The normal temperature compressive strength of refractory bricks (abbreviated as CCS) refers to the maximum pressure that the material can withstand per unit area at normal temperature.

The national standard (GB/T5072-1985) stipulates the normal temperature pressure test method for dense refractory bricks: at normal temperature, use a pressure testing machine to load a sample of specified size at a specified rate until the sample breaks. The compressive strength is then calculated based on the recorded maximum load and the area of the specimen bearing the load. The picture below shows the normal temperature compressive strength of some commonly used refractory bricks.

Room temperature compressive strength is one of the important technical indicators of refractory bricks. In general thermal equipment, the static load of refractory materials is not large, generally no more than 0.1-0.2MPa, and the furnace top does not exceed 0.4-0.5MPa. The large load of large blast furnace bottom bricks and hot blast stove tops does not exceed 1.0MPa, except for possible damage caused by impact and extrusion of the material due to improper transportation and masonry, it is rarely damaged due to the low normal temperature compressive strength of the material. Current standards stipulate that the normal temperature compressive strength of refractory bricks is not less than 10-15MPa, and the requirement for high-grade refractory bricks is above 25-30MPa, mainly because the normal temperature compressive strength of refractory bricks is a parameter of its organizational structure, especially the obvious Sensitive parameters of microstructure. The formation of the material's microstructure is restricted by various process parameters during its preparation, such as the characteristics of the raw materials and ingredient ratio, particle size and gradation, as well as the combination between particles, molding method and sintering state, etc., all of which have an impact on the material. has an important influence on the microstructure. Therefore, normal temperature compressive strength is a reliable method to test the current process conditions. In addition, the normal temperature compressive strength of the material can be used to indirectly evaluate the quality of other mechanical properties. For example, the normal temperature compressive strength of general refractory bricks is about 2-3 times the flexural strength and 5-10 times the tensile strength; Good wear resistance and impact resistance correspond to its high normal temperature compressive strength. Moreover, the method for measuring the normal temperature compressive strength is simple. Therefore, normal temperature compressive strength is a routine inspection item to judge the quality of bricks.

Load softening temperature and high temperature compressive strength of various refractory bricks

The load softening temperature of refractory bricks is the temperature at which the refractory bricks reach a certain compression deformation under the combined action of a certain heavy load and thermal load. It is a high-temperature mechanical property measured by the constant load continuous heating method to characterize the refractory bricks. . The ability to maintain stability against the combined effects of heavy loads and high temperature thermal loads.

The load softening temperature of refractory bricks is usually measured by the heating method, that is, a cylindrical sample with a diameter of 50mm, a height of 50mm, a center and aperture of 12 to 13mm is heated at a specified constant pressure and heating rate, and the temperature when it reaches the specified deformation is measured. . The temperature corresponding to this deformation is the load softening deformation temperature. The deformation temperature curve is often drawn (as shown in Figure 2-7, which shows the load deformation temperature curve of several refractory bricks) to determine the temperature at various deformations. my country's national standards stipulate that the aggravated load for ordinary refractory products is 0.2MPa, the heating rate when it is greater than 1000°C is 4 to 5°C/min, and the compression deformation from the high point of the curve will reach 0.5%, 1.0%, and 2.0% respectively. The temperatures at and 5.0% are marked with T0.5, T1.0, T2.0 and T5.0 respectively, and are used as the load softening temperatures of refractory bricks at all levels. For some refractory bricks, they suddenly burst or rupture when heated to a certain temperature. Various deformation temperatures cannot be measured, so the temperature at which this phenomenon occurs is regarded as the rupture point or rupture point.

The specific measurement method of the load softening temperature of refractory bricks is in accordance with the national standard GB5989-86.

The starting load softening temperature and load deformation temperature curve of refractory bricks are different. For example, the temperature at which clay bricks begin to soften and deform is relatively low, and the deformation temperature curve under load is gentle. The difference between the temperature at which deformation begins and when the deformation reaches 30% is nearly 350°C; the temperature at which magnesium bricks begin to soften and deform is relatively high, and the deformation continues after the initial deformation. If it is less than 10%, it will break; the starting softening and deformation temperature of the silica brick is very high, but after reaching the softening and deformation temperature, it will collapse almost immediately. All these changes mainly depend on factors such as their chemical mineral composition, the characteristics of the product structure, the quantitative ratio of the crystalline phase and the glass phase, and the liquid viscosity of the more fusible crystalline phase and the glass phase. Of course, the production process of the product also has a certain impact.

Load softening temperature is an important technical indicator for evaluating the quality of refractory bricks. The conditions under which the thermal load and heavy load interact when measuring the load softening temperature are close to many actual conditions of refractory bricks in service. Among them, the starting softening deformation temperature can be used as a reference value for the upper limit of the service temperature of most refractory bricks under similar working conditions. In addition, softening or the process from softening to cracking can be used as a criterion for the mineral composition and structural characteristics of refractory bricks and the rationality of its process system, thereby providing a basis for improving the quality of refractory bricks and correct material selection. However, the load softening temperature of refractory products is basically measured instantaneously, and in practice, the vast majority of refractory bricks serve for a long time, that is, they work under the combined action of thermal load and heavy load for a long time, resulting in deformation and cracks of refractory bricks. It is easy to develop continuously and may cause damage. Moreover, the heavy loads endured by refractory bricks during service are also different. The larger the load, the larger and faster the deformation will be. Therefore, the load softening temperature of refractory bricks can only be used as a reference to determine its maximum service temperature.