Abstract

The use of carbon-bonded alumina filters became a common way to increase the purity of steel by removing non-metallic inclusions from the melt. However, established filter processing routes such as the replica technique are restricted with regard to the mechanical strength and the pore structure of the produced filter systems. In this study, a novel gel-casting process is presented as a viable alternative. The desired filter structures have been casted using a water-based alumina-carbon slurry with sodium alginate as gelling agent. By pumping the material into a watery solution of calcium chloride dihydrate, the alginate forms a solid gel. This allows the computer-assisted manufacturing of three-dimensional lattice structures consisting of a continuous filter strut. The produced filter structures were immersed in a steel melt at 1585°C. Afterwards, the microstructure and the chemical composition of the filter surface were characterized by digital light microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The study showed that the developed processing route is suitable for the production of carbon-bonded alumina filters for steel melt filtration. The tested samples provided sufficient thermal shock resistance and refractoriness in contact with molten steel. Furthermore, in-situ formed layers and crystalline phases were found on the surface of the immersed filters. These observations prove the filter effect of the produced alumina-carbon structures. The novel processing route is very promising because it allows the production of full-strut filters with adaptable macro-porosity resulting in higher component strength and tailored melt flow conditions.