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Refractory castable technology for kiln mouth of cement rota

Date:2019-06-24 15:38     writer:cement editor     Views:

in that traditional cement rotary kiln, the unshaped refractory material is mainly used in the parts such as the front, the rear kiln mouth and the wet kiln chain belt, the non-shaped refractory material is also widely used in the parts such as a preheater, a tertiary air pipe, a kiln door cover and a cooling machine, and the type of the refractory material is as follows: the corundum and the high-aluminum refractory castable, the steel fiber reinforced refractory castable, the alkali-resistant pouring material, the self-flowing fire-resistant pouring material and the heat-insulating pouring material, and the like, The dosage is about 1/3 of the refractory material for the whole kiln. the refractory material is therefore not shaped It plays an important role in a new type of kiln.

1. Application conditions of refractory castable at rotary kiln mouth


The refractory lining of rotary kiln orifice is the weak link of kiln lining, especially the refractory lining at the front kiln mouth. The operating temperature is about 1100℃, which needs to withstand quench, hot air flow, high temperature cement clinker wear and high temperature harmful gas alkali corrosion, etc. The main damage of the lining is:cracking, peeling and abrasion, so the refractory material must have good thermal shock resistance, abrasion resistance and alkali resistance.
When the cylinder of rotary kiln is not deformed, it can be built with high aluminum brick, spinel brick and direct binding magnesia-chromium brick, and high quality mud can be used as joint material in order to form the whole, prevent the brick from falling and improve the life span. However, the deformation of the cylinder is common, so the refractory castable is poured with refractory castable, the steel shell is welded with rivets, and the castable is mixed with steel fiber reinforced refractory castable, which is constructed and baked according to the rules to meet the production needs of kiln tube lining.

In foreign countries, corundum and high aluminum steel fiber reinforced refractory castable are widely used in the front kiln mouth of cement kiln, and their service life can reach 2 to 8. The castable has high aluminum content and high strength. Therefore, the thermal shock resistance is poor, easy to crack and spalling, reduce the service life. The production practice has proved that the application effect of steel fiber reinforced high aluminum refractory castable is better than that of corundum castable.

2. Development of refractory castable for rotary kiln mouth


Steel fiber reinforced corundum and high aluminum refractory castable used in rotary kiln are prone to cracking and spalling in many years, that is to say, the thermal shock resistance is not good and the service life is low. Based on this, Beijing Tongda, Zhejiang Jincheng and Kaifeng special resistance units have developed high aluminum refractory castable, high aluminum mullite castable and mullite refractory castable, etc., which have a service life of more than one year and achieved good results.

It is well known that the thermal shock resistance and alkali resistance of the clay brick are superior to that of the high alumina brick, because the aluminum content is low, the strength is high, the wear resistance is good, and the shock resistance is poor. In the castable for kiln mouth, the content of Al2O3 is 50% ~ 70%, the strength is moderate (both wear resistance and thermal shock resistance are considered), and the drying and compressive strength (1100 ℃) are about 40 MPa and 70 MPa, respectively. It should be pointed out that the refractory castable is composed of aggregate, powder, binder and admixture (object), and the phase composition in the matrix is in a non-equilibrium state. In use, the components in the matrix will follow the phase equilibrium relationship. Reconstitute a new phase equilibrium (that is, obtain excellent performance and in situ reaction). Therefore, the suitable composition materials should be selected and the batching design should be optimized to achieve good sintering property, volume stability, corrosion resistance and high temperature mechanical properties.

Selection of the material of the main body


The refractory lining of the front kiln has the function of bearing the abrasion of the cement clinker and the alkali corrosion due to the rapid cooling, the rapid heating and the use temperature in the range of 800-1250 DEG C. The selection of the main material of the refractory castable must be determined according to the conditions of use, so as to achieve the purpose of low cost and good use.

The refractory aggregate is made of Grade II and III bauxite clinker, carastones and mullite. The critical particle size shall be amplified, and the particle size shall be reasonably graded to achieve densification, which is beneficial to improving the thermal shock resistance and strength of the material.

Refractory powder, binder and admixture are the matrix materials of refractory castable, and reasonable particle gradation must be carried out in order to improve their properties. At room temperature, the construction strength can be obtained, and under the action of high temperature, phase transformation is easy to occur and sintering is carried out. At the same time, there will be in-situ reaction between the materials, and its micro-expansion can counteract the sintering shrinkage and improve the thermal shock resistance and strength of castable.

Refractory powder materials such as corundum, bauxite clinker, mullite and silicon carbide are broken into various grain sizes. At the same time, superfine powder should be added to fill the gap, and the activity is large, so it is easy to produce in situ reaction and improve the properties of the matrix.

Calcium aluminate cement, ultra-fine powder and phosphate are used as binder, and their dosage should ensure the strength of mold removal and make the pressure strength of drying reach about 40MPa.

② Selection of admixtures(substances).


Amorphous refractory is a typical in-situ reactive refractory, so the selection of admixture is very important. It is necessary to ensure the construction performance, baking performance and in-situ reaction at high temperature to obtain excellent material properties. The admixtures used in refractory castable at kiln mouth mainly include dispersing agent, coagulant promoter, plasticizer, sintering agent, expansion agent and explosion-proof agent. This paper focuses on the sintering agent, its varieties of materials are raw clay, zircon, titanium and compound and so on. At the operating temperature, this kind of material reacts in situ to form a certain number of mullite crystals, zirconium phase, titanoaluminates crystal and inconsistent molten compounds ( 2Al2O3 ·B2O3), etc., accompanied by volume expansion to produce microcracks, can compensate for its sintering shrinkage, so that the castable has sintering strength, corrosion resistance and good thermal shock resistance.

The amount of the sintering agent varies according to the variety material (generally 1% to 7%), the excess sintering agent, in-situ reaction produces a large expansion and a liquid phase, so that the thermal shock resistance and the corrosion resistance of the casting material are reduced, and the using effect is also influenced. Therefore, the variety and dosage of the sintering agent should be selected reasonably according to the use temperature, the thickness of the sintering layer, the volume stability and the corrosion resistance, so as to meet the practical application requirements.

The admixture (object) mainly has heat-resistant steel fiber and the like. In the refractory castable for the kiln mouth, the No.446 and No.304 steel fibers are selected to meet the use requirements (in the amount of 1-4%). The invention has the function of inhibiting the matrix to generate cracks or preventing the crack propagation and improving the thermal shock resistance of the material. The experimental results show that the steel fiber reinforced refractory castable is 3-4 times higher than that of the non-steel fiber (i.e., the thermal shock resistance) after 10 times of cold and hot circulation, and the service life of the steel fiber reinforced refractory castable is more than one year. Therefore, in the refractory castable for the kiln mouth, heat-resistant steel fibers must be added. It should be noted that the preparation of steel fiber fire-resistant When pouring material, the steel fiber must be mixed evenly in the castable to prevent the steel fiber from forming into a cluster, otherwise the service life of the refractory lining at the kiln mouth will be reduced.

In a word, the material composition of refractory castable for rotary kiln mouth should be determined according to its application conditions, and the in-situ reaction, sintering and volume stability between matrix materials should be guaranteed, so as to obtain good bending strength, thermal shock resistance and corrosion resistance. At the same time, proper addition of admixture and reasonable selection of its variety and dosage can improve the construction performance and performance of the material. Steel fiber reinforced aluminum mullite refractory castable has achieved initial results in kiln mouth and should be popularized.

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