Uneven Individual Filament Thickness/Denier Fluctuation

The denier (linear density) of fibers from the same spinning position or the same spindle fluctuates along the length direction beyond the allowable range of the standard, manifested as uneven yarn thickness. Denier fluctuation directly affects the fabric surface uniformity and hand feel of the fabric — thick sections form thick spots on the fabric surface, and thin sections form weak links. A denier fluctuation amplitude exceeding ±3% is regarded as unqualified, and investigation is needed from two aspects: metering pump accuracy and melt stability.

1. Process parameter factor: insufficient accuracy or speed fluctuation of the feed pump or metering pump. 2. Process parameter factor: the melt extrusion amount is affected by fluctuations in melt temperature and pressure. 3. Mold/tooling factor: local micro-clogging of the spinneret causes random changes in hole flow. 4. Process parameter factor: winding speed fluctuation. 5. 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: use a high-precision metering pump and stabilize its drive. 2. Mold/tooling improvement and maintenance: stabilize the melt temperature and pressure. 3. Equipment inspection and system maintenance: strengthen spinneret maintenance and cleaning. 4. Material/formulation optimization: stabilize the winding speed system. 6. 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 denier fluctuation is that instability of the melt extrusion amount or winding speed causes the fiber cross-sectional area to change along the length direction. The core of the solution is "stabilizing flow + stabilizing speed": use a high-precision metering pump to stabilize the melt supply, strengthen spinning temperature control to stabilize the melt viscosity, and ensure the transmission accuracy and speed stability of the winding system.