The Effect of Vacuum Forming on the Quality of Refractory Materials

Various designs of furnaces for melting alloys are used in the foundry industry. Regardless of their design, they have one common detail, which is the lining of their interiors with refractory materials. This component in the design of a metal-melting furnace has a very important task-to protect the rest of the furnace assemblies from thermal and mechanical damage. Continuous technical progress and the quality requirements of casting production produce increasingly higher demands for refractory materials in connection with their development as well. The article presents the results of an innovative method of vibratory compaction of refractory material (high-alumina aluminosilicate) using reduced pressure. The analysis presents a comparative study of two methods used for forming refractory materials, i.e., the application of the mentioned innovative method and the classical (standard) method of compaction by vibration only. The effects of the introduced modification in the manufacture of ceramic shapes were evaluated by means of the material's resistance to thermal shock, linear expansion, and dimensional change due to firing, apparent density, open porosity, and apparent specific gravity, determination of total pore volume and pore size distribution by mercury porosimetry, and slag resistance. The tests performed indicate that the procedure of lowering the pressure during the vibratory compaction of the refractory material creates a more homogeneous structure with a smaller number and size of pores. This makes it possible to improve most of the parameters that determine the quality of the refractories used for the linings of the foundry furnace.