Cylindrical furnace for treating materials at high temperatures and pressures

A vertical furnace for isostatic hot pressing, comprising a pressure chamber formed by a high pressure cylindrical cylinder and end closures extending thereinto, means for taking up axial forces exerted by a pressure medium acting against the end closures, and insulation means defining a furnace compartment and located within the interior of the pressure chamber, the improvement wherein said insulation means comprises a tubular insulating portion and a cover closing the upper end of said tubular portion, said insulating portion comprising an inner support tube of graphite material, a plurality of outer layers of heat insulating material surrounding said tube, means pressing said outer layers against one another and against the outer surface of said tube, first foils of graphite material having low gas permeability surrounding said tube and each of said layers, and said cover comprising a plurality of cover discs covering said tube and each of said layers, second foils of graphite material being disposed on one of the sides of said discs.