Knowledge of the properties of refractory fibers

- Jan 30, 2018-

The properties of refractory fibers are usually expressed by chemical composition and fiber diameter, length, slag ball content, heating line shrinkage, thermal conductivity, compressibility and resilience.
The diameter of the fiber is measured by a microscope or other precision instruments. The diameter of the fiber can be measured by a microscope or other precision instruments. The diameter of the fiber can be obtained and the average diameter of the fiber can be obtained. The amorphous refractory fiber produced by melting method has a wide diameter distribution. It is generally 1~8 micron m, and the average diameter of refractory fiber produced by injection is 2.5 to 3.5 m, while the spinning method is 3~5 m. The diameter of fiber directly affects the strength and thermal conductivity of the fiber. The fiber has a large diameter, high thermal conductivity and poor thermal insulation. The ideal fiber diameter should be below 3 m.

Fiber length determination of fiber length by spinning method, which is a kind of statistical concepts, lack of effective unified method. The fiber produced by shredding method is longer, can reach 100 ~ 250mm, the injection method is shorter, the fiber length is 10 to 50mm, the fiber length is large, and the strength of the product is high.

Slag ball content pellets are spherical particles that are not fibrous during the process of fibrosis. The content of the slag ball is the percentage of the non fiber material that remains on the sieve 0.25mm sieve in the sample. The refractory fiber specimen is treated by heat treatment, and the fiber is separated from the slag ball by the lapping principle. Then the percentage of the slag ball was calculated by drying, screening, weighing and calculating the content of the slag ball. The slag ball is an inevitable product for the melting process. The content of the slag ball is as high as 20% ~ 40%. The national standard of China (GB3003 - 82) stipulates that the slag ball content of ordinary aluminosilicate refractory fiber felt should not be greater than 5%, so the refractory fiber needs to be deslagging before making products. The high slag content will reduce the insulation and insulation of the fiber, and reduce the strength and elasticity of the fiber.

Thermal conductivity at unit temperature gradient, through the heat flow rate per unit area of fiber material. It is usually expressed as a symbol lambda. There are two methods for measuring, namely, calorimeter and hotline. The thermal conductivity of the calorimeter is to determine the thermal conductivity of the sample under the condition of the steady state of the heat flow. The hot wire method is a kind of unsteady state method. Its principle is to measure the temperature rise of a line heat source in the sample along the length of the specimen in a certain time. The thermal conductivity is measured by measuring the temperature of the hot wire in the middle point of the hot wire with time. The degree of thermal conductivity largely depends on the void content and distribution inside the sample. Therefore, the fiber quality, fiber diameter and slag ball content all affect the thermal conductivity, while the volume density of the sample plays a decisive role. Therefore, when measuring the thermal conductivity of fiber products, it is very important that the sample method and the volume density of the sample are not representative.

The heating line changes the fiber to the sample, heated to the specified temperature, heat preservation for a certain time, and the percentage of shrinkage produced by the cooling to room temperature. The glass state refractory fibers start from about 800 degrees C, which is the process of anti vitrification, that is, crystallization. At this time, the single fiber will curl, and the test sample for the heating line contraction is the aggregate of the fiber, which is the volume contraction. As the temperature increases, the grain grows and the shrinkage increases. As for the crystalline fiber, with the increase of heating temperature, the transformation of small grain to large grain also occurs, resulting in the contraction of the fiber. The size of the heating line marks the degree of high temperature resistance of the fiber. In some countries, the temperature corresponding to the 24h of the sample and the shrinkage of the heating line to or close to 2.5% is defined as the maximum temperature of the fiber.

Compressive and resilient refractory fibers have excellent compressibility and resilience. Using this characteristic, the pre compression method can be used to counteract the shrinkage during the installation of the refractory fiber lining. The expansion joint of the lining is filled with refractory fiber, and the refractory fiber is compressed when the lining is heated and expanded. When the lining of the furnace is cooled and contracted, the fiber takes back the elasticity and makes the fiber occupy the gap. The compressibility and resilience of the refractory fiber are necessary for its high temperature sealing material.