Concept of thermal expansion and contraction
Thermal expansion and contraction refers to the property that an object expands when heated and shrinks when cooled. Since the movement of particles (atoms) in an object changes with temperature, when the temperature rises, the vibration amplitude of the particles increases, causing the object to expand; but when the temperature drops, the vibration amplitude of the particles decreases, causing the object to shrink.
01 Ceramic fibers do not expand when heated
Many objects in nature have the property of thermal expansion and contraction, but ceramic fibers do not expand when heated, and have a shrinkage rate of 0.03. The reason is due to the structural characteristics of the ceramic fibers themselves.
The organizational structure of ceramic fibers is a mixed structure composed of solid fibers and air, and its microstructural characteristics are that both the solid phase and the gas phase exist in the form of continuous phases. In this structure, the solid matter exists in the form of fibers with a diameter of 2~5Um and a length of 30~250mm, and constitutes a continuous solid phase skeleton, while the gas phase exists continuously in the skeleton gap of the fiber material, with a porosity of more than 90%.
Therefore, the expansion of ceramic fiber after heating will be folded by its own pores and will not be too obvious. This is the reason why ceramic fiber products do not expand after heating.
02 Ceramic fiber high temperature shrinkage
During the application of ceramic fiber products in high-temperature furnaces, due to long-term exposure to high temperature, the fiber filaments that make up the solid phase skeleton break due to their own weight or brittle fracture, resulting in skeleton collapse, fiber aggregation, and reduced void space. Therefore, from the appearance, ceramic fiber products will shrink to a certain extent, and the shrinkage rate is generally less than 0.03.
Application suggestions
a. The selection of ceramic fiber materials should follow the principle of high refractory temperature rather than low refractory temperature, and minimize the linear shrinkage of ceramic fiber;
b. The ceramic fiber blanket block structure should be squeezed as densely as possible during the construction process to prevent high-temperature shrinkage from causing gaps in the furnace lining and damaging the furnace body;
c. It is recommended to prepare a certain amount of ceramic fiber cotton blanket when selecting ceramic fiber module furnace lining, which is used to fill gaps later.
