JPS62223059A - Manufacture of refractories for aluminum and aluminum alloy - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for manufacturing a refractory used for lining melting furnaces, holding furnaces, ladles, troughs, etc., which have parts that come into contact with molten aluminum or aluminum alloy. .

[Conventional technology]

Conventional refractories for aluminum have a problem in that components in the refractories, such as silicon (Si), elute into the molten aluminum and contaminate the molten metal, resulting in a deterioration in the quality of the aluminum or aluminum alloy. Furthermore, there is a problem in that components in the molten metal, such as aluminum and magnesium, penetrate into the refractory and react with it, resulting in deterioration and functional deterioration of the refractory, resulting in a decrease in so-called durability, which has an adverse effect on the life of the refractory.

In order to solve these problems,
As disclosed in Japanese Patent No. 9971, a method of adding 9Al2O3.2B2O3 (hereinafter abbreviated as 9A2B) to a refractory composition was proposed. This method has significantly improved the above problems. In other words, the quality of aluminum has improved and the life of refractories has been extended.

[Problem that the invention seeks to solve]

The following problems remain in the conventional method of adding 9A2B to a refractory composition. That is, 9A2B is a new raw material and is not produced domestically, making it difficult to obtain. Since 9A2B is a synthetic product, it is expensive, and because of the refractory to which it is added, it is necessary to use a large amount of chemical binder, further increasing the cost.

[Means for solving problems]

The first means of the invention is to add one or more kinds of pickled aluminum compounds and boron compounds that produce 1 to 12% of 9A2B in the refractory upon firing to a refractory composition for aluminum, and add water. After kneading and shaping, 100 (
It is characterized by being fired at F or higher.

The second means of the invention is to add one or more kinds of aluminum compounds and boron compounds to a refractory composition for aluminum in an amount that produces 1 to 12% of 9A2B in the refractory upon firing, and add water. It is characterized in that it is kneaded and integrally formed as a surface layer, and then fired at a temperature of 1000°C or higher.

In the above means, the refractory composition for aluminum includes a refractory aggregate such as electric kite alumina, sintered alumina, calcined bauxite, chamotte, silicon carbide, etc., a kaolin clay ring as a binding clay, and optionally a chemical binder. It is a combination of certain aluminum phosphate, etc. The raw material is a refractory composition for aluminum to which at least one aluminum compound and one or more boron compounds are added for producing 9A and 2B.

The aluminum compounds include α, β, and γ.

ρ alumina, aluminum hydroxide, aluminum nitride,
Examples of the boron compound include anhydrous or hydrated boric acid, boric nitride, boric acid carbide, and the like.

The particle size of the aluminum compound and boron compound added to the refractory composition for aluminum is as small as possible, preferably 0.1 fi or less, in order to promote the reaction at low temperatures. However, when anhydrous boric acid or hydrated boric acid is used as the boron compound, since these dissolve in the added water and become a solution, they may be made somewhat coarser.

In addition, boric acid tends to react with silicic acid in the refractory composition for aluminum during firing to produce borosilicate glass, which deteriorates the properties of the refractory, especially the spalling resistance. It is better. Of course, in such a case, it is desirable not only to increase the particle size but also to increase the ratio of aluminum compounds used, and to consider the use of poorly water-soluble boron carbide, boron nitride, etc. as boron compounds.

The amounts of aluminum compounds and boron compounds added are as follows:
It can be easily determined from the reaction mechanism in which aluminum oxide decomposed and produced during firing reacts with boron oxide to produce 9A2B, and ultimately 1 to 12% of 9A2 is contained in the refractory.
Basically, it is set to contain B. Therefore, the amount ratio of the tank that generates 9A2B in the refractory is: 9Al2O3 + 2B2O3 - P9Al2O3 2B2O
The addition ratio may be determined according to the molar ratio shown in reaction formula 3, and the addition amount may be determined according to the desired content of 9A2B in the refractory.

The reason why the proportion of 9A2B produced in the refractory is set to 1 to 12% is because if it is less than 1%, it will not be possible to suppress the penetration of molten aluminum into the refractory, and if it exceeds 12%, the durability will decrease. be. Therefore, a more preferable ratio is 4 to 10
%.

The reason why the firing temperature was set to 1000°C or higher is that in a normal oxidizing atmosphere, aluminum compounds and boron compounds decompose due to heating and become alumina and boron oxide, respectively.
When the temperature exceeds 000°C, 9A2B starts to form, and 12O0
When the temperature exceeds 1400°C, the reaction progresses significantly and is almost completed at 1400°C. However, in consideration of thermoeconomic efficiency, it is desirable to set the firing temperature to 1300° C. or lower and allow a slow reaction time to complete the reaction.

[For production]

According to this invention, the sinterability of the refractory obtained is significantly improved compared to the conventional method of adding 9A and 2B. This is because aluminum oxide and boron oxide, which have strong activity starting from aluminum compounds and boron compounds, are released during firing.
When A2B is produced, it is thought that a part of it adheres to the surface of the refractory aggregate to enhance bonding, thereby following a sintering mechanism known as so-called reaction sintering. In addition, when mullite or chamotte is used as an aggregate, the silicic acid contained in the aggregate and the added boric acid react to form borosilicate glass, and sintering does not occur by the so-called liquid phase sintering mechanism. Regarding the doubt, even if high-purity alumina such as sintered alumina is used as aggregate, strength will be improved and 1. Since a dense structure is obtained, the concept of liquid phase sintering can be rejected.

Refractories for aluminum need to have a dense structure to suppress the penetration of molten aluminum, and high strength to withstand the impact of injecting metal and liquid abrasion caused by molten metal. The refractory for aluminum produced by the means of the present invention has a dense structure and excellent strength due to improved sinterability. This makes it possible to halve the amount of chemical binder used in conventional refractory compositions. For example, when this invention was applied to high alumina bricks that used 5% aluminum phosphate as a chemical binder, the amount of aluminum phosphate used was reduced to 1%.
．． Equivalents were obtained with a reduction to 5%.

A second means of the present invention is a configuration in which the first means of the present invention is applied to the surface layer of a conventional inexpensive aluminum refractory that comes into contact with molten aluminum, and the remaining back layer is left as is. This is a method for manufacturing refractories for aluminum, and the effect of suppressing penetration of molten metal is good until the surface layer wears away and the back layer is exposed, so if the application is limited to areas where wear does not progress much, it will be more effective. An inexpensive and highly durable refractory for aluminum can be obtained and is highly practical.

〔Example〕

Table 1 shows the refractory composition, additive composition, moisture content, and firing temperature for Example 1.2.3, Comparative Example 1.2, and Conventional Example. In the same table, sintered alumina is AI! The content of 2O3 is 99.5%, and it is made of flandom crystals, 4th to 1st period,
It is a commercially available product pulverized to particle sizes of 1 μm or less, 0.3 μm or less, and 44 μm or less. Calcined alumina has an Al2O3 content of 99.8% and consists of flundum crystals, and is a commercially available alumina with a particle size of 0.1 M or less produced at a relatively low temperature (about 1100° C.). Mizuhikibushi clay is A.
-12O3 content is 38.8%, SiO2 content is 4
1.7%, is a refractory bonded clay consisting of kaolin mineral, and is a commercially available product ground to particles of 0.3 quarts or less.

Fine powder alumina has an Al2O3 content of 99.9%, is made of highly pure corundum crystals, and has a maximum particle size of 2 μm.
It is a commercially available product containing ultrafine particles of 1 μm or less. Aluminum fluoride is AI! ,? It is a commercially available special grade reagent with a chemical composition of F3.H2O and a purity of 99.99%. However, the particle size is 0.3 g or less. Boric acid is a commercial grade reagent with a purity of 99%, having the chemical formula H3BO3, and a particle size of 0.63M or less.

Each compound shown in Table 1 was prepared in an amount of 5 kg, mixed in an experimental 101-capacity V-type mixer, and then kneaded with the water shown in Table 1 in an experimental Mitsukumar kneader. 350'/(MB2 molding pressure) using a hydraulic pressure machine to create a dish-shaped brick shape (65
x 114 x 230 art), then
They were dried in an electrically heated hot air dryer at 110° C. for 24 hours, and then fired in a silicon carbide resistance heating electric furnace at the temperatures shown in Table 1. After cooling, each fired body was taken out of the furnace and cut in half with a diamond cutter, the strength of one piece was measured using a hydraulic strength tester, and a hole with a diameter of 30 mm was drilled in the other piece using a diamond core. It was finished in a concave shape with a chisel so that the thickness of the bottom part was about 25 degrees, and it was dried again at 110°C to prepare a specimen for an erosion test.

Table 1 Erosion tests were conducted using Hydrocuff 994 alloy (aluminum alloy containing 5.5% magnesium), which is highly erodible. This alloy was previously melted in a graphite crucible and injected into the hole of each specimen, and an electric current was applied. Insert it into the furnace and heat it at 900℃ for 1
The situation after holding for 00 hours was observed. The penetration depth was determined by cutting the cooled specimen with a diamond cutter and observing the cross section.

The production status of 9A and 2B was determined by measuring the compressive strength, taking a portion from each crushed specimen, and pulverizing it in an agate mortar.
It was investigated using an X-ray diffraction analyzer using CuKa radiation.

These test results and evaluations are shown in Table 2. To explain this result, since the conventional example was fired at a high temperature, it was sintered and developed great strength, but it was corroded by the molten aluminum alloy. That is, the molten metal permeates into the refractory and adheres to the surface of the refractory. Since Comparative Example 1 was fired at a low temperature (800° C.), the sintered alumina particles fell off during drilling, making it impossible to obtain a smooth surface and thus making it impossible to use for the erosion test. Furthermore, as a result of X-ray diffraction Table 2 analysis, 9A2B was not produced. Although Examples 1, 2, and 3 were fired at a lower temperature than the conventional examples, there were no similar problems in the drilling process, and the required strength as a furnace material was developed, and the molten metal due to the formation of 9A2B The corrosion resistance of Example 1 is generally good, and that of Examples 2 and 3 is extremely good. Also, from this result, 1000℃
It can be seen that when fired in the above manner, 9A2B is reliably produced and corrosion resistance is improved. Example 1 is a formulation in which the amount of grain formation of 9A2B is 10%, but the firing temperature is 1000°C.
Since the 9A2B production reaction is insufficient and the amount of 9A2B produced is small, and unreacted substances remain, the corrosion resistance is lower than in Example 2.3. In addition, the third embodiment has 9A
This is a formulation in which the amount of grain formation of 2B is 3%, but since the firing temperature is high, the formation reaction is completed and no unreacted substances remain, so the corrosion resistance is good. In Comparative Example 2, the firing temperature was high and 9A2B was produced in accordance with the amount of 9A2B produced in the ring, but because the amount was large, a tendency for the corrosion resistance to decrease was observed.

Separately from the above example, as a fourth example, the refractory composition (A) and additive composition (B) of the second example were mixed in the proportions shown in Table 1, and the mixture was mixed with water and kneaded before forming. The dish-shaped brick is integrally formed into a two-layer structure in the thickness direction with a surface layer and a back layer using the fire-resistant composition (A) mixed in the proportions shown in Table 1 and kneaded with water. It was molded and fired in the same manner as in the second embodiment to obtain a refractory. Although the surface layer was a layer formed by 9A2B, it was confirmed that the degree of formation was the same as in the second example. Further, the bonding state between the surface layer and the back layer was good, and no particular abnormality was observed.

〔Effect of the invention〕

According to this invention, 9A2B is not added to the refractory raw material, but is generated during firing, and the raw materials for its generation are aluminum compounds and boron compounds, which are easily available and relatively inexpensive. Therefore, a good refractory for aluminum and aluminum alloys can be easily provided at low cost. Furthermore, since the sinterability is improved compared to the conventional method of adding 9A2B, a refractory with superior strength can be obtained.

Patent applicant Nippon Ramtite Co., Ltd. Nippon Crucible Co., Ltd.

Claims (2)

[Claims] (1) In the refractory composition for aluminum, 1 to 12% of 9Al_2O_3・2B_2O_3 is added to the refractory by firing.
Production of refractories for aluminum and aluminum alloys, characterized in that one or more of each of an aluminum compound and a boron compound are added in an amount to produce a Method. (2) In the refractory composition for aluminum, 1 to 12% of 9Al_2O_3・2B_2O_3 is added to the refractory by firing.
Add one or more of each of an aluminum compound and a boron compound in an amount that produces . A method for producing refractories for aluminum and aluminum alloys, which comprises integrally molding the kneaded material as a back layer and then firing at 1000°C or higher.