Ceramic fiber, as the third generation refractory after the traditional heavy refractory bricks and unshaped refractories, not only has good thermal insulation properties of low thermal conductivity materials, but also has excellent heat resistance for continuous operation at high temperatures. Due to the crystallization and grains growth of vitreous fibers, crystalline transformation and grain growth of polycrystalline crystal fibers, harmful impurities in fibers and corrosive substances in the use of fiber to promote fiber crystallization, glomerocryst and the sintering of fiber-contacted parts and other factors like high temperature creep result in changes in shrinkage deformation of fiber structure, fiber loss, brittle fracture, decreased fiber strength, densification until the sintering happens and the fibrous structure is lost. Therefore, the operating temperature of various types of ceramic fiber has a limiting temperature called the maximum temperature, also known as “classification temperature” or “grade temperature”, which is also a symbol of fiber heat resistance. According to the international practice, the ceramic fiber products can be divided into four grades of temperature as follows: 1000 ℃ type, 1260 ℃ type, 1400 ℃ type and 1600 ℃ type.
The maximum operating temperature of ceramic fiber, refers to the limiting temperature the ceramic fiber can withstand within a short time, to characterize the heat resistance indicators of ceramic fiber
products. The long-term working temperature of ceramic fiber products is generally 200℃ lower than the maximum operating temperature. To take the domestic 1260 ℃ type fiber products as examples, its long-term working temperature is about 1000 ℃. Therefore, the concept of maximum operating temperature is very important, which has a close relationship with the long-term working temperature and is the main reference of fiber application. In the past, some people mistakenly regard the maximum operating temperature as the long-term working temperature, which may causes unnecessary losses for them.
In addition, the long-term working temperature of the same ceramic fiber products under different conditions varies from each other. Industrial kiln operating system (continuous or intermittent kiln), fuel type, furnace atmosphere and other process conditions, all these factors can affect the operating temperature and life of ceramic fiber. There is no ideal method for determining the heat resistance of ceramic fibers right now. General practice is to heat the ceramic fiber product to a certain temperature and to assess the heat resistance of ceramic fiber products according to on the sample heating wire shrinkage changes and the degree of crystallization.