The deep bed filter is a new type of filter device developed in recent years. It is made up of multiple layers of alumina balls and a layer of alumina grit of appropriate size. The size and stacking method of alumina balls and gravel are determined according to the quality requirements of the final product.
The filter bed is a porous medium. The bed body is designed and calculated according to the requirements to ensure that the aluminum liquid achieves laminar flow, prevents secondary pollution from destroying the aluminum oxide layer, and makes the path of the aluminum liquid flow through the tortuous filter layer under the action of gravity as long as possible, so that the impurity particles are intercepted or deposited on the filter bed. It is suitable for the needs of high-demand, large-volume, semi-continuous casting production, and the single casting-rolling production line with small output is currently less used.
The use of a deep bed filter must fully immerse the molten aluminum in the filter bed, otherwise, it will cause some local temperatures to be too low, causing the aluminum to solidify, reducing the flow area, shortening the flow path, and affecting the effect and service life of the filter bed. Therefore, before the bed is filtered, on the one hand, it must be fully preheated, and the bed must be kept evenly heated; on the other hand, the filter bed must be filled with a proper temperature of aluminum liquid at a proper flow rate. The filling procedure is: inject liquid aluminum from the outlet of the filter bed, make the aluminum liquid rise from the bottom of the filter bed, and slowly spread over the top of the filter bed to ensure that the filter bed is 100% immersed in the liquid aluminum.
The advantages of the deep-bed filter are thick filter layer, long flow path, and many impurity particles adsorbed. Large over-flow, suitable for large-scale and mass production. However, deep bed filtration only uses filling to form a filter layer, and the filter medium is easy to loosen and move, causing some small impurities to be stirred into the melt and reduce the filtering effect.
The filter tube of the tubular filter adopts a fixed structure, the structure of the filter tube itself does not loosen and move like the filter layer of the deep bed, so the filtering effect is good. However, the initial pressure head of the filtration is large, the replacement of the filter tube is more troublesome, and the filtration cost is higher.
Compared with the corundum tube, the ceramic foam filter has a larger pore diameter, a smaller density and a lower filtration accuracy. Compared with the deep-bed filter, the filter layer is thin, and there are less impurities and particles that can be adsorbed. But this can be improved by increasing the number of filtration stages, that is, two-stage and three-stage filtration can be used to improve filtration accuracy. Its advantages are small initial pressure head, convenient replacement, simple operation and better filtering effect.