The invention relates to a method and to a device for stabilizing precursor fibers for the production of carbon fibers. In the method, precursor fibers are first heated to a first temperature and held at the temperature for a predefined duration. Subsequently, the precursor fibers are heated to at least one second temperature, which is higher than the first temperature, and held at said temperature for a predefined duration. During each heating and between the heating steps, the precursor fibers are in a gas atmosphere having a negative pressure in the range between 12 mbar and 300 mbar and having an oxygen partial pressure of 2.5 to 63 mbar. The device has at least one evacuable, elongate vacuum chamber for feeding the precursor fibers through, at least two lock units and at least one heating unit. At least one lock unit is used for the sealed insertion of precursor fibers into the at least one vacuum chamber, while at least one other lock unit is used for the sealed removal of precursor fibers from the at least one vacuum chamber. The heating unit has at least two individually controllable heating elements, which are suitable for heating the at least one vacuum chamber to at least two different temperatures in heating zones which are adjacent in the longitudinal direction.

A manufacturing method and an apparatus enable high productivity. A method for manufacturing an oxidized fiber bundle includes joining an upstream precursor fiber bundle and a downstream precursor fiber bundle together with a joining fiber bundle, and oxidizing the joined precursor fiber bundles by feeding the joined precursor fiber bundles through an oxidization furnace. The joining includes applying an oiling agent to a joint area of a joining target precursor fiber bundle before joining the joining target precursor fiber bundle and the joining fiber bundle together. A quantity of the oiling agent adhering to the joint area is 0.15 to 0.85 wt %.

Efficient production of high quality oxidized fiber bundles and carbon fiber bundles is described, comprising a step for heat-treating aligned acryl based fiber bundles in an oxidizing atmosphere while turning them back on guide rollers installed on both ends outside the furnace body of a hot gas heating type oxidation furnace wherein: supply nozzles for supplying hot gas into a heat treatment chamber are installed at an end in the traveling direction of the acryl based fiber bundles; a fiber bundle traveling passage(s) exists above and/or below each nozzle; hot gas is supplied from the supply face(s) located above and/or below the acryl based fiber bundle; and the requirements (1) and (2) are satisfied where Vf and V are defined as described.

1.5 m/s≤Vf≤15 m/s   (1)

1.5 m/s≤V≤10 m/s   (2)

The present invention provides an exhaust gas treatment method and an exhaust gas treatment device which prevent the generation of NO.sub.X, and treat a first exhaust gas and a second exhaust gas with a small amount of fuel, and the exhaust gas treatment method comprises a first combustion step which treats a first exhaust gas discharged from a carbonization furnace for carbonizing a fibrous substance in an inert atmosphere and a graphitization furnace for graphitizing a fibrous substance in an inert atmosphere and a second combustion step of treating a second exhaust gas discharged from a flameproofing furnace for flameproofing a fibrous substance in air atmosphere, wherein the first exhaust gas is combusted at an oxygen ratio of 0.8 or less in the first combustion step, and the second exhaust gas is combusted in the second combustion step using sensible heat and latent heat of a third exhaust gas discharged in the first combustion step.

A carbon fiber production method includes a carbon fiber production step including an oxidation step and a carbonization step; and an exhaust gas processing step including a heat exchange step; an external air mixing step; and a mixed external air supplying step in which the mixed external air is supplied to at least one step that uses heated gas in the steps in the carbon fiber production step; and among the exhaust gases, a high heating value exhaust gas having a heating value of 250 kcal/Nm.sup.3 or higher is supplied to an inlet side of an exhaust gas combustion apparatus and a low heating value exhaust gas having a heating value lower than 150 kcal/Nm.sup.3 is supplied to an outlet side of the exhaust gas combustion apparatus, respectively.

A carbon-fiber-precursor acrylic fiber bundle which can smoothly pass through a flame-resistance impartation step and a carbonization step. The carbon-fiber-precursor acrylic fiber bundle has a high-density part as a portion thereof, wherein the high-density part satisfies the following requirements (A) and (B). Requirement A: The high-density part has a maximum fiber density ρ.sub.max of 1.33 g/cm.sup.3 or higher. Requirement B: The portion extending between an intermediate-density point and a maximum-density-region arrival point has an increase in fiber density of 1.3×10.sup.−2 g/cm.sup.3 or less per 10 mm of the fiber bundle length.

A method of producing a precursor fiber for carbon fiber includes extruding a polyacrylonitrile copolymer solution from a spinneret into the air, immersing it in a coagulation bath liquid stored in a coagulation bath, redirecting traveling of the coagulating fiber bundle by a first guide immersed in the coagulation bath disposed below the spinneret, and pulling it out of the coagulation bath liquid into the air to prepare a coagulated fiber bundle, which is then subjected to at least a washing step in water, stretching step, oil agent applying step, and drying step, wherein the depth-directional coagulation bath immersion length, which means a distance between the starting point of the immersion of the spinning dope solution in the coagulation bath liquid and the first guide immersed in the coagulation bath where traveling of the coagulating fiber bundle is redirected, is 3 to 40 cm.

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).

A method manufactures a flame-retardant fiber bundle by flame retarding treatment of a polyacrylonitrile-based precursor fiber at 200-300° C. in an oxidizing atmosphere, wherein a fiber bundle is caused to travel so as to sequentially pass between an nth roller and an (n+1)th roller (n being an integer of at least 1 and no more than [m−1]) in a roller group formed from m (m being an integer of 3 or greater) contiguously set rollers, the roller axes of the m continuously set rollers being parallel to each other and perpendicular to the direction of travel of the fiber bundle, the roller diameter being 5-30 mm, and the specific gravity of the fiber bundle being 1.20-1.50.

A method of manufacturing a stabilized fiber bundle, including travelling an acrylic fiber bundle in an oxidation oven, with the acrylic fiber bundle being conveyed by guide rollers placed on both sides outside the oxidation oven, to subject the acrylic fiber bundle to a heat treatment in an oxidizing atmosphere, wherein a direction of hot air in the oxidation oven is horizontal to a travelling direction of the fiber bundle, and a contact probability P between adjacent fiber bundles, defined by expression (1), is 2 to 18%:

P=[1−p(x){−t<x<t}]×100  (1)

wherein P represents the contact probability (%) between adjacent fiber bundles, t represents an interspace (mm) between adjacent fiber bundles, p(x) represents a probability density function of a normal distribution N(0, σ.sup.2), σ represents a standard deviation of an amplitude of vibration, and x represents a random variable under the assumption that a median amplitude of vibration is zero.