Casting corundum brick product introduction
2019-08-23
The cast corundum brick is αAl2O3, rhombohedron or plate crystal, the true density is 3000~4000kg/m3, the melting point is 2050°C, the Mohs hardness is 9. It shrinks 25% when crystallized, the apparent porosity is 10%-12%, and the bulk density is 3000- 3300KG/m3, especially a-Al2O3 after crystallization, forms a weak tubular microstructure with no glass phase.
Because there is no glass phase, the thermal shock resistance of the product is very poor. The improvement method is to increase the 5% β-A2O3, and increase the bulk density to 3300~3500kg/m, or increase the bulk density of 5% metal aluminum. Up to 3800kg/m3, its disadvantages are not only poor thermal stability, but also easy to cause streaky threaded glass defects, so it is only suitable for borosilicate glass and high temperature tunnel kiln firing zone, graphite baking furnace lining and non-ferrous metal smelting furnace Masonry and so on.
Formulation design and raw material selection
Casting corundum brick (RA-A): Add a small amount of flux, such as boron oxide (B2O2) 0.25%-1%, industrial alumina Al2O3 not less than 98.5%.
The manufacturing process of fused cast corundum products is similar to that of fused zirconium corundum bricks. The difference is:
The pouring temperature is high, 1960~2400°C, and the riser volume of PT casting is 20% of the casting.
The mold should be made of graphite plate type (cross-section temperature difference greater than 1000 °C) or corundum sand type, metal water-cooled type (internal coating protective layer aluminum oxide or lime, etc.) with a scale of about 2%; must be demolded into the incubator, annealing temperature High, the insulation performance of the incubator is better than AZS. It not only prevents cracking, but also prevents the internal crystal from being dense. The processing of out-of-box products requires high precision and smooth finish.
Melt casting, thermal annealing
(1) The oxidized and melted arc cannot be as long as the smelting AZS. Because the voltage is high, the density of the casting will decrease. Secondly, there should be flue gas dedusting and ventilation to create an oxidizing atmosphere in the furnace.
(2) The temperature control of the thermal insulation annealing is very important, which is related to the crack of the product. Usually, after the aRA2O is poured into the mold, the hard shell component of the mold wall is aBA2O3, and the more the center, the Na2O migrates to the center of the shrinkage cavity to form aAl2O3 and The uneven distribution of Na2O(9-11)A2Q leads to the product being easily cracked.
