Since the first manufacture of castables with reduced cement content based on the French Prost patent, the formulation of refractory castables has undergone significant improvements. Recently, technical characteristics of LCC, ULCC, and NCC castables have been developed along with their construction technology, extending their application to high-temperature and severely erosive environments where only fired refractory bricks were previously used.
The proportion of modern refractory castables used in refractory materials has increased, and it has achieved an irreplaceable position in the ironmaking and steelmaking industries, which are the largest consumers of refractory materials. In addition to the traditional alumina (silicon dioxide) raw materials, a wide variety of new refractory castables have been developed and introduced for production and industrial applications. Some typical examples of industrial applications of castables are as follows.
In ironmaking production, various types of refractory castables from LCC to NCC are mainly installed in the lining of the iron and slag ditches of the blast furnace. Al2O3-SiO2-SiC-C castables are typically installed by pumping or gunning techniques (spraying, etc.), usually based on high-alumina raw materials and containing additives such as SiC, carbon (sometimes magnesium-aluminum spinel).
Metallic aluminum or other additives are often used in these castables to enable fast drying. The refractory linings of torpedo tanks, especially the throat and waist, are often made of alumina-based castables with SiC and carbon additions. This type of castable is also used to maintain the equipment mentioned above.
In steelmaking production, ladles are the main consumers of castables, usually used for the lining and bottom of sleeves. Only magnesia carbon bricks are used for the slag line, and most of them contain spinel (or synthetic, or in-situ generated) aluminum-based castables, which have shown good performance in these applications.
Various installation methods are used in these cases, depending on availability at the specific steelworks. In some steelworks, the concept of “continuous lining” is applied. However, ladles are not the only steelmaking installations lined with refractory castables. Tundish permanent lining for continuous casting, integral porous plug, seat brick, spray lance, desulfurization and deargon stirring lance, vacuum refractory lining of RH degassing vessel, triangular area of EAF furnace, refractory brick sleeve, submerged nozzle, etc. are just a few examples of other applications of hydration-bonded castables in steelmaking production.
Modern castables have also been widely used in smelting and holding furnaces in the aluminum smelting industry. These castables have a microstructure that reduces penetration by molten metal. Anti-wetting additives (Ba salt, CaF2, AlF3) are applied to modify the refractory surface in contact with molten aluminum. Recently, refractory materials with calcium hexaaluminate as aggregate have also been applied in these fields.
In the cement industry, castables are mainly used in the discharge end, discharge area, and cyclone suspension pre-calciner. The main requirements for refractory castables in these applications are excellent alkali attack resistance, corrosion resistance, and excellent thermal shock resistance. Mullite castables with high alumina or sometimes SiC have been used with good results. In some cases, special parts such as the discharge end of the rotary kiln are produced as prefabricated parts using SIFCA technology.
Modern refractory castables have found significant applications in refineries and petrochemical industries where they must endure harsh conditions such as alumina catalysts, carbon monoxide exposure, carbon penetration, and prolonged thermal shock. Typically, these castables are installed using spraying technology.
In waste incinerators, the refractory castables must be highly resistant to chemical corrosion. In this environment, SiC-based materials have proven to be the most effective due to their high thermal conductivity, which ensures the necessary heat transfer.
