Fiber bundle with pieced part, process for producing same, and process for producing carbon fiber

A production method for a fiber bundle having a fiber joint portion comprising applying a pressurized fluid emitted from a fiber interlacing apparatus to each of superposed fiber bundle portions in a fiber bundle that has either a superposed fiber bundle portion in which one end portion of a first fiber bundle of multiple fibers and one end portion of a second fiber bundle of multiple fibers are superposed or two superposed fiber bundle portions formed in a joint fiber bundle where one end portion of a first fiber bundle of multiple fibers and one end portion of a second fiber bundle of multiple fibers are respectively superposed on said joint fiber bundle, so that said fibers are interlaced with each other to join said fiber bundles in said superposed fiber bundle portions;

• wherein said fiber interlacing apparatus comprises a first fluid jetting hole series comprising a plurality of fluid jetting holes aligned at intervals along a first line in the width direction of said fiber bundles and a second fluid jetting hole series comprising a plurality of fluid jetting holes aligned at intervals along a second line that is parallel to the first line and that is positioned with an interval in the length direction of said fiber bundles to the first line, and works to emit pressurized fluid jets from said plurality of fluid jetting holes of said first fluid jetting hole series and said plurality of fluid jetting holes of said second fluid jetting hole series to produce, in said superposed fiber bundle portion, two or more interlaced fiber portions in which said fibers are interlaced and that are located apart from each other in the length direction of the fiber bundles and an unraveled fiber portion in which said fibers are unraveled and that is located between said two or more interlaced fiber portions, in such a manner that each of said interlaced fiber portions is composed of two or more interlaced sub-portions that are composed of said multiple fibers of one fiber bundle and said multiple fibers of the other fiber bundle interlaced in said superposed fiber bundle portion and that are located at intervals in the width direction of said fiber bundles, so that said fiber bundles are joined together in said superposed fiber bundle portion.