Two Questions and Answers about Refractory Castables Used in Furnace Lining

With the increase in the use temperature and service life of various high-temperature kilns and thermal equipment, refractory castables are widely used in production and use as unshaped refractory materials. In the modern era of rapid industrial technology, there are many types of refractory castables. Compared with refractory bricks, the advantages of using refractory castables are simple to process, energy-saving, low cost, and easy mechanized construction. It has been widely used in various types of thermal equipment such as cement, steel, glass, and electric power. As a result, the use of refractory castables in high-temperature kilns often encounters some problems. Experienced unshaped refractory castable manufacturers will take you to understand these problems and provide you with the most suitable refractory castable lining solution for your production needs.

Question 1: The operating temperature of the kiln is 1500℃, what refractory castable should be used?

When the temperature of the working part of the kiln is 1500℃, corundum castable should be selected according to the use temperature of the refractory castable. Many users do not understand but think that the price is high, so they choose general high-aluminum castables.

However, if the direct use temperature is 1500°C, the general high-aluminum castable is not acceptable. The brown corundum castable must be selected to meet the application requirements. There are also users who propose to use steel fiber castables, which is not acceptable. Because steel fibers begin to melt at temperatures above 1300°C. Therefore, steel fiber castables cannot be used.

Corundum Castable
Corundum Castable

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    However, some customers choose to use stainless steel. The answer given by refractory manufacturers is still no. Because the stainless steel used for the lining only serves as an anchor, it cannot resist high temperature and corrosion. The characteristics of corundum castable are the highest bulk density, lowest apparent porosity, high-temperature resistance, corrosion resistance, and thermal shock resistance. And at 1500℃, the characteristics of corundum castable can be fully reflected. If steel fiber castable is used, it cannot withstand the high temperature of 1500℃. The general high-aluminum castables can be used at a temperature of 1300℃-1400℃.

    Refractory castable manufacturers pointed out that if it is a different kiln, the working atmosphere inside the kiln is different and the degree of erosion is different, corundum wear-resistant castable or high-strength wear-resistant castable can also be selected. In this way, it is resistant to both high temperature and corrosion. For example, waste incinerators have low temperatures, but strong corrosion, sometimes with acid and alkali corrosion. At this time, the choice of corundum castable is not acceptable, the temperature is not high, and the corundum cannot be fully used. Wear-resistant castables with clean raw materials can be used to resist acid or alkali corrosion. Moreover, the price is lower than that of corundum castable, and it is also suitable for the special use of incinerators.

    In short, no matter what kind of refractory castable is selected, the appropriate refractory castable must be selected according to different kilns, different temperatures, and different degrees of erosion.

    Question 2: How much is a ton of corundum steel fiber refractory castable for the rotary kiln?

    Corundum steel fiber refractory castable is a high-quality refractory castable. It uses special grade bauxite clinker and sintered corundum as refractory aggregates and admixtures, and calcium aluminate cement as a binder. Unshaped refractory material mixed with a small amount of water reducing agent and a certain proportion of wear-resistant and heat-resistant steel fibers of different sizes and diameters using micro-powder technology. It is castable with good fluidity, high strength, good wear resistance, and good thermal shock resistance.

    Steel Fiber Reinforced Castable
    Steel Fiber Castable

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      The corundum steel fiber refractory castable has a good effect. Corundum steel fiber castables with different physical and chemical indicators are used in different industrial furnaces, such as steel-making electric furnaces, tundishes, heating furnaces, rotary kilns, and other thermal equipment. So, how much is a ton of corundum steel fiber refractory castable for the rotary kiln?

      Generally, the price of corundum steel fiber castable is about 6,500 yuan per ton. However, there are many factors affecting the price of castables, and the details need to be determined based on the actual kiln situation and the use of castables.

      The price of corundum steel fiber castable is a reference factor when customers purchase. But what you pay for is what you pay for. Refractory castables are different from other refractory products. Its quality is not only about the price, but also about the application. The better the effect of the application in high-temperature kilns, the more expensive it is. When purchasing high-quality corundum steel fiber refractory castables, it is best to provide refractory castable manufacturers with the working conditions of the furnace, such as operating temperature and service life. Then the refractory manufacturer will have a technical team to provide corresponding castable solutions to ensure the use of corundum steel fiber castables and calculate the cost of purchasing refractory castables.

      To learn more about refractory castables for furnace refractory linings, please continue to follow our blog. For the price of high-quality refractory castables, please contact us.

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        How to Solve the Phenomenon on the Surface of Refractory Castables Preforms

        Unshaped refractory castables and castable preforms have been widely used by more and more high-temperature industrial kilns due to their advantages of convenient, fast construction and low labor intensity. However, many enterprise users have found that refractory castables or preforms have found some abnormal phenomena during storage or maintenance, such as chalking, white hairs, and so on. So, how to solve the white hair and chalking on the surface of refractory castables preforms?

        Firstly, let’s understand how these phenomena are formed.

        In fact, these are caused by the contact of high-alumina cement hydration products in refractory castables with acid gases in the atmosphere. As the moisture in the castable evaporates, salt substances continue to migrate and precipitate to the surface, and then slowly aggravate the damage process of the refractory castable. We will analyze these phenomena today. Pulverization occurs during the storage of preforms made of cement-containing refractory castables. Some of them grow “white hair” on the surface, commonly known as white alkali, which causes the pulverization of the surface of the castable. In severe cases, the strength of the castable decreases.

        White-Hair and Chalking on the Surface of Refractory Castables and Preforms
        White-Hair and Chalking on the Surface of Refractory Castables Preforms

        Several Phenomena on the Surface of Refractory Castables after Construction

        Carbonation of Castables

        Carbonation of high-alumina refractory castables is often considered to be one of the main reasons that lead to the decrease of castable structure and spalling. The high-alumina cement-bonded refractory castable is exposed to the air, and the hydration products therein react with the CO2 gas in the air to undergo a carbonation reaction. In addition, refractory castables are more likely to undergo carbonation under high humidity conditions and compared with dense castables, lightweight castables with high water content are easier to pulverize. This shows that in the presence of water, the hydration product interacts with the CO2 acid gas, and the PH value of the liquid in the single pore of the phase drops sharply, which makes all the new hydration organisms in the refractory castable become unstable.

        Sulfation of Castables

        Compared with the carbonation of high-alumina cement hydration products, the sulfation phenomenon has not attracted enough attention from the construction party and the user. In the atmosphere, in addition to the CO2 acid gas, there are also SO2, H2S, and other gases, which also have a strong corrosive effect on the hydration products of the matrix part of the high alumina cement castable. Eventually, this lead to powdering and peeling of the castable.

        In addition to being sulphated by SO2 and H2S in the air, high-alumina cement hydrate may also interact with SO42- or H+ in the water source. As the activity and acidity of the two increase, the stability of the three high-alumina cement hydration products also decreases sharply.

        Salt Precipitation Phenomenon of Castable

        The salt precipitation phenomenon on the surface of refractory castables is another important factor that aggravates the structural damage of the castables. During the curing or natural drying process of refractory castable, some soluble carbonate, sulfate, chloride, phosphate, and other salt compounds will focus on the surface of refractory castable and crystallize with the evaporation of water. This phenomenon is often called salting out.

        As the water evaporates from the surface of the refractory castable, these ions migrate and aggregate with the water molecules from the inside to the surface of the castable, or react with acid gases in the air on the surface of the castable. The salts formed after the hydrate reaction are focused on the surface. Finally, these salt compounds crystallized out due to exceeding the solubility in water.

        In fact, all soluble salts containing crystal water include chloride, sulfate, carbonate, and so on. These salts all have the process of removing the crystal water, accompanied by the change of crystal form and volume change. These are some of the reasons that aggravate the pulverization, peeling, and lumps of the surface structure when the castable is cured in the air.

        Solutions to the Phenomenon after the Construction of Refractory Castables and Preforms

        • (1) Dry the castable as soon as possible after construction to remove water and eliminate the carrier of sodium salt in the cast, so that the alkali stays in the construction body and no longer migrates to the surface.
        • (2) If the construction conditions cannot be dried in time, the pouring material should be sealed and the surface should be covered with plastic film to prevent moisture from migrating to the surface with alkali.
        • (3) The refractory castable is made of refractory raw materials with low alkali content to increase the viscosity and fast hardening of the refractory castable. It can reduce the migration speed of sodium salt, strengthen quality management, and strictly control the amount of water added to the construction.
        Rongsheng Refractory Castable Manufacturer
        Rongsheng Refractory Castable Manufacturer

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          Rongsheng Refractory Castable Manufacturer

          Rongsheng is a refractory manufacturer with an environmentally-friendly and advanced unshaped refractory production line. Rongsheng’s unshaped refractory production line has an annual output of 80,000 tons. Our refractory products have been sold to more than 60 countries and regions all over the world. Our customers of refractory castables have a high degree of recognition of our product quality and a high rate of return orders. Our monolithic refractory products can be customized according to the customer’s specific furnace requirements. We have rich experience in the field of wear-resistant refractory castables and refractory plastic products. In addition, he has rich experience in prefabricated refractory castables on the roof of the furnace. For more information about monolithic refractories, please contact us.

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            What are the Lining of the Heating Furnace?

            The heating furnace is divided into furnace, fuel system, air supply system, smoke exhaust system, and cooling system. The furnace is a space composed of the furnace wall, the furnace top, and the furnace bottom, and different pouring materials are used for each part. Let us understand the refractory materials used in the lining of the heating furnace.

            Refractory Lining of the Heating Furnace
            Refractory Lining of the Heating Furnace

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              1. Low-cement castables are used to wrap the structure of water beam-columns. The column tube and the lower part of the supporting beam in the furnace are all made of low cement castables. Low-cement castables are also used in the low-temperature zone of the heating furnace, flue parts, and furnace body parts that do not exceed 1300°C.
              2. Self-leveling castables are used in the heating furnace where the structure is complicated and cannot be vibrated manually. The use temperature is 1500℃, which is characterized by good thermal shock resistance, high refractoriness, easy construction, and almost no need for vibration.
              3. Phosphate castables are suitable for heating furnace bottoms and other parts that are severely affected by material friction and hot air erosion. The operating temperature is between 1000-1600°C. It is a castable with phosphoric acid or phosphate as the binder and aluminum calcium cement and magnesia as the accelerator.
              4. Mullite castable. Because mullite refractory castable has high thermal shock resistance, erosion resistance, good erosion resistance, good volume stability, and high service temperature. It is generally used in key parts such as furnace walls, furnace roofs, and press beams.
              5. Anti-dry slag castable, suitable for the bottom of the heating furnace, and the place where iron oxide slag is deposited. The use temperature can reach 1600℃. Its main characteristics are high refractoriness, good thermal shock resistance, and good resistance to the corrosion of iron oxide slag in the heating furnace.
              6. Lightweight castable, suitable for heat insulation layer of the furnace wall, furnace roof, flue, etc. High-strength lightweight castables can also be used as working linings for smoke exhaust systems and hot air ducts. It is characterized by low bulk density, good thermal stability, low thermal conductivity, and certain refractoriness.
              7. Bauxite cement castable is a castable produced by mixing various refractory aggregates and powders in a certain proportion with aluminate cement as a cementing agent. It has the characteristics of fast solidification, high strength, thermal shock resistance, and slag resistance. It not only meets the refractory performance of the heating furnace body but also improves the construction performance of the furnace body.
              8. The advantage of fire-resistant plastic is that there are no gaps in the overall construction and good airtightness. The furnace lining uses a large number of plastic materials instead of castables and is mainly used for the top of the furnace.
              Low Cement Castable Refractory Material
              Low Cement Castable Refractory Material

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                What is the Meaning of the Refractory Castables Grades?

                The various castables used for the lining of the heating furnace have been introduced above. How to make a specific distinction between them? This introduces the definition of refractory castable grades. What is the meaning of refractory castable grades? It is usually used in combination with numbers and pinyin letters to distinguish the material, performance, and purpose of the castable. Refractory castable grades have refractory standards and the settings of different castable manufacturers. Next, we will learn about the types and grades of common refractory castables.

                Classification of Refractory Castables

                1. Classified by material, silicon castable, clay castable, high alumina castable, mullite castable, corundum castable, aluminum-magnesium castable, etc.

                2. According to the purpose, it can be divided into several types of castables for industrial furnaces, such as castables for steel rolling furnaces, castables for tapping channels, castables for mixing furnaces, and castables for cement kilns.

                3. According to the bulk density, it can be divided into light castable and heavy castable.

                4. According to its characteristics, it can be divided into refractory steel fiber reinforced castable, anti-skinning castable, low cement castable, high-strength castable, etc.

                Mullite castable price
                Mullite Refractory Castable with High-Quality

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                  Grades of Refractory Castables

                  1. Brands of silicon castables: rsg-70, rsg-60, rsg-50, etc. Among them, rs is the manufacturer of Rongsheng castables, G is the main material selected for castables is silicon, and the quantity is the silicon content.

                  2. Brand of castable clay: nn-45. Among them, the first n is clay as the binder, and the second n is the main material selected for the clay castable. The number is the main component content of the clay castable)

                  3. Grades of high-aluminum castables: nl-70, nl-60. Among them, n is clay as a binder, l is the main material selected for the castable is high aluminum material, and the quantity is the aluminum content of the high aluminum castable.

                  4, aluminum-magnesium castable grades: amc-70, amc-80, etc. Among them, a, m, and C are the English initials of alumina, magnesia, and castable. The number is the content of the main raw materials selected for aluminum-magnesium castables.

                  1. Castable grades for steel rolling heating furnace: zj-42, zj-60, zjs-65, etc. Among them, Z is the steel rolling heating furnace, J is the castable, and s is a part of the water-cooled tube of the heating furnace. The number is the main material content selected for the castable of the steel rolling heating furnace.

                  6. Grades of castable for iron ditch: Asc-1, Asc-2, Asc-3. Among them, a, s, and C are the English initials of alumina, silicon carbide, and carbon. The number is only used to distinguish the castable grade.

                  The above is the introduction of a refractory castable brand. Hope you can understand the meaning of the casting brand after reading it. There are many brands of refractory castables, some are set by the castable manufacturers themselves, and some are set in accordance with refractory standards. No matter what way the refractory castable is named, it is to distinguish the material, grade, performance, and purpose of the refractory castable.

                  Rongsheng Refractory Castable Manufacturer
                  Rongsheng Refractory Castable Manufacturer

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                    Rongsheng Refractory Castables Manufacturer

                    Rongsheng refractory castable manufacturer has an advanced and fully automatic unshaped refractory castable production line with an annual output of 80,000 tons. Rongsheng has provided high-quality refractory castables, mullite castables, self-flowing refractory castables, wear-resistant refractory plastics, corundum mullite refractory plastics, etc. for many turnkey projects. For more information about the refractory castables Lining of the Heating Furnace, Rongsheng’s monolithic refractory products, and Rongsheng refractory manufacturers, please contact us. We will provide you with services according to your specific needs.

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