Thermal insulating refractories

(Thermal insulating refractories)

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

 

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

1.  Porous particles, such as expanded vermiculite and expanded perlite.

 

2. Porous fiber: common are ultra-fine glass wool, asbestos and mineral rock wool and so on. This kind of material has good heat resistance and low thermal conductivity. It 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 and produce fiber dust in the air, which is harmful to human health and seriously hinders their popularization and application. In the 1980s, fiber thermal insulation materials accounted for a large share of the market, because of its excellent thermal insulation and fireproof performance, mainly used in building wall insulation. Because inorganic fiber has many outstanding advantages, such as light weight, low thermal conductivity and high heat capacity, it has been widely used in the thermal protection engineering of all kinds of advanced weapons in recent years. At present, the inorganic fibers that can be mass produced are aluminum silicate fiber, glass fiber, quartz fiber, zirconia fiber, carbon fiber and silicon carbide fiber, etc.

 

3. Foaming materials: including inorganic type, organic type and organic-inorganic mixed type. Common inorganic types include foam glass and cement. In the 1980s, calcium silicate samples were recognized as the best thermal insulation materials in hard bulk materials because of their low bulk density, low thermal conductivity, high fire resistance and excellent mechanical properties. However, in the 1990s, because of the asbestos in the sample, it was gradually replaced by pulp fiber. However, the pulp fiber is not resistant to high temperature, which significantly affects its application at high temperature. There are phenolic foam, polyethylene foam and polyurethane foam, which are widely used in the field of thermal insulation because of their low volume density, low thermal conductivity and water resistance.

 

According to the use temperature, it can be divided into low temperature thermal insulation material and high temperature thermal insulation material.

The temperature range of low temperature thermal insulation materials is 600 ℃ to 900 ℃, the temperature range of medium temperature thermal insulation materials is 900 ℃ to 1200 ℃, and the temperature of high temperature thermal insulation materials is generally higher than 1200 ℃.

 

According to the volume density, it can be divided into ultra-lightweight and lightweight bricks.

The bulk density of lightweight brick is lower than that of 0.4~1.3g/cm3; the bulk density of ultra-lightweight brick is lower than that of 0.4g/cm3.

 

According to the shape of the product.

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

 

According to the raw materials, it can be divided into alumina, high alumina, silicon and magnesia and other heat insulating refractories. The thermal insulation refractories of different materials have different use temperature and related performance characteristics.

 

According to the material, it can be divided into three types: organic thermal insulation material, inorganic thermal insulation material and metal thermal insulation material.

 

The heat loss on the surface of the furnace body and the heat storage loss of the masonry in the industrial kiln are generally about 24045% of the fuel consumption. When the structural material of the furnace body adopts light bricks with low hot melting and low thermal conductivity, the fuel consumption can be greatly reduced; at the same time, because the kiln can be rapidly heated and cooled, the production efficiency of the equipment can be improved; the weight of the furnace body can be reduced and the structure of the furnace body can be simplified. improve product quality, reduce ambient temperature and improve working conditions.

 

The light refractories have loose structure, large porosity and poor slag resistance, and the molten slag can quickly invade into the pores of the brick body and break it, so it can not be used in the parts that come into direct contact with liquid metal and molten slag; at the same time, because of its poor wear resistance, low mechanical strength and poor thermal stability, it can not be used as a load-bearing structure, nor can it be used in contact with furnace materials and parts that are easy to wear.

 

Because of the above shortcomings of lightweight refractories, lightweight refractories are generally not used in furnace parts in contact with furnace charge, slag and hot air flow with high flow velocity to neutralize parts with large mechanical vibration in industrial kilns. Lightweight refractories are mostly used as thermal insulation layer or insulation layer of kiln. At present, the commonly used lightweight refractory products mainly include zirconia hollow ball, alumina hollow ball, lightweight mullite brick, lightweight high alumina brick, lightweight clay brick and refractory fiber.

 

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(Thermal insulating refractories)