In the process of using high alumina bricks, it is subjected to physical, chemical, mechanical and other effects at high temperatures, and is easily melted or abraded and abraded, causing cracking and damage, causing interruption of operation and contamination of materials. According to the composition of high alumina bricks and its performance indicators, the use of high alumina bricks at high temperatures can be predicted.
1. For high alumina bricks with special requirements, thermal conductivity, electrical conductivity and gas permeability should also be considered.
2.High alumina bricks can resist high temperature heat load for sputum, does not soften, does not melt. The high alumina bricks are required to have a relatively high degree of refractoriness.
3.Fire bricks can resist the chemical erosion of molten liquid, dust and gas, no deterioration, no erosion. High alumina bricks are required to have good slag resistance.
4. Bricks can resist the sharp changes in temperature or uneven heat, no cracking, no peeling. High alumina bricks are required to have good thermal shock resistance.
5. Fire brick can resist the erosion, impact and wear of flame and charge, dust, no loss of surface. High alumina bricks are required to have a relatively high density and wear
resistance at normal temperature and high temperature.
6.Brick refractory can resist high temperature heat load, volume does not shrink and only uniform expansion. High alumina bricks are required to have high volume stability, residual shrinkage and residual expansion are small, no crystal transformation and severe volume effect.
7.Against high temperature vacuum operation and changes in the atmosphere, not volatile, not damaged. High alumina bricks are required to have low vapor pressure and high chemical stability. The shape is neat, the specifications and dimensions of the high-aluminum brick are accurate, the quality is high and the price is low, and it is convenient for transportation, construction and maintenance.
8.Fire brick can resist the combination of high temperature thermal yttrium and heavy load, without losing strength, no creep and collapse. High alumina bricks are required to have relatively high room temperature strength and high temperature thermal strength, high load softening temperature, and high creep resistance.
How to improve the performance quality of high alumina bricks?
High alumina bricks are made of sorghum soil composed of boehmite and kaolinite as main minerals. High alumina bricks are usually made of coarse, medium and fine three stage ingredients. The upper limit of the coarse particles is usually 2 to 3 mm, and the addition amount is 40% to 50% (for the shaped product, the upper limit of the coarse particles can be reduced to 2 to 1 mm), and the amount of the intermediate particles of 1 to 0.1 mm is preferably 10% to 20%; <0.1mm fine powder should be added in an amount of 40% to 50%.
The manufacture of refractory high alumina bricks generally uses soft clay, which has good plasticity. Therefore, the manufacture of high alumina refractory bricks usually uses soft clay as a binder. However, the free SiO2 in the clay and the free Al2O3 in the high alumina bauxite clinker undergo a secondary mullite reaction at 1200 ° C, resulting in a large body expansion, and the porosity of the silicon increases and the strength decreases. Therefore, the amount of the clay powder added in the furnish is preferably not more than 5%.
If the high alumina brick products are eliminated, the cracks are easily generated, the appearance quality is not good, and the material handling is difficult. However, the addition of high alumina brick fine powder is not only difficult to form, but also prone to cracking, large firing shrinkage, and increased scrap rate. Therefore, the amount of fine powder added is preferably 40 to 50%. In general, the amount of intermediate particles added is preferably 10%. The intermediate particles do not have the skeleton action of the group particles, nor the sintering effect of the fine powder. Therefore, the amount of intermediate particles added is usually limited to the minimum amount. However, the intermediate particles cannot be completely eliminated.
Production practice shows that appropriately increasing the size and number of coarse particles of high alumina bricks can increase the bulk density of the mud and is easy to form. When firing, the secondary mullite reaction around the material is weak and easy to sinter. However, there are limits to the size of the high alumina bricks. If it is enlarged to 4~5mm, it will easily cause the phenomenon of missing corners and the uniformity of tissue organization will be affected. Therefore, the maximum particle size is preferably 3 mm.
The addition of fine powder to the high alumina brick batching is beneficial to the sintering of the green body and increase the density of the product. The addition of fine powder is necessary because the firing shrinkage of the fine powder during sintering can attenuate or offset the volume expansion caused by the secondary mullite reaction. In addition, high alumina bauxite micropowder can be used as a binder; or high alumina bauxite micropowder and clay powder can be prepared in a certain ratio to prepare synthetic mullite as a binder. High alumina bricks without secondary expansion can be obtained by using these binders.
How to Improve the Toughness of High Alumina Bricks?
The toughness and thermal shock resistance of high alumina bricks are also one of the properties of high alumina refractory brick products, and they are also complementary. The method for improving the toughness of high alumina bricks: taking certain measures to form a certain microstructure of high alumina bricks, generating energy consumption mechanism, hindering crack growth and improving the toughness of high alumina bricks. The following is a simple analysis of the toughening problem of high alumina bricks by Henan refractory manufacturers.
There are structural defects, inherent pores and cracks in high alumina bricks. Under the action of external force, the cracks are easy to start, and there is no energy consuming mechanism. Brittle fracture is easy to occur. The toughening path of high alumina bricks can control the microstructure. The size of small cracks controls the amount and distribution of impurities and pores. It is also possible to prevent crack propagation by increasing the energy dissipation mechanism and setting obstacles. Phase transformation toughening, microcracking toughening, etc,can produce energy consuming mechanism, dispersing the second phase particles, which can cause crack propagation to encounter obstacles, and crack deflection and toughening occur.
