Abstract:
A cylindrical elongated furnace for treating material at high temperature in a gaseous atmosphere under high pressure is formed of a high pressure cylinder with end closures projecting into it and a furnace chamber arranged in the high pressure cylinder. The furnace chamber is insulated from the walls of the pressure chamber by a cylindrical casing having gas-impermeable tubes arranged one inside the other with an insulation between them. At least one layer of insulating material in the casing engages only the outer or inner surface of one tube and is spaced from the adjoining tube, the space between being filled with gas. The insulating material may be held against the outside of one of the tubes by rings or a spiral strip running helically.