WO1992004170A3 - Method of manufacturing articles from powdered materials - Google Patents

Abstract

Pasty materials from which green parts are molded before sintering, and which otherwise are difficult or impossible to mix while in the pasty state, are mixed and homogenised by forming a lump, placing it between two parallel flat platens, and pressing the platens together until the lump becomes a thin flat pancake; thereafter the pancake is remade into a lump or ball by moving its circumferential edges inwards. This press-mixing cycle is repeated until the process is sufficiently complete, typically involving from 10 to 50 repetitions, usually about 20 to 30. Molded ceramic articles with 'mirror-finish' surfaces are produced economically by employment of small amounts, 5 % or less, of superplastic shear deformation produced by molding the articles with the surfaces to be finsihed in contact with mold surfaces of the required finish. The starting powdered ceramic materials are of particle size one micrometer or less, and molded green parts are formed using slurrying, grinding, and mixing techniques that maintain material uniformity and keep the particle size below one micrometer. The green parts sintered using rate controlled sintering to maintain grain size below the one micrometer value critical for superplastic forging. The sintered parts are then molded as described at a temperature above the minimum superplastic tmeperature of 0.5 M, where M is the melting temperature of the ceramic material.