To prevent the deterioration of the spacer itself of a heating furnace which fixes a muffle and uses the spacer for sealing the muffle and a casing to each other.
The muffle 2, a heater 4 and a thermally insulating material 5 are disposed in the casing 1. The spacer 3 comes into tight contact with the outer peripheral surface of the muffle in a step part 2a where the outside diameter of the muffle is made small. The flank of the spacer comes into tight contact with the casing 1. The muffle extends outward beyond the portion into which the spacer comes into tight contact, by which the surface of the spacer is covered with the muffle so as not to be exposed into the muffle. Since the spacer is isolated from the atmosphere on the inner side of the muffle, the adhesion of SiO2 powder, carbon powder, or the like, to the surface of the spacer may be suppressed and the devitrification and failure of the surface of the spacer by radiation heat may be suppressed as well.
SUZUKI TOMIYOSHI
HIRAI HISANARI
