Study On The Thermal Insulation Of Ceramic Fibers Used In Experimental Furnace

Thermal insulation materials of the furnace lining affect the rising and reducing speed of temperature, heating efficiency and the temperature difference in the furnace. Thus, thermal insulation materials have to meet severe requirements. Although the heat insulation effect of a single fiber layer may be good, the price is expensive and it is to a waste to use high temperature material for a low temperature insulation. Take advantage of the temperature distribution in the furnace lining from inside to outside, alternatively using composite fibers layers for the furnace heat insulation benefits reducing the cost and promoting their wide application.Based on the studying on the heat resistance performance of rock wool, aluminum silicate fiber felt, mullite fiber board and alumina fiber board, this work aims to seek the best combination of compound heat insulation layers and to provide experimental data for practical application for reference. At high temperatures, the fiber products are easy to be sintered and pulverized. By spraying alumina slurry of on the fiber products, the coating can improve the performance of the fibers.The fibers were characterized by DTA, XRD and SEM. The results indicate that the rock wool and aluminum silicate fiber felt are crystalline materials. With the increase of heat treatment temperature, the fibers become crystallized and the grain grew larger with the surface turning from smooth to rough. The products show increasing shrinkage due to sintering. Heat resistance of rock wool is the worst among them, its using temperature is less than 950 oC. When the heat temperature is 1350 oC, the zirconia containing aluminum silicate fiber felt significantly shrinks, its using temperature is less than 1350 oC. And the mullite fibre board and alumina fiber board consists of crystalline materials and their temperature resistance is good. When the temperature is 1350 oC, alumina fibers still have very small grains, its using temperature can be higher than 1550 oC.According to the temperature test results of the composite insulation layers and the calculation and analysis of heat transfer, it can be concluded that when the furnace temperature is 950 oC, the best thermal insulation layer is the combination of mullite fiber board/containing zirconium aluminum silicate fiber/rock wool. When the furnace temperatureis 1150 oC, the best thermal insulation layer is the combination of mullite fiber board/mullite fiber board/containing zirconium aluminum silicate fibers. When the furnace temperature is1350 oC and 1550 oC, the best thermal insulation layer is the combination of three mullite fiber boards. When the temperature is from 950 oC to 1550 oC, the first and the fourth combination have the highest and smallest heat flux. According to the calculation, when the furnace temperature is 1550 oC,a thickness of 60 mm mullite fiber board, 124 mm aluminum silicate fiber felt and 53 mm rock wool can keep the furnace outermost layer less than 100 oC.Finally, alumina slurry layers were formed on the surface of ceramic fiber by spraying or dipping. It is confirmed that the coating has little effects on the thermal conductivity of the fiber products. The coating can reduce the sintering and shrinkage of fiber products. The application temperature of rock wool fibers with once dipping can be increased from 950 oC to 1000 oC. After three times of coating, the application temperature of mullite fiber boards can be increased from 1500 oC to 1550 oC. When the furnace temperature is from 950 oC to1350oC, the caoted fiber products used as composite lining in the furnace show improved ant-sintering behavior.