The liquid metal filter was developed in the 1970s. The liquid metal purification technology was first applied to aluminum alloys. Because the melting point of aluminum alloys is low, the density of alloys and oxides are close, and inclusions are difficult to float. Inclusions are the most common casting defect. In casting production, many process links are to reduce casting inclusions. Such as the selection of furnace materials, smelting control, covering the slag collector on the ladle, carefully removing the slag before pouring, using corkscrew bottom pouring ladle or teapot pouring ladle, designing closed or semi-closed pouring system, and horizontal runner set Slag bag, slag collecting tank, ceramic foam filter, etc.
Subsequently, liquid metal filter has also been widely used in cast iron, cast steel and copper alloys. Filters are used in the casting production to filter and purify the molten metal, which can effectively filter out the primary and secondary liquid/solid non-metallic inclusions in the molten metal, simplify the pouring system, prevent inclusion defects, improve the mechanical properties of the castings, and reduce the castings Machining allowance can improve the surface finish of casting and prolong the life of machining tools. Especially for some castings with complex structure and strict requirements on surface and internal quality, the filtration and purification of molten metal is irreplaceable by other technologies.
According to the type and melting point of the casting alloy, the metal liquid filtration and purification can use woven filters, glass fiber filters, and ceramic foam filters.
Foam ceramics generally use polyurethane foam as a carrier, filled with ceramic slurry made of refractory aggregate sintering aids, binders and other micro powders and water, and then extrude the slurry, and the rest is wrapped around the foam fiber After drying, baking, and sintering at high temperature, polyurethane is decomposed by heat, leaving a foamy ceramic product, that is, a foam ceramic filter. The ceramic foam filter is a third-generation product for filtering and purifying molten metal. The ceramic foam filter can be used in a variety of casting alloys and has been commercialized.