JPH03228860A - Production of magnesia-chrome firebrick - Google Patents

Abstract

PURPOSE:To obtain high quality bricks free from an unfired part and uniform in shape and dimensions by exposing brick body contg. a metal (alloy) such as Al, Cr or Ti to a firing atmosphere by a prescribed specific surface area and firing the brick body at a prescribed temp. for a prescribed time. CONSTITUTION:Brick body contg. one or more among Al, Cr, Ti, Fe, Mg, Si and Mn or an alloy of such metals added by 0.1-7% is prepd. and put on a conveyor so that it is exposed to the atmosphere in a firing furnace by >=0.2cm<2>/cm<3> specific surface area. In the furnace, the brick body is fired at >=1,750 deg.C by keeping at the max. temp. for >=7hr.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing metal-added maguro refractory bricks.

(Prior art) The purpose of adding metals Fe, Mg, Si, Q, Cr, Ti, Mn, or mixtures or alloys to the base material of maguro refractory bricks is to add them individually during the firing process to obtain refractory bricks. Refractory bricks are made by melting and diffusing the metals and alloys inside the brick matrix, crushing the pores existing between the particles, making the microstructure denser, and increasing the proportion of secondary spinel due to the easy reaction of metals to oxides. The objective is to improve corrosion resistance and infiltration resistance against slag. Therefore, in order to fully exhibit this effect, it is necessary to sufficiently diffuse the metal or alloy into the brick during the firing process and to oxidize it sufficiently.

However, with conventional technology, due to insufficient oxidation of metals and alloys, unfired parts occur inside the bricks, and irregular volumetric expansion occurs when the bricks react to oxides, resulting in irregularities in the shape and dimensions of the bricks, and in severe cases. Cracks appeared on the surface of the bricks, making it difficult to obtain good quality products. This is most influenced by the shape of the brick, and it cannot be denied that the larger the shape, the more noticeable the occurrence of unfired parts.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned problems in maguro refractory bricks obtained by adding metals, alloys, etc. and firing them. The following may be considered as the path of occurrence of unfired parts inside the brick.

First, when the maguro refractory brick matrix contains reducing agents such as metals or alloys as mentioned above, when the brick matrix contains, for example, chromite, Fe2O2 etc. contained in the chromite are mixed. If the reducing agent is reduced earlier than it is oxidized in the firing step, an unfired portion will remain, although sufficient spinel or solid solution can be produced.

Second, these metals as reducing agents are melted during the firing stage,
If the firing rate is too fast than the rate at which the liquid phase moves through the pores (mass transfer rate) or the rate at which the oxidation reaction occurs during the transfer, the
It is thought that when the oxygen concentration to sufficiently oxidize the valent and divalent iron is insufficient and the material balance is not balanced, the unfired portion remains inside the brick.

Therefore, in order to eliminate the unfired parts of the above-mentioned maguro refractory bricks, the solution is to optimize the mass transfer rate, oxidation reaction rate, oxygen concentration, etc. in the firing stage, but the current technology It is extremely difficult to numerically understand the behavior of metals in bricks.

Therefore, the wood inventors optimized the firing temperature, firing time (maximum temperature keeping time), specific surface area, etc. according to the shape of the brick, so that no unfired parts remained and the shape and dimensions were uniform. The present invention provides a method for producing quality maguro refractory bricks.

(Means for Solving the Problems) The present invention provides a furnace of a brick base to which 0.1 to 7% of aluminum, chromium, titanium, iron, magnesium, silicon, manganese seeds, two or more, or alloys thereof are added. Specific surface area in contact with atmosphere is 0.2 cm2/cm3
Load it on the baking furnace transfer stand so that the baking temperature is 175.
This is a method for producing maguro refractory bricks, which is characterized by firing at a temperature of 0° C. or higher and maintaining the maximum temperature for 7 hours or more.

The metals used in the present invention include AQ, Cr, and Tt.

The above-mentioned metals, such as Fe, Mg, Si, and Mn, are suitable because other metals have poor fire resistance when converted into oxides and are expensive. One or more of these metals may be mixed or alloyed.

Metals or mixed powders or alloy powders of these metals are oxidized during the firing process, but this is accompanied by volumetric expansion. Therefore, the pores are filled and the structure becomes dense, but if it exceeds 7% by weight, cracks will occur due to excessive volume expansion. Also, if the amount added is less than 0.1% by weight, it is a slight addition, so
It is difficult to uniformly disperse it, and there is no effect of adding it. Therefore, the amount of addition is preferably 0.1 to 7%.

In the loading method of individual bricks during firing, the specific surface area of the bricks in contact with the furnace atmosphere is 0.2 (cm2/cm3
), the surface in contact with the furnace atmosphere is too small and the contact with the furnace atmosphere is insufficient, resulting in uneven heating conditions for firing and decreasing firing efficiency, so unfired parts remain. It will take the form of Therefore, by loading the materials on the transfer table of the firing furnace so that the specific surface area in contact with the furnace atmosphere is 0.2 (am2/cm3) or more, a uniform firing effect without bias can be obtained.

[Example] The present invention will be explained in detail below.

The raw material composition ratio is magnesia 70; chrome ore 30, and the magcro direct bond brick has a chromium: iron ratio of 75:25.
4% by weight of the alloy was added, kneaded, press-formed and fired under the following conditions.

■ Firing a) Firing temperature 1700℃ 1750℃ 1800℃ b) Firing time 7H (maximum temperature keeping time) 8H 0H 2H Press-formed bricks with dimensions (shape) of (1) to (6) above are baked in a furnace. Load the brick material onto a transfer platform (in this example, a trolley) so that the specific surface area (cm2/cm3) of the brick material in contact with the internal atmosphere is 0.2 cm2/cm' or more, and ■a)
, b). After each brick was cooled, it was divided into two equal parts parallel to the plane of dimension (longitudinal direction) XBI/B2, and the presence or absence of an unfired part in the center was visually confirmed.

Table 1 shows the test results after visual confirmation.

In Table 1, O indicates that there is no unfired portion completely, Δ indicates that a slight unfired portion is observed, and × indicates that an unfired portion is clearly observed. Furthermore, in order to increase applicability to terrain, the shape factor is expressed not in terms of dimensions but in terms of specific surface area relative to the total surface area of bricks.

As shown in Table 1, the presence or absence of unfired parts inside the brick is greatly influenced by shape factors, and this tendency is clearly evident.

From this table, the specific surface area of the brick is 0.2cm2/cm
If it is 3 or more, it is possible to obtain a high quality product by firing at a temperature of 1750° C. or higher.

However, when firing maguro refractory bricks, Fed, Fe2O3, Cr2O3゜Mg contained in chromite
The spinel produced by O is largely controlled by the oxygen concentration in the furnace.

Therefore, there is a concern that increasing the oxygen concentration in the furnace simply because the shape becomes larger may affect quality, even if the unfired portion can be eliminated. In such cases, rather than increasing the oxygen concentration, it is safe to lengthen the firing time.

As shown in Table 2, the oxygen concentration in the furnace was changed to 5.0.15.0.18.0% with the same shape, the same firing, and the same firing time, and the oxygen concentration in the furnace was 18.0%. Although no unfired parts were observed, the quality was about 10% inferior to A and B, so it is important to focus on the firing keeping time, and it is important to keep firing by 15% or more as shown in Table 2. It is meaningless to set the amount of oxygen in the furnace to .

Therefore, by keeping the firing time longer than 7 hours as shown in Table 1, it is possible to obtain high quality products without degrading the quality and without any unfired parts.

Table 2 (Note) ○: Completely free of unfired parts Erosion test conditions Method Lining erosion test using a rusting furnace Crystallinity 1650℃ Time 4 hours 7 atmospheres Vacuum slag c/5-3 CaF2-20% m addition 400g X
After the two times viIJSIJS30410kg erosion test, the amount of reduction in size of the innermost erosion part of each sample was measured, and the amount of reduction in size of the sample with a code of 1 was standardized as 10 (l) and was used as the erosion index.The erosion index was smaller. The higher the corrosion resistance, the higher the corrosion resistance.

The raw material composition ratio of these co-translated materials A, B, and C is magnesia 70. Maguro Direct Honto bricks made of chromite 30 are kneaded with the addition of 4% by weight of a chromium/iron alloy of 7525, press-formed into a shape of 650 x 160/115 x 100, and fired.

As described above, refractories have superior performance to conventional refractories by using various metals and alloys, but up until now they have been quite limited in terms of manufacturing technology and shape. However, with this invention, this restriction has been resolved by providing firing conditions that match the shape of the refractory, making it widely applicable to refractories for steelmaking furnaces, extending the life of the furnace, and having great effects. is brought about.

[Effects of the Invention] The present invention is a method for firing magnesia-based refractories containing appropriate amounts of GJ, metals, metal alloys, or mixtures, and it is difficult to obtain high-quality products without unfired parts due to shape constraints. It is possible to obtain a product of constant quality.

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Claims (1)

[Claims] 1 The specific surface area in contact with the furnace atmosphere of a brick base containing 0.1 to 7% of one or more of aluminum, chromium, titanium, iron, magnesium, silicon, manganese, or an alloy thereof is 0.2 cm^2/ Load it on the firing furnace transfer table so that it is at least cm^3, and set the firing temperature to 1750.
A method for producing maguro refractory bricks, characterized in that firing is carried out at a temperature of ℃ or higher and a maximum temperature maintained for 7 hours or more.