- Time:Feb 17, 2023
During the use of refractory materials, they are subjected to physical, chemical, and mechanical effects at high temperatures (generally 1000~1800 ° C), and are easy to melt and soften, or be eroded, or cracked and damaged, which interrupts the operation, and Contaminated material. Therefore, it is required that refractory materials must have properties that can adapt to various operating conditions. The following are 4 indicators that determine the high temperature performance of refractory materials:
1. Refractoriness
Refractoriness refers to the temperature at which a material reaches a certain degree of softening under high temperature, which characterizes the material's resistance to high temperature. Refractoriness is the basis for judging whether a material can be used as a refractory material. The International Organization for Standardization stipulates that inorganic non-metallic materials with a refractoriness above 1500 °C are refractory materials. It is different from the melting point of the material, and it is a comprehensive performance of the mixture of multi-phase solids composed of various minerals.
The most fundamental factor that determines the refractoriness is the chemical mineral composition and distribution of the material. Various impurity components, especially those with strong flux effects, will seriously reduce the refractoriness of the material. Therefore, appropriate measures should be considered in the production process to ensure and improve the purity of raw materials.
Refractoriness is not an absolute physical quantity unique to a substance, but a relative technical index when the material reaches a certain degree of softening measured under specific test conditions. The test material is made into a truncated triangular cone (referred to as the test cone) according to the prescribed method, and a standard truncated triangular cone (referred to as the standard cone) with a fixed bending temperature at a specific heating rate. Heating, and measuring the refractoriness by comparing the bending degree of the test cone with the bending degree of the standard cone. The lower bottom of the truncated triangular cone is 8mm long on each side, the upper bottom is 2mm on each side, and the height is 30mm. During the measurement, a liquid phase may appear in the pyramid at high temperature. As the temperature rises, the amount of liquid phase increases, the viscosity of the liquid phase decreases, and the cone softens. When it softens to a certain extent, the cone gradually bends due to its own weight. When the test cone and the standard cone are bent at the same time until their apex touches the chassis, the bending temperature determined by the standard cone shall prevail as the refractoriness of the test cone.
2. High temperature load deformation temperature
Also known as refractory material load softening point or refractory material load deformation temperature, it indicates the resistance of refractory materials to the combined action of high temperature and load under constant load or the temperature range in which refractory materials exhibit obvious plastic deformation. The maximum service temperature of the refractory material can be inferred from the load softening temperature, which to a certain extent indicates the structural strength of the refractory material under similar service conditions, and can be used as the basis for determining the maximum service temperature of the refractory material.
The main factor that determines the softening temperature under load is the chemical mineral composition of the material, and it is also directly related to the production process of the material. The sintering temperature of the material has a great influence on the load softening deformation temperature. If the sintering temperature is increased appropriately, the deformation start temperature will be increased due to the decrease of porosity, crystal growth and good bonding. Improving the purity of raw materials and reducing the content of low-melt or flux will increase the load softening deformation temperature. For example, sodium oxide in clay bricks and alumina in silica bricks are harmful oxides.
3. High temperature volume stability of refractory materials
When refractory materials are exposed to high temperature for a long time, volume expansion occurs, which is called residual expansion. The size of the residual expansion (deformation) of refractory materials reflects the quality of high-temperature volume stability. The smaller the residual deformation, the better the volume stability; on the contrary, the worse the volume stability, the easier it is to cause deformation or damage of masonry.
The change of the reburning line is often used to judge the high temperature volume stability of the material, which is an important indicator for evaluating the quality of the material.
Most refractory materials will shrink under the action of high temperature. When reburning, most refractory materials will shrink, mainly because the liquid phase generated by the material at high temperature will fill the pores in it, so that the particles will be further tightened and stretched. Recently, recrystallization occurred, leading to further densification of the material. There are also a few materials that expand when reburned. For example, silica bricks expand due to polycrystalline transformation during use. Quartz, volume expansion, about 10% of unconverted quartz in silica bricks. In order to reduce the shrinkage and expansion of materials after refiring, it is effective to appropriately increase the firing temperature and prolong the holding time, but it should not be too high, otherwise it will cause vitrification of the material structure and reduce the thermal shock stability. Due to the expansion of the quartz particles in the material during firing and use, the town offsets the shrinkage of the clay, so the volume change of the semi-silica brick is small, and some expand slightly.
4. Thermal shock stability
The ability of refractory materials to resist rapid changes in temperature without damage is called thermal shock stability. This property is also known as thermal shock resistance or resistance to sudden temperature changes.
The main factor affecting the thermal shock resistance index of materials is the physical properties of materials, such as thermal expansion and thermal conductivity. Generally speaking, the larger the linear expansion rate of the material, the worse the thermal shock stability; the higher the thermal conductivity of the material, the better the thermal shock stability. In addition, the organizational structure, particle composition and material shape of refractory materials all have an impact on thermal shock stability.
ZHENJIN REFRACTORIES is committed to the research and development of refractory materials in cement, lime, non-ferrous metals, steel, glass and chemical industries, technical solution design, construction and supply of supporting products and other one-stop general contracting services, integrating production, sales, research and export Kiln overall solution service provider. The service chain runs through the life cycle of the entire project, including preliminary consultation, scheme design, R&D and production, furnace construction and safety production. Through the optimized combination of various brand products, it can meet different process requirements and create value for customers.
