Laboratory Scale Study of Reverse Priming in Aluminium Filtration

Inclusions are one of the most serious problems encountered in aluminium production and melt treatment. Even small inclusions, not larger than a few tens of micrometres, can potentially have considerable consequences for the down-stream processing and a detrimental effect on the final product. Ceramic Foam Filters (CFFs) are commonly used to remove inclusions from the melt before the casting process. The very first phase of the filtration is called the priming period. This is when the molten metal meets the filter and fills up the pores inside the filter. In order to obtain good priming and to avoid freezing of the metal inside the filter, the filter must be properly preheated. During standard operation in industry, the metal flow direction during priming is typically the same as the metal flow during filtration. In the present work, equipment for testing the effect of reverse priming has been developed. Tests with standard and reversed priming directions have been carried out and the spent filters have been examined. The interface between the metal and the filter has been studied and it is concluded that all filters were well primed no matter the priming direction.