Method of filtering molten metals using a monolithic refractory honeycomb filter

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, monolithic honeycomb filters of zircon, or zircon substituted with up to 50% by weight of a metal oxide sintering aid, are useful to remove impurities from molten metals.
The filters are shaped to provide a frontal surface, for initial contact with the molten metal, and contain a plurality of open cells which extend substantially longitudinally and substantially mutually parallel from the frontal surface through the filter, thereby defining channels for the flow of metal.
Filter shapes of the invention, to be described more fully herein, have the surface-to-volume ratio necessary for proper filtration of impurities in the metals, and the fluid-flow characteristics adequate to provide the desired throughput of the molten metal stream.
Impurities larger than a cell opening are strained from the metal stream at the frontal surface, and smaller impurities adhere to the interior cell walls as the metal passes through.
As used herein, "honeycomb" is not used in the limited sense of bees' honeycomb, but is any structure which has substantially parallel open channels, or longitudinally-extending cells, therethrough defined by relatively thin separator walls and in which the transverse cross-sectional configuration of the channels or cells is of any rounded (i.
e.
, circular or elliptical) or polygonal (i.
e.
, triangular, rectangular, hexagonal) shape.
The zircon-based materials from which the filters are formed provide the physical properties desired for the molten metal service.
The materials have high strength, good thermal shock resistance, and porosity to a degree which can aid in the filtering activity but does not adversely affect strength.
Specifically, the refractory material useful in this invention is zircon (zirconium silicate) or a mixture of 50-100% by weight zircon and 0-50% by weight of a sintering aid for the zircon.
The sintering aid is a metal oxide selected from the group consisting of magnesium oxide, zinc oxide, cerium oxide, manganese oxide, titanium oxide, chrome oxide, iron oxide, copper oxide, nickel oxide, and mixtures of these