GB1166779A - Hot Pressing Process and Apparatus - Google Patents

Abstract

1,166,779. Moulding refractory materials. E. I. DU PONT DE NEMOURS & CO. 17 July, 1968, No. 34100/68. Heading B5A. [Also in Division C7] Apparatus for the hot pressing of refractory powder materials comprises in combination: (a) reusable refractory open-ended shells 2 for containing the refractory materials, (b) pistons 7 which slidably fit in the two ends of the shells, (c) a housing 9 for maintaining a substantially oxygen free atmosphere or a vacuum around the powder during pressing, (d) means for introducing and conveying shells and associated pistons into and within the housing, (e) a member 17 in the housing with a cavity to receive and support the shell, (f) means 15 for heating the member 17, (g) means for positioning shells and associated pistons within the cavity, applying compacting pressure to the pistons and removing the shells and pistons therefrom, (h) means for cooling the compacted material and, (i) means for removing the shells and compacted material from the housing. The member 17 may be an electric resistance heater or may be graphite heated by induction and means may be provided in the housing for removing the compacted material from the shells either before or after cooling. The refractory material which is preferably in powder form is heated to a temperature between 500‹ and 2000‹ C. and is subjected to a pressure between 200 and 3000 p.s.i. for a time sufficient to compact the material to at least 95% of its theoretical density. Various heating and cooling cycles are described. In the apparatus shown, the lower piston 7, 36 is prevented from falling from the shell 2 by a rib 35. The powder is placed between two discs 6 in contact with but not connected to the faces of pistons 17. The loaded shells are mounted on tubes 38 (not shown) through which the pistons 4 can pass and are placed in the article 20 which may then be filled with an inert gas or evacuated. The shell is passed into the housing 9, optionally preheated and moved to the centre of the housing where it is engaged between the rams 11 and 12 and raised into the member 17, leaving the tube 38 on the conveyer 21. The shell and refractory material are raised to the moulding temperature by heat from member 17 and are maintained in this area during compaction by checking the positions of the rams 11, 12 against scale 13. After moulding the hot shell is replaced on the tube 38, is optionally cooled and the compact removed from the shell at 23 and the shell and compact are removed from the housing 9 via article 24. In alternative embodiments, several compacts may be formed at once by mounting several shells in a cylindrical container with axial parallel bores therethrough and the lower ram 11 may be surrounded by a resiliently mounted cylinder to support the shell container as it is raised into the heating area. The member 17 may be formed in several radially movable parts which clamp around the shell holding it rigidly in position and assist in heat transfer. The refractory material may be an oxide, nitride, carbide, silicide, beryllide, sulphide or mixture thereof, or these materials bonded with metal, e.g. tungsten carbide with cobalt. Specified materials are tungsten carbide, silicon carbide, aluminium oxide, tantalum carbide, titanium carbide and mixtures thereof when these materials are bonded with metals, e.g. cobalt, nickel and nickel molybdenum alloys.