What Are The Standards For Rotary Kiln Mouth Castables?

Steel fiber reinforced corundum and high-alumina refractory castables for rotary kiln mouths are prone to cracking and peeling after many years of use, that is, poor thermal shock resistance and low service life.

It is well known that clay bricks are better than high-alumina bricks in thermal shock resistance and alkali resistance because of low aluminum content; high strength, good wear resistance, and poor shock resistance. In the castables for kiln mouths, the Al₂O₃ content is 50% to 70%, the strength is moderate (taking into account both wear resistance and suitable thermal shock resistance), and the drying and compressive strength (1100℃) are about 40MPa and 70MPa respectively. It should be pointed out that refractory castables are composed of aggregates, powders, binders, and admixtures (substances). The phase composition in the matrix is in a non-equilibrium state before use. When used under high temperatures, the components in the matrix will follow the phase equilibrium relationship to re-form a new phase equilibrium (that is, obtain excellent performance and in-situ reaction). Therefore, suitable component materials should be selected and the batch design should be optimized to achieve good sinterability, volume stability, corrosion resistance, and high-temperature mechanical properties.

Selection of main materials

The front kiln mouth refractory lining is frequently cooled and heated rapidly, and the use temperature is within the range of 800℃～1250℃, which can bear the wear and alkali corrosion of cement clinker. The selection of the main material of refractory castables must be determined according to its use conditions to achieve the purpose of low cost and good use.

Selection of admixtures

Amorphous refractory materials are typical in-situ reaction refractory materials, so the selection of admixtures (materials) is very important. It is necessary to ensure the construction performance and baking performance. The in-situ reaction at high temperatures can obtain excellent material properties. The admixtures (materials) used in kiln mouth refractory castables mainly include a dispersant, accelerator, plasticizer, sintering agent, expansion agent, and explosion-proof agent. Now we will focus on introducing the sintering agent, whose varieties of materials include raw clay, zircon, titanium dioxide, and brazing compound. This type of material reacts in situ at the use temperature to generate a certain amount of mullite crystals, zircon phases, titanate crystals, and inconsistent molten compounds (2Al₂O₃·B₂O₃), etc., accompanied by volume expansion and microcracks, which can compensate for its sintering shrinkage, thereby making the castable produce sintering strength, corrosion resistance, and good thermal shock resistance.

In short, the material composition of the refractory castable for the kiln mouth of the rotary kiln should be determined according to its use conditions. Therefore, it is recommended that customers communicate some of the rotary kiln conditions with technicians or sales staff when purchasing.