Alkaline Castables and Magnesia Refractory Castables for Rotary Kilns

As a component part of the kiln body, the cement kiln mouth is the most vulnerable part of the cement kiln and the weakest link in the whole kiln lining. The kiln mouth has the shortest service life of the refractories used in cement kilns. When the refractory material in this part is corroded, it will often cause serious deformation of the kiln mouth shell, or even crack. Finally, the cylinder has to be replaced, which seriously affects normal production and brings great economic losses to the enterprise. Alkaline castable magnesia refractory castables for rotary kilns and new alkali-resistant castables, compared with traditional refractory materials, can increase the service life of the kiln mouth by more than double (up to 180 days or more). It has broad promotion prospects and obvious economic benefits.

Magnesia Refractory Castables
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    Alkaline castable magnesia refractory castable for rotary kiln

    Magnesia refractory castable is made of fused magnesia or sintered magnesia aggregate and fine powder. The binder uses periclase cement, magnesium chloride, magnesium sulfate, water glass, polyphosphate, etc.

    • (1) The magnesia castable with periclase cement as the binder has the characteristics of high purity, small line change after burning, and high load softening temperature.
    • (2) Magnesium castables using water glass as a binder have the advantages of high strength, and strong corrosion resistance to alkali and sodium salt melts.
    • (3) The magnesium castable combined with polyphosphate has the characteristics of high load softening temperature, high strength, and excellent thermal shock resistance.

    What is the composition of magnesia refractory castable?

    Magnesia refractory castable is prepared from fused magnesia or sintered magnesia aggregate and its fine powder. The binder uses periclase cement, magnesium chloride, magnesium sulfate, water glass, polyphosphate, etc. The magnesia refractory casting material combined with periclase cement has the advantages of high purity, a small change of line after burning, and high softening point under load. However, as the heat treatment temperature increases, especially between 400 and 1200 °C, the cementation will be lost due to the dehydration of the magnesium hydroxide generated by the hydration of magnesia. The combination of refractory aggregate and powder is very loose, and the solid phase reaction is very weak, resulting in a sharp drop in the strength of the refractory castable. It is prone to loosening and peeling.

    Magnesia refractory castables using water glass as a binder have the advantages of high strength, corrosion resistance to alkali and sodium salt melts, etc. However, due to the use of water glass as a binder, a large amount of Na2O (or K2O) and SiO2 are brought in. Therefore, the refractoriness and load softening point of magnesia refractory castables are greatly reduced, thereby limiting the maximum use temperature of water glass bonded castables.

    The magnesia refractory castable combined with polyphosphate has the advantages of high strength after firing, a small decrease in strength with the increase of heat treatment temperature, high softening point under load, and good thermal shock stability. However, at high temperatures (above 1400°C), the strength of magnesium castables decreases due to the large amount of volatilization of P2O5. In general, sodium polyphosphate is often used as a binder in magnesium castables, such as sodium tripolyphosphate, sodium hexametaphosphate or sodium polyphosphate. The degree of polymerization of polyphosphate and the content of P2O5 has a great influence on the strength of castables. When the average degree of polymerization of polyphosphate is 24, the castable has the highest strength.

    In addition, in order to improve the high-temperature strength of magnesia refractory castables, an appropriate amount of calcium-containing materials (such as calcium carbonate, etc.) is added to the components to form Na2O2CaOP2O5 phases with high bonding strength and stable existence at high temperatures. However, no matter what kind of binder is used, it is difficult to overcome the problem of easy hydration of magnesium refractory castables and the phenomenon of cracks in the drying process. For this reason, the method of adding an appropriate amount of silicon oxide ultrafine powder can overcome the problem of hydration.

    Magnesia Refractory Castable for Rotary Kiln
    Magnesia Refractory Castable for Rotary Kiln

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      Mixing ratio and properties of magnesia refractory castable

      Magnesia refractory castables usually use sintered and fused magnesia as refractory aggregate and powder. Its particle gradation is 5~2.5mm, 33%; 2.5~1.2mm, 1.2~0.6mm, 25%; 0.6~0.15mm; magnesia powder fineness <0.09mm is greater than 85%. Sodium hexametaphosphate solution with a concentration of 30% or an equivalent concentration of 4N is used as a binder, and aluminate cement is used as a coagulant. Some are mixed with a sintering machine, such as iron phosphorus or clay powder. The preparation process is to mix the refractory aggregate with two-thirds of the sodium hexametaphosphate solution, and then add the refractory powder after the surface of the aggregate is completely wet, and stir evenly. Finally, add the remaining sodium hexametaphosphate solution and continue to stir for 1-2 minutes; after vibration molding, it should be cured naturally for 3 days without water. The ambient temperature should not be lower than 10°C, the higher the better.

      The refractoriness of magnesia refractory castables is >1830°C, and the load softening temperature of 4% deformation is greater than 1400°C. The temperature of fused magnesia aggregate can reach 1520°C; the drying bulk density is larger and the apparent porosity is smaller. The use of aluminate cement coagulant does not reduce the refractoriness but increases the load-softening temperature. At the same time, the compressive strength after firing at 1000°C increased from 19.1MPa to 26.5~34.8MPa, which was caused by the formation of Na2O·2CaO·P2O5 minerals. From the perspective of strength change characteristics, the medium temperature strength has a large decrease, but the absolute value is still greater than 25MPa. Therefore, it does not affect the use of magnesia refractory castables. The reason for the decrease in strength can be seen from the petrographic analysis, which is caused by the change in the structure of sodium hexametaphosphate during the heating process and the lack of sintering of the base material.

      The relationship between concentration and strength of sodium hexametaphosphate solution. With the increase of its concentration, the compressive strength after burning at 1000°C is peak-shaped, that is, when the concentration of sodium hexametaphosphate solution is 23%~30%, the strength is the best, which can reach more than 30MPa. When preparing sodium hexametaphosphate refractory castable, its concentration should be selected as 25%~30%.

      In alkaline refractory castables, under the premise of ensuring the workability of the mixture, the amount of sodium hexametaphosphate solution should be used as little as possible to ensure its high-temperature performance. In addition, the type of refractory aggregate, particle gradation, amount of bone powder, type and amount of aluminate cement, etc. also affect the performance of refractory castables and should be selected reasonably.

      Rongsheng Refractory Castable Manufacturer
      Rongsheng Refractory Castable Manufacturer

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        Rotary kiln refractory castable manufacturer

        Rotary kiln refractory castable manufacturer is a powerful manufacturer and seller of refractory castables. Rongsheng’s monolithic refractory castable production line has an annual output of 80,000 tons. Moreover, it is equipped with an advanced and environmentally friendly fully automatic production environment and production equipment. Our production line has served the supply of monolithic refractories for many turnkey projects. And received praise from customers. If you are looking for a manufacturer of monolithic refractory materials and buy rotary kiln refractory castables, please try to contact us. We will provide you with the most suitable refractory castable products according to your specific production needs.

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          Solutions for Aluminum-Magnesium Castables in Use

          Alumina Magnesite Refractory Castable is a refractory castable with corundum as the aggregate, spinel and corundum powder as the matrix and pure calcium aluminate cement as the binder. Its chemical composition is Al2O3 89%~93%, MgO 5%~8%. It has good corrosion resistance and slag penetration resistance and can be used as a large ladle lining for continuous casting.

          Alumina Magnesia Refractory Castable
          Alumina Magnesia Refractory Castable

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            Application of aluminum-magnesium refractory castable

            Aluminum-magnesium refractory castables have been widely used in ladles for medium and small die-casting. The average package age is 60 to 80 times. Compared with clay ladle bricks, the refractory material consumption per ton of steel is reduced by about 70%.

            The raw materials of aluminum-magnesium castables for ladles are basically the same as that of aluminum-magnesium refractory ramming materials. In order to obtain normal temperature strength, sodium fluorosilicate should be added as coagulant. The load softening temperature of the ladle aluminum-magnesium castable is low, which is due to the combination of some low-baking substances formed by adding magnesia powder and the joint action of water glass and sodium fluorosilicate.

            The solution to cracks in aluminum-magnesium castables during use

            Aluminum-magnesium castables crack during use, which reduces the service life. The specific manifestation is: when the ladle is used for 5 heats, cracks begin to appear on the inner wall of the ladle, covering the entire ladle wall. As the number of uses increases, the cracks become deeper and wider. When more than 20 furnaces were used, they had to be forced to stop using them. In order to solve the problem of castable cracks, the following methods have been tried.

            • (1) Replace the bauxite clinker calcined by the shaft kiln with the bauxite calcined by the downdraft kiln, so that the sinterability and bulk density of the bauxite are increased. The theory was that this might reduce volume shrinkage caused by incomplete calcination of alumina and re-sintering during use, but without success.
            • (2) It is believed that the cracks are related to the total amount of fine powder in the castable. Try to reduce the fine powder in the castable to less than 30% (mass fraction), the lowest to 25%. Didn’t solve the problem either.
            • (3) Start to solve the crack from the chemical reaction. Because Al2O3 and MgO can generate aluminum-magnesium spinel under high temperature, accompanied by large volume expansion. After a series of experiments, adjusting the ratio of Al2O3/MgO did not achieve satisfactory results. Even when the MgO content is too high, peeling occurs instead.

            Solution: Finally, the following method was adopted to basically solve this problem.

            • (1) The upper limit of the aggregate particle size was raised from 15 mm to 5 mm, of which 20-25 mm accounted for 7.2% (mass fraction) of the total. This is due to the existence of super-large particles, which not only act as a skeleton, but also can change the direction of long cracks, helping to prevent the expansion of internal cracks.
            • (2) Add zircon powder into the matrix. This zircon powder is produced in Australia, and the ZrO2 content is about 66%. Since ZrO2 itself has a high melting point, it can absorb CaO in slag during use to generate CaZrO3 with high melting point and high corrosion resistance, which can close pores and cracks and strengthen the matrix. At the same time, due to the existence of zircon, micro-crack structures can also be formed in the castable, improving the high-temperature performance of the castable.
            • (3) Reduce the amount of active silica fume powder as much as possible. Since the quality of silica fume powder is unstable, if the amount added is large, there will be many impurities brought in, which is unfavorable for use. It is better to control the amount of silica fume in the castable below 1.5% (mass fraction).
            • (4) When pouring, it is also critical to strictly control the amount of water added and ensure uniform vibration.

            Rongsheng Refractory Castable Manufacturer

            Rongsheng refractory castable manufacturer is a powerful monolithic refractory manufacturer. Rongsheng Environmental Protection’s advanced fully automatic monolithic refractory production line has an annual output of 80,000 tons. Provide high-quality monolithic refractory products for thermal equipment of various furnace structures such as circulating fluidized bed boilers, gasification furnaces, fluidized furnaces, and waste incinerators. Our refractory products have been sold to more than 70 countries all over the world, such as South Africa, the Philippines, Chile, Malaysia, Indonesia, Vietnam, Kuwait, Turkey, Zambia, Peru, Mexico, Qatar, Egypt, Russia, Kazakhstan, etc. To purchase high-quality aluminum-magnesium refractory castables and get free refractory castable lining configuration solutions, please contact us. We will provide you with the configuration of refractory lining material that best suits your production needs.

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              Differences between Dense Castable Refractory and Lightweight Refractory Castable

              What are the commonly used refractory castables? What is the difference between dense castables refractory and lightweight refractory castables? Castable refractory, also known as refractory castable, is an unshaped refractory material, also called monolithic refractory castable. The refractory castable is easy to construct and has good integrity. It can be used for the lining of various industrial kilns and can also be used to manufacture prefabricated parts.

              Lightweight Insulation Castable
              Lightweight Insulation Castable
              High-Alumina Refractory Castables Manufacturer
              High-Alumina Refractory Castables – Dense Refractory Castable

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                Classification of Commonly Used Refractory Castables

                There are many types of refractory castables, which can be distinguished according to different dimensions.

                • 1) According to the characteristics of refractory castables, they can be divided into high-strength wear-resistant castables, high-temperature-resistant castables, low-cement castables, steel fiber castables, acid-resistant, and heat-resistant castables, etc.
                • 2) According to refractory raw materials, it is divided into clay castable, high alumina castable, silicon castable, mullite castable, corundum castable, silicon carbide castable, etc.
                • 3). According to the applicable industrial kiln environment, including aluminum-silicon carbide castables for ladle ditch, aluminum-magnesium spinel castables for ladle, etc.
                • 4) According to the density, it is divided into lightweight castables and dense castables refractory.
                • 5) According to the composition of the binder, organically bonded castables and inorganic bonded castables, such as resin bonded castables and cement bonded castables;
                • 6). According to chemical properties, refractory castables can be divided into acid-resistant castables, neutral castables, and alkali-resistant castables.
                High-Quality High Alumina Castable of Rongsheng
                High-Quality High Alumina Castable of Rongsheng

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                  What is the difference between dense castables refractory and lightweight insulation castables?

                  1. Analyze the difference between dense castables refractory and lightweight insulation castables. The main difference between dense refractory castables and lightweight castables is the difference in bulk density. Lightweight castables with a density lower than 1.6 and dense castables with a density higher than 1.8.
                  2. The characteristics of dense castables differ from lightweight insulating castables. Dense castables have high-temperature resistance, erosion resistance, erosion resistance, thermal shock resistance, spalling resistance, etc. Lightweight castables have low thermal conductivity and a good thermal insulation effect.
                  3. Dense refractory castables and lightweight insulating castables are also used differently, that is, they are used in different environments. The dense refractory castables are wear-resistant, high-temperature-resistant, and corrosion-resistant, and are used in kilns with harsh environments. Lightweight castables are generally used for heat insulation layers to avoid heat loss from the kiln and have the effect of heat insulation. And because the kiln skin temperature is low, fuel can be saved.
                  4. The raw materials used for dense castables and lightweight castables are also different. Bauxite particles and powders with high density are generally used for heavy castables, and materials with low specific gravity such as floating beads and alumina hollow spheres are used as raw materials for lightweight castables.
                  5. The amount of water added to heavy castables and light castables is different, and the amount of water added to lightweight castables is larger than that of dense castables. Because lightweight castables have higher water absorption than dense castables.
                  6. The addition of binders for heavy castables and light castables is different. Lightweight castables are added more than heavyweight castable binders, the purpose of which is to increase the initial strength of lightweight castables.
                  Lightweight Insulating Castable
                  Lightweight Insulating Castable

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                    How to choose refractory castable?

                    Heavy castables and light castables are selected according to the characteristics of the castables. Dense refractory castables can exert the maximum performance of castables at different positions, different temperatures, and different degrees of erosion in the kiln, and different castables are used. Lightweight castables are made of materials with different bulk densities according to different kilns and different temperature requirements to play the role of heat insulation.

                    Rongsheng Refractory Castable Manufacturer
                    Rongsheng Refractory Castable Manufacturer

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                      Rongsheng refractory castable manufacturer

                      Castable is a kind of amorphous refractory material that does not need to be formed and has fluidity. It is composed of aggregates, powders, and binders according to technological proportions. Under certain conditions, it can replace the refractory brick products with complex shapes and a high degree of irregularity. It has the advantages of convenient construction, a short construction period, and light labor intensity. For more product information about refractory castables, please contact Rongsheng refractory castable manufacturer. Based on your specific needs, we will provide you with the product that best suits your thermal kiln production needs. Contact us for free samples and quotes.

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