Method for drafting spun yarns in three stages

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

• said method comprises the following steps:
• step 1. a fiber strip whose twist and weight are detected in advance is fed from the entrance of the drafting mechanism, said fiber strip is drafted in the first-stage draft zone to obtain a fiber strand;
• 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;
• the draft ratio in said first-stage draft zone is 1.01 to 1.40;
• step 2. said fiber strand is drafted in the second-stage draft zone to obtain a non-discrete fiber band without twist redistribution;
• 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;
• the draft ratio in said second-stage draft zone is 1.01 to 1.52;
• step 3. said fiber band is drafted in the third-stage draft zone to obtain a twist less fiber assembly;
• the weight of said fiber assembly is 0.3% to 9.8% of that of the fiber strip;
• the draft ratio in said third-stage draft zone is 10 to 150;
• the obtained fiber assembly is output from the exit of the drafting mechanism and is twisted into spun yarns.