JPH0324425B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvements in magnesia-chromium fired refractory bricks. Conventionally, fired magnesia/chromium bricks include direct bonded maguro bricks, ribbon-dead maguro bricks, and semi-ribboned maguro bricks. Direct bond maguro bricks are made mainly of magnesia clinker and chromite, with the addition of a small amount of chromium oxide as needed, kneading, shaping, and drying followed by firing at a high temperature of 1,700℃ or higher to create bonds between particles. It has a strong bonding form using so-called "direct bonding", maintains high strength even at high temperatures, and has hot properties such as high-temperature volume stability and load-bearing softening properties. In addition, by incorporating chromite, the structural spalling characteristic of magnesia bricks is reduced, and it exhibits excellent corrosion resistance, especially against slag with low basicity (CaO/SiO ₂ weight ratio <2). Furthermore, due to the difference in thermal expansion and contraction rates between magnesia particles and chromite particles, micro-cracks are generated between the two particles during cooling during the firing process, and these micro-cracks absorb thermal stress and improve spall resistance. ing. Ribbon-dead Maguro bricks are bricks made by crushing, kneading, shaping, drying, and firing the electrofused Maguro raw material produced by electromelting magnesia clinker and chromite, and are more durable than direct bond Maguro bricks. It has excellent erosion properties but has the disadvantage of poor spalling resistance. Semi-rebond maguro bricks are made by combining magnesia and chromite with electrofused maguro, adding chromium oxide as necessary, kneading, shaping, drying, and firing.Direct bond maguro bricks and ribbon maguro bricks shows intermediate properties. That is, the corrosion resistance is superior to direct bond maguro bricks, and the spalling resistance is superior to ribbon bond maguro bricks. The present invention relates to improvements in the above-mentioned direct bonded maguro bricks and semi-ribboned maguro bricks. When these bricks are used in certain types of kilns for long periods of time, their structure deteriorates and they become brittle. As a result of investigating the cause of this, we focused on the fact that the iron oxide contained in the bricks undergoes a change to FeOFe ₂ O ₃ due to temperature fluctuations or atmospheric changes within the kiln, and the accompanying volume change causes structural deterioration. . As a result of various studies on this countermeasure,
We have discovered that by setting the Cr ₂ O ₃ /Fe ₂ O ₃ weight ratio to 3.5 to 4.5, structural deterioration is extremely small and durability in various furnaces is dramatically improved, and the present invention has been completed. It came to this. That is, the present invention provides a fired magnesia/chromium brick containing a combination of electrofused magnesia and/or magnesia clinker and chromite, or further addition of electrofused magnesia/chromium, chromium oxide, or both. ₂ O ₃ content is 5 to 35% by weight, and the weight ratio of Cr ₂ O ₃ content and amount of iron oxide converted to Fe ₂ O ₃ Cr ₂ O ₃ /
This is a magnesia-chromium fired refractory brick characterized by Fe ₂ O ₃ of 3.5 to 4.5. The present invention will be explained in more detail below. In addition,
All percentages shown below are by weight. The electrofused magnesia or magnesia clinker used in the present invention is a commercially available product, and contains 98% MgO.
As mentioned above, SiO ₂ is desirably 0.5% or less. As chromite, C ₂ O ₃ 30% or more, Fe ₂ O ₃ 20%
The above are used. In the present invention, the Cr ₂ O ₃ content contained in the brick needs to be adjusted to 5 to 35% from the viewpoint of both spall resistance and corrosion resistance. If it is less than 5%, the spalling resistance will be reduced, and if it is more than 35%, the corrosion resistance against basic slag will be reduced. If the firing temperature is below 1750℃, the hot strength will be low.
If the temperature is higher than 1900°C, the firing cost increases and the firing deformation increases, so it is preferable to perform the firing at a temperature between 1750 and 1900°C. It is desirable to set the Cr ₂ O ₃ /Fe ₂ O ₃ weight ratio to 3.5 to 4.5, which is the most important feature of the present invention, from the viewpoint of economical efficiency and less structural deterioration due to temperature fluctuations or atmospheric fluctuations. In other words, the weight ratio of Cr ₂ O ₃ /Fe ₂ O ₃ is
If it is less than 3.5, the structure will become weaker due to temperature or atmosphere fluctuations, resulting in a large decrease in strength, so by making it more than 3.5, this decrease in strength will be reduced, and the durability will be significantly improved when used in various types of kilns. I'll come. Even if the Cr ₂ O ₃ /Fe ₂ O ₃ weight ratio is increased to 4.5 or more, there is no improvement, and in order to increase this, the amount of chromium oxide added becomes uneconomical. Next, the experimental results that led to the present invention will be described. Using magnesi aclinker, chromite A, and chromium oxide, which have the chemical components shown in Table 1,
2% of 10 Baume bittern was added as a binder to the chemical composition shown in Table 2, kneaded, molded at a pressure of 1000 kg/cm ² and baked at 1750° C. for 5 hours. A test piece of 25 x 40 x 120 mm was cut out from this brick and heated in an electric furnace.
After increasing the temperature at a rate of °C/min and heating at 1500 °C for 3 h,
Naturally cooled. The bending strength after repeating this heating and cooling five times was measured, and the ratio to the bending strength before heating was calculated. The results are shown in FIG. It can be seen that when the Cr ₂ O ₃ /Fe ₂ O ₃ weight ratio is less than 3, the bending strength is only about 20% of the original brick due to repeated heating and cooling, and the structure is significantly deteriorated. 3～
The strength increased between 3.5 and 55% of the original brick when it reached 3.5 or higher. The present invention will be explained below based on examples. Example 1 2% of 10 Baumé bittern was added to the raw materials of chemical components obtained according to the compounding ratio shown in Table 3, kneaded, and molded at a pressure of 1000 Kg/cm ² to obtain 8 types of molded products. . All of these molded bodies were dried at 120°C for 24 hours, and then fired at 1800°C for 5 hours. The products 4, 5, 6, 7, and 8 of the present invention are the conventional products 1 and 2.

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[Table] As shown in Table 3, there is less change in bending strength due to repeated heating and cooling than in Example 3. When these bricks were attached to the side walls of the chambers of an RH vacuum degassing device, the rate of hair loss was significantly improved with the product of the present invention compared to the conventional product. Example 2 2.5% of 10 Baume bittern was added as a binder to the blending ratio shown in Table 4, kneaded, and then molded at a pressure of 1000 Kg/cm ² to obtain two types of molded products. This molded body was dried at 120°C for 24 hours and then fired at 1770°C for 5 hours.
As shown in Table 4, compared to the conventional product 9, the present invention 10
There was little change in bending strength due to repeated heating and cooling. When this brick was used on the side wall of the lower tank of an RH vacuum degassing device, the wear rate of the product of the present invention was significantly improved compared to the conventional product.

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【table】 [Brief explanation of drawings]

Figure 1 shows magnesia with the chemical composition shown in Table 2.
Chromium fired bricks were heated to 1500℃ and cooled 5 times, and the bending strength before and after was measured.
Bending strength change index calculated from bending strength after heating / bending strength before heating × 100 = bending strength change index (%) and Cr ₂ O ₃ /
This is a plot of the relationship between Fe ₂ O ₃ weight ratio.

Claims (1)

[Claims] 1 Electrofused magnesia and/or a combination of magnesia clinker and chromite, or further electrofused magnesia chromium, or chromium oxide,
Alternatively, in a fired magnesia/chromium brick containing both of them, the Cr ₂ O ₃ content in the brick is 5 to 35% by weight, and the Cr ₂ O ₃ content and the amount of iron oxide converted to Fe ₂ O ₃ are A fired magnesia/chromium refractory brick characterized in that the weight ratio Cr ₂ O ₃ /Fe ₂ O ₃ is 3.5 to 4.5.