METHOD FOR PREPARING CARBON FIBER

PROBLEM TO BE SOLVED: To provide a method for preparing a carbon fiber at high yield by stabilizing infusibilization reaction by maintaining a certain state of the penetration of an oxidizing gas regardless of the fluctuation in basis weight of a precursor mat of a carbon fiber and regardless of the clogging of its protection filter for protecting a heating device without using a shape-retention mechanism. SOLUTION: The method for preparing a carbon fiber employs a continuous-charge type infusibilization furnace having a plurality of chambers in series in a direction of transferring a carbon-fiber precursor mat 16, having the function of circulating an oxidizing gas in the furnace, and having an air feeding/discharging function, in an infusibilization step by measuring a face wind velocity V of the oxidizing gas penetrating the carbon-fiber precursor mat 16 in each of the chambers to control the velocity V to be the target value ±10% by adjusting the pressure of circulating air according to the rate of change in the velocity V. The method for preparing a carbon fiber is further measures the amount of air supplied (Q1) and the amount of air exhausted (Q2) at the individual chambers of the infusibilization furnace to control the ratio of Q1 to Q2, Q1/Q2 to be 1.0±0.3 by varying the amount of air supplied (Q1) and the amount of air exhausted (Q2) according to the variation in pressure of air circulating therein. COPYRIGHT: (C)2009,JPO&INPIT