A filter for use in the filtration of molten metals comprises a ceramic foam filter with gasket made from fibrous material surrounding its peripheral surface.
Due to dimensional variations in ceramic foam filters of a particular nominal size, and in the case of filtration of molten metal in a permanent mold or die due to erosion of the die surface or to variation in the thickness of the coating which may be applied to the die surface, there is a tendency for metal to bypass the filter around its outer surface so that some unfiltered metal can pass through the apparatus or into the mold or die. In extreme cases, the filter may actually move out of its proper location during casting. Filtration efficiency is therefore decreased and non-metallic inclusions can be formed in the cast metal.
It is known to use a gasket made from ceramic fiber to surround the surface of a ceramic foam filter which mates with part of the filtration apparatus or with the mold, in order to fix and seal the filter in position. As the gasket is relatively soft it is not wear-resistant and can be damaged during transportation or handling, and fibers can become detached from the gasket and pass through the filtration apparatus or into the mold.
Adtech provides a ceramic foam filter having its peripheral surface surrounded by a gasket made from fibrous material.
The horizontal cross-section of the ceramic filter may be any desired shape but will usually be circular, square, or rectangular.
The gasket may be made from a soft, flexible strip of ceramic fibrous material, which is preferably free of organic compounds so as to avoid the possibility of hydrogen pick-up by the metal when filtering a metal such as aluminum. The thickness of the strip will usually be from 3 to 6 mm, and such a strip is compressible to 1 to 2 mm. Alternatively, the gasket may be made from a woven glass fiber cloth. The width of the gasket may be the same as the thickness of the filter or less than the thickness of the filter.
The gasket of the filter enables the filter to be fixed and sealed in position in metal filtration apparatus or in a permanent mold or die, thus avoiding movement of the filter during filtration and bypass of metal around the filter.