Abstract: An acrylonitrile based fiber is disclosed which is composed of copolymers comprising at least 96 mole % of acrylonitrile and 1.times.10.sup.-2 to 70.times.10.sup.-2 mole % of a vinyl component or vinyl components containing acidic groups, and containing a specific amount of zinc. The fiber is used in production of oxidized or flame resistant fiber. The oxidized or flame resistant fiber is produced by heat-treating or oxidizing the acrylonitrile based fiber in an oxidation furnace equipped with a plurality of roller units while limiting the shrinkage of the acrylonitrile based fiber within specific limits as the oxidation proceeds. On carbonizing the above oxidized or flame resistant fiber while limiting the shrinkage thereof a carbon fiber which is of high strength and low fluffing is obtained.

Abstract: A vertical heating apparatus for production of graphite fibers from preoxidized fibers or carbon fibers comprises of a tubular heating element which generates heat by high frequency induction. A heat-insulating material layer surrounds the tubular heating element coaxially. The layer is composed of carbon particles having specific grain diameters and angles of repose. A high frequency induction unit is provided around the heat-insulating material layer also in a coaxial relation thereof.

Abstract: A process for producing carbon fibers which comprises feeding an inert gas into a vertical furnace at about 500 to about 1,000.degree. C. and into a transverse furnace at about 800 to about 2,000.degree. C. connected thereto so that the inert gas flows from the transverse furnace toward the bottom of the vertical furnace and then to the top of the vertical furnace, and feeding preoxidized fibers from the top of the vertical furnace to pass the fibers countercurrent to the inert gas flow through the two furnaces to thereby carbonize the fibers. Apparatus of the type shown in the drawing for the production of carbon fibers by the above process. Carbon fibers having good performance can be produced with good efficiency.

Abstract: A process for continuously producing carbon fibers which comprises preoxidizing polyacrylonitrile fibers containing at least about 90% by weight of acrylonitrile at a temperature of about 200.degree. to about 300.degree. C in an oxidizing atmosphere while allowing the fibers to shrink about 40 to about 70% (of the free shrinkage of the fibers determined under a load of 1 mg/d) with the progress of preoxidation; then carbonizing the preoxidized fibers at about 500.degree. to about 1,000.degree. C in a non-oxidizing atmosphere so that the shrinkage of the fibers finally becomes about 40 to about 70% (of the free shrinkage of the preoxidized fibers determined when the fibers are placed under a load of 1 mg/d and heated at 1,000.degree. C for 15 minutes); and then heat treating the carbonized fibers at constant length at a temperature of up to about 3,000.degree. C in a non-oxidizing atmosphere.