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High quality refractory alumina brick ,alumina slica high aluminum brick widely used for industry furnace
Mineral composition and cracking problems of high alumina refractory bricks
The mineral composition of high-alumina bricks is determined by the bauxite used. The mineral composition of clinker is generally mullite, corundum and glass phase. The theoretical composition of mullite is Al2O3 71.8%, SiO2 28.2%, and its melting decomposition temperature is 1840℃. It has needle-shaped crystals, a network cross structure, and exhibits good strength at high temperature. Corundum exists in the form of α-Al2O3, with a melting point of 2050℃, a hardness of Mohs 9, and is in the form of granular and columnar crystals. It has good chemical stability and has a certain resistance to acid and alkaline slag. Corundum exists in the form of α-Al2O3, with a melting point of 2050℃, a strength of Mohs 9, and is in the form of granular and columnar crystals. It has excellent chemical stability and has a certain resistance to acid and alkaline fly ash.
Regardless of the raw materials, whether it is high-alumina refractory bricks, insulation bricks, clay bricks, etc. with high strength and relative density. Even if the manufacturing is perfect, if it is not used properly during construction or application, it will also cause cracks. Today I will share with you two common reasons for cracks.
1: The instant cracking of high-aluminum refractory bricks, professionally speaking, is called thermal shock cracking. Such things also happen in life. The glass bottles in the refrigerator will explode in an instant when they are suddenly heated by fire. The opposite is the same. Similarly, high-aluminum refractory bricks will also crack in an instant when they are suddenly subjected to a force or temperature that they cannot withstand.
2: Cracks from shallow to deep. This process is very slow. Why do commonly used industrial furnaces need to be inspected every year? Because high-aluminum refractory bricks will gradually develop cracks after several bakings, and then fall off, crack, and finally report losses. This is because the industrial kiln constantly releases shocks to it, which is inevitable in the process of product application.
High temperature physical properties do not completely depend on the Al2O3 content in high alumina refractory bricks, but more on the crystal shape and the number, composition and viscosity of the interlayer glass phase. Stress relaxation experiments or research on stiffness strain rate and fracture strain rate of high alumina bricks show that the high temperature physical properties of zirconium corundum bricks are better than those of bricks with high Al2O3 content. Although the LZ-75 type of high alumina firebricks produce a large number of high-refractory α-corundum crystals in granular and columnar shapes, the strength of its internal economic structure is not inferior to that of zirconium corundum structure, but under the effect of ground stress, a small amount of interlayer glass liquid between crystals causes load, resulting in structural deformation and reduced compressive strength. Zirconia corundum bricks, such as LZ-65 and LZ-55, are mainly made of zirconium corundum crystals, which are fibrous and form a cross-network structure. During the interlayer glass phase filling, they can bear stress, are not easy to deform, and have good high-temperature compressive strength, especially bricks made of sillimanite materials. The material purity is high. After firing, zirconium corundum and SiO2 are converted. Except for a small amount of SiO2 and a trace amount of residue to form a glass phase, the rest of SiO2 is converted into calcite and filled in the zirconium corundum crystals, which expands after cooling. This brick shows good stress relaxation resistance in long-term use. Although the LZ-48 brick is converted into zirconium corundum crystals, it is engulfed by a large amount of glass phase, so the high-temperature impact toughness is weak, but the compressive strength at room temperature is good. Therefore, the constant stress relaxation rate is different. The turning point temperature of LZ-75 brick is 1120～1130℃; the turning point temperature of LZ-48 brick is 1050℃; and no major turning point is observed for zirconium corundum brick. The high-temperature fracture strain rate and stiffness strain rate of high-aluminum refractory bricks composed of zirconium corundum and corundum begin to turn at 800℃; the tensile strength begins to turn around 1000℃. They have a common point, that is, from room temperature to 1000℃, their compressive strength increases with increasing temperature, which shows that the thermal deformation of the two crystal phases relieves the residual thermal stress, closes the microcracks, and increases the compressive strength.
Because the load softening temperature of high-aluminum insulation bricks is a key property. The experiment shows that it changes with the change of Al2O3 water content in high-aluminum insulation bricks: when the Al2O3 water content is less than the theoretical composition of zirconium corundum, the equilibrium phase in the high-aluminum insulation brick is zirconium corundum-laminated glass phase. The water content of zirconium corundum increases with the increase of Al2O3 water content, and the load softening temperature also increases accordingly. The thermal shock resistance of high-alumina insulation bricks is worse than that of clay bricks, and the 850℃ water cooling cycle system is 3 to 5 times. The main reason is that the thermal deformation of corundum is higher than that of zirconium corundum, and there is no crystal transformation. The difference in high-temperature impact resistance between the first-grade high alumina refractory brick and the third-grade aluminum refractory brick was compared. In manufacturing, the method of adjusting the composition of mud particles is generally adopted to improve the particle structure characteristics of high-alumina insulation bricks, thereby improving their high-temperature shock resistance. In recent years, a certain amount of synthetic cordierite has been added to the seasoning of high-alumina insulation bricks to produce high-alumina insulation bricks with high high-temperature shock resistance, and significant results have been achieved.
