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Lightweight refractory materials, as the main material for the lining, insulation layer and other parts of high-temperature kilns and high-temperature equipment, have the characteristics of low bulk density, low thermal conductivity and compressive strength, and high apparent porosity compared to dense refractory materials. They can effectively prevent heat flow from being transmitted outward through the enclosing structure and reduce heat loss of high-temperature equipment such as kilns.
The bulk density of lightweight refractory materials is very low, generally between 0.6 and 1.2 g/cm3; while the bulk density of semi-lightweight materials is generally between 1.2 and 1.8 g/cm3. As one of the main factors for measuring lightweight materials, in the production of lightweight refractory materials, the bulk density of the material is generally reduced as much as possible while meeting the use intensity of kilns or high-temperature equipment.
Thermal conductivity is one of the main factors to measure the thermal insulation effect of refractory materials. Under the condition of ensuring the strength of material use, the lowest possible thermal conductivity is conducive to maintaining the heat flow of kilns or high-temperature equipment and reducing heat loss. Lightweight refractory materials have a large number of pores, and the gas in the pores has a good thermal insulation effect, which makes the heating effect obvious and the thermal conductivity is low. Whether the pores inside the product are small and uniform directly determines the thermal conductivity and use strength of the material. Generally, the smaller the pore diameter, the better the thermal conductivity of the product. The thermal conductivity of lightweight refractory materials is relatively small, mostly less than 1.0W/(k·m)(600℃x3h), while the thermal conductivity of semi-lightweight refractory materials is generally less than 1.26W/(k·m)(600℃x3h).
Lightweight refractory materials have a large apparent porosity and low bulk density, and there is no effective and dense connection between the internal structure crystals. Therefore, compared with dense refractory materials, their compressive strength is relatively low, and their wear resistance and erosion resistance are poor. In daily use, they are generally not used as a working layer but placed behind the working layer as an insulation layer. Therefore, on the basis of ensuring the use strength (for load-bearing), the bulk density and thermal conductivity are generally reduced as much as possible.
For lightweight thermal insulation refractory materials, pores mainly come from external pore-forming agents, which are formed through foaming, burning or reaction. Generally, they can be divided into three types: (1) open pores; (2) closed pores; (3) through pores. Among them, through pores are the most harmful to the material, while closed pores have better insulation effect.
Generally speaking, the apparent porosity of lightweight thermal insulation refractory materials is greater than 45%, and when preparing lightweight materials with a volume density of about 0.5g/cm3, the apparent porosity can even be as high as 80%.
The above characteristics of lightweight refractory materials can help us better use lightweight refractory materials, thereby improving our production efficiency and economic benefits.
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