Depending on the density and shape of the finished product, there are sintering, casting, and melt-blown methods. The sintering method involves pre-calcining some raw materials into clinker, crushing and screening them, then mixing them with raw materials in a specific ratio, followed by shaping, drying, and firing. The purpose of pre-calcining the raw materials is to remove moisture, organic impurities, and gases from the decomposition of sulfates, thereby reducing firing shrinkage and ensuring the accuracy of the product's dimensions. After crushing and grinding, the raw materials also need to be screened, as the gradation of powders of different particle sizes ensures the densest packing and a dense green body.
To homogenize the composition and particle size of the various raw and clinker materials, mixing is necessary, and binders are added to enhance the bonding strength of the green body. For example, binder clay is added to aluminosilicate green bodies, sulfite pulp waste liquor is added to magnesia green bodies, and lime slurry is added to siliceous green bodies. Depending on the moisture content of the raw materials, semi-dry molding (approximately 5% moisture), plastic molding (approximately 15% moisture), and slip casting (approximately 40% moisture) can be used. Then, drying and firing are performed. The fusion casting method involves mixing and finely grinding the raw materials, melting them at high temperatures, directly casting them, and then cooling, crystallizing, and annealing to obtain the finished product. Examples include fused casting mullite bricks, corundum bricks, and magnesia bricks. These materials have dense bodies, high mechanical strength, high-temperature structural strength, and good slag resistance, and their applications are constantly expanding. The melt-blown method involves melting the raw materials and then blowing them with high-pressure air or superheated steam to disperse them into fibers or hollow spheres. The products are mainly used as lightweight refractory and insulation materials. In addition, powdered or granular unshaped refractory materials can be made, which are then bound with binders such as tar, asphalt, cement, phosphates, sulfates, or chlorides before use, and can be used directly without molding and sintering.
