Method of preparing molten metal filter

A method of preparing a disposable filter for filtering molten metal which comprises:

• A. providing an open cell flexible organic foam material having a thickness of from 1/4 inch to 4 inches and having a plurality of interconnected voids surrounded by a web of said material, wherein said foam contains from 5 to 100 pores per inch;
• B. providing an aqueous ceramic slurry containing from about 10 to 40% water, wherein said ceramic is selected from the group consisting of alumina, chromia, zirconia, magnesia, titanium dioxide, silica and mixtures thereof, and impregnating said material therewith by immersing said material in said aqueous ceramic slurry so that the web is coated therewith and the voids are filled therewith;
• C. compressing the impregnated material and releasing the compression by passing said impregnated material through preset rollers to expel from 25 to 75% of said slurry therefrom while leaving the web coated therewith;
• D. forming said slurry coated flexible foam into a desired curved configuration, drying said material while in said configuration and retaining said material in said configuration throughout the drying step;
• and
• E. heating the dried material to burn off the web of flexible foam and to sinter the ceramic coating while avoiding collapse thereof, wherein the dried impregnated material is heated in two stages, with the first stage being to slowly heat at a rate less than 10.degree. C per minute to a temperature of from 350.degree. to 700.degree. C and hold within said temperature range for from 15 minutes to 6 hours to burn off the web of flexible foam, and with the second stage being to heat at a rate less than 100.degree. C per minute to a temperature of from 1200.degree. to 1600.degree. C and hold within said temperature range for from 15 minutes to 10 hours to sinter the ceramic and wherein said dried material is retained in said configuration throughout said heating step,
• thereby providing a fused ceramic foam having a desired curved configuration and having a plurality of interconnected voids surrounded by a web of fused ceramic in the configuration of said flexible foam, wherein the resultant fused ceramic foam has a density of less than 30% of the theoretical density for a ceramic material of the same size.