Method for drafting spun yarns in three stages

A method for drafting spun yarns in three stages using a drafting mechanism that has an entrance and an exit, four lines of rollers arranged in turn from the entrance to the exit to form a first-stage draft zone, a second-stage draft zone, and a third-stage draft zone, and each draft zone is respectively located between adjacent two lines of rollers;

• said method comprising:
• feeding a fiber strip whose twist and weight are detected in advance from the entrance of the drafting mechanism;
• drafting said fiber strip in the first-stage draft zone to obtain a fiber strand wherein a the twist of said fiber strand is 75% to 95% of that of the fiber strip and the weight of said fiber strand is 71% to 99% of that of said fiber strip and a first-stage draft ratio in said first-stage draft zone is 1.01 to 1.40;
• drafting said fiber strand in the second-stage draft zone to obtain a non-discrete fiber band without twist redistribution, wherein the twist of said fiber band is 15% to 60% of that of the fiber strip, and the weight of said fiber band is 47% to 98% of that of the fiber strip and a second-stage draft ratio in said second-stage draft zone is 1.01 to 1.52;
• drafting said fiber band in the third-stage draft zone to obtain a twist less fiber assembly wherein the weight of said fiber assembly is 0.3% to 9.8% of that of the fiber strip, and a third-stage draft ratio in said third-stage draft zone is 10 to 150, and the obtained fiber assembly is output from the exit of the drafting mechanism and is twisted into spun yarns.