METHOD FOR MANUFACTURING SPUN THREAD BUNDLE, AND METHOD FOR MANUFACTURING CARBON FIBER IN WHICH RESULTING SPUN THREAD BUNDLE IS USED

Provided is a method for manufacturing a combined yarn bundle including the steps of bringing the two or more carbon fiber precursor yarns which travel in approximately parallel to one another into contact with a first roller at a wrap angle of 20° or more; then splitting the two or more carbon fiber precursor yarns into two to be brought into contact with a pair of second rollers, so that the carbon fiber precursor yarns are rotated approximately 90° between the first roller and the pair of second rollers; next, sequentially bringing the carbon fiber precursor yarns delivered from one second roller into contact with a third front roller and a third rear roller, and also bringing the carbon fiber precursor yarns delivered from the other second roller into contact with the third rear roller without bringing them into contact with the third front roller, so that these carbon fiber precursor yarns are combined on the third rear roller; and thereafter, bringing the carbon fiber precursor yarns delivered from the third rear roller into contact with a fourth roller to obtain a combined yarn bundle, so that a ratio of a distance L between axes of the first roller and of the pair of second rollers to a yarn width W of the carbon fiber precursor yarn on the first roller, L/W, is 18 or more and a tension of the combined yarn bundle after delivered from the fourth roller is 0.11 cN/dtex or more.