Because the cement rotary kiln has an alkaline atmosphere, alkaline refractory bricks are used in both the high-temperature zone and the low-temperature zone, and the proportion of refractory castables is gradually increasing. For example, alkali-resistant castables and high-strength alkali-resistant castables for preheaters and tertiary air ducts. Cement rotary kiln preheater 4-5 level cone, blanking pipe, decomposition furnace, kiln tail smoke chamber with anti-skinning castable. Steel fiber reinforced refractory castable for cement rotary kiln door cover and cooler. If it is a large cement kiln mouth and coal injection pipe, plate-shaped corundum castable should be selected, and so on. In this article, we will learn more about anti-skinning castables and refractory castables for cement kiln openings.
Cement Rotary Kiln Anti-Skinning Castable
Anti-skinning castables are used in cement rotary kilns, which mainly play the role of abrasion resistance and prevent the burning materials from forming loops. Because the raw materials are seriously corroded by alkaline. By adjusting the amount of silicon carbide added, the mechanical properties, alkali resistance, and anti-skinning properties of the anti-skinning castable are improved. Anti-skinning castables can also be said to be silicon carbide castables, which are most suitable for rotary kiln decomposition systems.
The anti-skinning castable is combined with pure calcium aluminate cement, and the alkali resistance and anti-skinning properties are different through the difference in silicon carbide content. When using, adjust the dosage according to the site of use to adapt to different sites.
The dust from the decomposition system of the rotary kiln and the alkali, sulfur, chlorine, and other alkaline vapors volatilized from the fuel will seriously corrode the castables and refractory bricks, causing crusts and blockages, preventing the passage of materials. The alkali resistance and abrasion resistance of anti-skinning will prevent the material from forming or clogging in different parts. It is also the meaning of anti-skinning castable.
Characteristics of Anti-Skinning Castable
Anti-skinning castables are characterized by stable chemical properties. The alkaline gas reacts to generate a viscous liquid phase, which will attach to the surface of the castable to form a glaze-like protective layer to prevent alkali corrosion. The material composition of silicon carbide is that it is resistant to erosion, abrasion, and is not easy to form the skin. An oxide layer on the surface will also be formed at high temperatures.
In addition, the anti-skinning castable has stronger wear resistance and corrosion resistance due to the addition of silicon carbide. The calciner used in the rotary kiln can form a surface glaze with strong anti-skinning and alkali resistance. The greater the silicon carbide content, the greater the volume density of the anti-skinning castable. As the temperature increases, the volume density will gradually decrease. This is the process of gradually removing free water and crystal water as the temperature rises, so the bulk density becomes smaller. The volume density will increase to a certain extent when the temperature is 1350℃.
Special Refractory Castable for Cement Kiln Mouth
The castable for cement kiln mouth can be said to be the part with the shortest service life among all refractory materials used in cement kiln. Because the temperature of the cement kiln entrance varies constantly, the castable is severely damaged by cement clinker abrasion and alkaline erosion, and the cement kiln entrance is frequently repaired with castable.
The previous formula of the special castable for the kiln mouth is to add mullite to increase the flexibility, corundum, and other binders combined with micro powder technology, usually 8-10 months. As the castable manufacturers and users continue to sum up their experience in the process of use, the process formula of the castable has been improved.
The ZrO2 component is added to the original process, so that the special kiln mouth castable has ZrO2 distribution in the aggregate, and the overall performance of the kiln mouth castable is improved. The addition of zircon has improved the density and bending resistance of the kiln mouth castable. In addition, thermal shock resistance and wear resistance are stronger.
Sintered mullite, silicon carbide, zircon fine powder, SiO2 fine powder, and alumina fine powder used in raw materials. The bonding agent is combined with CA70 and CA80 cement. Especially the special castable for kiln mouth, with the increase of zircon addition, the wear resistance is particularly good. But the ratio must be controlled appropriately, otherwise, microcracks will appear.
The ratio of different processes is different. The previous corundum mullite castables have good flexibility, but the wear resistance is not very good, and the service life is not very long. Later, many manufacturers improved the addition of silicon carbide to increase the wear resistance of the kiln mouth castable. The wear resistance of silicon carbide is good, and the use effect is also improved, but the service life of comprehensive improvement will increase to 10 months.
With the continuous improvement in the later period, the performance after adding zircon is more perfect. The use period will reach 12 months. But in the control, we must pay attention to the proportion of addition. A proper ratio not only improves the thermal shock resistance but also the phase change will help buffer thermal stress and inhibit the growth of large cracks. Adding too much or too little zircon will deteriorate the performance, reduce the thermal conductivity, and increase the thermal expansion coefficient.
In short, the addition of proportions in the improvement is very important. The fusion of other raw materials in the most appropriate proportion will make the service life of the special castable for the kiln mouth longer.
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