the course of use, refractory materials are often subjected to abrupt changes in the ambient temperature, causing cracks in the product, eventually peeling off or even collapsing. This destructive effect not only limits the heating and cooling rate of the refractory product and refractory material for klin, but also limits the strengthening of the kiln operation, which is one of the main reasons for the rapid damage of the refractory product and the kiln.
The property of a refractory material against rapid changes in temperature without being destroyed is called thermal shock stability, and this property is also called thermal shock resistance or temperature sharpness.
Due to the intermittent operation characteristics of the converter, strict requirements are imposed on the thermal shock stability of the magnesia chrome refractory. Increasing the thermal shock resistance of the refractory material can be achieved by preventing crack propagation, consuming crack propagation power, increasing material fracture surface energy, increasing plasticity, reducing linear expansion coefficient, and increasing thermal conductivity.
1. Appropriate porosity of refractory brick. Surface cracks do not immediately cause cracking, and severely are spalling and fracture caused by internal thermal stress. When the porosity of fire brick is appropriately increased, the crack length of the refractory product becomes shorter and the number increases with the thermal shock. The cracks are interlaced and the degree of mesh formation is enhanced. Therefore, the fracture energy required for the product to break is increased, which can be effectively improved. Thermal shock stability of the refractory product. The optimum porosity of refractory products is usually controlled at 13% to 20%.
(2) Control the particle gradation of refractory raw materials and select low expansion, high thermal conductivity materials. In order to obtain a magnesia chrome refractory with good thermal shock resistance, which is required to increase the critical particle size and reduce the fine powder content in the chrome ore particles. Refractory raw material having a small coefficient of linear expansion and a raw refractory material having a high thermal conductivity such as Cu2O are used.
(3) Adding fine cracks and forming a network structure. By utilizing the inconsistent characteristics of the refractory product particles and the linear expansion coefficient of the matrix and the volume effect of the phase change, fine cracks are generated in the product, which has a significant effect on resisting catastrophic damage (hot peeling or fracture) of the product. Tests have shown that increasing the A1203 content in the refractory material or adding the most suitable ZrO2 to the magnesia-chromium refractory material can significantly improve the thermal shock stability of the magnesium-chromium material. Compared with the sample incision, the sample with ZrO2 has a large number of fine cracks inside. It is because of the existence of these fine cracks that the energy of crack propagation is absorbed, which enhances the thermal shock stability of the sample. The amount added should not exceed 5%.
