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Small Rotary Kiln Lining Should Use Phosphate Bricks, Not High Alumina Bricks!
Dec 18, 2018

This morning, I received an order from a customer who was purchasing a small cement rotary kiln. I wanted to purchase high-alumina bricks. After listening to the customer's needs and application parts, colleagues in the technical department strongly recommended the use of phosphate bricks. It is also explained why the use of phosphate bricks in rotary kiln is better than that of high alumina bricks.

Phosphate brick is made of special grade clinker clinker as the main raw material, adding appropriate amount of phosphoric acid aqueous solution, pre-mixing, trapping, mixing, forming, drying, heat treatment and other processes. Phosphoric acid itself has no cohesiveness, and it exhibits good adhesion when it reacts with a neutral oxide of a raw material such as premium alumina clinker and a weakly basic oxide to form a phosphate. The resulting binding, in addition to the chemical reaction with the material being bonded, is primarily due to the polymerization and adhesion of the acid phosphate. Phosphate-based ions are bonded in a variety of ways to the macromolecules of the chain-like network or space-frame structure, and the oxygen in the phosphate-based PO4 acts as such a bond to solidify the body. The acid phosphate formed depends on the degree of neutralization during the reaction, that is, the degree of hydrogen substitution, and is mainly aluminum dihydrogen phosphate or aluminum hydrogen phosphate, which is generally considered to be a main component. Since it is soluble in water at normal temperature, it can maintain plasticity for a long time after being used to form a mixture, but when heated to a certain extent, the aluminum phosphate can be changed into aluminum pyrophosphate and aluminum metaphosphate, and The polymerization reaction then occurs. Therefore, phosphate bricks have the characteristics of high strength and good wear resistance.

Phosphate bricks contain 4%~5% moisture in the brick after forming, so the brick must be dried to improve its mechanical strength, facilitate transportation, kiln operation, and ensure the appearance quality of the product. Before the brick enters the drying kiln, it must be Natural drying, drying time is not less than 12h, the temperature of the kiln is 60~80°C, the temperature of the kiln is 110~130°C, the drying time is not less than 48h, and the residual moisture after drying is ≤1%.

Compared with high-aluminum bricks, phosphate bricks have a 1- to 2-fold increase in service life in small-scale cement rotary kiln: its load-softening temperature is low, the surface is rough, it is easy to bond with materials, and the key is evenly hung. Once the kiln skin, the brick and kiln skin are flat and firm; if the kiln skin is defective, it is easier to make up the hang, especially in the abnormal operating conditions of the kiln, the phosphate brick does not burst, does not peel off the block, The kiln skin does not collapse, does not crack, and has strong adaptability to materials.

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