Fabrication of Alumina Ceramic Filters and Performance Tests for Aluminium Castings

Alumina ceramic foam filters are developed for filtering impurities from aluminium and aluminium alloys while molten metal is entering to the mould. Cleaning liquid metal results in higher-quality castings, less scrap, and fewer inclusion defects. Al2O3 ceramic foam filter has been recently developed as a new type of molten metal filter to decrease casting flow in recent years. Foam filters can effectively remove inclusions, reduce trapped gas from liquid metal and provide laminar flow, and then the filtered metal significantly becomes cleaner. In this study, bentonite containing Al2O3 ceramic filters were developed rather than honeycomb ceramic filters so that laminar flow is obtained and velocity of molten Al can be controlled. Replica technique was used to make reticulated ceramic foam from the sponges. Bentonite was used to bind alumina particles both in room temperature and sintering temperature. Number of pores per inch and pore sizes were optimised for sufficient molten aluminium flow. Surface properties of the ceramic filters are also improved in order to control flow velocity.