Melt Flow Fluctuation During Spinning Accompanied by Longitudinal Resonance of the Long Pipeline

The output frequency of the high-pressure metering pump coincides with the natural frequency of the conveying pipe section, causing amplified vibration. Countermeasures: replace the pump head or change the pipe length to change the vibration mode frequency.. When this defect appears in melt-spun products, it is usually closely related to the spinning temperature, metering pump accuracy, spinneret condition, or cooling air field uniformity. Spinning defects have the characteristic of being distributed along the yarn length direction, and defects at the individual filament level can affect the quality of the entire yarn bundle. Continuous occurrence will lead to increased filament breakage frequency, decreased yarn package quality and difficulties in subsequent processing, requiring systematic troubleshooting from two aspects: spinning components and process parameters.

1. Spinning temperature factor: the spinning temperature determines the melt viscosity and rheological behavior, directly affecting the spinnability, thickness uniformity and surface quality of the fiber. Excessively high temperature leads to degradation, yellowing and filament breakage, while excessively low temperature leads to poor plasticization and increased extrusion pressure; it needs to be precisely set according to the chip IV value and stably controlled. 2. 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: replace the pump head or change the pipe length to change the vibration mode frequency. 2. 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. 3. 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 melt flow fluctuation during spinning accompanied by longitudinal resonance of the long pipeline 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.