polycrystalline mullite fiberWhat is the scope of application?

　　polycrystalline mullite fiberThe product can be used for a long time for high temperature thermal equipment below 1600 such as silicon carbide electric furnace, silicon molybdenum electric furnace, various steel heating furnace, mechanical forging furnace, etc., which greatly improves the thermal efficiency of the equipment, greatly saves energy, improves productivity, and improves product quality.

Can be applied to a variety of high temperature industrial furnace insulation materials. Ceramic kiln machine and metallurgical heating furnace; heat treatment furnace and other industrial furnace opening lining; high temperature fire flame; kiln door, kiln car, expansion joint and other insulation materials; glass furnace insulation.

　　polycrystalline mullite fiber(PMF) is a new type of ultra-light high-temperature refractory fiber at home and abroad. It is one of the all-Al2O3-SiO2 ceramic fibers. The operating temperature is 1500-1700, which is 200-400 higher than that of glass fiber. So how to evaluate the quality of polycrystalline mullite fiber?

1. chemical composition

According to the development of polycrystalline mullite fiber production, foreign countries have gradually replaced natural raw materials with high-purity synthetic raw materials in order to improve the purity of the chemical composition of polycrystalline mullite fiber products.

In the composition of 1 grade of polycrystalline mullite fiber products, the requirements of Al2O3, SiO2, ZrO2 and other high temperature oxides are guaranteed. Example: Al2O3 SiO2 = 99% in high purity (1100C) and high aluminum (1200C) fiber products, SIO 2 O3 Zro 2 > 99 in zirconium containing (> 1300C) products

2 Fe2O3, Na2O, K2O, TiO2, MgO, CaO. harmful impurities below the specified content.

To a certain extent, it is more important to strictly control the content of harmful impurities in the fiber product than to ensure the high temperature oxide content in the chemical composition of the fiber product. Amorphous fibers are heated to crystallize and grain growth degrades fiber properties until the fiber structure is lost. High impurity content can not only promote the formation and crystallization of crystallization nuclei, but also reduce the liquid phase temperature and vitreous viscosity, and promote grain growth. Strictly controlling the content of harmful impurities is an important link to improve the performance of fiber products, especially the heat resistance. Impurities play a spontaneous role in the crystallization process, accelerate the speed of particle and promote crystallization. The sintering and polycrystalline of impurities in the fiber contact increase the grain growth rate, make the grains thicker, and increase the line shrinkage rate, which is an important reason for the decline of fiber performance and service life. (David, Exposure of the North).

Two: increase the hot line shrinkage rate

Hotline shrinkage is a measurepolycrystalline mullite fiberThe index of heat resistance of dimensional products, the international unified use of polycrystalline mullite fiber products, heated to a specific temperature under no-load state, and the high-temperature linear shrinkage rate of 24 hours of heat preservation indicates heat resistance. Only the linear shrinkage value measured in accordance with this regulation can truly reflect the heat resistance of the product, that is, the continuous use temperature of the product. At this temperature, the amorphous fiber is crystallized, the particles will not grow too large, the performance is stable and elastic. According to Japanese opinion, if the grain size is smaller than the fiber diameter, the fiber properties do not change qualitatively. Third: The thermal conductivity is an index to evaluate the thermal insulation performance of polycrystalline mullite fiber, and it is also an important parameter in the design of kiln wall structure. How to accurately determine the thermal conductivity value is the key to determine the rationality of the lining structure design. The thermal conductivity depends on the structure of the fiber product, bulk density, temperature, ambient atmosphere, humidity and other factors.

Among various substances, the thermal conductivity of gas is very low, and the thermal conductivity of air at room temperature is 0.025 W/M.K. In industry, gases are widely used as thermal insulators. But only in the case of gas does not cause convection, there is excellent insulation performance.