Standards for Castables at the Mouth of Rotary Kilns

The steel fiber reinforced corundum and high alumina refractory castables used for the kiln mouth of the rotary kiln are prone to cracking and peeling after many years of use, that is, the thermal shock resistance is not good and the service life is low.

As we all know, the thermal shock resistance and alkali resistance of clay bricks are better than those of high alumina bricks because of the low aluminum content; high strength, good wear resistance, and poor shock resistance. In castables for kiln mouth, the Al2O3 content is 50% to 70%, the strength is moderate (both wear resistance and thermal shock resistance are considered), and the drying and compressive strength (1100°C) are about 40MPa respectively. and 70MPa. It should be pointed out that refractory castables are composed of aggregates, powders, binders, and admixtures (materials). The phase composition in the matrix before use is in a non-equilibrium state. A new phase equilibrium will be reconstituted according to the phase equilibrium relationship (that is, to obtain excellent performance and in-situ reaction). Therefore, suitable constituent materials should be selected and the batching design should be optimized to achieve good sinterability, volume stability, corrosion resistance, and high-temperature mechanical properties.

Selection of main material

Due to frequent rapid cooling and rapid heating, the refractory lining at the front kiln mouth can be used at a temperature of 800 ° C to 1250 ° C, which can withstand the wear and alkali corrosion of cement clinker. The selection of the main material of the refractory castable must be determined according to its use conditions in order to achieve the purpose of low cost and easy use.

Selection of admixtures (substances)

Unshaped refractories are typical in-situ reaction refractories, so the selection of admixtures (substances) is very important. It must ensure construction performance, baking performance, and in-situ reaction at high temperatures to obtain excellent material properties. The admixtures (substances) used in kiln mouth refractory castables mainly include dispersants, coagulants, plasticizers, sintering agents, expansion agents, and explosion-proof agents. Now focus on introducing the sintering agent, the materials of which include raw clay, zircon, titanium dioxide, and stilbium compounds. This type of material reacts in situ at the service temperature to generate a certain amount of mullite crystals, zircon phases, titanate crystals, and inconsistent melting compounds (2Al2O3·B2O3), etc., accompanied by volume expansion and microcracks. It can compensate for its sintering shrinkage so that the castable can produce sintering strength, corrosion resistance, and good thermal shock resistance.

In short, the material composition of refractory castables for the kiln mouth of the rotary kiln should be determined according to its service conditions. Therefore, it is recommended that customers must communicate clearly with the technical personnel or sales personnel about the rotary kiln when purchasing.