Method of producing flame-resistant fiber bundle and carbon fiber bundle and flameproofing furnace

An oxidation oven for heat-treating an acrylic fiber bundle comprising:

• (i) a heat treatment chamber having a slit through which aligned fiber bundles can enter and exit;
• (ii) a plurality of supply nozzles disposed separately from one another in a vertical direction apart in the heat treatment chamber for supplying hot air including first hot air in a direction substantially parallel to a running direction of the fiber bundle between a pair of opposed direction-changing rollers;
• (iii) a plurality of suction nozzles disposed separately from one another in a vertical direction in the heat treatment chamber for suctioning hot air supplied from the supply nozzle;
• (iv) at least one blower that circulates hot air through the supply nozzle and the suction nozzle;
• (v) at least one heater disposed on a flow channel for circulated hot air;
• (vi) a direction-changing roller disposed outside the heat treatment chamber and reciprocating the fiber bundle two or more times in the heat treatment chamber through gaps between the adjacent suction nozzles;
• and
• (vii) openings on lower surfaces of supply nozzles that supply second hot air at an angle of 20 to 160° with respect to a wind direction of the first hot air and allow passage of at least a part of a running fiber bundle in a longitudinal direction.