Refractory materials refer to inorganic non-metallic materials with a refractoriness not less than 1580°C. They are used as structural materials for high-temperature furnaces and other thermal equipment, as well as materials for industrial high-temperature containers and parts, and can withstand corresponding physical and chemical changes. And mechanical action.
Refractory materials are high-temperature resistant structural materials manufactured after processing natural ores such as bauxite, silica, magnesite, and dolomite as raw materials. In addition to natural raw materials, refractory materials manufactured from certain industrial raw materials and synthetic mullite, spinel, silicon carbide and other raw materials are also increasing. Refractory materials used for the smelting of pure metals or special alloys and the manufacture of oxides and refractory compounds in high-temperature technology have also been greatly developed. These refractories constitute a diverse and complex refractory system. Different refractories have different compositions, preparation processes, structural characteristics and performance; refractories of the same composition can also have different preparation processes and appearance shapes. Therefore, in order to facilitate research and reasonable use, it is necessary to scientifically classify refractory materials. According to different viewpoints, there are multiple classification methods.
①According to composition
Can be divided into siliceous products, aluminum silicate products, magnesium products, dolomite (quality) products, chromium products, carbon products, zirconium products, pure oxide products and non-pure oxide products. This classification method can characterize the basic composition and characteristics of various materials, and has practical significance in production, use and scientific research. Table 1 lists various refractory materials classified by chemical composition.
②According to the process method
It can be divided into slurry casting products, plastic forming products, semi-dry pressing forming products, powdered non-plastic tamping forming products, products poured from molten materials, products formed by injection or drawing, and natural sawn from rock. Products, etc. This classification method intuitively shows the technological characteristics of refractory products.
③According to the degree of refractoriness
It can be divided into ordinary refractory products with a refractoriness of 1580~1770℃; advanced refractory products with a refractoriness of 1770~2000℃; super-grade refractory products with a refractoriness above 2000℃. This classification method shows the high temperature performance of refractory materials.
④According to the shape of refractory
Can be divided into shaped refractory products, such as fired bricks, fused bricks (fused cast bricks), refractory insulation bricks, and experimental and industrial crucibles, utensils and other special products; unshaped refractory products, referred to as bulk materials, in the place of use It is made into the required shape and subjected to heat treatment, such as castables, ramming materials, projecting materials, spray materials, refractory mud, etc.; refractory fibers, such as aluminum fibers, aluminum silicate fibers, etc., are generally processed into carpets after secondary processing. , Felt, board, rope, assembly and fiber block products. This classification method intuitively reflects the shape of refractory materials.
1. Silica refractory materials
Silica refractories refer to refractories with SiO2 as the main component. The main products are silica bricks, amorphous siliceous refractories and quartz glass products.
Silica refractories are typical acidic refractories. Its mineral composition: the main crystal phases are tridymite and cristobalite, and the matrix is quartz glass phase. Silica-based refractories have strong resistance to acidic slag, but are strongly corroded by Chinese slag; load softening temperature is high; residual expansion ensures that the masonry has good air tightness and structural strength; good wear resistance and thermal conductivity; thermal stability It has low performance and low refractoriness, which limits its wide application. Silica bricks are mainly used in coke ovens, glass melting furnaces, acid steelmaking furnaces and their thermal equipment.
2. Magnesium refractory materials
Magnesia refractories refer to refractories that use magnesite, seawater magnesia and dolomite as raw materials, periclase as the main crystal phase, and MgO content of 80%-85% or more. Magnesium refractories are alkaline refractory materials. They have good corrosion resistance to alkaline substances and high refractoriness. They are the most widely used and most widely used in steelmaking alkaline converters, electric furnaces, iron furnaces, and many non-ferrous metal smelting. An important type of refractory is also a refractory commonly used in high temperature zones of glass regenerators, cement kilns and ceramic kilns.
Magnesia refractory products can be divided into two categories: metallurgical magnesia and magnesia products. According to chemical composition and use, it can be divided into metallurgical magnesia, magnesia brick, magnesia silica brick, magnesia alumina brick, magnesia calcium brick, magnesia carbon brick and other varieties. Its performance is greatly affected by the ratio of CaO/SiO2 and impurities. The load softening point and thermal shock resistance of high-purity magnesia bricks are far better than those of general magnesia bricks. It has high refractoriness and good resistance to alkaline slag and iron slag. It is an important high-grade refractory material. Magnesium products are mostly produced by the sintering method, and the sintering temperature is generally between 1500 and 1800°C. In addition, chemical bonding agents can also be added to make unburned bricks and unshaped refractory materials.
3. Fused cast refractory materials
Fused cast refractory materials refer to products in which raw materials and batch materials are melted at a high temperature and then cast into a certain shape. There are two methods for melting batch materials: electric melting method and thermite method. The electric melting method is to melt batch materials in an electric arc furnace or resistance furnace. The thermite method uses the heat released by the thermite reaction (2Al+Fe2O3→2Fe+Al2O3+Q) to melt the batch material. The electrofusion method is currently the main method for producing fused cast refractories.
There are many types of fused cast refractory products, and the most widely used one is fused cast zirconia corundum bricks. Other fused-cast products include fused-cast mullite bricks, fused-cast zirconium-mullite bricks; fused-cast corundum bricks, magnesia, spinel and olivine, and other fused-cast products. Compared with sintered products, fused-cast products have the following characteristics: the products are very compact, have less pores, and have high density; high mechanical strength; high structural strength at high temperatures; high thermal conductivity and good slag resistance.
4. Carbon-containing refractories
Carbon-containing refractories refer to refractory materials mainly composed of carbides, which are neutral refractory materials and are divided into two categories: carbonaceous products, graphite clay products and carbonized cinnamon products.
Carbon-containing refractories have high refractoriness (the melting temperature of pure carbon is 3500°C, and actually begins to sublime at 3000°C. Silicon carbide decomposes above 2200°C), good thermal and electrical conductivity, load deformation temperature and high temperature strength Excellent, slag resistance and thermal shock resistance are better than other refractory materials. However, this type of product has the disadvantage of being easy to oxidize.
Carbon products are products made with carbon as the main component, using coke, graphite or heat-treated anthracite as raw materials, and using carbon-containing organic materials as binders. Such products include carbon bricks with coke or anthracite as the main component and graphitized artificial graphite and semi-graphite carbon bricks. Carbon products have good heat resistance, corrosion resistance, high-temperature strength and high-temperature thermal conductivity, and are currently mainly used in blast furnaces.
Graphite clay products are refractory materials made of natural graphite as raw material and clay as a binder. It has good thermal conductivity, high temperature resistance, does not interact with metal melt, and has low thermal expansion. Such products include graphite clay crucibles, distillation tanks, cast steel plug bricks, nozzle bricks and steel bucket lining bricks. Among them, graphite clay crucibles for steelmaking and smelting of non-ferrous metals are the most produced and widely used.
Silicon carbide products are advanced refractory materials produced with silicon carbide (SiC) as raw materials. Its wear resistance and corrosion resistance are good, high temperature strength, high thermal conductivity, low thermal expansion coefficient, good thermal shock resistance, and its application fields have been expanding in recent years. Silicon carbide products are currently used in steel smelting for ladle lining, nozzles, plugs, blast furnace bottoms and hearths, tapping troughs, converters and electric furnace taps, and heating furnaces without water-cooled slide rails. In the smelting of non-ferrous metals (zinc, copper, aluminum), it is widely used in stills, rectification tower trays, electrolytic tank side walls, molten metal pipelines, suction pumps, and smelting metal crucibles.
5. Lightweight refractory materials
Lightweight refractories refer to refractories with high porosity, low bulk density and low thermal conductivity. Lightweight refractories are characterized by a porous structure (the porosity is generally 40% to 85%) and high thermal insulation. Used as thermal insulation material in industrial kilns and other thermal equipment. Compared with general refractory bricks, it has poor slag corrosion resistance, mechanical strength, and abrasion resistance, and has a larger volume shrinkage at high temperatures.
According to the bulk density, lightweight refractories can be divided into two types: lightweight bricks and ultra-light bricks. Those with a bulk density of 0.3~1.3g/cm3 are lightweight bricks; those with a bulk density of less than 0.3g/cm3 are ultra-lightweight bricks.
According to the use temperature, lightweight refractories can be divided into three categories: low temperature, medium temperature and high temperature. Use temperature 600~900℃ for low temperature insulation material; 900~1200℃ for medium temperature insulation material; over 1200℃ for high temperature insulation material.
According to the shape of the product, lightweight refractories can be divided into two types: fixed and unshaped. Shaped lightweight refractory bricks include clay, high-alumina, silicon, and certain pure oxide lightweight bricks; unshaped lightweight refractory materials, such as lightweight refractory concrete.
6. Unshaped refractory materials
Unshaped refractory is a refractory that is composed of reasonably graded granular and powdery materials and a binder that is directly used without forming and firing. Generally, the granular materials that make up this material are called aggregates, the powdered materials are called admixtures, and the binders are called cements. This kind of material has no fixed shape and can be made into slurry, mud and loose shape, so it is also collectively referred to as bulk refractory. This kind of refractory can be used to form an integral structure without joints, so it is also called integral refractory.
There are many types of unshaped refractories, and there are many classification methods. Generally, they can be divided into basic refractories, acidic refractories and neutral refractories according to their chemical composition. According to chemical composition, they can be divided into silicon, aluminum silicate, aluminum, Magnesium, silicon carbide, aluminum carbon, etc.; according to the bonding method can be divided into cement bonding, chemical bonding, cohesive bonding, etc.; according to the installation method can be divided into castables, plastics, ramming materials, spray coatings, preforms, etc.
Refractory materials used in the iron and steel industry account for about 70% of the total refractory materials. The main function of refractories is to withstand high temperature, abrasion, corrosion, etc., to protect the integrity of the steel structure of thermal equipment, and to provide better working conditions.
