satisfy both spalling resistance and corrosion resistance is when the amount is 5 parts by weight or more but does not exceed 15 parts by weight. In addition, regarding aluminum phosphate, it was shown that the lack of aluminum phosphate (No. 17) drastically reduced the corrosion resistance, and the addition of a small amount (No. 18) sharply improved it.
The results show that the spalling resistance decreases as the amount increases (No. 20). Furthermore, the one using sodium silicate (No. 21) was inferior in both corrosion resistance and spalling resistance, indicating that it was necessary to use aluminum phosphate. On the other hand, the relationship between physical property tests and corrosion resistance tests is 800
As in the case of °C heat-treated bodies, the air permeability is more dependent than the apparent porosity, and by forming a structure with a small air permeability on the order of 10 ^-4 cm ² , corrosion resistance can be greatly improved. It suggests that.

【table】

【table】

[Table] Table 5 shows the heat treatment temperature according to the present invention using a combination of aggregates of calcined bauxite and sintered alumina (corundum + mullite) and a mixture of kaolin clay and aluminum phosphate as binders. The results are shown below. Hygroscopicity is a property of furnace materials that absorb moisture in the air during storage, resulting in deterioration or softening and deformation, resulting in loss of product value. This test result is for heat treated at 150℃ (No. 22)
is hygroscopic, and those treated at temperatures of 600°C or higher (Nos. 23 and 24) do not absorb moisture.
However, to determine hygroscopicity, while measuring the apparent porosity, the specimen is boiled in water to degas and saturate it, and after cooling, the saturated weight is weighed in water. It was judged as having no hygroscopicity, and those whose weight gradually increased during weighing were judged to be hygroscopic. This phenomenon occurs because aluminum phosphate is partially dehydrated by heat treatment and is in an active (unstable) state, but a hydration reaction gradually proceeds in water. Furthermore, when the heat treatment is high (No. 24), the corrosion resistance does not decrease much, but the spalling resistance decreases.
These results indicate that it is necessary to conduct heat treatment in a temperature range of 600°C or higher but not exceeding 1200°C. As mentioned above, the refractory produced by the method of the present invention is made by adding aluminum phosphate to kaolin clay in a relatively large amount for refractory bricks to a refractory material such as corundum, friction press molding, and medium temperature firing (600
~1200℃) As a result, it is possible to obtain dense and strong bricks with a low porosity and low air permeability composition, resulting in an aluminum melting furnace with low permeability to molten aluminum and excellent spalling resistance. It is possible to obtain refractories for general use.

【table】

Claims (1)

[Claims] 1 100 parts by weight of aggregate containing one or more of corundum, mullite, silica glass, zircon and spinel (MgO・Al ₂ O ₃ ), 7 to 15 parts by weight of kaolin clay and 1.5 to 6.5 parts by weight in solid terms 1. A method for producing a refractory for an aluminum melting furnace, which comprises adding 100% of aluminum phosphate, kneading with water, performing friction press molding, and then heating at 600 to 1200°C.