Metal filtration efficiency is affected by the thickness, pore size, and the effective flow area of the molten metal filter.
The greater the thickness of the filter, the better the strength of the filter, and the higher the filter’s deep metal filtration efficiency, of course, the higher the cost of use. Considering the most suitable strength and filtration efficiency, a 22m thick filter is recommended.
The smaller the pore size, the better the metal filtration effect, but the greater the obstacle to flow. The filter pore size standard is 10 PPI (10 holes per inch) (coarse), 15ppi (15 holes per inch) (medium) and 25ppi (25 holes per inch) (fine).
In some foundries, the ratio of the cross-sectional area of each part of the gating system is set to ensure the appropriate flow rate. Various ceramic filter media show a certain degree of pressure drop because they greatly adjust the flow of molten aluminum. In order to reduce the influence of the filter on the velocity of molten iron, the flow area of the filter should be much larger than the flow control area of the gating system. The filter should not become the flow control section of the gating system. Therefore, it is recommended that the area of the filter be at least 2 to 5 times the flow control area.
All molten metal filters have a limit metal overflow before they are completely blocked. Due to the filtering out of the inclusions, the effective flow area of the foam ceramic filter is reduced and flow obstruction occurs. In extreme cases, exceeding this limit can cause the flow through the filter to stop completely. The flow capacity of the ceramic filter varies greatly with the inclusion content in the molten iron, the pouring temperature and the design of the pouring system. The foundry can determine how much flow area the filter needs based on the flow value and the pouring weight of the casting.