Classification of thermal insulation refractory materials

Thermal insulation materials (also known as thermal insulation materials) refer to materials or material composites with significant resistance to heat flow. The porosity of thermal insulation refractories is generally above 45%, and the bulk density is low (not higher than 1.5g/cm3), Materials with low thermal conductivity (≤1.0 w·m-1k-1). There are many kinds of thermal insulation materials, which can generally be classified according to material, use temperature, shape and structure.

(1) According to its internal organizational structure, it can be divided into three categories:

One is porous particles, the more common ones are expanded vermiculite and expanded perlite; the other is porous fibers: the common ones are ultra-fine glass wool, asbestos and mineral rock wool. This type of material has good heat resistance and low thermal conductivity, and is usually a single or several composite fiber cloth or felt made of inorganic fibers, which has the characteristics of low thermal conductivity and good temperature resistance. However, glass wool and mineral wool samples are easy to absorb water during application, and produce fiber dust in the air, which is harmful to human health and seriously hinders their promotion and application. In the 1980s, fibrous thermal insulation materials had a large market share, and were mainly used in building wall insulation due to their excellent thermal insulation and fire resistance properties. Due to the many outstanding advantages of inorganic fibers, such as light weight, low thermal conductivity and high heat capacity, they have been widely used in thermal protection engineering of various advanced weapons in recent years. At present, the inorganic fibers that can be mass-produced include aluminum silicate fibers, glass fibers, quartz fibers, zirconia fibers, carbon fibers and silicon carbide fibers. The third is foaming type: including inorganic type, organic type and organic-inorganic hybrid type. Common inorganic types include foam glass and cement. In the 1980s, due to the advantages of low bulk density, low thermal conductivity, high refractoriness and excellent mechanical properties of calcium silicate samples, it was recognized as the best thermal insulation material among hard block materials. . However, in the 1990s, due to the asbestos contained in its samples, it was gradually replaced by pulp fibers. However, pulp fibers are not resistant to high temperatures, which significantly affects their high-temperature applications. Organics include phenolic foam, polyethylene foam and polyurethane foam, etc. This type of foam insulation material has low bulk density, low thermal conductivity and water resistance, and is widely used in the field of thermal insulation.

(2) According to the temperature of use, it is divided into low temperature insulation materials and high temperature insulation materials.

The operating temperature range of low temperature thermal insulation materials is 600~900℃; the operating temperature range of medium temperature thermal insulation materials is 900~1200℃; the operating temperature of high temperature thermal insulation materials is generally higher than 1200℃.

(3) According to the bulk density, it can be divided into ultra-light and lightweight bricks.

Lightweight bricks with a bulk density of 0.4~1.3g/cm3; ultra-lightweight bricks with a bulk density below 0.4g/cm3.

(4) Classification by product shape.

One is shaped lightweight refractory bricks, including clay bricks, silica, high alumina and some pure oxide lightweight bricks, etc.; the other is amorphous lightweight refractory materials, such as lightweight refractory concrete.

1. According to the raw materials, 

   it can be divided into alumina, high alumina, siliceous and magnesia and other heat-insulating refractories. Different materials of thermal insulation refractories have different operating temperatures and related performance characteristics.

2. According to the material, it can be divided into three categories:  

   organic thermal insulation materials, inorganic thermal insulation materials and metal thermal insulation materials.

   In industrial kilns, the heat dissipation loss of the furnace body surface and the heat storage loss of the masonry are generally about 24-45% of the fuel consumption. When the structural material of the furnace body is made of lightweight bricks with low heat capacity and small thermal conductivity, the fuel consumption can be greatly reduced; at the same time, because the furnace can heat up and cool rapidly, the production efficiency of the equipment can be improved; it can also reduce the furnace body. Weight, simplify furnace structure, improve product quality, reduce ambient temperature, and improve working conditions.

   Lightweight refractory has a loose structure, large porosity in the material, and poor slag resistance. The slag can quickly penetrate into the pores of the brick body, causing it to break, and cannot be in direct contact with liquid metal and molten metal. At the same time, due to its poor wear resistance, low mechanical strength, and poor thermal stability, it cannot be used as a load-bearing structure, and it is not suitable for parts that are in contact with the charge and are prone to wear.

   Due to the above shortcomings of light refractory materials, in industrial kilns, light refractory materials are generally not used in the parts of the furnace that are in contact with the charge, where there are slag and hot air with high flow velocity and large mechanical vibrations. Lightweight refractory materials are mostly used as thermal insulation or thermal insulation layers of kilns. Currently commonly used lightweight refractory products mainly include zirconia hollow spheres, alumina hollow spheres, lightweight mullite bricks, lightweight high-alumina bricks, lightweight clay bricks and refractory fibers. hot material.