The production of high-alumina refractory castables is inseparable from the castable formulation. The high-temperature performance of high-alumina castables varies, and the ratio of various refractory raw materials is adjusted through the formulation to ensure that the combination of raw materials has good high-temperature performance at high temperatures.
The high-alumina castable formulation ratio is: 65-70% high-alumina bauxite aggregate, 7-10% high-alumina cement, 5-8% silica fume and alumina powder, 15-24% bauxite fine powder, and 0.2% water reducer. Retarder or accelerator may be added depending on the construction environment.
Bauxite is the most important aluminum-containing mineral. Natural bauxite is high in density, opaque, and brittle, making it unsuitable for use as a mortar or concrete aggregate. However, sintered bauxite has strength and hardness far exceeding most natural rocks, making it commonly used in ultra-high-strength, high-wear-resistant mortars or concrete.
Bauxite aggregate refers to sintered bauxite aggregate, which is actually a high-strength and high-hardness artificial aggregate similar to ceramic.
Refractory Cement Proportions
Refractory cement often refers to cement primarily composed of calcium aluminate. Refractory cement is the basic binder for monolithic refractory materials, particularly castables. The properties of refractory cement are primarily determined by its mineral composition. Calcium aluminate, the primary mineral component of refractory cement, has a high hydraulic activity and sets rapidly, albeit slowly. This is the primary source of high-alumina cement’s strength, particularly its early strength. The exothermic temperature and time it takes to reach this temperature for a single cast of different types of high-alumina cement are determined by the exothermic properties and content of the calcium aluminate.
Refractory cement is a type of binder that can function at both room and elevated temperatures. The refractory properties of refractory cement are crucial for monolithic refractory materials. Generally speaking, the higher the iron content in refractory cement, the lower its refractory performance. In practice, ordinary high-alumina refractory cement is used at temperatures below 1300°C, high-alumina cement is used below 1500°C, and low-calcium high-alumina cement (high-grade high-alumina cement) is used above 1600°C.
Three Major Functions of Water Reducers
Water reducers have three primary functions. First, they reduce the water consumption of refractory castables. Second, they increase the castable’s fluidity, improve workability, and enhance its plasticity during construction. They can also regulate the castable’s setting time.
Wollastonite has high purity, a fine needle-like structure, low loss on ignition, and low levels of harmful components (MnO and Fe₂O₃). Its performance surpasses similar ores domestically and internationally. After refined processing, wollastonite exhibits a high aspect ratio and high whiteness.
In the formulation of high-alumina refractory castables, the ratios of various refractory raw materials and additives must be strictly controlled. Only when all raw materials reach a balanced value can the high-alumina refractory castable exhibit excellent high-temperature properties.
Refractory mortar is divided into two categories: heavy-duty and light-duty. Based on the binder, it can be categorized into phosphate mortar, water glass mortar, and organic binder mortar. Based on the material, it can be categorized into clay, high-alumina, magnesium silicon, and carbon mortar. Refractory mortar, composed of refractory aggregate, binder, and admixtures, is a joint material for molded products. It is used to bond gaps between refractory bricks in the linings of various industrial kilns. Different refractory mortars have different mix ratios. Refractory mortars from Rongsheng Refractory Materials. Flexural strength of refractory cement mortar: 6.0 MPa after 24 hours; 7.0 MPa after 72 hours. Compressive strength of refractory cement mortar: 45.0 MPa after 24 hours; 55.0 MPa after 72 hours.
Characteristics of Refractory Mortar
Good plasticity and easy construction.
High bond strength and strong corrosion resistance.
High refractoriness, reaching 1650°C ± 50°C.
Excellent slag resistance.
Excellent thermal spalling resistance.
The application scenarios of refractory mortar vary depending on the material used. Magnesia refractory mortar is primarily used for laying magnesia bricks in converters, electric furnaces, and non-ferrous metal smelting furnaces. Silica refractory mortar is primarily used in coke ovens and glass kilns. Refractory mortars are widely used and play a significant role in construction, industry, metallurgy, and other sectors.
