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Application Optimization of Mullite Light Bricks
Mullite polylightweight bricks are a high-performance refractory material with a wide range of applications. In the insulation layer, their excellent thermal insulation properties effectively reduce heat loss and contribute to energy savings. They also perform well in the less corrosive working layer of the furnace lining, the area in direct contact with the flame. For example, JM23, 26, 28, 30, and 32 bricks can all be used in neutral furnace lining environments with direct flame contact. JM30 and 32 bricks, like alumina hollow sphere bricks, are particularly suitable for high-temperature applications. Not only do they provide excellent insulation, their lightweight also makes them particularly effective in lightweight kilns.
Clay Lightweight Bricks and Mullite Insulation Bricks
Currently, the main brick materials used for insulation layers on the market include clay lightweight bricks and high-alumina lightweight bricks, as well as new micro-nano insulation bricks. Clay lightweight bricks are the most widely used because their thermal conductivity is similar to that of poly-lightweight mullite bricks and, at appropriate temperatures, can meet insulation requirements by selecting lightweight bricks with the appropriate density.
However, as a high-end insulation material, poly-lightweight mullite bricks can achieve even greater insulation and energy savings at higher furnace temperatures by selecting bricks with varying bulk densities and operating temperatures. In some specialized furnace linings, especially where low external furnace temperatures are required, mullite poly-lightweight bricks can be used for insulation layers and in direct flame contact.
Application Limitations of Mullite Poly Lightweight Bricks in Different Furnace Lining Environments
Mullite poly lightweight bricks are not suitable for all furnace lining environments. In the working layer of a furnace lining exposed to strong acids and alkalis, poly lightweight bricks lack strength and are easily eroded by the corrosive slag, making them unsuitable for use. In contrast, hollow alumina sphere bricks can function normally in such environments.
Recommendations for the Suitable Selection of Mullite Poly Lightweight Bricks
Based on current market usage, mullite poly lightweight bricks are primarily used for insulation. When the external furnace shell temperature requirement is low and the temperature and environmental conditions are suitable, mullite poly lightweight bricks can be used. When using a multi-layer masonry system, JM23 bricks can be used near the furnace shell, while JM28, 30, or 32 bricks can be used in areas exposed to the flame. This layered selection approach fully utilizes the advantages of mullite poly lightweight bricks, meeting the needs of different areas and achieving both insulation and fire resistance.
Types and Characteristics of Mullite Refractory Bricks
Mullite refractory bricks are a high-alumina refractory material with mullite as the primary crystalline phase. They offer high refractoriness and excellent thermal shock resistance. Common mullite refractory bricks include sintered mullite bricks, fused mullite bricks, zirconium mullite bricks, corundum mullite bricks, and lightweight mullite insulation bricks. Their prices vary depending on their physical and chemical properties and composition. So, what are their characteristics?
Sintered Mullite Brick: The main raw material for sintered mullite brick is high-alumina bauxite, with a small amount of clay or raw bauxite added as a binder. After high-pressure molding, it is fired at high temperature. Its refractory temperature can reach 1790°C. The softening-under-load onset temperature is 1600-1700°C. The apparent porosity is 20.88%, and the bulk density is 2.61g/cm³. The room-temperature compressive strength is 84.4MPa at 1550°C. The 50-hour high-temperature creep rate is 0.796%. Its refractoriness is primarily determined by the alumina content.
Fused Mullite Brick: This brick is made from high-alumina, industrial alumina, and refractory clay, with charcoal or coke fines added as a reducing agent. After molding, it is manufactured using a reduction fusion process. Its Al₂O₃ content is approximately 72-74%, the apparent porosity is approximately 17%, and the bulk density is 2.58g/cm³. Its room-temperature compressive strength is approximately 39.2 MPa, and its softening temperature under load of 0.2 MPa is 1620-1660°C. Compared to sintered mullite bricks, it offers improved thermal shock resistance, a low thermal expansion coefficient, and strong resistance to molten glass corrosion.
Zirconium Mullite Brick: Zirconium mullite bricks incorporate zirconium dioxide into mullite bricks to improve their chemical resistance, thermal shock stability, and reduce their expansion coefficient. They are generally produced by the electric fusion process, but can also be produced by sintering.
Corundum Mullite Brick: Corundum mullite bricks are high-alumina refractory products with corundum and mullite as the primary crystalline phases. Its refractoriness can reach approximately 1800°C, with an Al₂O₃ content of 72%-90%, an apparent porosity of 19%, a room-temperature compressive strength exceeding 55 MPa, and a refractoriness under load exceeding 1700°C. It features high refractoriness, chemical and oxidation resistance, excellent thermal stability, and high room-temperature compressive strength. It is widely used in various high-temperature kiln linings and thermal insulation layers.
Lightweight Mullite Insulation Bricks: Lightweight mullite insulation bricks, also known as mullite polylight bricks or mullite insulation bricks, have low thermal conductivity and low thermal conductivity. They can reduce the volume of masonry within the kiln, reducing overall weight, shortening heating time and ensuring a uniform furnace temperature, thereby reducing heat loss and saving energy. Its refractoriness temperature exceeds 1500°C. Currently, the most common grades, depending on the alumina content, are JM23, JM26, and JM28, with common bulk densities of 0.6, 0.8, and 1.0. Depending on the bulk density and alumina content, their refractory temperature and thermal insulation properties vary.
Mullite, a component of mullite refractory bricks, is widely used due to its excellent high-temperature mechanical properties and chemical stability. Its low thermal conductivity and low heat flux give refractory products excellent thermal insulation properties, while also effectively reducing furnace weight and saving energy. These common mullite refractory bricks are widely used in applications such as hot blast furnace roofs, blast furnace bodies and floors, glass kiln superstructures, material channels and linings, and as thermal insulation layers in firing and refining kilns, heating devices, and other furnace linings.
