To prevent a heater from being broken owing to a lining heat insulating member being blown up owing to return pressure upon vacuum replacement by disposing an atmospheric gas insertion hole in a lower furnace chamber and an upper terminal chamber, and using a ceramic board on an in-furnace wall.
Atmospheric gas insertion holes 7, 8 are disposed in a lower furnace chamber 5 and an upper terminal chamber 6, and ceramic boards 2, 3 are applied to an in-furnace wall. More specifically, the ceramic boards 2, 3 are provided on a ceiling, and many U-shaped heaters 4 are hung from the ceramic board 3 on the ceiling. A line of gas introduction ports 7, 8 in a furnace chamber 5 and a terminal chamber 6 is opened and closed with a solenoid valve, and its vacuum replacement operation is controlled with a sequence program. Hereby, the atmosphere is controlled and variations of a product are reduced while replacement time is shortened, and the heater 4 is prevented from being broken and the cost is sharply reduced.
SHIBANO JUN
MURAKAMI KATSUMI
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