Improper Draw Ratio/Insufficient Drawing

The draw ratio does not reach the optimal orientation level, the fiber strength is unsatisfactory or the elongation is too high, and the mechanical properties deviate from the product design indicators. Fibers with insufficient drawing have low molecular chain orientation, and their tensile strength is only 60%~70% of that of fully drawn fibers; excessive drawing makes the fiber elongation extremely low, with insufficient toughness and easy brittle fracture. The draw ratio is one of the most core parameters in the melt spinning process, and precise control is crucial.

1. Process parameter factor: the yarn supply (as-spun yarn) speed is too fast or the drawing machine guide roller speed is too low, causing the actual draw ratio to deviate from the set value. 2. Comprehensive factor: the drawing temperature is too low for effective drawing. 3. Cooling air field factor: the temperature, wind speed and uniformity of the side-blowing air or ring-blowing air determine the solidification and forming quality of the fiber — too fast cooling leads to rough surface and increased internal stress, uneven cooling leads to inconsistent thickness of individual filaments in the same bundle, and low wind speed leads to filament sticking and filament breakage; the air field parameters need to be precisely controlled.

1. Process parameter optimization and adjustment: precisely calibrate the speed sensors and actuators of each roller. 2. Mold/tooling improvement and maintenance: ensure the drawing temperature is within the drawable window of the material, and precisely calculate the draw ratio according to the product specifications. 3. Troubleshooting of spinning problems follows the sequence of "chips → temperature → metering → spinneret → cooling air". First check the chip dryness and IV value, then verify the temperatures of each section of the spinning box and pipeline, next verify the metering pump accuracy and pressure stability, further check the spinneret cleanliness and hole shape condition, and finally adjust the cooling air field parameters to make the wind speed and temperature evenly distributed. 4. Preventive management: establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or the 5Why analysis method to trace the root cause, and solidify the countermeasures as PFMEA control points. Establish a regular equipment maintenance system, and implement life management for key tooling such as dies/spinnerets/calender rolls/coating heads.

This problem is a typical manifestation of improper draw ratio/insufficient drawing in melt spinning. The core of the solution lies in the precise stability of the spinning temperature, the high-precision control of metering supply, and the optimized maintenance of the spinneret/cooling air field. It is recommended to start from chip quality and spinning parameters, and gradually troubleshoot to the equipment and component level.