| 摘要 |
1,186,530. Isostatic compaction. ENGLEHARD INDUSTRIES Ltd. 1 Oct., 1968 [4 Oct., 1967], No. 45298/67. Heading B5A. In the production of green compacts for sintering by the isostatic compression of particulate materials within a mould 9, comprising a reversible gel e.g. a gelled highly plasticized polyvinyl chloride composition, distortion and/or fracture of the compacted material 12 upon release of compacting fluid pressure and expansion of the mould 9 is avoided by surrounding the mould cavity with a body of particulate material 10 which is readily compactible and which is located within the body of the mould 9 and, after compaction by the fluid pressure, withstands the expansion stresses exerted by the portion of the gel between the compact 10 and the compact 12, and which portion is then removed by the melting thereof e.g. by heating to 170‹ C. or, alternatively, by cutting away if the gel incorporates a release agent. The body of material 10 is in the form of a ring for the illustrated compact 12 of a crucible, and desirably approximates in form to that of the compact 12 which may also comprise a tube, nozzle or capsule. The mould 9 is surrounded by a perforated brass cylinder 6, comprising two soft soldered halves whereby it is readily removable from around the mould 9. The particulate material 12 to be compacted may comprise ruthenium, iridium, and other platinum group metals and alloys thereof as well as refractory metal oxides and other ceramic material. The material 10 may comprise iron, nickel or copper powder. The moulding of a crucible from iridium powder is described under a water pressure of 25 tons/sq. inch, the compact being sintered in an atmosphere of hydrogen within an electric furnace wherein the temperature is raised over five hours to 1550‹ C. at which it is maintained for three hours before cooling slowly over eight hours. The mould 9 is moulded by casting the polyvinyl chloride at 170‹ C. within the cylinder 6, the cavities for the materials 10 and 12 being respectively defined by mild steel members (5 and 4), Fig. 9 (not shown), located upon a slotted mild steel base-plate (8), the open ends of the cavities thereby formed being sealed with gel after insertion of the respective materials 10 and 12. |
