Evaluation of filtration efficiency for single layer and double layers alumina filter using aqueous suspension

The quality of molten aluminum is dependent on the methods used for its treatment to remove impurities. Of these, rigid media tube filter (RMF) has been the most reliable. RMF bound coarse grain of alumina by 9Al2O 3·2B2O3 has been used widely all over the world. The purpose of this study was to examine the filtration efficiency of RMF using an aqueous suspension of ceramic powder instead of molten aluminum. During actual operation, inclusions accumulate on the surface of RMF to form a cake layer. But the cake formation was not expected in aqueous suspension, since its filtration efficiency showed initial operational conditions, i.e. surface and internal filtration. The results of our experiment clearly showed that filtration efficiency of RMF depended upon pore size and the operation condition. Namely, the filtration efficiency of small pore RMF allowed as high as possible removal of fine inclusions. It was confirmed that maximum inclusion size that could possible be filtered, was approximately 10% of maximum RMF pore size. Also, the operation conditions for higher filtration efficiency, was a slower flow rate and an aqueous suspension of low inclusion concentration. The filtration performance for double layers RMF was influenced by a smaller pore size and the filtration resistance reduced as compared to single layer. As the result of aqueous suspension was similar to that of TiB2 added molten aluminum, it was assumed that the aqueous suspension examination method was reliable.