Title：Introduction of magnesia carbon brick for converter
Keyword：Converter, Magnesia-carbon brick, Fused magnesia
Description：Magnesia-carbon brick is a refractory product made of magnesia and graphite as the main raw materials, plus an appropriate amount of binder, which is formed by high pressure and low temperature heat treatment. Magnesia carbon brick started in Japan, a new type of refractory product developed in the early 1970s. Mainly used for steelmaking converters, electric furnace working linings, and working linings of out-of-furnace refining ladle.
- The main composition of magnesia carbon brick
Magnesia-carbon brick is a refractory product made of magnesia and graphite as the main raw materials, plus an appropriate amount of binder, which is formed by high pressure and low temperature heat treatment. Magnesia carbon brick started in Japan, a new type of refractory product developed in the early 1970s. Mainly used for steelmaking converters, electric furnace working linings, and working linings of out-of-furnace refining ladle.
- Introduction of the main raw materials used in the production of magnesia-carbon bricks
- Fused magnesia: It is an alkaline refractory material made of natural magnesite, light-burned magnesia or sintered magnesia by electric arc furnace melting. The main crystalline phase of fused magnesia is periclase, the melting point is 2800 ℃, it begins to sublime at 1600 ℃ in a vacuum, and begins to sublime when it is above 2000 ℃ in a reducing atmosphere, the density is greater than 3.40g/cm3, the porosity is 0%-10 %, Mohs hardness of 5.5, strong corrosion resistance to alkaline slag, stable chemical properties, no reaction or weak reaction with various refractories except silica bricks at a high temperature of 1500 ° C. The appearance should be obvious after complete melting and crystallization, and other magnesia or sundries are not allowed to be mixed.
- Graphite: It is a natural mineral with carbon as the main component. It has properties such as high temperature resistance, thermal conductivity, electrical conductivity, lubrication, plasticity and corrosion resistance. It is the main raw material for carbon-containing refractories. Graphite for refractory materials is mostly flake graphite, which is divided into high-purity, high-carbon, medium-carbon, and low-carbon graphite according to the fixed carbon content. Colors are iron black, steel gray. The density is 2.09-2.23g/cm3, the melting point is 3700℃±100℃ (in vacuum), the thermal conductivity is large, the expansion coefficient is small, the elastic modulus is small, the lubricity is good, the electrical conductivity is good, and the chemical properties are stable. , alkali and organic solvent do not react, it is difficult to wet with molten steel, and has good corrosion resistance.
- Phenolic resin: It is a non-aqueous organic binder for refractory materials. It is obtained by polycondensation of a mixture of phenol (or cresol, xylenol, or resorcinol) and formaldehyde (or uronic acid) under the action of a catalyst. The main advantages are (1) high carbonization rate (52%); (2) good adhesion and high strength of the formed green body; (3) high bonding strength after firing; (4) hardening speed at room temperature can be controlled; ( 5) The content of harmful substances is small, which can improve the working environment. Classified by heating properties or structural forms, there are thermosetting phenolic resins and thermoplastic phenolic resins, classified by product form, there are liquid phenolic resins and solid phenolic resins (granular and powdery), classified by curing temperature, there are high temperature curing type 130℃-150 ℃; there are medium temperature curing type 105℃-110℃; room temperature curing type 20℃-30℃.
Thermosetting phenolic resin binder generally requires that the moisture in the aldehyde resin should be less than 1.8%, and its viscosity changes with temperature, and the viscosity decreases when the temperature rises. At the same time, there is a phenomenon that the viscosity changes with the storage time. If the storage time is prolonged, the viscosity changes greatly. If the storage period is too long, it will solidify and cannot be used. Generally, the storage time is 30 days (in the warehouse) when the temperature is high in summer, and longer in winter. The relative storage time of thermoplastic phenolic resin will be longer. The magnesia-carbon bricks combined with this combination can be trapped for 30 days without affecting the molding viscosity, but a curing agent (urotropine) should be added to ensure drying strength.
- Technical specifications for the production process of magnesia-carbon bricks for converters Magnesia-carbon bricks are generally unburned products, and the production process mainly includes raw material processing preparation, batching, mixing, forming, and heat treatment.
A. Batching process: It is an important process . It should be measured strictly according to the formula particle size and ratio requirements, which is the most fundamental requirement. As a batching person, you can first identify the raw materials and use the measuring tools correctly and skillfully; during the work, you should pay attention to observe whether the raw materials have changes in color, particle size, odor, concentration, feel, etc., and if there is any abnormality, it should be reported immediately. All granules and powders used should not be wet or agglomerated, and be careful to prevent rain and moisture. The fine powder below 1-0 should be packed in double plastic moisture-proof packaging.
B. Mixing process: It is also an important process, because the molding performance of the mixed mud directly affects the quality of the brick. The general requirements for the feeding sequence: coarse magnesia particles, medium particles (3-6, 1-3, 1-0) — phenolic resin — graphite — fine magnesia powder, additives. After adding the granular material, add the binder and mix at a low speed for a period of time to make the liquid resin adhere evenly on the particles, then start adding graphite, and make it stick to the liquid film of the magnesia particles through mixing, The graphite on the outer shell of the magnesia particles presses onto the particles and squeezes out a portion of the excess resin. At this time, high-speed mixing can be carried out, otherwise the graphite will float on the material and it will not be possible to produce a good mud. Because graphite has good thermal conductivity and small heat capacity, while the heat capacity of coarse magnesia particles is large, the frictional heat generated during high-speed mixing is beneficial to wetting graphite. Only when the above series of operations are completed, can the fine magnesia powder and additives be added to continue mixing. When the graphite, magnesia particles, fine powder and additives have been wetted, and the excess binder on the particles is basically all The kneading can be finished only when the graphite is extruded out and the graphite wrapped by the magnesia particles is densely pressed onto the particles.