1. What is refractory fiber?
Answer: Refractory fiber, also known as ceramic fiber, is a man-made inorganic non-metal fiber material. It is a glass phase or crystalline phase binary compound composed of AL2O3 and SiO2 as the main components. Using refractory fiber as the hot surface material or thermal insulation material of industrial furnaces can generally save energy by 15% to 30%.
2.What are the main characteristics of refractory fiber?
Answer: The main characteristics of refractory fiber are high temperature resistance, low thermal conductivity, good chemical stability, and good thermal shock stability and vibration resistance.
(1) High-temperature performance The service temperature of aluminum silicate refractory fiber is 1000~1200C, and the polycrystalline alumina refractory fiber can reach 1600C, and some are even higher. However, general fiber materials such as asbestos, rock wool, slag wool, etc. The maximum operating temperature is generally below 650C.
(2) Thermal insulation performance The thermal conductivity of refractory fiber at high temperature is very low. At 1000C, it is only 1/20~1/10 of that of refractory clay bricks, and 1/3 of that of lightweight refractory bricks, and its heat capacity is small. High thermal efficiency. Due to its low volume density, it can be used as a heat insulation layer to reduce the thickness by about half.
(3) Chemical properties Refractory fiber is more resistant to chemical attack than rock wool and glass wool. Except for strong alkali and hydrofluoric acid, it is hardly corroded by various chemicals, steam and oil. It does not interact with acid at normal temperature, and does not wet liquid aluminum, copper, lead, tin and their alloys at high temperatures, so it can be used as a heat insulation material for a variety of metal melting furnaces.
(4) Thermal shock resistance Refractory fiber is soft and elastic, so it has good resistance to thermal shock and rapid cooling and heating. No matter how fast the heating and cooling speed is, it will not break and break. It can withstand mechanical vibration, but cannot withstand direct impact and friction.
(5) Other characteristics The compression resilience and air resistance of refractory fiber are better, and the sealing performance is better than that of sand. According to this performance, it can be used as a sealing material for frequently opened parts such as masonry expansion joints, furnace doors, side seals and rear seals of trolley furnaces; refractory fibers are soft and have good workability, and are constructed with refractory fibers. The furnace lining is thin and light, the construction is convenient, and the labor intensity is low.
The disadvantages of refractory fiber products are: low strength, easy to be damaged by mechanical collision, air flow erosion, and material friction; when in direct contact with slag and molten liquid, they are easy to invade and lose heat insulation. In addition, physical and chemical changes (such as crystallization of amorphous fibers and crystal growth of polycrystalline fibers, etc.) caused by long-term use at high temperatures can cause damage to the product. Therefore, refractory fiber products cannot be used to pave the bottom of the furnace, cannot bear the load, and cannot be used for parts that are too high in air velocity, directly contacted with molten slag or subjected to mechanical collisions, and are not suitable for use as the lining of a heat treatment furnace with hydrogen as a protective atmosphere. .
3. What problems must be paid attention to when choosing refractory fiber?
Answer: When choosing refractory fiber, you must pay attention to the following matters:
(1) High temperature crystallization of refractory fiber The refractory fiber with a mass fraction of 50% AL2O3 is a standard aluminum silicate refractory fiber, and its maximum use temperature is 1260C. This fiber is amorphous when it is cold and has good flexibility. However, after long-term high-temperature use, the fibers crystallize, become brittle, shrink, and increase their bulk density. The higher the temperature, the more serious the crystallization, and when the temperature is too serious, the fiber will pulverize.
(2) Shrinkage of refractory fiber under thermal load Generally, the product specification of refractory fiber only gives the shrinkage rate of short-term heating without thermal load or thermal load. For example, when heated at a high temperature of 1200C for 4-6 hours, the shrinkage rate is generally ≤4%. However, under thermal load, the shrinkage rate of refractory fibers far exceeds this value. When selecting refractory fibers, both operating temperature and thermal load conditions should be considered. Therefore, the safe use temperature of refractory fiber should be lower than the nominal maximum working temperature.
(3) Selecting refractory fibers in a controllable atmosphere In an endothermic atmosphere, hydrogen constantly penetrates into the refractory fibers to improve their thermal conductivity and increase the temperature outside the furnace wall. Refractory fiber is a low-density and porous material. The hydrogen molecules are very small and easily penetrate people. In practical applications, the thickness of the refractory fiber should be increased by 50~100mm. In the carburizing atmosphere, carbon is deposited on the refractory fiber to increase its thermal conductivity, which can be removed by carbon burning.
(4) Wind erosion resistance of refractory fiber When used as a lining, refractory fiber must be able to withstand the scouring of the airflow in the furnace and should have sufficient wind erosion resistance. The maximum allowable wind speed of various fiber products is shown. For ordinary burners with low flame speed, various products can be used, and wind speed factors should be considered when using high-speed burners.
(5) The bonding strength of the refractory fiber layer The refractory fiber is often combined with refractory clay bricks, lightweight refractory bricks and other thermal insulation materials to form an integral furnace lining with a certain compressive strength. Therefore, it is necessary to use refractory fiber-reinforced coatings to improve their own strength, and use appropriate high-temperature adhesives to bond with other furnace building materials.
(6) The influence of flame on refractory fiber When T refractory fiber is used as the lining of the fuel furnace, attention should be paid to the length and angle of the flame spraying, and the flame should not be sprayed directly on the refractory fiber lining.