1. Introduction to several concepts of refractory fiber:
(1) Refractory fiber: Refractory fiber refers to a general term for crystalline and amorphous fibrous materials having a refractoriness of more than 1,580 °C. Therefore, it includes aluminum silicate fiber with Al2O3 and SiO2 as main components, alumina crystal fiber with alumina as main component, and other zirconia crystal fiber and forsterite fiber with a refractoriness of more than 1500 °C. Oxide fiber.
Note: Refractoriness refers to the temperature at which a material reaches a certain degree of softening at high temperatures. It characterizes the resistance of a refractory material to high temperatures. It differs greatly from the melting point and temperature of the refractory material. For example, the refractory fiber of aluminum silicate refractory fiber is about 1750~1770 °C, its melting point is 2000~2200 °C, and its use temperature is only between 1000~1350 °C.
(2), aluminum silicate refractory fiber: aluminum silicate refractory fiber refers to the general name of fibrous materials with Al2O3, SiO2 as the main component, according to the use temperature, it is divided into ordinary aluminum silicate refractory fiber, standard type Aluminum silicate refractory fiber, high-purity aluminum silicate refractory fiber, high-aluminum aluminum silicate refractory fiber, zirconium-aluminum refractory fiber, zirconium-containing aluminosilicate refractory fiber, polycrystalline mullite fiber, and the like.
(3) Ceramic fiber: Ceramic fiber is a common name for fibrous materials with Al2O3 content of 45-60% in aluminum silicate refractory fiber. All ceramic fibers are amorphous fibers, which can also be called glass fibers. It is an amorphous solid fiber in which a substance is formed by cooling in a molten liquid state.
2. Types and forms of refractory fiber products
See Table 1 and Figure 2.

Second, refractory fiber design parameters
Through research and experiments on a series of problems occurring during the heating process of refractory fibers, especially in use. The changes that occur during the use of refractory fibers can be summarized as follows:
1. The fiber shrinks due to recrystallization, sintering and new phase generation, and reaction between the inorganic binder and the fiber. When a certain temperature is reached, the fiber material is damaged by the heat due to the accelerated grain growth and the acceleration of the sintering process. This raises the following questions:
(1) When designing the application of refractory fiber, it is necessary to clarify the relationship between the heat shrinkage of the refractory fiber and the temperature and the expected life.
(2) When applying refractory fibers, the elasticity and thermal shock resistance of the refractory fibers must be clarified.
2. When applying refractory fiber, it must be clarified that the corrosive effect of the fiber material during use accelerates its deterioration, thereby lowering its use temperature. Some of the components in the furnace atmosphere, such as H2, CO, CH4 and NH3, as well as alkali metals, fluorine, chlorine and SO32-, can affect the recrystallization process, including nucleation and crystal growth rate. They react with fiber materials, reducing their temperature and product properties.
3. The fiber material has good wind erosion resistance, and its wind erosion resistance varies with the specific shape of the product. Moreover, the anti-scour ability of the fiber wall lining against high-speed airflow decreases with the increase of the use temperature. It is a factor that must be noted.
4. The heating and corrosion of the anchoring system is also an important factor affecting the service life of the fiber material.
In summary, the design parameters of refractory fibers mainly include classification temperature and long-term safe use temperature, bulk density, thermal conductivity, thermal stability, chemical stability, heat shrinkage, wind erosion resistance, elasticity and gas permeability, heat capacity, Blackness, tensile strength, etc.

a), classification temperature and use temperature
1. Classification temperature: The classification temperature is the highest use temperature, which refers to the highest use temperature of the fiber material in actual use. Specifically defined as the test temperature at which the refractory fiber product is heated for 24 hours under non-load conditions and at a high temperature linear shrinkage of 4%. The refractory fiber is used for a long time at this temperature, and its life will be short. Therefore, it should not be taken lightly in practice.
2. Long-term safe use temperature: Long-term safe use temperature refers to the test temperature when the refractory fiber is kept at a certain temperature for 24 hours and the high-temperature line shrinkage is ≤ 2.5%. At this temperature, the amorphous fiber crystallizes, the crystalline fiber crystal form changes and the grain growth rate is slow, the fiber performance is stable, and the fiber is soft and elastic.
3. Relationship between temperature and fiber life: The service temperature and service life of refractory fiber are closely related to the conditions of use (kiln atmosphere, composition and content of corrosive substances).
(1) The refractory fiber is used under the conditions of allowable use temperature, the crystal development is slow, the fiber property is relatively stable, and the life can reach 5-10 years in the case of no impact by an external force in an oxidizing atmosphere.
(2) Reductive furnace gas should be made of high-purity synthetic material as raw material for walling of industrial furnace, and anti-corrosion coating should be applied on the surface of refractory fiber lining, which not only improves the chemical stability of fiber lining, but also improves The wind resistance of the fiber lining and the reduction of the heat shrinkage of the fiber lining. In order for the fiber wall lining working under a reducing atmosphere to obtain the same heat insulating effect as that under an oxidizing atmosphere, it is also necessary to calculate the thickness of the thickened fiber wall lining according to the composition of the reducing atmosphere.
(3) The service temperature of the refractory fiber should be determined according to the type of fuel used in the kiln (gas, oil, coal), the kiln atmosphere, and the composition of the corrosive substances in the kiln atmosphere.
A. The use temperature in the reducing atmosphere is 100 to 150 ° C lower than that in the oxidizing atmosphere, and the standard aluminum silicate fiber is used in a reducing atmosphere at a temperature of 850 to 900 ° C.
B. For the fuel industry kiln, the refractory fiber wall lining should be used at a temperature lower than that of the electric heating industrial kiln fiber wall lining 150~200 °C.
C. The use temperature in a vacuum atmosphere is lower than that in an oxidizing atmosphere by 200 to 250 °C.
2), weight tolerance
Two important characteristics of refractory fiber are small bulk density and small thermal conductivity. The reason why aluminum silicate refractory fiber has good energy saving effect lies in these two characteristics.
1. Bulk density: Also known as bulk density, it is an important quality index of refractory fiber, which refers to the mass of refractory fiber per unit volume. The bulk density of refractory fiber products is generally: felt (200~220kg/m3), plate (280~320kg/m3), fiber component (200~240kg/m3) fiber blanket (64kg/m3, 96kg/m3) , 128kg/m3, 160kg/m3).
Since the bulk density of the aluminum silicate refractory fiber is small, and the heat storage loss of the lining is proportional to the bulk density of the lining material, the use of refractory fiber as the lining can not only greatly reduce the heat storage loss of the furnace wall, but also greatly reduce the furnace. the weight of. In addition, the heating time can be greatly shortened.
2. Thermal conductivity: Thermal conductivity is a physical property of a substance. It characterizes the thermal conductivity of a substance. The value of the thermal conductivity is the amount of heat per unit area per unit length of temperature difference per unit length per unit time. It is w/mk; it is the main indicator to measure the thermal insulation performance of materials. Another important characteristic of aluminum silicate refractory fibers is their low thermal conductivity and good thermal insulation properties.
c), anti-air scouring performance
For fuel furnaces and furnaces that use fan circulation, refractory fibers are required to have a certain resistance to airflow. The following table is the reference data for the resistance to airflow of aluminum silicate refractory fibers.
Product Name Fiber Needle Blanket Vacuum Forming Mat Vacuum Forming Board Fiber Folding Module
Maximum allowable wind speed m/s 15-18 8 ≥25 20-25
If the air flow rate exceeds the value range listed above, the surface of the fiber product should be hardened.
d) thermochemical stability
The thermal stability of refractory fiber is unmatched by any dense or lightweight refractory material. Generally, the dense refractory brick will crack or even peel off after several times of rapid cooling. The refractory fiber product is a porous product composed of fibers having a diameter of 2-5 um intertwined with each other, and does not cause structural stress even if the temperature is drastically changed, and does not peel off under the conditions of rapid cooling and rapid heat, and can resist bending. , distortion and mechanical vibration. Therefore, in theory it is not limited by any temperature volatility. Since the refractory fiber product itself is a soft and elastic porous material, the expansion of the monomer fiber is absorbed by the fiber itself, so that the expansion joint and the oven problem can be completely ignored in use, and the kiln steel structure does not need to be considered. The expansion stress of the product makes the structure lighter and saves the amount of steel for building the furnace.
5), elasticity and resistance to gas permeability
The refractory fiber is used as a sealing material and a gasket material for a high-temperature gas, and is required to have elasticity (compression recovery property) and gas permeability resistance. The compression rebound rate of the refractory fiber increases as the bulk density of the fiber product increases, and the gas permeability resistance also increases accordingly, that is, the gas permeability of the fiber product decreases. Therefore, when used as a sealing material and a backing material for a high temperature gas, it should be selected. A fiber product having a large bulk density (at least 128 kg/m3) to increase its compression rebound rate and gas permeability resistance. In addition, the fiber product containing the binder has a greater compression resilience than the fiber without the binder.
Six), heat capacity
The heat capacity of the refractory fiber refers to the heat absorbed by the refractory fiber as a furnace lining when the temperature of the furnace is raised by 1 ° C when the furnace is heated. The table below lists the average heat capacity of aluminum silicate fibers for reference only.

Heat capacity of aluminum silicate refractory fiber products
Average temperature (°C)
140
245
350
445
550
Heat capacity (J/kg.k)
850
988
1050
1088
1105

Seven), blackness
(Additional concept) The blackness test of standard aluminum silicate fiber and high aluminum fiber by Mackeny UK showed that the blackness of both fibers was 0.95.
VIII) tensile strength
In order to meet the strength requirements of refractory fiber products during construction, refractory fiber products should have a certain tensile strength, and the tensile strength value of the fiber-punched blanket without adhesive at room temperature fluctuates according to the fiber-forming process. 0.08 MPa.
3. Indicators for assessing the quality of refractory fibers
Main indicators for assessing the quality of refractory fibers:
(1) Chemical composition
The development of refractory fiber production shows that foreign countries have gradually replaced natural raw materials with high-purity synthetic raw materials to improve the purity of the chemical composition of refractory fiber products, which means:
A. To ensure the required content of high temperature oxides such as Al2O3, SiO2 and ZrO2 in the composition of refractory fiber products of various grades. For example, in high purity (1100 ° C), high aluminum (1200 ° C) fiber products, Al2O3 + SiO2 = 99%, zirconia (> 1300 ° C) containing SiO2 + Al2O3 + ZrO2 > 99%.
B. Strictly control harmful impurities such as Fe2O3, Na2O, K2O, TiO2, MgO, CaO, etc. below the specified content.
To a certain extent, strict control of the harmful impurities content of fiber products is more important than ensuring the high temperature oxide content in the chemical composition of fiber products. The amorphous fiber is subjected to thermal crystallization and grain growth causes deterioration of fiber properties until the fiber structure is lost. The high impurity content not only promotes nucleation and crystallization, but also causes a decrease in liquidus temperature and vitreous viscosity, and promotes grain growth. Strict control of harmful impurities is an important part of improving the performance of fiber products, especially heat resistance. The impurities act as spontaneous nucleation in the crystallization process, which not only increases the granulation rate but also promotes crystallization. The sintering and polycrystallization of impurities at the fiber contact increases the grain growth rate, resulting in grain coarsening and increased linear shrinkage, which is an important cause of fiber performance deterioration and service life.
General natural fiber impurities 3-4%
High purity fiber impurity content <1%
(2) The shrinkage rate of the heating wire is an index for evaluating the heat resistance of the refractory fiber product. The internationally stipulated refractory fiber product is heated to a certain temperature under non-loading, and the high-temperature linear shrinkage rate of the heat-resistant 24 hours indicates its heat resistance. Only the line shrinkage value measured according to 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 crystallizes, the crystal grain does not grow significantly, the performance is stable, and the elasticity is strong. From the Japanese point of view, as long as the grain size is smaller than the fiber diameter, the fiber properties do not undergo a qualitative change.
The above figure shows that the fiber is crystallized under heat, and the grain growth causes the fiber to shrink. When it is kept at a certain temperature for 24 hours, its 75% shrinkage has been reflected, and the remaining 25% shrinkage will be slowly reflected in the long-term use. In some factories in China, the shrinkage rate of 6 hours at a certain temperature is used as an index of heat resistance of the product. Actually, only the line shrinkage of about 30% is exhibited, so the heat resistance of the fiber product cannot be reflected.
(3) Thermal conductivity is the only index to evaluate the thermal insulation performance of refractory fibers. It is also an important parameter for the design of kiln wall structure. How to accurately determine the thermal conductivity value is the key to determining the reasonable design of the lining structure. The thermal conductivity depends on changes in the structure, bulk density, temperature, ambient atmosphere, humidity, etc. of the fibrous product. Among various substances, the gas thermal conductivity coefficient is the smallest, and the air thermal conductivity at room temperature is 0.025 W/M.K. In the industry, gases are widely used as thermal insulators. However, it has excellent thermal insulation properties only when the gas does not convect. The still air is an excellent heat insulating material with low thermal conductivity and low heat capacity, and the refractory fiber has a thermal conductivity close to that of air. It is precisely because the refractory fiber is a mixed structure composed of solid fiber and air, its porosity is 93%, a large amount of low thermal conductivity air is filled in the pores, and the continuous network structure of the solid molecules is destroyed, thereby obtaining excellent heat insulation performance.
Porosity of different refractories Table 2
Product name
Porosity %
Dense refractory products
10-16
Common refractory products
20-30
Light refractory products
45-85
Ultra-light insulation products
>85
Refractory fiber products
93
Determination of thermal conductivity:
A, test method
There are two kinds of plate method and hot wire method. Table 3 summarizes the thermal conductivity values ??of different products tested by Luyang Company in 1998-2000 (including the test results of Luoyang and Beijing National Refractory Testing Center).
Thermal conductivity of aluminum silicate refractory fiber (measured value) Table 3
Product name
Bulk weight, kg/m3
Average temperature (°C)
Thermal conductivity (w/m.k)
Standard silk carpet
128
200
0.055
400
0.076
500
0.106
700
0.150
High purity silk carpet
128
200
0.058
400
0.085
500
0.122
700
0.178
Zirconium-containing silk carpet
128
325
0.107
600
0.147
700
0.190
Standard fiberboard
260
248
0.066
377
0.081
512
0.101
749
0.124
High-purity fiberboard
280
247
0.085
375
0.112
511
0.139
Standard fiber castable
600
650
0.156
800
650
0.197
1000
650
0.219
High-purity fiber castable
600
650
0.159
800
650
0.197
1000
650
0.228
Zirconium-containing fiber castable
600
650
0.174
800
650
0.17