Lightweight refractory material, also known as thermal insulation refractory and thermal insulation material, is a refractory material with high porosity, low volume density and low thermal conductivity. It includes heat insulating refractory products, refractory fibre and refractory fibre products. Light refractory material is a multiphase structure of crystalline phase, amorphous phase and gas phase. Most of the solid phase is a non metal oxide, relatively speaking, the thermal conductivity of these non metal oxide itself is very high, but with a high degree of fire resistance, can not afford the heat insulation effect. Because the gas exists in the solid phase of the gas hole, gas thermal conductivity is very low, the air at 0 degrees when the coefficient of thermal conductivity is 0.023W/m, the temperature coefficient of heat conduction is less than 0.03W/m, 500 degrees Celsius is 0.06W/m. Therefore, the light refractory material with high porosity and high porosity which is composed of solid phase and gas has good heat insulation effect, and the dispersed material or fibrous material filled with gas has good heat insulation effect.

One, the main characteristics of lightweight refractories

      As one kind of refractory material, the lightweight refractory has some high temperature mechanical properties and good volume stability, which is the necessary material for all kinds of high temperature thermal equipment. Compared with the dense refractory, the material has a high porosity, low volume density and good heat insulation performance, which has a good effect on heat shielding. Therefore, the main characteristics of lightweight refractories are:

1, the apparent porosity is high

      One of the main properties of lightweight refractory materials is the apparent porosity. The air hole is formed by the air hole of the refractory material and the pore formed among the particles. Can be divided into three types: closed WIP not and communicated with outside the closed pores; closed at one end, and the other end is communicated with the outside of the open pores; through internal product, at both ends and communicated with the outside through pores. The ratio of the gas volume and the total volume of the material is the significant porosity. The apparent porosity of the dense refractory is generally less than 20%, and the porosity of the lightweight refractory material is very high, which is generally 65~78%.

2, small volume density

      Volume density is the ratio of the mass to the total volume of the dried product. Lightweight refractory material volume density is very small, not more than 1.3g/cm no, the industry commonly used lightweight refractory material volume density 0.5~1.0g/cm University. The volume density of refractory material can reflect the number of significant porosity in the product. It is a means to judge the degree of sintering of products, which indicates the density of refractory materials. In order to increase the apparent porosity and reduce the thermal conductivity, the volume density of the product should be reduced in order to improve the production of the lightweight refractory material.

3, low coefficient of thermal conductivity

      The physical meaning of the thermal conductivity is: the heat of the vertical area per unit of time under the unit temperature gradient. It is an important performance index of the quality of light refractory material, and it is also an important index in thermal design. It indirectly reflects the apparent porosity and bulk density of the product. For refractory products, the lower the coefficient of thermal conductivity, the greater the apparent porosity. The thermal conductivity of the lightweight refractory is very small, mostly less than 1.26W/m.

4, low compressive strength

      Due to the large porosity and low volume density, the light refractory material has not formed a tight connection between the crystals. Therefore, compared with the dense refractory material, the pressure resistance is low, and the wear resistance is poor.

      Due to the low thermal conductivity, the heat loss of industrial furnace brick masonry can be reduced, the fuel consumption is saved, and the production efficiency is improved. However, due to the large porosity of the products, loose tissue structure, poor resistance to chemical erosion, lightweight refractories can only be used for thermal insulation layer, lining and insulation layer and other parts. While the general should not be used in direct contact with the furnace hearth and large load-bearing parts.

      In summary, the characteristics of light refractory material marks that it is a thermal equipment and the necessary material to prevent heat loss. With industrial development and scientific and technological progress and advanced equipment for large, continuous and efficient production, the development of lightweight refractory material toward the use of high temperature, low heat conduction rate, erosion resistant performance, high strength. With the increasing shortage of energy in the global scope, the light refractory material is more prominent in energy saving.

Two, lightweight refractory material pore forming process

      The formation of pores is a key link in the process of producing lightweight refractory materials. The size, shape, number and distribution of the pores directly affect the quality of the product. A lot of methods to form pores, mainly used in the production of refractory materials in China, chemical method, foam and fuel to join the law.

1, chemical method

      Chemical method is to add some of the material can be produced by chemical reaction of the bubble. Because the reaction is rapid, the bubble formation is not suitable for the control. According to the process requirement, a proper amount of inhibitor is added.

2, foam method

      Bubble method is to add a foaming agent in the mud, similar to chemical method, bubble method of bubble stability is not good, to join the fixed agent control.

      So-called kyropoulos method for the production of light brick is to the surface tension of small substances to be added to the slurry to foam, poured into the model, and then the same model with dry, then under a certain temperature sintering, then shaping process is the product, most clay, high alumina light goods are available this method production.

3, adding fuel to the law

      Fuel adding method is to add in the mud can burn material. These additives are burnt out when the refractory materials are synthesized at high temperature, and the air holes are produced. However, this method has the disadvantages of low strength, easy deformation, and so on. It is needed to control the synthesis process to overcome the defects.

      When using the method of adding fuel to the fuel, the fuel additive should have high volatility and combustible; it should be able to generate small uniform pores; it should also have a smaller elasticity, so that it can be easily formed.

Three, the application of lightweight refractories

       As an important part of the furnace, boiler, thermal container and other equipment, the light refractory material is widely used in industry. Due to the lightweight refractory material porosity high to make it in high efficiency and reduce heat loss occupies the position can not be replaced, but the product significantly porosity pitched chemical erosion performance is poor, people can not directly and fuel contact. So far, light refractory material is still used in the insulation layer of high temperature equipment.