Stiff Filament/Hard Filament

The fiber shows local or whole-length hardening, loss of elasticity, and stiff sections with extremely low elongation, with a hand feel obviously different from normal soft yarn. The essence of stiff filament (hard filament) is local over-drawing or over-crystallization — the molecular chains of the cold-drawn section after the necking point are highly oriented and cannot recover, or the local residence time is too long, causing abnormally increased crystallinity. Stiff filaments cannot bend and form normally during weaving, producing hard spots on the fabric surface and needle breakage.

1. Comprehensive factor: local over-drawing forms permanent cold drawing and deformation (after the necking point). 2. Comprehensive factor: local residence time is too long (local over-crystallization after an intermediate pause due to winding or drawing failure). 3. Mold/tooling factor: improper heat setting temperature causes stiffness. 4. 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: ensure the pulling speeds of the guide rollers are accurately matched. 2. Mold/tooling improvement and maintenance: reduce operation interruptions. 3. Equipment inspection and system maintenance: adjust the heat setting conditions to match the material physical properties. 4. 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. 5. 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.

The essence of stiff filament is that local over-drawing or over-crystallization causes the fiber to lose its normal elastic recovery ability. The core of the solution is "stabilizing drawing + preventing over-crystallization": ensure precise matching of the guide roller speeds to eliminate local over-drawing, reduce operation interruptions to avoid local over-long residence and over-crystallization, and adjust the heat setting conditions to match the material characteristics.