Refractory high alumina bricks are usually used for masonry blast furnaces, hot blast stoves, electric furnace tops, blast furnaces, reverberatory furnaces, rotary kiln linings, open hearth regenerative lattice bricks, plugs for gating systems, nozzle bricks, etc.
What are the production materials of refractory high alumina bricks?
The manufacture of refractory high-alumina bricks generally uses soft clay. This material has good plasticity. Therefore, the manufacture of refractory high-alumina bricks usually uses soft clay as a binder. However, in the free SiO2 and high alumina bauxite clinker in the clay. The free mullite reaction of free Al2O3 at 1200 °C produces a large body expansion, and the porosity of silicon increases and the strength decreases. Therefore, the amount of clay powder added in the material is preferably not more than 5%.
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. These binders can be used to obtain no secondary expansion. Refractory high alumina brick.
Refractory high alumina bricks are usually made of coarse, medium and fine grades. The upper limit of coarse particles is usually 2~3mm, and the addition amount is 40%~50%. (For high aluminum shaped bricks, the upper limit of coarse particles can be reduced to 2~1mm. The amount of intermediate particles added from 1 to 0.1 mm is preferably 10% to 20%; the amount of fine powder of <0.1 mm should be controlled at 40% to 50%.
Adding fine powder to the material is beneficial to the sintering of the green body and increasing the density of the product. Since the firing shrinkage of the fine powder during sintering can weaken or offset the volume expansion caused by the secondary mullite reaction, it is necessary to add fine powder. However, the addition of fine powder is too much, not only difficult to form, but also prone to cracks, large shrinkage and increased scrap rate. Therefore, the amount of fine powder added is 40-50%.
The intermediate particles do not have the skeleton effect of the group particles, nor the sintering effect of the fine powder. Therefore, the amount of the intermediate particles is usually limited to the minimum amount, but the intermediate particles cannot be completely eliminated. If it is eliminated, the product is prone to cracking after burning. The appearance quality is not good and it brings certain difficulties to the material handling. Generally speaking, the amount of intermediate particles added is 10%.
Production practice shows that appropriately increasing the size and quantity of coarse particles 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 be sintered. However, the size of the enlarged particles is also certain. Limit, if it is enlarged to 4~5mm, it is easy to produce missing edge and angle, and the uniformity of tissue is affected. Therefore, the particle size is 3mm.
