Muffle furnace for continuous heat treatment

Claim 1

A muffle furnace for continuous heat treatment, during passage of the material, of refractory and carbon-containing products which are impregnated with a carbon-containing material the pyrolysis of which produces combustible vapors, the production cycle of these products having a passage of predetermined duration at a temperature which may be from about 1100° to about 1150° C., the furnace being heated by a flame burner without combustion gases directly contacting the products to be treated, and comprising the following zones through which said muffle passes: (a) an inlet zone defined by a double casing (7) provided around the muffle (10), through which recycled combustion gases circulate to serve as a heating means in indirect heat exchange relationship; (b) a heating zone defined by a heat-insulated chamber (4), provided with said flame burner and at least one means (12) for circulating the combustion gases around the muffle portion passing through said chamber; and (c) an outlet zone provided with at least one means for controlling the cooling rate of the treated products; wherein said chamber includes a partition (21) which divides the heating zone into three sections comprising, in the direction of movement of material through the muffle: (d) a zone for volatizing and removing volatile materials from the carbon-containing impregnated material, in which zone the muffle comprises an aperture (22) opening into a passage delimited by the partition (21) and an outer wall (24) of the furnace, said passage having an outlet which is situated in the vicinity of the flame of the burner (11), whereby said volatile materials are combusted by the burner flame to provide heat in said heating zone; (e) a zone (25) for pyrolyzing and carbonizing the carbon-containing impregnated material; and (f) a final firing zone (26) in which the maximum temperature of from about 1100° to about 1150° C. required for the heat treatment is reached, and wherein said means for circulating the combustion gases comprises: (g) a fan (12); and (h) a separating partition (13) within said heat insulated chamber, which defines with a wall (14) of the furnace, a passage (15) having one end opening into the heat insulated chamber and the other end opening adjacent said muffle in a transition region between said heating zone and said outlet zone.