The refractory commonly used as neutral furnace lining is high alumina refractory, which belongs to aluminum silicate refractory, and the content of Al2O3 is more than 46%. When the mass fraction of Al2O3 is greater than 71.8%, the equilibrium phase group becomes mullite and corundum, and the liquid phase does not appear until 1810 ℃. Therefore, it is suitable for crucible lining.
The mass fraction of Al2O3 in corundum refractory is more than 95%, and its crystal form is. α- Al2O3 belongs to hexagonal system. It has high chemical stability, stable volume at high temperature and high load softening point. It can be used as furnace lining of more than 10t.
When melting aluminum and aluminum alloy, the main cause of furnace lining damage is aluminum penetration; Strong reduction reaction of elements in molten liquid to oxides in furnace lining, etc. The common damage of furnace lining is blackening, nodulation and cracking, and this reaction will increase silicon in molten aluminum and affect the composition of molten liquid. Refractories suitable for melting aluminum and aluminum alloys must have the advantages of good sintering strength, small pore system diameter, low content of SiO2, Na2O and K2O, and wetting of surface with molten liquid. In addition, the furnace lining should have good sintering performance at 800 ℃.
Alumina magnesia dry beating material takes fused corundum as the main raw material, plus an appropriate amount of MgO and additives. In the process of furnace drying and operation, due to the formation of AI mg · s and the structure of additives, it can well resist the corrosion of high-temperature liquid steel. Compared with MgO, its thermal expansion rate is lower, coupled with the formation of secondary spinel, which can effectively prevent cracking.
Alumina spinel ramming material is made of high-purity electrolytic alumina as the main raw material and an appropriate amount of high-purity magnesium oxide. It not only has excellent corrosion resistance, but also has lower coefficient of thermal expansion and good thermal stability than magnesium oxide and magnesium aluminum spinel. Therefore, it is recommended to be used for medium frequency induction furnace for large cast steel of about 6T, and its service life can reach more than 200 heats.