Abstract: A method of producing an oxidized fiber bundle includes heat-treating an acrylic fiber bundle aligned in a heat treatment chamber in which hot air is circulated while causing the acrylic fiber bundle to run on direction-changing rollers disposed on both ends of an outside of the heat treatment chamber, wherein first hot air is supplied in a direction substantially parallel to a running direction of the acrylic fiber bundle, and second hot air is supplied from above the acrylic fiber bundle at an angle of 20 to 160° with respect to a wind direction of the first hot air, so that the second hot air passes at least a part of a running acrylic fiber bundle in a longitudinal direction.

Abstract: There is provided an oxidation heat treatment oven including a heat treatment chamber configured to heat-treat a fiber bundle that is an aligned acrylic fiber bundle in an oxidizing atmosphere to form an oxidized fiber bundle; a slit-shaped opening configured to take the fiber bundle in and out of the heat treatment chamber; guide rollers installed at both ends of the heat treatment chamber and configured to turn the fiber bundle back; a hot air supply nozzle that has a longitudinal axis along the width of the fiber bundle traveling and that blows out hot air, in a direction substantially parallel to a traveling direction of the fiber bundle, above and/or below the fiber bundle traveling in the heat treatment chamber; and a suction nozzle configured to suck the hot air blown out from the hot air supply nozzle, in which the hot air supply nozzle satisfies disclosed conditions (1) to (3).

Abstract: A method of manufacturing a stabilized fiber bundle is described, which includes subjecting an acrylic fiber bundle aligned, to a heat treatment in an oxidizing atmosphere, with the acrylic fiber bundle being turned around by a guide roller placed on each of both ends outside a hot air heating-type oxidation oven, wherein an air velocity Vm of first hot air sent through a supply nozzle(s) disposed above and/or under a fiber bundle travelled in the oxidation oven, in a substantially horizontal direction to a travelling direction of the fiber bundle, and an air velocity Vf of second hot air flowing in a fiber bundle passing a flow channel in which the fiber bundle is travelled that satisfies expression 1) 0.2?Vf/Vm?2.0 ??1) to produce a high-quality stabilized fiber bundle and a high-quality carbon fiber bundle at high efficiencies without any process troubles.