1. Fire Resistance
Fire resistance refers to the temperature at which a material reaches a specific degree of softening under high temperature action, characterizing the material's resistance to high temperature action. The fire resistance of a product mainly depends on its mineral composition, the amount of fusible impurities, the mutual binding of minerals, and the degree of diffusion of each component. Some commonly used refractory products refer to the fire resistance of clay bricks at 1300~1650 ℃, high alumina bricks at 1500~2000 ℃, silicon bricks at 1600~1730 ℃, and magnesium bricks above 2000 ℃.
2. Load Softening Temperature
Load softening temperature, also known as the load deformation temperature, it refers to the temperature at which refractory products undergo deformation under a constant compressive load under specified heating conditions. It represents the resistance of the product to the simultaneous action of high temperature and load, to a certain extent indicating the structural strength of the product under similar usage conditions. It also indicates that the product exhibits significant plastic deformation at this temperature, which is an important quality indicator of usage performance. Carbon bricks are less prone to deformation when working at high temperatures. The load softening point of clay bricks is lower, and the load softening temperature of high alumina bricks is higher than that of clay bricks.
3. Apparent Porosity
It refers to the percentage of the volume of open pores in refractory products to the total volume of the product. The apparent porosity not only reflects the density of refractory materials, but also characterizes whether the particle size composition, molding, and firing are reasonable in their manufacturing process. Except for lightweight refractory products, low porosity raw materials or products are beneficial for improving product quality, improving mechanical strength, reducing surface area in contact with slag, and extending service life. Porosity of Refractory brick is distributed in coarse particles, binders and between coarse particles and binders, which improves the thermal insulation performance of Refractory brick and reduces the corrosion resistance of Refractory brick. The apparent porosity of magnesium bricks ranges from 14% to 20%, while that of high alumina bricks can reach 18% to 23%. The apparent porosity of clay bricks is relatively high, ranging from 18% to 26%. Increasing the forming pressure and sintering temperature can both reduce the porosity of the product.
4. Room Temperature Compressive Strength
At room temperature, use the pressure testing machine to load the Refractory brick sample with the specified size at the specified rate until the sample is broken, and calculate the room temperature compressive strength according to the maximum load recorded and the area of the sample under load. The normal temperature compressive strength of Refractory brick is generally greater than 30MPa. The compressive strength of Refractory brick mainly depends on the strength of raw material particles themselves, the firmness of particle bonding, the number and existing form of pores, and the binding capacity of the binder added.
5. Reburning Linear Change
The linear change of reburning is the index of Refractory brick expressing high temperature volume stability. It refers to the residual expansion or contraction of Refractory brick samples after being heated to the specified temperature for a certain time and cooled to room temperature. This process leads to irreversible changes in the size (length) of Refractory brick, which represents the linear change rate of re firing in%. Under certain conditions, the residual expansion hazard is relatively small. Appropriate residual expansion can bridge the masonry joints and improve the service life of the masonry, but excessive expansion will damage the shape of the masonry and cause it to collapse. Excessive residual shrinkage can increase the brick joints of the masonry, affect the integrity of the masonry, and even cause the masonry to collapse. The allowable linear change rate of Refractory brick with different materials is generally not more than 0.5%~1.0%.
6. Thermal Shock Stability
The performance of Refractory brick that can resist the rapid change of temperature without damage is called thermal shock stability. This performance is also known as thermal shock resistance or resistance to sudden temperature changes. The number of quenching and heating times of Refractory brick from 1100 ℃ to room temperature shall be taken as the measurement. Refractory brick is a heterogeneous brittle material. Compared with metal products, its thermal expansion rate is larger, its thermal conductivity and elasticity are smaller, its tensile strength is lower, and its ability to resist thermal stress without damage is poor, leading to its low thermal shock resistance.
