part.1
Furnace building materials are mainly refractory bricks, heavy clay castables or high alumina castables. Due to the large material capacity, large heat capacity, and high thermal conductivity, the heat storage and heat dissipation losses of the furnace body are relatively serious. Moreover, due to the large heat capacity of the material, it takes a long time to bake the furnace and stop the furnace to cool down, which limits the energy saving and efficient operation of the heating furnace. In order to save energy and improve operating efficiency, it is an effective method to use lightweight castables with light bulk density, small heat capacity, and low thermal conductivity. However, most of the lightweight castables are currently difficult to meet the requirements of high temperature and flame erosion in the heating furnace due to their low operating temperature. The lightweight composite furnace lining is adopted, that is, the heavy castable (contact fire filling) on the inner layer is covered with light castable (insulation and energy saving). The construction process is complicated, and the effect is not ideal. Due to the different expansion coefficients of the lightweight castables, it will also cause a large shear stress on the hanging bricks, which increases the risk of the furnace roof collapsing. This has been proven in practice.
part.2
The key raw material of lightweight castables is lightweight refractory aggregate that can make the castables lighter in bulk density. Lightweight aggregates generally account for 50% to 70% of the total pouring, and the volume ratio can reach more than 90%. Therefore, the performance of castables mainly depends on the performance of lightweight aggregates. In the past, the reason why the use temperature of lightweight castables was lower was that the use temperature of the aggregate was lower.
In order to use castables with a long-term service temperature of 1400~1500°C, lightweight mullite aggregates have been successfully used. Mullite is a refractory mineral with good mechanical and high temperature properties. Its melting point can reach 1910°C, with high hardness and low creep. Refractory products with mullite as the main mineral phase have high refractory performance.
The lightweight mullite castable is prepared by using the lightweight mullite aggregate. The refractoriness of this castable is as high as 1710°C, and it has the characteristics of small bulk density and high temperature, and can be used at an ambient temperature of 1500°C for a long time.