High-frequency Oscillation of Pipes in the Sizing Sleeve

The pipe exhibits high-frequency amplitude radial shaking inside the vacuum sizing sleeve. When this defect occurs in extrusion molded products, it is usually closely related to process links such as die design, screw plasticizing state, cooling and sizing system, or haul-off stability. If the defect persists, it will cause product dimensions to be out of tolerance, unqualified appearance, or decreased mechanical properties, increasing scrap rate and rework costs. Timely diagnosis and troubleshooting from both extrusion process parameters and equipment status is a basic requirement for ensuring stable continuous production.

1. Mold/tooling factors: the water film in the gap between the die and the sizing sleeve produces hydrodynamic instability. 2. Cooling/environmental factors: vacuum degree pulsation close to the natural frequency of the pipe produces resonance. 3. Cooling and sizing factors: The cooling rate and uniformity of extruded products determine crystallinity, internal stress level, and dimensional stability. Uneven cooling leads to pipe ovality, profile deformation, and internal stress concentration, requiring optimization of cooling water channel layout and water temperature control.

1. Process parameter optimization and adjustment: Adjust the distance between the die and the sizing sleeve to break the resonance condition. 2. Mold/tooling improvement and maintenance: Add an inlet damping structure. 3. Equipment inspection and system maintenance: Adjust the vacuum chamber volume to change the natural frequency of the vacuum system. 4. Systematic troubleshooting method: Troubleshooting of extrusion problems follows the order of "temperature → pressure → speed → die → cooling". First check and stabilize the temperature control of each section, then observe head pressure fluctuations to judge the feeding and screen condition, then verify the matching relationship between screw speed and haul-off speed, further check the condition of the die flow channel and sizing sleeve, and finally optimize the cooling water channels and water temperature distribution. Change only one variable at a time to confirm the effect. 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 5Why analysis to trace the root cause, and solidify 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 high-frequency oscillation of pipes in the sizing sleeve in extrusion molding. The core of the solution lies in eliminating the root cause of the defect through systematic optimization of process parameters (temperature, speed, pressure) and precision correction of the die/sizing system. It is recommended to start with parameter adjustment and gradually go deeper into the equipment and tooling level.