Compression Testing of Ceramic Foam Filters (CFFs) Submerged in Aluminium at Operating Temperature

Particles and inclusions are commonly removed from molten aluminium with the use of Ceramic Foam Filters (CFF). The mechanical properties of CFFs are of great importance not only during transportation, storage, and mounting, ut also in view of securing the integrity of the filters during operation. Data on the compression strength of CFFs at room temperature are available in the literature, but this is not the case for their performance under operating conditions. The main aim of the present study has therefore been to develop an experimental procedure enabling compression testing of CFFs submerged in molten aluminium at operating temperature, i.e. when exposed to actual casthouse conditions. The effect of temperature and holding time was investigated with tests performed at room temperature, at operating temperature with varying duration of filter sample preheating and submerged in molten aluminium. The developed procedure for the measurement of the compression strength for samples submerged in aluminium showed realistic and reproducible data in comparison with previous studies and testing at room temperature. The filter tested was a commercial 30 ppi Al2O3-based CFF, which as expected revealed a significant decrease in compression strength for the filter samples submerged in aluminium. The weakened structure of the ceramic foam is believed to be due to a reaction occurring between the CFF and the molten aluminium. Additionally, the exposed filter samples also exhibited a less brittle behaviour compared to the unexposed samples, indicating that even a softening of the ceramic structure had taken place.