Clay refractory bricks are refractory products produced from refractory clay. It is widely used in industry. Clay bricks are divided into ordinary clay bricks, multi-clinker clay bricks, all-raw clay bricks and high-silica clay bricks.
01Chemical composition
Due to different raw materials, the chemical composition of clay bricks varies greatly. Its main components are Al2O3 and SiO2. The approximate range of various components is as follows: Al2O3 30%~46%, SiO2 50%~70%, Fe2O3 1.0%~3.0%, TiO2 1.0%~2.5%, (R2O+RO) 1.0%~4.0%. There is also a semi-acidic clay brick whose composition is: AI2O3 11%~16%, SiO2 81%~85%, Fe2O3 1.0%~2.0%, (R2O+RO) 1.0%~3.0%.
02Crystal phase composition
The clay brick crystals are mainly mullite 3Al2O3·2SiO2 (Al2O371.8%, SiO228.2%) and SiO2 crystals. SiO2 crystals are mainly cristobalite with a small amount of tridymite. The glass phase is mainly Al2O3, SiO2 and a small amount of other oxides. Calculated from the theoretical value of the phase diagram, when Al2O3 is 35%, mullite and SiO2 crystals each account for 50%. In fact, due to the presence of impurities such as Fe2O3 and R2O in the bricks, the amount of mullite produced is small. this part
Al2O3, SiO2 and various other oxides make up the glassy phase. The content of the glass phase is greatly affected by the type of raw materials, chemical composition, and firing conditions. Generally speaking, when the content of SiO2, Fe2O3 and R2O is high, there is more glass phase.
03 Properties and applications of clay bricks
Clay bricks have good thermal vibration resistance and a large fluctuation range, generally greater than 10 times (1100°C water cooling), which is consistent with the linear expansion coefficient of clay products not too large (the average linear expansion coefficient between 20 and 1300°C is 4.5×10-6~5.8×10-6/℃), no polycrystalline transformation phenomenon and obvious granular structure. Therefore, clay bricks are often used as large bottom bricks in glass kilns.
Clay products are weakly acidic refractory products, and their acidity increases as the SiO2 content increases. It has certain corrosion resistance to acidity, but poor resistance to alkaline corrosion. Therefore, clay products are suitable for use as refractory materials in acid kilns. Large clay refractory bricks for glass kilns refer to clay refractory bricks with a unit weight of not less than 50kg for building glass kilns. The metallurgical industry standard (YB/T5106-1993) divides clay refractory bricks into N-1, N-2a, N-2b, N-3a, N-3b, N-4, N-5, N- based on physical and chemical indicators. 6 eight brands.
This standard also makes the following provisions on the cross-section cracking of bricks.
① Bricks with cross-section spalling length less than 400mm: when the spacing width is 0.26~0.50mm, the length is no more than 40mm; when the spacing width is 0.51~1mm, the length is no more than 25mm. Bricks with a length greater than 400mm: when the spacing width is 0.26~0.50mm, the length is no more than 80mm; when the spacing width is 0.51~1mm, the length is no more than 50mm.
② For cracks with a crack width less than 0.25mm, the length is not limited.
③ There should be no gaps or cracks larger than 1mm on the cross section.
04 Precautions when using clay bricks
① Clay brick products produced by different forming methods have different properties
Clay bricks produced by various forming methods except high-pressure forming methods have a relatively high content of binders, so the firing temperature cannot be too high. This kind of brick has low softening temperature under load, large re-burning shrinkage and high porosity. The clay bricks produced by the slurry casting method and the high pressure forming method have a relatively uniform structure. However, clay bricks produced by other forming methods have uneven organizational structures and may have layered structures, causing directional cracking and internal cracks.
②Aggregate and combination
Generally, the corrosion resistance of bonded refractory aggregates and bonded materials is different. Aggregate has better corrosion resistance than binder. When there is a large difference in corrosion resistance between the two, the combination will be corroded first, causing damage to the entire refractory material. However, in order to produce clay bricks with low porosity, a small amount of quartz and R2O are often added to the combination. This increases the mechanical strength of the clay bricks, but also results in a decrease in the corrosion resistance of the combination.
According to this characteristic, different clay bricks can be used in different parts of the furnace due to different erosion conditions. The lower grate and checker bricks in the lower part of the regenerator are less eroded by batch dust and volatile matter, have a lower temperature, and have a heavy load, which mainly requires high mechanical strength. Therefore, the combination in the brick can contain an appropriate amount of SiO2, Fe2O3, and R2O. However, clay bricks used in high-temperature locations mainly require high refractoriness and low impurities in the combination.
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