METHOD FOR MANUFACTURING ACRYLONITRILE BASED FIBER BUNDLE AND METHOD FOR MANUFACTURING CARBON FIBER BUNDLE

An object is to provide a drawing method which enables a pressurized steam drawing of an acrylonitrile-based fiber bundle used as the precursor fiber of the carbon fiber bundle, and in particular, a drawing method which realizes a high processability when this treatment is conducted at a high draw ratio and high speed. This invention is a method for producing an acrylonitrile-based fiber bundle comprising the steps of spinning a spinning solution containing an acrylonitrile-based copolymer, and subjecting the fiber bundle (7) to a pressurized steam drawing in a pressurized steam drawing apparatus (A) having at least 2 zones which are a preheating zone (1) on the fiber bundle inlet side and a heating zone (2) on the fiber bundle exit side, the 2 zones being separated by a seal member (3b1, 3b2) ; wherein the preheating zone (1) is in a pressurized steam atmosphere at 0.05 to 0.35 MPa, the heating zone (2) is in a pressurized steam atmosphere at 0.45 to 0.70 MPa, temperature difference ΔT1 in the preheating zone of the steam drawing apparatus in the fiber bundle-moving direction defined in the specification is up to 5°C, and temperature difference ΔT2 in the preheating zone of the steam drawing apparatus in the cross-sectional direction of the steam drawing apparatus defined in the specification is up to 5°C.