Four kinds of magnesia-carbon bricks commonly used refractory raw materials, what are the main roles?

High purity magnesia

Magnesite, brucite, seawater magnesia and other raw materials are fully sintered at 1600~1900℃ to obtain magnesia, magnesia is divided into sintered magnesia and seawater magnesia, sintered magnesia is burned by natural ore, seawater magnesia is burned by seawater gasification magnesium. The main component of magnesia is magnesium oxide, also contains a small amount of SiO2, CaO, Fe2O3, B2O3, etc., the color is yellow to brown, the main crystal phase is cubic magnesite, the grain size is 0.02~0.05mm, the density is 3.50~3.65g/cm3. It has good resistance to alkaline slag erosion.

graphite

Graphite has excellent thermal conductivity and fire resistance, melting point as high as 3500℃, low thermal expansion rate of graphite (1.4×10-6 at 1000℃), high thermal conductivity, good resistance to acute cooling and acute heat, is one of the few materials whose strength increases with the increase of temperature. The infiltration Angle of graphite on slag is also quite large, and there is no eutectic relationship with Al2O3, SiC, SiO2, which can prevent the slag from penetrating into the product. Because carbon can reduce the iron oxide in the slag to metal iron, the viscosity of the slag is improved, and the migration of the slag components to the brick is reduced to achieve the effect of reducing erosion.

Special grade bauxite clinker

The main mineral composition of bauxite raw materials in China is hydrobauxite and kaolinite. The change of the Al2O3/SiO2 ratio corresponds to the relative change of the proportion of the two minerals, hydrobauxite and kaolinite. Bauxite clinker is the product of high temperature calcination, the Al2O3 content of super grade bauxite clinker is more than 88.2%, up to 91.3%. Although the erosion resistance of Al2O3 is strong, the simple Al2O3 expansion coefficient is large, and it is not resistant to spalling. When the simple Al2O3 is used as the matrix, the matrix part is easy to be penetrated and melted by the slag, exposing the aggregate, resulting in structural spalling.

High purity magnesia

Magnesite, brucite, seawater magnesia and other raw materials are fully sintered at 1600~1900℃ to obtain magnesia, magnesia is divided into sintered magnesia and seawater magnesia, sintered magnesia is burned by natural ore, seawater magnesia is burned by seawater gasification magnesium. The main component of magnesia is magnesium oxide, also contains a small amount of SiO2, CaO, Fe2O3, B2O3, etc., the color is yellow to brown, the main crystal phase is cubic magnesite, the grain size is 0.02~0.05mm, the density is 3.50~3.65g/cm3. It has good resistance to alkaline slag erosion.

Magnesia carbon brick is made of magnesia, heavy burned magnesia, fused magnesia, high purity magnesia and high quality graphite and bauxite additives. The price of magnesia carbon brick has a great relationship with the graphite content in the brick. With the increase of graphite content, the strength of brick decreases, the thermal expansion rate decreases, and the residual expansion rate increases.

Therefore, the graphite content in the brick should be controlled at about 20%. Magnesia carbon brick has little wettability to slag, excellent spalling resistance and erosion resistance, and is suitable for slag line parts of ladle, especially for multi-furnace continuous pouring. In order to meet the need of producing clean steel, the application part of magnesia-carbon brick has been expanded from the slag line to the side wall during the refining of ladle.

When laying magnesia-carbon bricks on ladle, care should be taken not to mix with bricks containing high Si02. Otherwise, the local melting loss of magnesia-carbon brick will be increased, and the melting loss mechanism is as follows.

It is mainly used for lining and outlet of oxidizing reconversion furnace, hot spot of wall of high-power electric furnace, inner lining of refining furnace and slag line of steel drum outside the furnace.

1, chemical stability, graphite at room temperature has good chemical stability, acid resistance, alkali resistance, resistance to organic solvent corrosion.

2. Plasticity. Graphite has good toughness and can be ground into very thin sheets.

3, the melting point of high temperature resistant graphite is 3850 ° C ±50 ° C, the boiling point is 4250 ° C, even if the ultra-high arc burning, the mass loss is very small, the linear expansion coefficient is also very small. The strength of graphite is strengthened with the increase of temperature. At 2000℃, the strength of graphite is doubled

4. Lubricity. The lubricity of graphite depends on the size of the graphite flake, the larger the flake, the smaller the friction coefficient, the better the lubrication performance

5, electrical and thermal conductivity. The electrical conductivity of graphite is twice that of ordinary non-metallic ores. Thermal conductivity exceeds that of steel, iron, lead and other metal materials. The thermal conductivity decreases with the increase of temperature, and even at extremely high temperatures, graphite is an adiabatic body.

6, thermal shock resistance. When graphite is used at high temperatures, it can withstand drastic changes in temperature without damage, and when the temperature changes, the volume of graphite does not change much, and cracks will not occur.

The binder plays the role of connecting the matrix and particles. In the actual production and use process, the matrix and binder system are the two weak links of magnesia carbon brick.